Earthing design

Engineering Encyclopedia Saudi Aramco DeskTop Standards

Design And Application Of Equipment Grounding

Note: The source of the technical material in this volume is the Professional Engineering Development Program (PEDP) of Engineering Services. Warning: The material contained in this document was developed for Saudi Aramco and is intended for the exclusive use of Saudi Aramco’s employees. Any material contained in this document which is not already in the public domain may not be copied, reproduced, sold, given, or disclosed to third parties, or otherwise used in whole, or in part, without the written permission of the Vice President, Engineering Services, Saudi Aramco.

Chapter : Electrical File Reference: EEX20502

For additional information on this subject, contact W.A. Roussel on 874-1320

Engineering Encyclopedia

Electrical Design and Application of Equipment Grounding

CONTENTS

PAGES

Locating Equipment Grounding Information...............................................................1 Basis For Installing Equipment Grounds In Saudi Aramco Electrical Systems .....................................................................................................................6 Determining The Equipment Grounding Requirements For Saudi Aramco Electrical Systems ......................................................................................15 Determining The Stationary Equipment Grounding Requirement For Saudi Aramco Electrical Installations.......................................................................27 Determining The Mobile Equipment Grounding Requirements For Saudi Aramco Electrical Installations.......................................................................38 Determining The Building And Structure Grounding Requirements For Saudi Aramco Installations ......................................................................................42 Determining The Lightning Protection Requirements For Saudi Aramco Installations.................................................................................................44 Determining The Static Grounding Requirements For Saudi Aramco Installations ..............................................................................................................54 Determining The Grounding Requirements For Saudi Aramco Offshore Platforms ...................................................................................................62 Determining The Grounding Requirements For Digital Equipment Used At Saudi Aramco Installations.........................................................................64 Work Aid 1: Saudi Aramco And Industry Standards Applicable To Equipment Grounding ..........................................................................67 Work Aid 2: Formula And Table Of Wire Sizes And Ampacity ................................68 Work Aid 3: Formula To Determine Conductor Size And References For Determining Stationary Equipment Grounding Requirements.......................................................................................74

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Work Aid 4: Formula To Determine Conductor Size And References For Determining Mobile Equipment Grounding Requirements.......................................................................................75 Work Aid 5: References For Determining Building And Structure Grounding Requirements.....................................................................76 Work Aid 6: References For Determining Lightning Protection Requirements And Tables For Calculating Risk Index ........................77 Work Aid 7: References For Determining Static Grounding Requirements.......................................................................................80 Work Aid 8: References For Determining Offshore Platform Grounding Requirements.......................................................................................81 Work Aid 9: References For Determining Digital Equipment Grounding Requirements.......................................................................................82 Glossary...................................................................................................................83 Addendum A ............................................................................................................87

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LOCATING EQUIPMENT GROUNDING INFORMATION The Engineer should consult the following Saudi Aramco Standards and Industry Standards for answers to questions on locating equipment grounding information: _ _ _ _

Saudi Aramco Design Practices Saudi Aramco Engineering Standards IEEE Standards National Electrical Code

Saudi Aramco Design Practices The Saudi Aramco Design Practice, SADP-P-111, applies to the design and the application of equipment grounding for Saudi Aramco electrical installations. The following chapters of SADP-P-111 contain information on equipment grounding: _ _ _ _ _

Chapter 6 Chapter 8 Chapter 9 Chapter 12 Chapter 13

Chapter 6

Chapter 6 of SADP-P-111, titled "Equipment Grounding," discusses the specific Saudi Aramco requirements for the grounding of the metallic parts of equipment that does not normally carry current. The following specific topics are discussed in Chapter 6: _ _ _ _ _ _ _ _ _ _ _ _ _

General Requirements Generators and Motors Switchboards Transmission Substations Transmission Lines Overhead Distribution Industrial Plant Areas Distribution and Utilization - 600 V and Below Cable Sheaths Fences Instruments, Meters, Relays, Instrument Transformers Cable Trays Conduits

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Saudi Aramco Design Practices (Cont'd) _ _ _ _

Cranes and Mechanical Handling Equipment Computer Installations Portable Equipment Lightning Protection

Chapter 8

Chapter 8 of SADP-P-111, titled "Offshore Platforms," discusses the specific grounding practices for use on Saudi Aramco offshore platforms. The following specific topics are discussed in Chapter 8: _ _ _ _

General Requirements Grounding Electrode Grounding Conductors Installation

Chapter 9

Chapter 9 of SADP-P-111, titled "Lightning Protection of Buildings and Structures," discusses the general lightning protection requirements for Saudi Aramco buildings and structures such as flag poles and floodlighting poles. Chapter 9 does not apply to the lightning protection requirements in substations or to the problems associated with flammable liquids or gases. The following specific topics are discussed in Chapter 9: _ _ _ _

General Requirements Need for Protection Materials Component Parts of a Lightning Protection System

Chapter 12

Chapter 12 of SADP-P-111, titled "Communication Facility Grounding," discusses the design criteria for the grounding and the bonding of communication facilities. The following specific topics are discussed in Chapter 12: _ _ _ _ _

General Requirements Terminology Design Criteria Earth Resistance and Bonding Requirements Review and Adoption of GTE Practices

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Saudi Aramco Design Practices (Cont'd) Chapter 13

Chapter 13 of SADP-P-111, titled "Safeguards Against Static Electricity, Lightning, and Stray Currents," describes current Saudi Aramco practices and requirements to safeguard against possible ignitions from static electricity, lightning, and stray currents when a hazard exists in the handling of flammable materials. Chapter 13 is intended to supplement but not to replace Article 250 (Grounding) of the National Electrical Code (NFPA 70), which deals with the protection of electrical installations by grounding or bonding. Chapter 13 also discusses the Saudi Aramco requirements to safeguard against possible degradation or possible failures, as a result of the presence of static electricity, of microelectronic components currently in use in communications and in process control computers. The following specific topics are discussed in Chapter 13: _ _ _

Definitions and Fundamentals General Requirements Protection of Specific Installations and Operations

Saudi Aramco Engineering Standards Saudi Aramco Engineering Standard SAES-P-111 applies to the design and application of equipment grounding for Saudi Aramco electrical installations. SAES-P-111 contains the minimum mandatory requirements for the design and the installation of equipment grounding. Any deviations from these requirements must have written approval from the Saudi Aramco Chief Engineer in Dhahran. User/specifier requirements that exceed the minimum requirements need no waiver approval even though they are different. SAES-P-111 contains the minimum mandatory requirements for the design and the installation of the following types of grounds: _ _ _ _

Equipment Grounding Fence Grounding Tank Grounding Lightning Protection

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IEEE Standards IEEE Standards give information on how to This information is the consensus opinion of standard that applies to the design and the Standard 142. The following sections of equipment grounding: _ _

design, specify, test, and measure equipment. a group of subject matter experts. The IEEE application of equipment grounding is IEEE IEEE Standard 142 contain information on

Section 2 Section 3

Section 2

Section 2 of IEEE Standard 142 is titled "Equipment Grounding." Section 2 discusses the problems caused by connection of the frames and the enclosures of electrical apparatus (such as motors, switchgear, transformers, buses, cables, conduits, building frames, and portable equipment) to a ground system. Section 2 outlines the fundamentals of making the interconnection system or the ground-conductor system between electrical equipment and the ground rods. The following specific topics are discussed in Section 2: _ _ _ _ _ _ _ _

Basic Objectives Fundamental Concepts Equipment Grounding as Influenced by Type of Use Outdoor Open-Frame Substations Outdoor Unit Substations Outdoor Installations Serving Heavy Portable Electric Machinery Interior Wiring Systems Interior Unit Substations and Switching Centers

Section 3

Section 3 of IEEE Standard 142 is titled "Static and Lightning Protection Grounding." Section 3 discusses the problems (such as how static electricity is generated) associated with static electricity, what processes produce static electricity, what must be done to prevent static electricity generation, or what must be done to drain static electric charges to earth to prevent sparking. Section 3 also discusses the methods for protection of structures against the effects of lightning. The following specific topics are discussed in Section 3: _ _

Static Grounding Lightning Protection Grounding

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National Electrical Code (NEC) The purpose of the NEC is to practically safeguard persons and property from the hazards that can arise due to the use of electricity. NEC Article 250, titled "Grounding" applies to equipment grounding at Saudi Aramco electrical installations. Article 250 discusses the general requirements for the grounding or the bonding of electrical installations. Grounding and ground system installation must be in accordance with Article 250 (as supplemented by SAES-P-111). The following specific sections of Article 250 apply to equipment grounding: _ _ _ _ _ _ _ _ _

Section A, General Requirements Section B, Enclosure Grounding Section E, Equipment Grounding Section F, Methods of Grounding Section G, Bonding Section H, Grounding Electrode System Section J, Grounding Conductors Section K, Grounding Conductor Connections Section L, Instrument Transformers, Relays, Etc.

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BASIS FOR INSTALLING EQUIPMENT GROUNDS IN SAUDI ARAMCO ELECTRICAL SYSTEMS The installation of equipment grounds at Saudi Aramco is based on solid Electrical Engineering practices. These practices are determined by known parameters or welldocumented theories. This section provides information on the following topics: _ _ _ _

Voltage Exposure Minimum Equipment Damage Isolation of Fault Minimize Electric Noise in the System

Voltage Exposure Voltage exposure is defined as the unintentional contact between an energized electrical conductor and the metal frame or the structure that encloses (or is adjacent to) the conductor. This unintentional contact causes the metal frame or the structure to become energized at the same voltage level that exists in the energized conductor. The method for reducing the possibility of voltage exposure is to install an effective equipment grounding conductor on the metal frame or the structure that encloses the energized conductor. An effective equipment grounding conductor must provide a low impedance path from the metal frame (or structure) to the zero-potential ground reference junction that is located at the equipment power supply. The impedance of the grounding conductor must be low enough to carry full ground-fault current without creating an impedance (IZ) voltage drop large enough to be dangerous to personnel. Minimum Equipment Damage Electrical equipment that does not have an equipment ground connection or that has an improperly installed equipment ground connection can easily be damaged under ground fault conditions. The damage can be caused by the heat that is produced from the increased current flow, the magnetic forces that are produced from the increased current flow, or the energy that is released from an arcing ground fault. The possibility of the occurrence of equipment damage depends on the following variables: _

The length of time that the ground fault current is allowed to flow (amount of time before protective devices isolate the ground fault).

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Minimum Equipment Damage (Cont'd) _

The magnitude of the ground fault current.

_

The resistance of the equipment ground return path.

_

The type of conductors that are used as the ground return path (insulated or non-insulated).

The possibility of equipment damage increases with the length of time that the ground fault current is allowed to flow. This length of time can be minimized by ensuring that a sufficient amount of ground fault current is available to quickly operate the protective equipment. The major step involved in providing a sufficient amount of ground fault current is to ensure that the equipment ground return path has the lowest possible impedance. A low impedance ground return path can be achieved through use of the following techniques: _

The installation of only safety-listed ground return path components.

_

The interconnection of all equipment grounding conductors to a common grounding electrode system.

_

The elimination of the use of separate isolated or dedicated grounding conductors.

_

The elimination of the use of actual earth as part of the equipment ground return path.

_

The use of proper bonding methods when the conductors in the equipment ground return path are connected.

_

The installation of equipment grounding conductors so that the conductors are physically running with the equipment power conductors.

_

The installation of equipment grounding conductors so that the fault loop area is small.

_

Proper protection corrosion of all terminated/spliced connections of the grounding conductors.

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Minimum Equipment Damage (Cont'd) The possibility of equipment damage also increases with the magnitude of the ground fault current. The maximum amount of ground fault current that can flow in a circuit is equal to the phase voltage of the circuit divided by the total impedance of the ground return path. The maximum amount of ground fault current can only be reduced through insertion of impedance in the ground return path. The maximum amount of ground fault current should not be limited to less than 10 to 15 times the current rating of the ground fault protective devices to ensure that sufficient ground fault current is available to operate the ground fault protective devices. The only step that can be taken to reduce the possibility of equipment damage from excessive ground fault currents is to ensure that all of the components in the ground return path are rated to carry the maximum ground fault current. The possibility of equipment damage also increases with the amount of impedance in the equipment ground return path. The portions of the equipment ground return path that are most likely to result in an increase in the impedance of the ground return path are the bonding connections between the conductors. The following steps can be taken to reduce the possibility of high resistance bonding connections between conductors: _

The bonding surfaces should not be painted.

_

Simple screw connections should not be relied on to make an adequate bonding connection between two pieces of sheet metal.

_

The bonding surfaces should not be made from raw (untreated) metal.

_

The bonding surfaces should not be made from dissimilar metals.

_

The bonding connection should be made through use of approved compression hardware, brazing, or welding. Bonding connections should not be made through use of soldering.

The possibility of equipment damage also increases with the use of non-insulated equipment ground conductors. Large voltage differences can exist between components such as raceways and a non-insulated equipment ground conductor under ground fault conditions. This voltage difference can cause arcing between the non-insulated equipment ground conductor and the raceway. This arcing can damage adjacent conductors. The possibility of equipment damage from non-insulated equipment ground conductors can be eliminated through use of insulated equipment ground conductors.

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Isolation of Faults An electrical fault is defined as a physical condition that causes a device, a component, or an element to not perform in a required manner. Although this definition applies to all types of electrical faults, this section is only concerned with ground faults. The specific definition of a ground fault is an insulation failure between a conductor and a ground or a frame. The following methods of system grounding are used in Saudi Aramco electrical systems: _ _ _ _

Solid grounding Resistance grounding Impedance grounding Ungrounded

The method of system grounding that is applied in a given Saudi Aramco electrical system has no bearing on the method of equipment grounding for use in a Saudi Aramco electrical system. The only method of equipment grounding is to connect a suitable conductor size between the noncurrent-carrying metal parts of all equipment, raceways, and other such enclosures and the system ground conductor and/or the grounding electrode conductor. The use of this method of equipment grounding will allow the protective devices to quickly isolate the ground faults should a ground fault occur. The following two types of protective devices are used to isolate ground faults: _ _ _

Fuses Circuit Breakers E2 starters for H.V. motors or NEMA starts for low voltage motors

Figure 1 shows the use of fuses to isolate a ground fault in a motor. The fuses that are shown in Figure 1 contain internal conductors or links that melt when the current that is passing through the fuse exceeds the rating of the fuse. The fuse isolates a ground fault through reaction of an open circuit when the internal link melts. The following sequence of events occurs during the isolation of a ground fault in a motor by fuses: _

A ground fault develops between one of the motor windings and the motor enclosure.

_

Ground fault current in excess of the rating of the fuses begins to flow from the transformer secondary windings through the fuses.

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Isolation of Faults (Cont'd) _

The ground fault current flows through the motor windings to the motor enclosure through the ground fault.

_

The ground fault current causes the internal links in the fuses to melt. This melting creates an open circuit and isolates the ground fault.

Use of Fuses to Isolate a Ground Fault in a Motor Figure 1

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Isolation of Faults (Cont'd) Figure 2 shows the use of circuit breakers to isolate a ground fault in a motor. The circuit breaker (52) shown in Figure 2 functions as a switch to open and to close the circuit that connects the transformer secondaries to the motor. However, the circuit breaker cannot sense the ground faults. The circuit breaker must use ground sensing relays to detect a ground fault. The ground sensing relays (50GS) send an input signal to the circuit breaker control circuit when a ground fault occurs. The input signal then causes the circuit breaker to open. This opening of the circuit breaker isolates the ground fault. The following sequence of events occurs during the isolation of a ground fault in a motor by circuit breakers: _

A ground fault develops between one of the motor windings and the motor enclosure.

_

The ground fault current flows through the motor windings to the motor enclosure through the ground fault.

_

The ground fault current then flows through the motor enclosure to the separate equipment ground conductor and back to the power source through the system ground.

_

The ground fault current in excess of the setpoints of the 50GS ground sensing relays begins to flow from the transformer secondary windings through the current transformers to the 50GS ground sensing relays.

_

The ground fault current that flows through the current transformers of the 50GS ground current sensing relays causes the 50GS ground sensing relays to activate.

_

The 50GS ground sensing relays send a signal to the circuit breaker (52) that causes the circuit breaker to open to interrupt the power and to isolate the ground fault.

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Isolation of Faults (Cont'd)

Use of Circuit Breakers to Isolate a Ground Fault in a Motor Figure 2 Minimize Electrical Noise in the System Noise is defined as an electrical disturbance on a circuit that interferes with or that prevents the reception of signals or of information. The circuits most effected by noise are digital circuits, computer circuits, instrumentation circuits, and communication circuits. The following types of disturbances are classified as noise; each type of disturbance has a slightly different effect on the circuit. _

Impulse noise jitter

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_ _

Crosstalk Hum

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Minimize Electrical Noise in the System (Cont'd) Impulse noise jitter is a transient disturbance separated in time by quiescent intervals. Impulse noise jitter can cause interruptions in communication circuits, digital circuits, and computer circuits. Instrumentation circuits (particularly 4-20 mA circuits) are not seriously effected by impulse noise jitter. Crosstalk is an extraneous signal introduced to a circuit from an adjacent circuit carrying AC or pulse-type signal. The effect of crosstalk on a given circuit depends on the magnitude of the extraneous signal introduced and the magnitude of the adjacent AC or pulse-type signal that is creating the crosstalk. Crosstalk can cause unwanted acoustic sound in communication circuits and inadvertent operations in other types of circuits. Crosstalk also represents a power loss to the circuit that is causing the crosstalk. Hum is similar to crosstalk because hum is also an extraneous signal that is introduced to a circuit from an adjacent circuit. The term "hum" is normally used in reference to a constant 60 Hz or 400 Hz extraneous audio signal. The term "crosstalk" is normally used in reference to a transient or intermittent extraneous audio signal. Hum affects a circuit by masking of the desired signal. The problem that is caused by noise in a circuit is the creation of a signal error. Signal error is the sum or the difference between the normal circuit signal and the noise signal. Signal errors can cause electronic circuit functions ot operate before or after the design setpoint of the function.

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DETERMINING THE EQUIPMENT GROUNDING REQUIREMENTS FOR SAUDI ARAMCO ELECTRICAL SYSTEMS Each piece of equipment must be grounded in order to provide the maximum protection against the inadvertent energization of the metal frame structure of a piece of equipment. This section provides information on the following topics: _ _ _ _ _ _ _

Single Point Grounding Grounding Conductor Conduit Grounding Connections to Earth Bonding Motor/Generator Grounding High Voltage Switch Grounding

Single Point Grounding Single point grounding is defined as a method of equipment grounding in which there is only one connection to earth ground. Single point grounding is used in electronic instrumentation and communication circuits to help eliminate the noise that can be created due to the flow of ground loop currents. Ground loop currents are eliminated because a complete path for current flow from a ground connection at one potential to a ground connection at a different potential does not exist when there is only one connection to earth ground. Single point grounding is only effective in circuits that operate below 50 kHz. Circuits that operate above 50 kHz will have multiple connections to earth ground due to the capacitive coupling to ground that occurs at high frequencies. Grounding Conductor All Saudi Aramco electrical equipment must be grounded through use of a grounding conductor. A grounding conductor is defined as a conductor that is used to connect equipment or the grounded circuit of a wiring system to a grounding electrode or electrodes. Each piece of electrical equipment should be connected to the system grounding electrode through use of a separate equipment grounding conductor. Equipment grounding conductors should not be looped from one piece of electrical equipment to a different piece of electrical equipment. Equipment grounding conductors should also be continuous (not cut or spliced).

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Grounding Conductor (Cont'd) Equipment grounding conductors must be made from soft-drawn copper wire or, in case of ground rods, copperweld wire. The conductors should be installed so that the conductor is protected from mechanical damage. SAES-P-111 covers the selection and installation of grounding conductors. The following sizes of wires are preferred by Saudi Aramco for grounding conductors for standardization: _ _ _ _ _ _ _ _ _

No. 4 AWG Stranded or Solid No. 2 AWG Stranded or Solid No. 1/0 AWG Stranded No. 2/O AWG Stranded 250 MCM Stranded No. 4/O AWG Stranded 350 MCM Stranded 500 MCM Stranded 750 MCM Stranded

The grounding connection will be made through use of thermite welding, brazing, or approved compression grounding connections (Burndy Hyground System or equivalent). Bolted or a ready means of disconnection for testing purposes, such as bolted connections, shall be provided in the grounding connection to the following: _ _ _

Generator neutrals Transformer neutrals Grounding electrodes such as grounded well or groups of grounded rods.

The sizing of the ground conductor is dependant on the voltage level and the short circuit of the power system of the electrical system to which the equipment is connected. The conductor size for the higher voltage system should be used for mixed voltage systems. The voltages are broken down as follows: _ _

Conductor sizes - systems 600V and below Conductor sizes - system over 600V

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Grounding Conductor (Cont'd) Conductor Sizes - Systems 600V and below

The size of the copper grounding conductors for power source transformer tanks, transformer neutrals, main switchboards, or other equipment that is supplied directly from the LV (low voltage) side of a transformer, without an intervening protection device in a system rated 600V and below, depends on the following: _

The kVA rating of the power source transformer.

_

The type of protection that is provided for the primary winding of the lower source transformer (e.g., fuses or circuit breakers).

Section 1 of Work Aid 2 contains the formula, the table, and the procedure for use in determining the size of the grounding conductors that were previously described. The size of equipment grounding conductors for equipment that is beyond the main switchboard or the transformer output protection device in systems rated 600V and below must comply with Article 250-95 of the National Electrical Code (NEC). Article 250-95 states that the size of the equipment grounding conductor is based on the rating of the automatic overcurrent device in the circuit that is ahead of the equipment. Section 2 of Work Aid 2 contains a procedure and a table for use in determining the size of the equipment conductors that were previously described. Conductor Sizes - Systems Over 600V

The size of the grounding conductor for electrical systems over 600V is based on the following type of system grounding that is used. _ _

Solidly Grounded Systems Impedance Grounded Systems

Solidly Grounded Systems - Grounding conductor sizes for solidly grounded systems

over 600V are based on the three-second, short-time current capabilities of the circuit breaker that is ahead of the grounding conductors. The three second, short-time current capability must be derived through use of a formula in cases where a circuit breaker is not installed or where a three-second, short-time current capability is not assigned.

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Grounding Conductor (Cont'd) Section 3 of Work Aid 2 contains the formula, the table, and the procedure for use in determining grounding conductor sizes in solidly grounded systems over 600V. This section of Work Aid 2 applies to determination of the size of all grounding conductors in grounded systems over 600V. These grounding conductors include the following: _ _ _ _

Equipment grounding conductors (Column 2 of the table) Neutral grounding conductors (Column 2 of the table) Ground bus conductors (Column 2 of the table) Ground grid conductors (Column 3 of the table)

Impedance Grounded Systems - Grounding conductor sizes for impedance grounded

systems over 600V are based on the ten second rating of the neutral grounding device, or the ten second rating of the combined neutral grounding devices for systems that have multiple grounding devices that are connected in parallel. This basis applies to most impedance grounded installations. The two exceptions to the basis for the sizing of grounding conductors in impedance grounded systems over 600V are as follows: _

A minimum grounding conductor size of No. 2/0 AWG must be used for all installations to ensure that the conductor has sufficient mechanical strength.

_

The three-second, short-time current capability of an equivalent solidly grounded system is the basis for the size of the grounding conductors when there is a possibility of two- or three-phase fault current flowing through the grounding conductor.

Section 4 of Work Aid 2 contains the table and the procedure to be used to determine grounding conductor sizes in impedance grounded systems over 600V. This section of Work Aid 2 applies to determining the size of all grounding conductors in impedance grounded systems over 600V. These grounding conductors include the following: _ _ _ _

Equipment grounding conductors (Column 2 of the table) Neutral grounding conductors (Column 2 of the table) Ground bus conductors (Column 3 of the table) Ground grid conductors (Column 4 of the table)

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Conduit Grounding Conduit must be satisfactorily grounded to prevent creating electrical shock hazards due to voltage exposure. A faulted conductor that contacts metal conduit will raise the conduit to the voltage level of the failed conductor. A person that contacts this energized conduit and ground will receive an electrical shock unless the conduit is satisfactorily grounded. All conduits must be directly grounded regardless of the system voltage. Conduit that does not comply with the termination methods listed above must have a separate grounding connection bonded to both ends of the conduit. Metal conduit that contains conductors of systems above 600V must also have a separate grounding connection bonded to both ends of the conduit. Connections to Earth A very important aspect of grounding equipment is the final connection to the earth. This section provides information on the methods for use in making ground connections to earth in the following locations: _ _

Below Ground Line Above Ground Line

Below Ground Line

Saudi Aramco uses the following approved methods for ground connections below ground line: _ _ _

Thermite Welded Connections Brazed Connections Compression Connections

Thermite Welded Connections - Thermite welding is an exothermic process for use in

making electrical connections between two pieces of copper or between copper and steel. The thermite welding process does not require an outside source of heat to produce the weld. The weld is produced by mixing powdered aluminum and iron or copper oxide in a container and by placing this mixture in a graphite crucible (mold). The mixture is then ignited through use of a flint lighter, which starts the highly exothermic reaction. The heat from the exothermic reaction turns the two metals into a superheated liquid that flows through and around the conductors to be joined, thus welding the conductors together.

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Connections to Earth (Cont'd) An electrical connection produced from the thermite welding process has the following characteristics: _

The current-carrying capacity of the connection will be equal to the current- carrying capacity of the conductors.

_

The connection will be permanent and will not loosen or corrode.

Ground connections between the equipment ground conductors and the earth electrodes that are made through use of thermite welding must also be equipped with a separate disconnecting means, such as bolted joints. The separate disconnecting means must facilitate separation of the equipment ground from the system ground during testing. Brazed Connections - Brazed connections are for use in making electrical connections

between the following: _ _ _

Two grounding conductors A ground conductor and an earth electrode A ground conductor and a lug

A brazed connection is made by placing together the two surfaces to be joined and then applying heat to the surface through use of a torch. The two surfaces are preheated with the torch, and then a copper alloy filler material is applied to the surfaces to be joined. The filler material will melt when heated by the torch and will flow through and around the surfaces to be joined. The filler material solidifies and fuses the two surfaces together after the heat is removed. The electrical connection that results from brazing has characteristics that are similar to the characteristics of a thermite welding connection. Thermite welding connections are preferred over brazed connections because thermite welding connections require fewer skills, less equipment, and less time to install than brazed connections. Compression Connections - A compression connection is made by placing a compression fitting (lug) over the end of the grounding conductor and by crimping the fitting to the conductor through use of a special compression tool and die. The only approved compression connectors for use in making ground connections in Saudi Aramco electrical systems are Burndy Hyground Systems or an equivalent. An acceptable compression grounding connection must have the following characteristics:

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Connections to Earth (Cont'd) _

Freeze-thaw cycling tests should not significantly change the resistance of the connector-conductor assemblies and should not impair the ability of the assemblies to function properly when exposed to a short circuit test to failure.

_

The tensile strength and the torque strength of the connection joint should be greater than the tensile strength and the torque strength of the conductor.

_

The grounding connector must be able to stand, without damage, a repeated, short-circuit current load that is equal to 80 percent of the short circuit of the conductor.

_

Heat cycles with sufficient current to raise the conductor temperature to 350oC followed by short circuit tests should not damage the grounding connector.

_

The sequential aging test (sequential heat cycle, freeze-thaw cycle, salt spray test, heat cycle, and short circuit) should not damage the grounding connector.

_

Heat cycles that have sufficient current to raise the conductor temperature to 350oC that are followed by a corrosion test in which the test sample is immersed in a 20 percent nitric acid solution and then followed by a short-circuit test should not damage the grounding conductor.

_

The connector should be marked with the cable size that is accommodated and with the DIE index number.

_

The compression tool that is used on the connector should be designed to lock in during compression and to be released only after the compression stroke is completed or when a safety release trigger is activated.

_

After compression, the DIE should leave a mark on the connector that matches the original DIE index number on the connector.

Above Ground Line

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For ground connections that are made above the ground line in Saudi Aramco electrical systems, the three methods that apply to ground connections made below the ground line must be used, in addition to bolted connections.

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Bonding Bonding is defined as the permanent joining of metallic parts to form an electrically conductive path that will assure electrical continuity and the capacity to safely conduct any current likely to be imposed. There is a difference between equipment bonding and equipment grounding. Equipment bonds are installed to ensure that continuity exists between all the noncurrent-carrying metal portions of electrical equipment. Equipment grounds are installed to ensure that continuity exists between the noncurrent-carrying metal portions of electrical equipment and an earth ground. Equipment bonds should be installed when it is possible that continuity will not exist between one noncurrent-carrying metal portion of electrical equipment and the noncurrentcarrying metal portion of the electrical equipment that is connected to the equipment ground conductor. Figure 3 shows an example of when an equipment bond should be installed.

Equipment Bond Figure 3

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Figure 3 shows that the equipment ground conductor is terminated at the ground terminal on the back of the noncurrent-carrying, metal outlet box. Figure 3 also shows an equipment bonding jumper that connects the noncurrent-carrying metal portions of the receptacle to the ground terminal. This bonding connection is necessary to ensure that there is continuity between the noncurrent-carrying metal portions of the receptacle and the noncurrent-carrying metal outlet box.

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Bonding (Cont'd) Equipment bonding is accomplished through use of approved bonding jumpers. following are examples of approved bonding jumpers:

The

_

Bonding screws that are included as part of electrical equipment for the sole purpose of equipment bonding.

_

A copper conductor with approved lugs that are attached to both ends of the conductor.

_

Approved threaded couplings and approved threaded bosses on enclosures.

_

Approved threaded couplings and connectors on conduit.

_

Approved bonding-type locknuts and bushings.

Motor/Generator Grounding Saudi Aramco requires the frames of generators to have at least two grounding connections and the generator prime mover to have a separate grounding connection. Saudi Aramco also requires motor frames to have at least one grounding connection. Care should be taken to ensure that insulated components, such as insulated bearing pedestals, remain ungrounded. A shorting strap should be installed across the insulation on the coupling end to maintain the motor frame at ground potential. This shorting strap should contain a test link that is to be removed when the bearing insulation is tested. The bearing on the noncoupling end of the motor should remain insulated at all times to prevent shaft currents. High Voltage Switch Grounding For high voltage disconnecting switches to be hand operated, an operator must be present near a grounded structure, at a point where an opening of an energized circuit or a mechanical failure and electrical breakdown of the switch insulator could result in an arc to the structure. Because a large percentage of fatal accidents is associated with the operating handles of high voltage switches, high voltage switches must be grounded.

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High Voltage Switch Grounding (Cont'd) A metallic platform should be provided for the operator of a disconnecting switch that is rated 34.5 kV and above. This platform should be bonded with a 120 sq. mm (No. 4/0 AWG) stranded copper conductor to the operating handle or crank of the disconnect. The operating mechanism should be directly connected to the grounding system by means of a 120 sq. mm (No. 4/0 AWG) stranded copper conductor. The platform should have no direct connection to the ground system. For fault current from the operating handle to ground, these connections will ensure a direct path that will avoid the operator's platform. The operator's hands and feet will remain at the same potential. Disconnects (but not their mechanisms) and insulator anchorages on steel structures may rely on the steel structure itself for equipment grounding. Each leg of the steel structure should be grounded, at a point near the base of the structure, with a conductor that is appropriate to the equipment mounted on the structure. All other equipment on steel structures should have a separate grounding conductor. The conductors should be supported along the structure at 0.9 m (3 ft.) intervals through use of clamps.

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DETERMINING THE STATIONARY EQUIPMENT GROUNDING REQUIREMENT FOR SAUDI ARAMCO ELECTRICAL INSTALLATIONS For the purpose of this section, the term "stationary equipment" will be defined by the list of items given below. Other sections of this module will cover mobile equipment grounding, building and structure grounding, offshore platform grounding, and digital equipment (computer) grounding. _ _ _ _ _ _ _ _ _ _ _

Generators and Motors Switchboards, Switchgear, Motor Control Circuits Transmission Substations Transmission Lines Overhead Distribution Industrial Plant Areas Distribution and Utilization Equipment Cable Sheaths Fences Instruments, Meters, Relays, and Instrument Transformers UPS System and Batteries

SAES-P-111 and SADP-P-111 present the following general guidelines concerning grounding requirements for stationary equipment in Saudi Aramco installations: _

All accessible non-current carrying metal parts of electrical equipment should be grounded. All accessible metal parts of non-electrical equipment should be grounded if they are likely to become energized under abnormal conditions.

_

Equipment should be grounded by means of grounding conductor(s) connecting the equipment to a ground bus, ground grid, or other grounding electrode.

_

The grounding conductor termination at the equipment must be at the studs or holes provided by the equipment manufacturer. The termination point on equipment above 600V should be specified to NEMA standard 15 mm (9/16 in) holes, 1/2 in studs, or 45 mm (1-3/4 in) centers. When the manufacturer does not provide a grounding conductor termination point, the grounding conductor must be terminated on a main structural part of the equipment with an approved lug or clamp. Lugs must be brazed or hydraulically crimped. Paint is to be removed to give a bare metal mating surface. On completion, the whole termination is to be bitumen painted (bitumastic No. 50 or equal) for protection against corrosion.

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_

Equipment and system grounds are to be connected to the ground bus or to the ground grid by separate conductors.

_

A grounding bus is to form a closed loop so that the equipment grounds and the system neutrals that are connected to the grounding bus have two current paths to the main ground electrode.

_

Conduit, cable tray, cable armor, or cable shield is not to be the sole means of grounding equipment. A segment equipment grounding conductor also must be installed in the conduit, cable tray, cable, or cord. Metallic conduit and cable tray is to be grounded at both end points.

_

Generators and motors larger than 185 kW (250 HP), power transformers, switchgear ground buses, and similar equipment are to have a minimum of two grounding connections to a made electrode or a ground grid.

_

The shields and the armor of power cables are to be grounded at both ends. The continuity across splices is to be maintained through bonding across the splices.

Generators and Motors As previously explained, the grounding requirements of SAES-P-111 and SADP-P-111 for generators and motors are as follows: _

The frames of generators are to have at least two grounding connections and the prime mover is to have its own grounding connection. Motor frames are to have at least one grounding connection.

_

The insulated components that are associated with the prevention of shaft circulating currents are to be left ungrounded (e.g., such as insulated pedestals or insulated bearings). A shorting strap is to be installed across the insulation on the coupling end of motors to maintain the motor frame at ground potential when horizontal motors are supplied with both pedestals insulated. This shorting strap is to contain a test link that is to be removed when the bearing insulation is tested. The bearing on the non-coupling end of the motor shall remain insulated at all times to prevent shaft currents.

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Switchboards SAES-P-111 and SADP-P-111 establish the following grounding requirements for switchboards: _

All switchboards are to be equipped with a grounding bus that runs the length of the switchboard and that is mounted in or on the switchboard. This grounding bus is usually supplied by the manufacturer. The grounding bus is to be connected at each end to the installation ground bus or ground grid.

Transmission Substations SAES-P-111 and SADP-P-111 contain the grounding requirements for transmission substations. These requirements are sub-divided as follows: _ _ _ _ _ _

Power Transformers and Potential Transformers Circuit Breakers Disconnects Lightning Arresters Substation Equipment on a Steel Structure Substation Equipment on a Wood Structure

Power Transformers and Potential Transformers

The equipment grounding connections are to be separate from the system or neutral grounding connection. Power transformer tanks due to have two grounding connections. Cooler banks, control kiosks, and other such equipment associated with power transformers are to have separate grounding connections. Circuit Breakers

Circuit breakers with separate pole construction are to have a separate grounding connection to each pole. Operating mechanisms are to have a separate connection unless the mechanism is integral to the breaker.

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Transmission Substations (Cont'd) Disconnects

A metallic platform is to be provided for the operator of a disconnecting switch. This platform is to be bonded with 120 mm2 (No. 4/0 AWG) stranded copper to the operating handle or the crank of this disconnect. The operating mechanism shall be directly connected to the grounding system by means of 120 mm2 (No. 4/0 AWG) stranded copper, and the platform shall have no direct connection to the ground system. These connections ensure that a direct path for fault current from the operating handle to the ground will enable current to avoid the operator's platform. Lightning Arresters

The grounding terminals of lightning arrestors shall be directly connected to the ground grid or ground bus with a minimum of bends. The grounding conductor shall be of a size appropriate to the other equipment on the same system, and the conductor shall not be run through any conduit or metal enclosure. The grounding conductor is to have no 90 degree bends and is to be as short as possible to the ground grid. Substation Equipment on a Steel Structure

Provided that the structure is grounded, disconnects (but not the operating mechanisms) and insulator anchorages on steel structures can use the steel structure itself for grounding. Each leg of the steel structure shall be grounded at a point near the structure base with a conductor appropriate to the equipment mounted on the structure. All other equipment on the steel structures shall have separate grounding conductors. The conductors shall be supported at 0.9 m (3 ft) intervals through the use of clamps. Substation Equipment on a Wood Structure

All electrical equipment (e.g., transformers, disconnects, insulated anchorages) and the steel associated with the electrical equipment (e.g., steel platforms and cross-arms) are to be grounded to the same standard as other equivalent electrical equipment in the substation.

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Transmission Lines SAES-P-111 and SADP-P-111 establish the following grounding requirements for transmission lines: _

The continuation of the transmission line's overhead ground wires across the substation protects transmission line substations against direct lightning strikes. These overhead ground wires can be supplemented with earth masts, peaks, heights or shielding angles.

_

The overhead ground wires that are terminated on a substation steel structure must be jointed through use of a bi-metal connector to an equivalent cross section copper conductor that is connected to the grounding grid or bus.

_

The grounding downlead of wood pole structures that are inside substations, that are in the immediate vicinity of substations, or that are within plant areas having a ground grid must be connected (by buried conductor) to the ground grid. The pole butt wrapping must be retained on these structures.

Overhead Distribution SAES-P-111 and SADP-P-111 establish the following grounding requirements for overhead distribution: _

At transformer locations, where a system ground (600V or below) is established, the connections linking transformer neutral, system neutral conductor, transformer tank(s) and any system disconnecting devices must be sized in accordance with Sections 1 and 2 of Work Aid 2. The downlead must also be of the same size if connected to an extensive ground grid or bus. If the downlead connects solely to a local, made ground, an 8 mm (5/16 in) copperweld, 8 foot ground rod(s) must be used.

_

At other locations, and at all other voltages, the equipment and the metal hardware must be grounded through use of a minimum 25 mm2 (No. 4 AWG) conductor or of an 8 mm (5/16 in) copperweld ground rod. Downleads and pole butt wrappings must be 8 mm (5/16 in) copperweld. Pole downleads within industrial plant areas having a ground grid must be connected to the ground grid with a conductor whose minimum size is 25 mm2 (No. 4 AWG).

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Overhead Distribution (Cont'd) _

PVC insulated grounding conductor must be used for downleads.

_

Disconnects that are rated above 600 V, that are operated from a mechanism at ground level, and that are located in plant areas where a ground grid exists are to be treated as disconnects in a transmission substation.

Industrial Plant Areas SAES-P-111 and SADP-P-111 establish the following grounding requirements for industrial plant areas: _

Grounding conductors must be installed such that a metallic grounding connection must exist from all equipment to the neutrals of all systems local to the plant area.

_

Equipment above 600V must be connected to the ground grid when a ground grid is provided. When a ground grid is not provided, the equipment above 600V must be connected to the system neutral by methods that conform to NEC Articles 250-57 and 250-91 (b).

_

For grounding equipment 600V and below, the Distribution and Utilization Equipment guidelines are to be used.

_

Where a transmission voltage substation is located within or adjoining an industrial plant area, a ground grid must be established in the plant area. This grid must consist of sufficient conductors to pick up the equipment grounds. The ground grid must be designed in conjunction with the transmission voltage substation ground grid. All pipelines entering and exiting vital facilities are to be buried 18 m on either side of the security fence.

The equipment grounding conductor that is run with or that encloses the circuit conductors must be a copper conductor or other corrosion-resistant conductor. This conductor can be solid or stranded; insulated, covered, or bare; and in the form of a wire or a busbar.

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Distribution and Utilization Equipment SAES-P-111 and SADP-P-111 establish the following grounding requirements for distribution and utilization equipment: _

A multiple grounded neutral system (whether cabled or overhead) is to be used in residential and non-industrial locations. The neutral conductor is taken to all locations on the system and is grounded at points of utilization. In overhead systems, the neutral conductor is also grounded at each pole. Grounding at points of utilization must be in accordance with the National Electrical Code, Article 250-H, Grounding Electrodes, except that the water piping must not constitute the grounding electrode, but it is to be bonded to the grounding electrode. Equipment at points of utilization is to be grounded by connection to the multiple grounded neutral and the local electrode.

_

A single-point grounded neutral system is to be used in industrial plants where cabling will normally predominate. The neutral is to be grounded at the transformer only and cannot be brought out for system use.

_

Utilization equipment is to be grounded by a metallic connection to the system neutral and to the ground grid or ground bus. The grounding connection is to conform to Articles 250-57 and 250-91 (b) of the National Electrical Code.

The ground loop impedance of the circuit that is formed by the line conductor from the power source to the equipment and by the grounding path from the equipment back to the power source neutral must be low enough to allow sufficient fault current to pass to operate the protection device. The following equation should be satisfied:

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Distribution and Utilization Equipment (Cont'd) where: Zgl

=

ground loop impedance, ohms

E

=

line to neutral voltage, V

I

=

current rating of fuse or trip setting of overcurrent device,

K

=

constant, 3 for fuses, 1.5 for other overcurrent devices

A

Difficulties in attaining an adequately low value of Zgl are unlikely to arise but can occur at low voltages/high ratings. Residential occupancies must have ground-fault circuit protection for all 115V, 15A, and 20A receptacle outlets or feeders supplying the outlets that are installed outside or in bathrooms. Construction sites are to have ground-fault circuit protection for all 115V, 15A, and 20A receptacle outlets or feeders supplying the outlets that are not part of the permanent wiring. Conduit is not to be the sole means of grounding equipment, except for overhead lighting within buildings that are installed with rigid conduit. A bonding jumper is to be installed at flush-mounted, grounding-type receptacles to connect the receptacle grounding terminal and the box. Reliance is not to be placed upon contact devices or yokes to provide the connection (exception 2 of NEC, Article 250-74 is excluded). Lighting fixture outlet boxes are to be grounded and a bonding jumper is to be installed to connect the fixture to the box.

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Cable Sheaths SAES-P-111 and SADP-P-111 establish the following grounding requirements for cable sheaths: _

The lead sheaths, the shields, and the armor of multi-conductor power cable must be bonded and grounded at both ends. The continuity at splices is to be assured by bonding across the splice. Steel wire armor is to be bonded and grounded at both ends but must not constitute a grounding conductor.

_

The metallic sheath and the armor, if any, of single core power cables below 240 mm2 (500 MCM) is to be bonded and grounded at both ends. At 240 mm2 (500 MCM) and above, short lengths (such as road crossings and line terminations into substations) are to be treated similarly.

_

Terminators for aluminum sheathed cable are to be the positive grounding type, with positive ground set screws. OZ type terminators (SPKHK/SPKGK or similar) are to be specified for use with aluminum sheathed cable.

_

Signal cables used in instrumentation, telemetering, and communications are to have shields that are grounded only at one end to reduce the interference from stray sources.

Fences SAES-P-111 and SADP-P-111 establish the following grounding requirements for fences: _

For transmission substation fences, the peripheral conductor of the ground grid is to be run 0.6 m to 1 m (2 to 3 ft) outside the fence and parallel to the fence. The fence is to be bonded to the peripheral conductor at maximum intervals of 6 m (20 ft) with a minimum of size 70 mm2 (No. 2/0 AWG) conductors.

_

For industrial plant area fences where a ground grid is installed, a peripheral conductor is to be run 0.6 m to 1 m (2 to 3 ft) outside of and parallel to the fence. In cases where a common boundary exists between a transmission substation and an industrial plant, the fence is to be run 0.6 m to 1 m (2 ft to 3 ft) inside the industrial plant fence. The fence is to be bonded to the peripheral conductor at maximum intervals of 15 m (50 ft) with a minimum of size 35 mm2 (No. 2 AWG) conductors.

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Fences (Cont'd) _

For distribution substation fences (13.8 kV and below), the peripheral conductor is to be run 0.6 m to 1 m (2 ft to 3 ft) outside of and parallel to the fence. The fence is to be bonded to the peripheral conductor at maximum intervals of 15 m (50 ft) with a minimum of size 35 mm2 (No. 2 AWG) conductors.

Instruments, Meters, Relays and Instrument Transformers The grounding requirements for instruments, meters, relays, and instrument transformers are found in SAES-P-111, SADP-P-111, NEC Articles 250-121, 122, 123, 124, 125 and SAES-J31. These requirements are summarized as follows: _

Secondary circuits of current transformers (CT) and potential transformers (PT) are to be grounded when the primary windings are connected to circuits that have a potential of 300 volts or more to ground. CT's or PT's mounted on switchboards are to be grounded irrespective of the voltage.

_

The cases or the frames of instrument transformers that are accessible are to be grounded.

_

Instruments, meters, and relays operating with windings or working parts that are energized by voltages less than 1000 volts are to be grounded as follows:

-

Instruments, meters, and relays that are not located on switchboards, that operate with windings or working parts at 300 volts or more to ground, and that are accessible are to have the cases and the other exposed metal parts grounded.

-

Instruments, meters, and relays (whether operated from current and potential transformers or connected directly in the circuit) on switchboards that do not have live parts on the front of the panels are to have the cases grounded.

_

The grounding conductor for the secondary circuits of instrument transformers and for the instrument cases are not to be smaller than No. 12 copper or No. 10 aluminum. The cases of instrument transformers, instruments, meters, and relays that are mounted directly on the grounded metal surfaces of enclosures or grounded metal switchboard panels are to be considered to be grounded. Additional grounding conductors are not required.

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Example of Stationary Equipment Grounding Assume that a new installation of an electrical motor is being planned and that the grounding requirements have not yet been determined. The motor is a 250 HP, 480 volt, three-phase motor. The full load current of the motor is 350A, and motor protection is provided through a 500A inverse-time circuit breaker. This information can be used to determine that two grounding conductors are required because the motor is at 250 HP. NEC Article 250-95A can be used to determine that the grounding conductors must be at least a No. 2 AWG copper cable. One of the grounding conductors should be connected directly from the motor to the plant's grid. The other grounding conductor should be run with the motor's power conductors from the motor to the motor's power source transformer, and then to the grid.

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DETERMINING THE MOBILE EQUIPMENT GROUNDING REQUIREMENTS FOR SAUDI ARAMCO ELECTRICAL INSTALLATIONS Mobile equipment is defined as equipment mounted on wheels, treads, or other such devices that can easily be relocated. The following Saudi Aramco Standards and NEC Sections provide guidance for grounding portable equipment: _

Saudi Aramco Engineering Standards SAES-P-111

_

Saudi Aramco Design Practice SADP-P-111

_

NEC Section 250-6 covers portable generators and vehicle-mounted generators.

_

NEC Section 250-154 covers the special requirements for grounding of high voltage (1 kV and above) portable or mobile equipment. This section applies to outdoor equipment such as power shovels, drag lines, or dredges.

_

NEC Section 400-C applies to multiconductor portable cables that are used to connect mobile equipment and machinery.

_

NEC Article 515 provides information on electrical and grounding safety in bulk storage plants. Bulk storage plants are locations where flammable liquids are received by tank vessel, tank car, or tank vehicle.

_

NEC Section 550-4(a) covers mobile homes that are not intended as dwelling units. A particular application of this Article would be electrical installations at construction sites where trailers are required.

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DETERMINING MOBILE EQUIPMENT GROUNDING REQUIREMENTS FOR SAUDI ARAMCO ELECTRICAL INSTALLATIONS (CONT'D) SADP-P-111 contains the following sections on the grounding of mobile equipment: _ _

Cranes and Mechanical Handling Equipment Portable Equipment

Cranes and Mechanical Handling Equipment The grounding requirements for Cranes and Mechanical Handling Equipment are found in SAES-P-111 and SADP-P-111 as follows: _

The grounding practices should avoid the passage of ground currents (either ground fault or arc welding return currents) through the bearing surfaces at the wheels and the pivot points. The grounding practice should also avoid the reliance on travelling crane rails for grounding.

_

A grounding conductor within the trailing cable serving the crane or a trolley wire for grounding is the preferred method of grounding.

Portable Equipment The following grounding requirements for Portable Equipment are found in SAES-P-111 and SADP-P-111: _

Portable equipment includes electrical equipment that can be manhandled and vehicle and skid-mounted equipment. Complete electrical systems such as mobile flood-lighting plants, specialized vehicles, and other such vehicles that are confined to one vehicle, enclosure, or frame are excluded from consideration. Grounding to the earth may also be required to prevent static charges. The following articles of the NEC apply to portable equipment having electrical power connections:

250-6 Portable and Vehicle Mounted Generators 250-45Equipment Connected by Cord and Plug

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Portable Equipment (Cont'd) 250-59

Cord - and Plug - Connected Equipment

250-154

Grounding of systems supplying portable equipment (1 kV and over)

_

All portable equipment requires grounding except for certain low voltage or double insulated items.

_

Portable equipment, 600V and below:

_

A metallic connection must exist from all equipment to the system neutral. The grounding connection from the portable equipment will usually consist of a grounding conductor run with the power supply conductors in a cable assembly or flexible cord. Vehicle and skid-mounted equipment that is installed at a location that has a suitable accessible grounding conductor must have a temporary grounding connection placed between the equipment and the existing grounding conductor. This ground is in addition to any grounding conductor running with the power supply cables.

_

Portable equipment, above 600 V:

_

The requirements of Section 250-154 of the National Electrical Code apply for utilization equipment. These requirements include the following:

_

An impedance grounded supply system.

_

Equipment grounding connection to the system neutral grounding point.

_

Ground fault protection and monitoring of the continuity of the grounding conductor.

_

System grounding electrodes must be separated from any other electrodes by a minimum distance of 6 m (20 ft).

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Portable Equipment (Cont'd) -

When the requirements of Section 250-154 cannot be satisfied, the equipment must be immobilized and grounded in the same function as the equivalent stationary equipment.

-

Generation and distribution equipment must be immobilized and grounded in the same fashion as equivalent stationary equipment.

-

All portable equipment grounded in the same fashion as equivalent stationary equipment must have a minimum of two grounding conductors in parallel between the equipment and the ground grid, ground bus, or other grounding electrode. These conductors must be physically separated and either removed from or protected from sources of mechanical damage.

Example of Mobile Equipment Grounding Assume that a mobile diesel generator has been purchased and that the grounding requirements for the mobile diesel generator must be established. The unit is mounted on a truck and can produce 200 kW of electrical power at an output of 277/480V, three-phase. The frame of this vehicle can serve as the grounding electrode if the following conditions are in place: _

The frame of the generator is bonded to the vehicle frame.

_

The noncurrent-carrying metal parts of the equipment and the equipment grounding conductor terminals of the receptacles are bonded to the generator frames.

_

The system complies with all other provisions of NEC Article 250.

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DETERMINING THE BUILDING AND STRUCTURE GROUNDING REQUIREMENTS FOR SAUDI ARAMCO INSTALLATIONS The following is a list of applicable codes and standards that apply to Saudi Aramco buildings and structures: SAES-P-111

Grounding

SADP-P-111

Grounding

AA-036572 Switch

Drawing, "Grounding Arrangement for 115 kV Disconnect Structure"

AB-036562

Drawing, "Standard Switch Operating Platform"

SAES-O-101

Standard Security Fence

SAES-P-100

Basic Criteria

SAES-P-119

Substations

SAES-T Series

Communications Standards

IEEE 80

Guide for Safety in Alternating-Current Substation Grounding

IEEE 81

Guide for Measuring Earth Resistivity, Ground Impedance, and Earth Surface Potentials of a Ground System

IEEE 142

Recommended Practice for Grounding of Industrial and Commercial Power Systems

IEEE 367

Guide for Determining the Maximum Electric Power Station Ground Potential Rise and Induced Voltage from a Power Fault

NFPA 76A

Essential Electrical Systems for Health Care Facilities

NFPA 76B

Electricity in Patient Care Areas of Hospitals

NFPA 78

Lightning Protection Code

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DETERMINING THE BUILDING AND STRUCTURE GROUNDING REQUIREMENTS FOR SAUDI ARAMCO INSTALLATIONS (CONT'D) This section will familiarize the Participants with the application of the basic safety codes to different facilities. This section includes the more important aspects of safety grounding for the following types of buildings and structures: _ _ _ _

Residential Building Industrial Building Manned Structures Unmanned Structures

Residential Building Grounding for residential buildings starts with the system grounding at the service disconnect(s). Ground wires are then run from the main service panel, with the power conductors, to the equipment or the electrical outlets. System grounding is normally accomplished through connection of the grounded conductor and the grounding conductor to the grounding electrode conductor. In the case of small residential buildings, the grounding electrode conductor often consists of underground metal piping and building steel. Ground loops for grids are seldom required for residential buildings. Industrial Building An industrial building is a facility in which products are manufactured or stored. Industrial buildings are usually part of a complex with large power requirements. Substation grid grounding, building ground loops, and an extensive system of ground conductors that tie all necessary items back to their respective power source are used. Manned Structures Manned structures are facilities that are occupied during normal business hours or on a 24hour basis. Manned structures are grounded in the same manner as industrial buildings. Unmanned Structures An unmanned structure is a building that is not occupied during normal business hours. Examples of unmanned structures are pumping stations and water treatment plants. The same grounding rules apply to unmanned structures and to manned structures.

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DETERMINING THE LIGHTNING PROTECTION REQUIREMENTS FOR SAUDI ARAMCO INSTALLATIONS This section will familiarize the Engineer with the hazards to life and to equipment that are created by lightning, as well as the grounding methods used at Saudi Aramco to reduce the dangers. This section includes the following information: _ _ _ _

Nature of Lightning Equipment and Structures to be Considered Requirements for Good Protection Practices for Lightning Protection

Nature of Lightning Lightning is the discharge of high-potential cells (usually negative) between clouds or from a cloud to the earth. These charged cells normally attract the charges of opposite polarity on the surface of the earth or on high objects. When the charge reaches a critical level (when the air insulation between the cloud and the earth breaks down), the charge develops a stepped ionized path, resulting in a high current discharge (stroke) that neutralizes the cloud charge and earth charge. The discharge current increases from zero to a maximum in 1 to 10 _s, then declines to half the peak value in 20 to 1000 _s. This discharge can be repeated one or more times over the same path, in rapid succession, because of the recharging in the cloud. The average peak stroke current is about 20,000 A, although some peak stroke currents are as great as 27,000 A. SAES-P-111 assists the Electrical Engineer in deciding when to protect or when not to protect a building or structure from lightning. Specifically, SAES-P-111 provides information on how to determine the "Risk Index." The Risk Index Tables are in Work Aid 6. Each table has a list of conditions. The Electrical Engineer selects the condition that is correct for the building or structure that is being considered for lightning protection and then records the risk figure for that condition. Once the risk figure for all seven tables has been determined, the Electrical Engineer sums the seven risk figures. The total is known as the Risk Index. If the Risk Index is 40 or greater, lightning protection must be provided.

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DETERMINING THE LIGHTNING PROTECTION REQUIREMENTS FOR SAUDI ARAMCO INSTALLATIONS (CONT'D) The seven tables provided in Work Aid 6 are as follows: _ _ _ _ _ _ _

Table 1 - Usage of Structure Table 2 - Type of Construction Table 3 - Contents of Structure Table 4 - Degree of Isolation Table 5 - Type of County Table 6 - Height of Structure Table 7 - Lightning Prevalence

Equipment and Structures to be Considered The following buildings and structures should always be provided with a satisfactory lightning protective system: _

Buildings and structures over 30 m (100 ft) in height.

_

Schools

_

Hospitals

_

Buildings and structures where the "Risk Index" is 40 or greater.

Equipment and structures can be separated into five classifications according to the need for lightning protection. These classifications are listed in IEEE Standard 142 and are as follows: _ _ _ _ _

First Class Second Class Third Class Fourth Class Fifth Class

First Class

First class equipment and structures need very little or no additional protection. This class includes the following:

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Equipment and Structures to be Considered (Cont'd) _

All metal structures except tanks or other enclosures of flammable materials.

_

Water tanks, silos, and similar structures that are largely constructed of metal.

_

Flagpoles made of conductive material.

The only real requirement for this class is to connect the equipment or structure to a suitable grounding electrode. A typical Saudi Aramco example of first class equipment or structure would be a water tank. Second Class

Second class equipment and structures consist of buildings with conducting surfaces and nonconducting framework, such as metal-roofed and metal-clad buildings. This class requires the addition of down conductors to connect the exterior roof and cladding to suitable grounding electrodes. A typical Saudi Aramco example of a second class structure would be a chemical storage building. Third Class

Third class equipment and structures consist of metal-framed buildings with nonconducting facings. These buildings need the addition of conducting air terminals that are suitably located and connected to the frame. The conducting air terminals must project beyond and above the facing in order to act as the lightning terminal points and to thus eliminate the potential of a puncture of the facing. Chemical processes are often housed in this type of structure and are an example of the third class structures at Saudi Aramco. Fourth Class

Fourth class equipment and structures consist of non-metallic structures, either framing or facing. These structures require extensive protection treatment. The following are examples of fourth class structures:

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Equipment and Structures to be Considered (Cont'd) _

Buildings that are constructed of wood, stone, brick, tile, or other nonconducting materials and that are without metal reinforcing members.

_

High stacks and chimneys. Even with reinforcing members, these stacks and chimneys should have full lightning protection treatment of air terminals, down conductors, and grounding electrodes.

An example of this class at Saudi Aramco includes the stacks for boilers. Fifth Class

Fifth class equipment and structures consist of items of high risk or loss consequences that normally receive full lightning protection treatment, including air terminals or diverters, down conductors, and grounding electrodes. This class includes the following: _

Buildings of great aesthetic, historical, or intrinsic value.

_

Buildings containing readily combustible or explosive materials.

_

Structures containing substances that would be dangerous if released by the effects of a lightning stroke.

_

Tanks and tank farms.

_

Power plants and water pumping stations.

_

Transmission lines.

_

ower stations and substations.

There are many examples of this class at Saudi Aramco.

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Requirements for Good Protection Direct lightning protection (lightning protection systems) consists of placement of air terminals at the top perimeter of the structure to be protected, and connection of the air terminals by adequate down conductors to the grounding electrodes (earth). The down conductor should not include any high-resistance or high-reactance portions or connections and should present the least possible impedance to earth without sharp bends or loops. Steelframed structures, which are adequately grounded, meet these requirements with only the provision for terminating the stroke on a metallic air terminal. The metallic air terminal is connected to the frame structure, to avoid the possibility of puncturing any roofing or siding to reach the frame. In the absence of a steel framework, a down conductor providing at least two paths to earth for a lightning strike to any air terminal is generally adequate. Air terminals that are attached to the structure itself are pointed solid rods or pipes at least 10 inches (0.25m) long to possibly 2 feet (0.61m) long. On building edges, 10 inches (0.25m) terminals should not be separated by more than 20 feet (6.1m), and 2 ft. (0.61m) terminals should not be separated by more than 25 feet. (7.6m). Fifty feet (15.2m) of spacing will suffice within the periphery. At least two down conductors should be provided on all structures; only one down conductor is needed for masts, spires, and flagpoles. The greater the number of down conductors and grounding electrodes, the lower the voltage that will be developed within the protection system, and the better the protection. Every down conductor must be connected, at its base, to an earthing or grounding electrode. This grounding electrode should be within 2 feet (0.61m) of the base of the building and should extend below the building foundation, if possible. Interior metal parts of a non-metal-framed building within 6 feet (1.83m) of a down conductor should be connected to the down conductor. Exterior emergency ladders should also be bonded to the nearest down conductor. On a flat-top building protected by air terminals, all metallic parts and equipment that are projecting higher than the air terminals (such as airconditioning equipment) should be bonded to the lightning protection system. For high-rise buildings and towers, an equalizing horizontal bonding loop should be installed approximately every 100 feet (30m).

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Requirements for Good Protection (Cont'd) Component Parts of a Lightning Protection System

SAES-P-111 and SADP-P-111 provide detailed information on the components of a lightning protection system. The principle components of the lightning protection system are as follows: _ _ _ _

Air Terminals Down Conductors Joints and Bonds Ground Terminations

Air Terminals - NFPA 78 contains detailed information on air terminal design and support. No part of a flat or gently sloping roof on structures is to be more than 7.5 m (25 ft) from the nearest horizontal conductor. Down Conductors - Two or more down conductors must be provided on most kinds of

structures. One down conductor is permitted for flag poles, masts, spires or similar structures. The total number of down conductors on structures having a flat or gently sloping roof, and on irregular shaped structures are to be such that the average distance between the down conductors does not exceed 30 m (100 ft). The bend in a conductor that embraces a portion of a building, such as an eave, must have a radius that is greater than 200 mm (8 in). The angle of any turn must not exceed 90o, and the conductors must preserve a downward or horizontal course. Enforcing rods that are butt-welded together are acceptable as down conductors, but reinforcing rods that are overlapped and bound with tye-wire are not acceptable as down conductors. Down conductors should be installed within the building or the structure to avoid the potential "removal for gain" that can occur with external copper conductors. In order to prevent lightning from "jumping" off the down conductor and to the conduit, down conductors must not be installed inside a metallic conduit. Joints and Bonds - Joints and bonds must be made to the same standard as required for

electrical installations.

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Requirements for Good Protection (Cont'd) Grounding Terminations - The earth resistance of all lightning protection grounding

terminations must be tested through use of an earth tester that is to be clamped to any convenient part of the lightning protective system. The combined resistance to earth of the whole of the lightning protection system must be as low as economically possible but must not exceed 25 ohms. Other grounds, such as substation grids or consumer grounding, must be bonded to the lightning protection grounds. The intent of the grounding is to minimize the risk that is due to differential voltages that could cause hazards to personnel or "sideflash" possibilities. Reinforcing rods in reinforced concrete foundations are not required to be bonded to the ground termination. Practices for Lightning Protection IEEE Standard 142, Section 3.3.4 provides the practices for lightning protection. information is divided into the following seven (7) sections: _ _ _ _ _ _ _

This

General Tanks and Tank Farms Non-Conducting Heavy-Duty Stacks Steeples High Masts Power Stations and Substations Communication Towers

General

Buildings and structures involving hazardous liquids, gases, or explosives require additional protection. In these buildings and structures, the object of the additional protection is to keep the current away from the structure without use of the building's metal skin or the framework as a down conductor. A separate diverter protection system is employed for these buildings and structures (e.g., tanks, tank farms, and explosive manufacture and storage).

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Practices for Lightning Protection (Cont'd) The diverter element consists of one or more masts, or one or more elevated wires (between masts or poles), that meet the requirements of lightning protection. The masts or poles are normally at least 10 feet (3m) from any part of the structure to be protected. Similarly, elevated wires that are above the structure must remain not less than 10 feet (3m) above the structure. Metal masts can act as grounding conductors. Wood poles should have an air terminal securely mounted to the top of the pole. Copper or copper-weld conductor should be provided along the pole as a grounding conductor. The guy wires for an elevated wire span can be designed to serve as grounding conductors. Suitable earthing electrodes are necessary, as with all other types of grounding conductors. Tanks and Tank Farms

Provided that the base of the tank is adequately grounded, a tank that contains flammable liquids or gases does not always need to be protected against lightning. Direct lightning strikes to the tank top or walls are permitted as long as the steel is thicker than 3/16 inches (0.476cm). These strikes are allowed because there is little danger of the lightning strikes puncturing the tank. Steel tanks with steel roofs and floating metal roofs are generally considered to be self-protecting. Tanks with nonmetallic roofs are not self-protecting and should be protected with air terminals, conducting masts, or elevated ground wires. In all cases, joints and piping connections should be electrically continuous. All vapor or gas openings should be closed or flame-proof. The possibility of a direct strike to the vicinity of a vent or leak is eliminated by an air terminal of suitable length. Refer to the Addendum, Saudi Aramco Drawing AB-036387, for grounding of floating tanks. Non-Conduction Heavy-Duty Stacks

Heavy-duty stacks (including stacks in petroleum and in chemical plants) require air terminals that are connected to a loop conductor around the top of the stack and at least two down conductors that are connected to grounding electrodes at the base of the stack. Air terminals should be made of solid copper or stainless steel and should be uniformly distributed around the top of cylindrical stacks, at intervals not exceeding 8 feet (2.44m). On square or rectangular stacks, air terminals should be located not more than 2 feet (0.61m) from the corners and should be spaced not more than 8 feet (2.44m) apart around the perimeter.

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Practices for Lightning Protection (Cont'd) The length of the terminals for nonflammable stack gas may be as little as 18 inches (0.46m). The length of the air terminals for ventilating stacks that emit explosive gas or dust should be not less than 5 feet (1.52m). The length of the air terminal where the gas or dust is explosive and under forced draft should be not less than 15 feet (4.57m). Also, the terminals should be tilted outward at 30o from the vertical. When the effluent is corrosive, as in flue gas, a 1/16 inch (1.6mm) thick lead coating on the air terminal is required. The loop is also kept below the top of the stack. Steeples

Steeples are similar to stacks except that they are sharp peaked and thus require only one air terminal. This one air terminal should project far enough above the top ornamentation to meet the requirements of lightning protection. Otherwise, multiple air terminals or a multipointed terminal should be used to provide equivalent protection. Steeples are frequently framed with wood, not metal, so adequate down conductors are a basic requirement. High Masts

Equipment on the sides of very high masts, such as television or FM antennas, can be protected from direct stroke damage through the addition of lateral spikes or thorns projecting outward from the sides of the mast. At heights above the critical radius of 100 or 200 feet (30 or 60m), spikes in a horizontal or near horizontal position with suitable spacing will cause strokes coming from the side to terminate on the spikes rather than on the mast itself. This practice will greatly reduce the possibility of damage to electrically fragile components by the termination of the lightning stroke arc. The number of spikes around the mast (three, four, five, or six), the length of the spikes, the vertical spacing along the mast need to be determined for optimum economics, and in accordance with the principles of lightning protection. When masts are installed on top of a building, the bottom of the mast structure must be bonded to the building grounding network at a minimum of two points. Power Stations and Substations

While transmission-line protection against lightning is an inherent part of the design and is well documented, the protection of stations and substations has received little attention. Lower stations and substations require protection from direct strokes. Masts or overhead wires (or both) can be used to ground lower stations and substations to the grounding network of the power station or substation.

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Practices for Lightning Protection (Cont'd) Protection of the attached overhead lines by means of an overhead grounded conductor or diverter (static wire) for 2000 feet (610m) away from the station or substation is recommended to preclude direct strokes on this section of the line and to reduce the duty on the station surge arresters. The spacing of this overhead grounded conductor or diverter and the associated down conductors from the phase conductors must not be less than the basic impulse insulation level of the lightning protection system. Otherwise, side flashes to the phase conductors will occur and cause unnecessary outages. The installation of overhead grounded conductors is not practical unless the attached overhead lines are 66 kV or above. Communication Towers

SAES-P-111 and SADP-P-111 provide the following specific information on lightning protection for communication towers: _

Communication towers must be grounded by two 35 mm2 (No. 2 AWG) conductors from points on diagonally opposite tower legs. These conductors are to run as directly as possible, but preferably by separate routes, to the ground grid or other grounding electrode.

_

Towers at transmission substations or industrial complexes are to located within the resistance area of the installation either by proximity or by suitable configuration of the buried grounding conductors.

_

Towers in remote locations will require a grounding electrode. This electrode is not to exceed 2 ohms of ground resistance. Ground rods will suffice in areas of low soil resistivity; otherwise, a ground grid is to be installed. Unless a power system that utilizes the ground grid requires a larger conductor, a 35 mm2 (No. 2 AWG) conductor is to be used for the grid.

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DETERMINING THE STATIC GROUNDING REQUIREMENTS FOR SAUDI ARAMCO INSTALLATIONS This section will discuss the hazards that static electricity can create and the methods that are available to eliminate these hazards. Specifically, the following topics will be discussed: _ _ _

Causes of Static Electricity Conditions for Buildup of Static Electricity Hazards of Static Electricity and Control in Various Areas

Causes of Static Electricity Static electricity is generated by the movement of electrons that occur when unlike materials are in contact with each other and are then separated. When two unlike materials are in intimate contact, electrons from one material move across the interface to the surface of the other material. The protons remain on the original material. When the materials are separated, electrical charges are produced on the materials. If the two materials are good conductors, the excess electrons will easily flow back to the material with the positive charge, and there will not be a static electricity discharge. But, if either or both of the materials are insulators and are not grounded, some of the excess electrons will be entrapped when the separation occurs, and the materials will be charged with static electricity. The potential of the static electrical charge is related directly to the amount of charge that is deposited on the material and is inversely proportional to the capacitance of this material. The relationship is expressed by the following equation: where: V Q C

= = =

potential, in Volts charge capacitance in farads

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Causes of Static Electricity (Cont'd) The developed potential can continue to grow if there is continuous charge generation. At some voltage level, the leakage current will equal the rate at which the charge is being generated, and a stabilized condition will be reached. If the sparking potential is reached, sparking will occur. Static electricity can be generated in the following situations: _

Pulverized materials passing through chutes or pneumatic conveyors.

_

Belt drives that use belts of non-conductive material.

_

Gas, steam, or air flowing through an opening.

_

Motion that involves changes in the relative position of contacting surfaces.

_

The human body in a low-humidity area. This generation can occur as a result of the contact of shoes with floor coverings or by personnel working near machinery that generates static electricity.

Conditions for Buildup of Static Electricity The possibility that static electricity will be produced and the rate at which static electricity will be produced depends on the following: _ _ _ _ _

Material Characteristics Speed of Separation Area in Contact Effect of Motion Between Substances Atmospheric Conditions

Material Characteristics

One of the materials or substances must have a higher insulating property than the other material or substance to generate static electricity. The amount of static electricity that exists between two materials will be proportional to the difference between the dielectric constants of the materials.

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Conditions for Buildup of Static Electricity (Cont'd) Speed of Separation

As the speed of separation of two substances is increased, the potential of the static electricity is increased. Area in Contact

The area of the contact between the substances has a direct bearing on the amount of static electricity. A larger contact area allows a greater charge to be transferred from one substance to the other. As the area in contact increases, the potential of the static electricity increases. Effect of Motion Between Substances

Static electricity is often thought to be a property of friction. This misunderstanding occurs because "rubbing" two materials together will cause static electricity. This static electricity occurs because the seemingly smooth items actually have peaks. When the items are rubbed together, the area of contact is increased. Increased motion will increase the amount of static electricity. Liquids that are sprayed from a nozzle can generate static electricity, and liquids in a tank that are agitated (stirred) can generate static electricity. These static electrical charges are caused by the motion of the liquid against the stationary components. Another very good example of static electricity that is increasing due to motion is a belt and pulley. As the speed of the belt increases, the amount of static electricity increases. Atmosphere Conditions

It is well known that humidity conditions are related to the production of static electricity. As humidity increases, the potential for static electricity decreases; therefore, the hazard of static electricity increases in an operation that requires controlled low-humidity conditions. Hazards of Static Electricity and Control in Various Areas The accumulation of static electricity on equipment, on materials being handled or processed, and on operating personnel introduces a potentially serious hazard in any area where flammable liquids, gases, dusts, or fibers are present. The discharge of the static electricity from an object to ground or to another object can be the cause of a fire or an explosion if the discharge takes place in the presence of readily flammable materials or combustible vapor and air mixtures.

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Hazards of Static Electricity and Control in Various Areas (Cont'd) The following parts of SAES-P-111 and SADP-P-111 provide direction on how to prevent the buildup of a static electricity charge and the subsequent discharge: _ _ _ _ _ _ _ _

Agitators, Stills and Similar Equipment Belts - Pulleys Pipelines - Manifolds Steel Equipment and Process Units Tank Cars - Loading Racks - Spur Tracks Tanks - Atmospheric Tanks - Floating Roof Tankers and Barges - Marine Facilities

Agitators, Stills and Similar Equipment

The requirements for preventing a static electrical charge from accumulating on agitators, stills and similar equipment and the subsequent discharge are found in SAES-P-111 and SADP-P-111, as follows: _

Vessels resting on earth, rock and oil, concrete, or brick foundations, or on concrete or steel supports are adequately grounded to prevent the accumulation of static electricity; no special grounding devices are required. However, where insulation exists between the vessel and the supports, grounding must be provided.

Belts-Pulleys

Belts that are made of rubber, leather, or other insulating materials, that are running at moderate or high speeds, generate considerable quantities of static electricity. Generation occurs when the belt separates from the pulley. The charges will exist on the pulley (regardless of whether the pulley is conducting or nonconducting) as well as on the belt. The requirements for preventing a static electrical charge from accumulating on belts and pulleys and the subsequent discharge are found in SAES-P-111 and SADP-P-111: _

If the pulley is made of a conducting material, such as metal, the charge will be dissipated through the shaft and bearing to ground and offer no ignition hazard. Where the machinery frame is insulated, or, the bearings are composed of insulating materials such as nylon, provisions for bonding and grounding are required.

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Hazards of Static Electricity and Control in Various Areas (Cont'd) _

A conductive belt or a belt made conductive through use of belt dressings must be used to prevent the accumulation of static charge. The belt dressings must be renewed frequently to be considered reliable and effective.

_

The use of flat belts in hazardous areas must be avoided. The risk of static ignition from V-belts is negligible.

_

Static combs are ineffective in draining off the static electrical charge and should not be used.

Pipelines-Manifolds

The requirements for preventing a static electrical charge from accumulating on pipelinesmanifolds and the subsequent discharge are found in SAES-P-111 and SADP-P-111, as follows: _

Permanent bonds between the separate lines in the piping system or between piping systems must be provided at tank car racks and in buildings where volatile materials are handled.

Steel Equipment and Process Units

The requirements for preventing a static electrical charge from accumulating on steel equipment and process units and the subsequent discharge are found in SAES-P-111 and SADP-P-111, as follows: _

Process equipment, (mainly steel vessels resting on steel or concrete structures) is required to be adequately grounded to prevent the accumulation of static charges.

_

Where electrical devices are installed on process equipment, grounding must be provided in accordance with SAES-P-111 and NFPA 70 (NEC).

Tank Cars-Loading Racks-Spur Tracks

The requirements for preventing a static electrical charge from accumulating on tank cars, loading racks and spur tracks and the subsequent discharge are found in SAES-P-111 and SADP-P-111, as follows:

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Hazards of Static Electricity and Control in Various Areas (Cont'd) _

Tank cars are considered to be adequately grounded through the rails to prevent any hazardous accumulation of static charges on the tank body.

_

Where a tank car is unloaded or where rack installations are unloaded, a bond wire must be provided between the nearest rail and fill line or to the rack structure. A number of fill pipes can be electrically connected, and a single bond wire from the group can be attached to the rail.

_

No additional bonding of the tank car is required because the car is adequately bonded to rails.

_

To prevent arcing where stray currents are likely to occur, the rails must be bonded to each other. This bond must be a conductor not smaller than 25 mm2 (No. 4 AWG), and it must be an adequate ground.

_

Additional protection against stray currents must be provided through installation of insulated pipe joints between the loading and unloading facilities and the connecting yard piping.

_

If the spur track is connected to a railroad equipped with rail-circuit signal systems, the spur must be isolated by rail joints that are insulated.

Tanks-Atmospheric

The requirements for prevention of accumulation of a static electrical charge on atmospheric tanks and for prevention of the subsequent discharge are found in SAES-P-111 and SADP-P111, as follows: _

The shells of petroleum product storage tanks must be grounded at a minimum of four points that are spaced equidistantly around the base of the tank. Each point must be bonded to the area ground grid or to a ground rod. The resistance between the tank shell and remote earth must not exceed 10 ohms.

Tanks-Floating Roof

The requirements for prevention of the accumulation of a static electrical charge on tanks with a floating roof and for prevention of the subsequent discharge are found in SAES-P-111 and SADP-P-111, as follows:

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Hazards of Static Electricity and Control in Various Areas (Cont'd) _

The roof seal must be maintained to provide a tight closure that reduces the chance of a vapor ignition at the seal. The possibility of vapor ignition at the seal must be further reduced by the installation of metallic shunt strips at each pantagraph hangar in the sealing mechanism from the roof to the tank shell. These metallic shunt strips must be spaced a maximum of 3m (10 ft.) apart and must be bolted to the sealing ring and to the roof per Standard Drawing AB-036387, which is located in the Addendum. The metallic shunt strips and the roof also must be bonded to the tank shell.

Tankers and Barges - Marine Facilities

The requirements for prevention of accumulation of a static electrical charge on tanks and barges and for prevention of the subsequent discharge are found in SAES-P-111 and SADPP-111, as follows: _

Insulated flanges and insulation for gangplanks must be provided at marine terminals where stray currents can enter a tanker or a barge via gangplanks or piping as follows:

_

Leakage from power systems where return circuits through the earth can cause currents to flow through nearby piping in contact with the earth.

_

Potentials generated by galvanic action through contact between piping and certain types of soil.

_

From cathodic protection systems.

_

Separated bodies and insulated flanges can become electrostatically charged when the product flows through the loading arm or hose. Such flanges must be bonded to the pier and/or ship piping. All metal on the shore side of the insulating flange must be electrically continuous and grounded via the dock piping, and all metal on the ship side must be electrically continuous and grounded via the ship piping.

_

Where cathodic protection is not provided, and where conductive hoses or metallic loading arms are used, insulating flanges must be permanently installed between the loading hose and pier piping. These insulating flanges will electrically insulate the ship from the pier piping.

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Hazards of Static Electricity and Control in Various Areas (Cont'd) _

Where cathodic protection is provided on submarine loading lines, insulating flanges must be provided on the shore end of the submarine lines. At least one joint of the loading hose must be certified by the manufacturer to be electrically nonconductive. Submarine lines used for crude or fuel oil cannot accumulate static charges on isolated flanges due to high electrical conductivity of these oils. Two grounding connections on separate platform legs must be provided for grounding barges.

_

An insulated flange must have an insulated material between the standard flange faces. Each flange bolt must be encompassed by an insulating sleeve and must have insulating washers at both ends of the bolt.

_

Insulating gaskets, bushings and washers must be of a material that is electrically nonconductive and nonhygroscopic on all surfaces. Flange edges must be sealed with a 50 mm (2") wide polyethylene pipe wrap tape.

_

Gangplanks must be insulated at the pier end or at the ship end or at both ends. As an alternative, the gangplank can have an insulating joint between pier end and ship end. The insulation must be provided through use of rubber tires, rubber rollers, rubber mat or insulating joints similar to the method for use with insulating pipe flanges.

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DETERMINING THE GROUNDING REQUIREMENTS FOR SAUDI ARAMCO OFFSHORE PLATFORMS An offshore platform is a large structure with a deck-like construction on which the drill rig of an oil or gas well is erected. This platform is supported by a number of steel jacket legs. The following mandatory requirements for offshore platform grounding are listed in Saudi Aramco Engineering Standard SAES-P-111: _

Two or more of the steel platform legs must be used as the grounding electrode. Where two or more platforms are connected by walkways, two insulated grounding conductors must be installed to interconnect the grounding electrodes between each pair of connected platforms.

_

A ground bus with a minimum size of 120 sq. mm (4/O AWG) must be established in the main electrical room or area. Equipment and system neutral grounds must be connected to this bus by grounding conductors. This bus must extend to the grounding electrode by two separate conductors that are each sized to carry the rated bus current.

_

Exposed grounding conductors must be covered by green PVC. Exposed connections and terminations must be thoroughly covered with bitumastic (No. 50 or equal) and then taped.

_

Grounding conductors must not be installed in conduit except when necessary to protect the conductor against mechanical damage.

Saudi Aramco Design Standard SADP-P-111 provides the following additional guidelines for offshore platform grounding: _

A connection via grounding conductors should exist between all electrical equipment required to be grounded, all system neutrals, and the grounding electrode. Ground-fault currents should not rely on the structure of the platform for a return path.

_

Conductors should be selected in accordance with SADP-P-111 Chapter 3. A minimum size of 120 sq. mm (No. 4/0 AWG) should be used for ground bus conductors. All outdoor conductors should be PVC insulated and colored green (e.g., cable type TW).

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DETERMINING THE GROUNDING REQUIREMENTS FOR SAUDI ARAMCO OFFSHORE PLATFORMS (CONT'D) _

A ground bus should be established in the main electrical plant room or area. Equipment and system neutral grounds should be connected to this ground bus. From this ground bus, additional buses will extend to the grounding electrode, (the platform steel jacket legs) and to all parts having electrical equipment.

_

Upon completion, all grounding conductor connections and terminations should be thoroughly coated with bitumastic No. 50 or a product that is equivalent to bitumastic No. 50. Connections in PVC insulated conductors should then be taped so that the tape overlaps the point at which the PVC insulation was removed to make the connection.

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DETERMINING THE GROUNDING REQUIREMENTS FOR DIGITAL EQUIPMENT USED AT SAUDI ARAMCO INSTALLATIONS This section will cover the grounding of electronic equipment for both safety and the elimination of electrical noise from the system. The following publications provide techniques for grounding computers and related equipment in a safe and reliable manner: _ _

IEEE Paper Number PCIC-91-11 Grounding and Shielding in Facilities, Chapter 6 and 7

IEEE Paper Number PCIC-91-11 This paper discusses the problems that are encountered in the design of grounding systems for digital systems that meet the requirements given in the National Electrical Code (NEC) and in the equipment manufacturer's site planning manuals and installation instructions. Specifically, the paper describes an integrated grounding practice that can be followed by the equipment manufacturers, the engineering companies, and the construction companies. The key to grounding digital systems is to minimize, over the range of signal frequencies in use, the differences in ground potential between components in the system. One of the primary means of meeting this goal is to provide an integrated grounding system that meets the requirements of the NEC and that minimizes the noise in the system. The Addendum contains a copy of IEEE Paper Number PCIC-91-11, which provides a detailed discussion of the integrated grounding practices for digital systems. Grounding and Shielding in Facilities Chapter 6 and 7 Chapter 6 of the text "Grounding and Shielding in Facilities" provides details on the following topics: _ _ _ _ _ _ _ _ _ _ _ _

Interference - An Introduction Energy Storage in Electric Fields Energy Storage in Magnetic Fields Signal and Power Transfer Electrical Power and signal Transport Poynting's Vector Reflection of Energy at a Surface A New Look at Voltage Fields and Ground Planes Using Ground Planes The Measurement of Interference Passive Filters

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Grounding and Shielding in Facilities Chapter 6 and 7 (Cont'd) _ _ _ _ _ _ _

Power Filter Location Modes of Interference Differential Mode Receptacle Filtering Transient Protection Equipment Ground Current at Power Frequencies Conductive Emission Control at Power Frequencies Conduit and RF Processes

Chapter 7 of "Grounding and Shielding in Facilities" contains detailed information on the following topics: _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

The Search for the Perfect Ground Shielding and Electric Field The Transformer in Buildings and Equipment Common-Mode Shielding in Transformers Differential-Mode Coupling High-Frequency Power Filtering Transformers Again Computer Floors Cellular Raised Floor Utilization in a High-Frequency Noise Environment Ground Planes Lightning and Zero Signal Reference Grids and Planes The Issue of Ground Loops Power and the Ground Plane Fields Entering a Facility Shielded Room Multiple Grounding Problems LC Filters and Shielded Rooms Double (Nested) Walled Shielded Rooms The Magnetic Field Problem Internal Equipment Containing Radiation Inside a Screened Room Fiber Optics and Shielded Rooms The Role of Skin Effect Radiation from a Shielded Room The Aperture Problem in Shielded Rooms Narrow Apertures and Arrays Anechoic Shielded Rooms Shielded Buildings Electrostatic Discharge (ESD) The ESD Process ESD Best Practices

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_

ESD Tests

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WORK AID 1: SAUDI ARAMCO AND INDUSTRY STANDARDS APPLICABLE TO EQUIPMENT GROUNDING Saudi Aramco Engineering Standard _

SAES-P-111 : Grounding

Saudi Aramco Design Practice _

SADP-P-1111 : Grounding

IEEE Standards _ IEEE STD 80-1986 : IEEE Guide for Safety in AC Substation Grounding _

IEEE STD 142-1982 : IEEE Recommended Practice for Grounding of Industrial and Commercial Power Systems.

National Electrical Code _

Article 250

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WORK AID 2:

FORMULA AND TABLE OF WIRE SIZES AND AMPACITY

Section 1 Procedure, Table and Formula for Determining the Size of Copper Grounding Conductors for Equipment Connected Directly to the LV Side of a Transformer Without an Intervening Protection Device, for Systems Rated 600V and Below. 1.

Obtain the kVA rating of the power source transformer whose secondary is directly connected to the equipment without an intervening protection device, through us of the transformer nameplate or the following formula:

where:

V I

= =

System Voltage Current

2.

Determine the type of protection (fuses or circuit breaker) provided for the primary side of the power source transformer. This determination can be made through the use of personal knowledge of the system, electrical drawings, or a visual inspection.

3.

Determine the size of the copper grounding conductor needed from the table of Ground Conductor Sizes shown in Figure 14, through the use of the kVA rating obtained in step 1, and the type of protection determined in step 2.

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Table of Ground Conductor Sizes Figure 14 Section 2 Procedure and Table for Determining the Size of Equipment Grounding Conductors for Equipment Beyond the Main Switchboard or the Transformer Output Protection Device, for Systems Rated 600V and Below. 1.

Determine the rating of the automatic overcurrent protection device in the circuit that is ahead of the equipment. This determination can be made through the use of personal knowledge, electrical drawings, or a visual inspection.

2.

Determine the size of the equipment grounding conductor needed from Table 250-95 of the NEC (shown in Figure 15) through use of the automatic overcurrent protection device rating determined in step 1.

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WORK AID 2 (Cont'd)

Table 250-95 Figure 15

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WORK AID 2 (Cont'd) Section 3 Table, Formula, and Procedure for Determining Grounding Conductor Sizes in Solidly Grounded Systems Over 600V. 1.

Determine the three second short-time current capability of the circuit breaker ahead of the grounding conductors. This determination can be made through use of personal knowledge, the circuit breaker nameplate, electrical drawing, or the following formula:

Note: The formula must be used in cases where circuit breakers are not installed or where three second short-time capabilities are not assigned. 2.

Determine the size of the grounding conductor needed from the table of grounding conductor sizes for solidly grounded systems over 600V (shown in Figure 16) through use of the three second short-time current capability determined in step 1.

Grounding Conductor Size for Solidly Grounded systems Over 600V Figure 16

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WORK AID 2 (Cont'd) Section 4 Table and Procedure for Determining Grounding Conductor Sizes in Impedance Grounded Systems Over 600V. 1.

Answer the following question to determine the basis for the size of the grounding conductor in question.

2.

Determine the 10 second current rating of the neutral grounding device or the 10 second current rating of the combined neutral grounding devices for systems with multiple neutral grounding devices connected in parallel. This determination can be made through use of personal knowledge, the circuit breaker nameplate, or electrical drawings.

3.

Determine the size of the grounding conductor needed from the table of grounding conductor sizes for impedance grounded systems over 600V shown in Figure 17, through use of the current rating determined in step 2.

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Grounding Conductor Size for Impedance Grounded System Over 600V Figure 17

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WORK AID 3: FORMULA TO DETERMINE CONDUCTOR SIZE AND REFERENCES FOR DETERMINING STATIONARY EQUIPMENT GROUNDING REQUIREMENTS Use the following formula to calculate equipment ground conductor sizes for systems over 600V. where:

tc

=

3 seconds

ar

=

0.00393 @20oC for soft drawn copper

pr

=

1.7241 _ohm-cm @ 20oC

ko

=

234 inverse of thermal coeff of resistivity 0oC

TCAP

=

3.422 j/cm3/oC

Tm

=

1083oC (fusing temperature of copper)

Ta

=

40oC (ambient temperature)

I

=

RMS current in kA

For stationary equipment grounding requirements the Engineer should refer to Saudi Aramco Engineering Standard SAES-P-111-6 and Design Practice SADP-P-111 Chapter 3 & 6.

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WORK AID 4: FORMULA TO DETERMINE CONDUCTOR SIZE AND REFERENCES FOR DETERMINING MOBILE EQUIPMENT GROUNDING REQUIREMENTS Use the following formula to calculate equipment and systems neutral ground conductor sizes for systems over 600V or for impedance grounded systems where short circuit levels exceeds 12 kA.

where:

tc

=

3 seconds

ar

=

0.00393 @20oC for soft drawn copper

pr

=

1.7241 _ohm-cm @ 20oC

ko

=

234 inverse of thermal coeff of resistivity 0oC

TCAP

=

3.422 j/cm3/oC

Tm

=

1083oC (fusing temperature of copper)

Ta

=

40oC (ambient temperature)

I

=

RMS current in kA

For mobile equipment grounding requirements, the Engineer should refer to Saudi Aramco design practice SADP-P-111 Chapters 3 and 6 as well as Article 250 NEC.

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WORK AID 5: REFERENCES FOR DETERMINING BUILDING AND STRUCTURE GROUNDING REQUIREMENTS NEC Article 250: Grounding Saudi Aramco Design Practice SADP-P-111, Chapters 3 and 6.

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WORK AID 6: REFERENCES FOR DETERMINING LIGHTNING PROTECTION REQUIREMENTS AND TABLES FOR CALCULATING RISK INDEX Saudi Aramco Design Practice SADP-P-111, Chapter 9, Lightning Protection of Buildings and Structures. "Risk Index" To assist in deciding "when to protect or when not to protect" a building or structure against lightning a "Risk Index" must be determined. For a specific application the summation of all the relevant risk figures from Table 1 to 7 inclusive provides the "Risk Index". When the "Risk Index" totals 40 or greater lightning protection must always be provided. TABLE 1 - USAGE OF STRUCTURE Houses and other buildings of comparable size with outside aerial .. .. .. .. .. .. Factories, workshops and laboratories .. .. .. Office blocks, hotels, blocks of flats and other residential buildings other than those included below .. .. .. .. .. .. Places of assembly, e.g. halls, theaters, museums, exhibitions, department stores, post offices, airports, and stadium structures .. .. .. .. .. .. .. .. .. Schools, hospitals .. .. .. .. .. .. .. .. ..

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Risk Figure 2 4 6 7

8 10

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WORK AID 6 (Cont'd) TABLE 2 - TYPE OF CONSTRUCTION Steel framed encased, with any roof other than metal + .. .. .. .. .. .. .. .. Reinforced concrete with any roof other than metal .. .. .. .. .. .. .. .. .. Brick, plain concrete or masonry with any roof other than metal .. .. .. .. .. .. Steel framed encased or reinforced concrete with metal roof .. .. .. .. .. .. .. .. Timber framed or clad with any roof other than metal .. .. .. .. .. .. .. .. .. Brick, plain concrete, masonry, timber framed but with metal roofing .. .. .. .. .. +

Risk Figure 1 2 4 5 7 8

A structure of exposed metal which is continuous down to ground level is excluded from the tables as it requires no lightning protection beyond adequate grounding arrangements.

TABLE 3 - CONTENTS OF STRUCTURE Ordinary domestic or office buildings, factories and workshops not containing valuable or specially susceptible contents .. .. .. .. .. .. .. .. .. .. Industrial buildings with specially susceptible contents + .. .. .. .. .. .. .. Power stations, gas works, telephone exchanges, radio stations .. .. .. .. .. Industrial key plants, museums, art galleries or other buildings with specially valuable contents .. .. .. .. Schools, hospital, places of assembly +

2 5 6 8 10

Indicates items of particular value or materials vulnerable to fire or the results of fire.

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WORK AID 6 Cont'd) TABLE 4 - DEGREE OF ISOLATION Structure located in a large area with structures of the same or greater height (e.g., in a large town) .. .. .. .. .. Structure located in an area with few other structures of similar height.. .. Structure completely isolated or exceeding at least twice the height of surrounding structures .. .. .. .. .. .. .. ..

Risk Figure

2 5 10

TABLE 5 - TYPE OF COUNTRY Flat country at any level .. .. .. .. Hill country .. .. .. .. .. .. .. .. Mountain country between 300 m and 900 m (1000 ft and 3000 ft) Mountain country above 900 m (30090 ft) ..

2 6 8 10

TABLE 6 - HEIGHT OF STRUCTURE Exceeding 9 m (30 ft) 9 m (30 ft) 15 m (50 ft) 18 m (60 ft) 24 m (80 ft)

Not Exceeding 15 m (50 ft) 18 m (60 ft) 24 m (80 ft) 30 m (100 ft)

2 4 5 8 11

Structures higher than 30 m (100 ft) require protection in all cases. TABLE 7 - LIGHTNING PREVALENCE Risk Figure for Arabian Conditions

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WORK AID 7: REFERENCES FOR DETERMINING STATIC GROUNDING REQUIREMENTS This Work Aid is designed to help the Participants in performing Exercise 7. _

SAES-P-111

_

SADP-P-111 Chapter 14

_

IEEE STD.142, Section 3

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WORK AID 8: REFERENCES FOR DETERMINING OFFSHORE PLATFORM GROUNDING REQUIREMENTS This Work Aid is designed to help the Participants in performing Exercise 8. _ _

SAES-P-111 SADP-P-111 Chapter 8

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WORK AID 9: REFERENCES FOR DETERMINING DIGITAL EQUIPMENT GROUNDING REQUIREMENTS

This Work Aid is designed to help the Participants in performing Exercise 9. _

IEEE Paper Number PCIC 91-11

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GLOSSARY dielectric constants

The property that determines the electrostatic energy that is stored per unit volume for unit potential gradient.

effectively grounded

Grounded through a grounding connection that has sufficiently low impedance (inherent or intentionally added or both) to prevent the buildup of voltages in excess of limits that are established for apparatus, circuits, or systems so grounded, in the event a ground fault does occur.

equipment ground

A ground connection to non-current carrying metal parts of a wiring installation, electric equipment, or both.

ground

A conducting connection, whether intentional or accidental, by which an electric circuit or equipment is connected to the earth or to some conducting body, of relatively large extent, which serves in place of the earth.

ground bus

A bus to which the grounds from individual pieces of equipment are connected and that, in turn, is connected to ground at one or more points.

ground clamp

A clamp that is used in connecting a grounding conductor to a grounding electrode or to something that is grounded.

ground conduit

A conduit that is used solely to contain one or more grounding conductors.

ground current

Current that is flowing in the earth or in a grounding connection.

ground detector

An instrument or equipment that is used for indicating the presence of a ground on an ungrounded system.

ground grid

A system of grounding electrodes that consists of interconnected bare cables buried in the earth to provide a common ground for electric devices and metallic structures.

ground lug

A lug that is used to connect a grounding conductor to a grounding electrode or to something that is grounded.

ground-return circuit A circuit in which the earth is utilized to complete the circuit.

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grounded

Connected to earth or to some extended conducting body that serves instead of the earth, whether the connection is intentional or accidental.

grounded circuit

A circuit in which one conductor or point (usually the neutral conductor or neutral point of transformer or generator windings) is intentionally grounded, either solidly or through a grounding device.

grounded concentric wiring system

A grounded system in which the external (outer) conductor is solidly grounded and that completely surrounds the internal (inner) conductor throughout its length. The external conductor must be jacketed.

grounded conductor

A conductor that is intentionally grounded, either solidly or through a current limiting device.

grounded electrode

A conductor used to establish a ground: for instance, ground grids, ground rods, ground wells, etc.

grounded system

A system of conductors in which at least one conductor or point (usually the middle wire or neutral point of transformer or generator windings) is intentionally grounded, either solidly or through a current limiting device.

grounding conductor

The conductor that is used to establish a ground and that connects an equipment, device, wiring system, or another conductor (usually the neutral conductor) with the grounding electrode or electrodes.

grounding connection A connection that is used in establishing a ground and that consists of a grounding conductor, a grounding electrode and the earth (soil) that surrounds the electrode. grounding outlet

An outlet that is equipped with a receptacle of the polarity type and that has, in addition to the current-carrying contacts, one grounded contact that can be used for the connection of an equipment grounding conductor.

grounding

A transformer that is intended primarily to provide a neutral point for grounding purposes.

transformer

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guard wire

A grounded wire that is erected near a lower-voltage circuit or public crossing in such a position that a high (or higher) voltage overhead conductor cannot come into accidental contact with the lower-voltage circuit, or with persons or objects on the crossing without first becoming grounded by contact with the guard wire.

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impedance grounded

Grounded through impedance.

neutral ground

An intentional ground applied to the neutral conductor or neutral point of a circuit, transformer, machine, apparatus, or system.

reactance grounded

Grounded through impedance, the principal element of which is reactance.

resistance grounded

Grounded through impedance, the principal element of which is resistance.

solidly grounded

Grounded through an adequately grounded connection in which no impedance has been inserted intentionally.

system grounding conductor

An auxiliary solidly grounded conductor that connects the individual grounding conductors in a given area.

ungrounded

A system, circuit, or apparatus without a conducting body that serves instead of the earth, whether the connection is intentional or accidental.

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ADDENDUM A Saudi Aramco Drawing AB-036387 IEEE Paper PCIC-91-11

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