High Voltage Techniques

Transmission of Electric Energy

High Voltage Power System Components and Technology Main components used in high voltage power systems are as follows: • Synchronous generators • Power transformers • Disconnectors • Circuit breakers • Overhead lines and conductors • Towers • Insulators • Cables • Bus bars

Transmission of Electric Energy

High Voltage Power System Components and Technology Measuring and protection components used in high voltage power systems are as follows: • Voltage and current transformers • Relays • Surge arresters • Control circuits • Voltage dividers • Earthing switches Voltage regulating components used in high voltage power systems are as follows: • Series and shunt reactors • Series and shunt capacitors

Insulators to insulate means "to separate or cover with a nonconducting material in order to prevent the passage or leakage of electricity, heat, or sound." Communication and electric line wires in service must be kept as dry as possible in order to function efficiently, and to cut down on loss of current. The wires are kept off of the ground by being strung between poles. But something was needed to keep the wires and (sometimes wet) poles apart. This "something" had to meet three basic needs: • it must be made of a fast-drying nonconducting material • it must be able to hold the line wire in place • it must stay on the pole This "something" is the insulator. It was developed and improved upon over the years to meet those basic requirements is most commonly made of glass or porcelain

Insulators There are a lot of insulator types used for various purposes:

• • • • • • • •

Post insulators Pin type insulators String insulators Transformer bushing insulators Lightning arrester insulators Wall bushing insulators Capacitive voltage transformer bushings Special type insulators.

Insulators

Insulators

Insulators

Insulators

Insulators

Disconnectors Disconnectors are used for galvanic isolation of networks or sections of switchgear installations. As an independent air insulated-device, they form a visible isolating distance in their open position. More than 10 different designs are in use around the world. The most important are: • knife -contact disconnectors • rotary disconnectors • two column vertical break disconnectors • single-column disconnectors.

Disconnectors

Knife-contact disconnectors The classic design of the disconnector is the knife-contact disconnector. Their moving contacts have the knife shape. There are indoor and outdoor types. They can be actuated manually and in remotely operated installations by motor or compressed air drives.

Indoor knife-contact disconnectors Indoor types are used in switchgears in buildings. Control arm is brought out to a safe distance . They are used in 10,15,30,45 KV systems with current ratings of 400, 630 and 1250 Amps. They have a simple and standard structure. The parts are: chassis, post insulator, fixed and moving contacts and armed moving mechanism.

Outdoor knife-contact disconnectors Outdoor types are used out of the buildings and are subject to environmental conditions like rain, dust, wind etc.

Disconnectors with fuse These connector include a pair of fuse for protection against short circuits. There are indoor and outdoor knife-types. They are used at the feeders of consumers with low power demand, at measuring voltage transformer feeders, and at auxiliary transformer feeders for substations.

Two column rotary disconnectors This disconnector type is used for rated voltages of 72.5 to 420 kV preferably in smaller installations and also in larger switchgear installtions as incoming feeder or sectionalizing disconnector. An earthing switch can be installed on both sides. Two rotating bases are mounted on a sectional steel frame and connected by a braced tie-rod. Post insulators are fixed to the rotating bases and carry the swivel heads with the arms and the high-voltage contacts. Both arms swivel 90 degrees with their insulators during the switching movement. Two column rotary disconnectors in their open position form a horizontal isolating distance. The rotary bases should be weather protected and should have maintenance-free ball bearings.

Two column rotary disconnectors

Two column rotary disconnectors

Three column rotary disconnectors These disconnector types are used with a side-by-side configuration of the three poles of a group. In comparison to two column rotary disconnectors, they allow smaller pole spacings and higher mechanical terminal loads. The two outer insulators are fixed to the base frame and carry the contact system. The middle insulator is fastened to a rotating base and carries the one-piece arm, which rotates approximately 60 degrees during a switching operation and engages the contact systems on the outer insulators.

Single column (pantograph) disconnectors In installations for higher voltages (> 170 kV) and multiple busbars , the single column disconnector (also referred to as pantograph or vertical-reach disconnector) requires less space than other disconnector designs. For this reason and because of the clear station layout , it is used in many switchgear installations. The switch status is clearly visible with the vertical isolating distance. The base of the disconnector is the frame, which holds the post insulator carrying the head piece with the pantograph and the gearbox. The actuating force is transferred through the rotating insulator to the gearbox. The suspended contact is mounted on the busbar situated above the disconnector. On closing, it is gripped between the pantograph arms. During the closing movement, the pantograph arms swivel through a wide range and are therefore capable of carrying the fixed contact even under extreme position changes caused by weather conditions. The feeder line is connected to the highvoltage terminal of the gearbox. In general, the single column disconnector allows higher mechanical terminal loads than the two column rotary disconnector.

Single column (pantograph) disconnectors

Single column (pantograph) disconnectors

Single column (pantograph) disconnectors

Two column vertical-break disconnectors This type of disconnector is preferred for higher voltages (>170 KV) as a feeder or branch disconnector. It differs from two-column rotary disconnectors by smaller space savings (with side-by-side configuration) and higher mechanical terminal loads. In its open state there is a horizontal isolating distance with the contact arm open upwards. The two post insulators are mounted on a frame. The gearbox with contact arm and high-voltage terminal and the fixed contact with high-voltage terminal are mounted on them. The rotating insulator fastened to the rotary bearing transfers the actuating force to the gearbox, which transmits the force into a torque for opening the contact arm. For rated voltages up to 245 KV one mechanism per three-phase disconnector is sufficient, at higher nominal voltages one mechanism per pole is generally used.

Two column vertical-break disconnectors

Circuit Breakers High voltage circuit breakers are mechanical switching devices capable of making, carrying continuously and breaking electrical currents both under normal circuit conditions and for a limited period, abnormal circuit conditions such as in the event of a short circuit. Circuit breakers are used for switching overhead lines, cable feeders, transformers, reactor coils and capacitors. They are also used in bus ties in installations with multiple busbars to allow power to be transmitted from one busbar to another. The following points are important when selecting circuit breakers. • • • • • • •

Maximum operating voltage on location Maximum load current occurring on location Maximum short circuit current occurring on location Network frequency Duration of short circuit current Switching cycle Special operational and climatic conditions

Circuit Breakers Important standards are IEC 62271-1 General and definitions 62271-100 Classification, Design and construction, Type and routine testing, Selection of circuit breakers for service, Informationin enquiries, tenders and orders ANSI (American National Standards Institute) C37 04 – 1979 Rating structure C37 06 – 1979 Preferred ratings C37 09 – 1979 Test procedure C37 10 – 1979 Application guide C37 11 – 1979 Application guide for transient recovery voltage C37 12 – 1979 Capacitance current switching

Electrical Characteristics Rated value: Value of a characateristic quantity used to define the operating conditions for which a switching device is designed and built and which must be verified by the manufacturer. Rated normal current: The current that the main circuit of a switching device can continuously carry under specified conditions. Rated short-time withstand current: Current that a switching device in closed position can carry during a specified short-time under prescribed conditions. Standardized rated normal currents: 200, 250, 400, 500, 630, 800, 1000, 1250, 1600, 2000, 2500, 3150, 4000, 5000, 6300A.

Standardized rated short-time currents: 6.3, 8, 10, 12.5,16, 20, 25, 31.5, 40, 50, 63, 80, 100 kA.

Electrical Characteristics Rated voltage: upper limit of the highest voltage of the network for which a switching device is rated. Standardized rated voltages: 3.6, 7.2, 12, 17.5, 24, 36, 52, 72.5, 100, 123, 145, 170, 245, 300, 362, 420, 550, 800 kV.

Peak making current: peak value of the first major loop of the current in one pole of a switching device during the transient period following the initiation of current during a making operation. Breaking current: current in one pole of a switching device at the instant of initiation of an arc during a breaking process.

Electrical Characteristics Applied voltage: voltage between the terminals of a circuit breaker pole immediately before making the current. Recovery voltage: voltage occurring between the terminals of a circuit breaker pole after interrruption of the current

Opening time: interval of time between application of auxiliary power to the copening release of a switching device and the seperation of contacts in all three poles. Closing time: interval of time between application of auxiliary power to the closing circuit of a switching device and the contact touch in all poles.

Electrical Characteristics Break time: interval of time between the beginning of opening time of a switching device and the end of the arcing time Make time: interval of time between application of the auxiliary power to the closing circuit of a switching device and the instant in which the current begins to flow. Rated insulation level: standardized combination of the rated values for the lightning impulse voltage, the switching impulse withstand voltage and the short time power frequency withstand voltage assigned to a rated voltage.

Electrical Characteristics Rated short duration power frequency withstand voltage : rms value of the sinusoidal a.c voltage at operating frequency that the insulation of a device must withstand under the specified test conditions for 1 minute. Rated lightning impulse withstand voltage: peak value of the standard voltage surge 1.2/50us that the insulation of a device must withstand Rated switching impulse withstand voltage: peak value of the unipolar standard voltage surge 250/2500us which the insulation of a device with a rated voltage of 300 kV and above must withstand.

Electrical Characteristics

1. Transient recovery voltage 2. Recovery voltage 3. Breaking time

e(t) system voltage ea(t) arcing voltage ik short circuit current

Circuit breaker types There are still a number of “small-oil-volume” circuit breakers in use for rated voltages up to 52 kV in systems, but for new installations only vacuum or SF6 circuit breakers are used. Circuit breakers can be stationary mounted or integrated into the panel in withdrawable unit design ith appropriate interlocking mechanism. Circuit breakers must be capable of making and breaking all-short circuit and service currents occurring at the operational site.

Vacuum circuit breakers Vacuum circuit breakers are available for short circuit breaking currents up to 63 KA with rated currents from 400 to 4000 A with rated voltages 12, 17.5, 24 and 36/40.5 KV.

Vacuum circuit breakers

Vacuum circuit breakers The components of the main current path (upper breaker terminal, vacuum interrupter, lower terminal etc.) are embedded in cast resin and thus completely enclosed by insulating material. The contacts are copper/chromium composite material, a copper base containing evenly distributed fine-grained chromium particles, which has a good extinguishing and arc-resistant response when switching short-circuit currents. Vacuum circuit breaker contains no arc extinguishing and quenching media.

Vacuum circuit breakers Actuating systems The travel of the moving contact between the open and closed positions in the vacuum circuit breaker is between 8 and 14 mm depending on the rated voltage. At the end of closing stroke , the energy for tensioning the contact pressure spring is required. The relatively low total energy requirement for vacuum circuit breaker is generally provided by mechanical spring stored energy operating mechanisms. Tripping is initiated by magnetic releases or manually.

SF6 circuit breakers Sulphur hexafluoride (SF6) is an inert, heavy gas having good dielectric and arc extinguishing properties. The dielectric strength of the gas increases with pressure and is more than of dielectric strength of oil at 3 kg/cm2. The puffer type arc quenching principle provides an effective arc-quenching gas flow by a mechanically driven piston.

SF6 circuit breakers

During the arcing period SF6 gas is blown axially along the arc. The gas removes the heat from the arc by axial convection and radial dissipation. As a result, the arc diameter reduces during the decreasing mode of the current wave. The diameter becomes small during the current zero and the arc is extinguished. Due to its electronegativity, and low arc time constant, the SF6 gas regains its dielectric strength rapidly after the current zero, the rate of rise of dielectric strength is very high and the time constant is very small.

SF6 circuit breakers

SF6 circuit breakers

Switchgear There are two types of switchgear commonly applied today for switching and protection of high voltage power distribution systems. One is metal-clad switchgear using draw-out circuit breakers and relays for protection. The other is metal enclosed switchgear using interrupter switches for load switching and power fuses for fault protection. Metal-clad switchgear contains drawout circuit breakers which are removed for required scheduled maintenance and removal of a breaker interrupts its load. Metal-clad switchgear also contains insulated bus which, when tested periodically, requires a shutdown of the gear. Metalenclosed switchgear is available with interrupter switches and fuses that require no scheduled maintenance, and the air-insulated bus does not require periodic dielectric testing. Annual maintenance normally consists of little more than a visual inspection through the windows of the gear. This switchgear should be seriously considered if only infrequent Interruptions can be tolerated by plant operations.

Switchgear Switchgears are designed to comply with fixed minimum clearances of live components from one another, from earth potential and from protecting barriers. When setting up these installations in electrical equipment rooms with restricted accessibility, protection against accidental contact with live components is sufficient. Metal enclosed switchgear are generally assembled from type-tested panels. The metallic and earthed enclosure protects personnel against approach to live components and against contact with moving parts. It also protects the installation against the penetration of foreign bodies. Switchgear of this type has the largest market share worldwide.

Switchgear

Switchgear

Switchgear

Switchgear

Switchgear

Switchgear A third type of switchgear is the gas insulated switchgear (GIS). The term “gasinsulated” refers to the fact that atmospheric air is not used as the gaseous insulating material inside the panels, i.e. The enclosure of the installation must be gas-tight against the environment. The advantage of gas-insulated switchgear compared to an air insulated installation is its independence from environmental influences such as moisture, salt fog and pollution. This results in less maintenance, increase operational safety and high availability. The samller dimensions due to compact design and increased dielectric resistance of the gaseous insulating material are also advantages.

Switchgear

Control systems for Switchgear A wide range of devices for protection, control and monitoring tasks is available for conventional secondary technology in medium voltage switchgear installations. The planning engineer selects the required units and combines them into one installation. The outputs are predominantly standardized to 1 A for current and 100 V for voltage.

Circuit breakers > 52 KV Basic design of HV outdoor circuit breakers with the following components is shown in the next figure: operating mechanism, insulators, interrupting chamber . Higher voltages and higher capacities are dealt with by increasing the number of interrupting chambers. Single chamber breakars are used for voltages up to 300 KV and breaking currents of 50 KA. Multiple chamber breakers are used for higher currents up to 80 KA in this voltage range. Multiple chamber breakers are used for voltages >300 KV. In the lower voltage range and for three-phase autoreclosure, it is best to mount the three poles on a common base frame. Single pole mounting and a seperate mechanism for each pole are standard for voltages above 245KV. The same interrupting chambers and mechanisms as indoor circuit breakers are also used with the integrated circuit breakers of gas insulated switchgear installations.

Circuit breakers > 52 KV

Circuit breakers > 52 KV

Circuit breakers > 52 KV

Circuit breakers > 52 KV

Circuit breakers > 52 KV

Circuit breakers > 52 KV

Some requirements for electrical control of circuit breakers SF6 Gas monitoring : The breaking capacity of a circuit breaker is dependent on the gas density in the breaker chamber. This is measured by a temeperature-compensated pressure gauge. If the gas pressure falls to aspecified value, an alarm is triggered. Local/remore control: To allow work on the breaker, it can generally be controlled from the local control cubicle; control can be switched from remote local by a selector switch. Autoreclosing: A single or three-pole autoreclosing is selected on the type of system earthing, the degree of the interconnection, the length of the lines and the amount of infeed from large power plants.

Instrument transformers for switchgear installations Instrument transformers are transformers used to feed measuring instruments, electricity meters, protection relays and similar equipment. Their function is to transform high voltages and currents to values that can be unified or measured safely with low internal losses. With current transformers , the primary winding carries the load current, while with voltage transformers, the primary winding is connected to the service voltage. The choice of a current transformer is based on the values of the primary and secondary rated current, the rated output of the transformer cores at a given accuracy class rating and the overcurrent limit factor or accuracy limit factor. Selection of the values for the primary and secondary rated currents should be based on standard levels. Secondary rated currents of 1A, 2A or 5A are available. Modern protection devices and measuring instruments have a relatively low burden, and so 1A is becoming the most frequently used secondary current.

Instrument transformers for switchgear installations Measuring instruments or meters, for instance KW,KVAR or KWH measure under normal load conditions. These devices require high accuracy, a low burden and low saturation. They normally function in the range of 5-120% of the rated current in accordance with accuracy classes 0.2 to 0.5. Burden is the load which may be imposed on a transformer secondary by cables and connected devices without causing an error greater than the stated accuracy classification. For protection relays and disturbance recorders, the information about the fault on the primary side has to be transmitted to the secondary side. Measurement under fault conditions in the overcurrent range requires lower accuracy, but the ability to transmit high fault currents which enable the protection relay to measure and selectively shut down the fault. Typical classes are 5P, 10P or TP. Several measuring and protection cores can be combined in each transformer.

Instrument transformers for switchgear installations

Instrument transformers for switchgear installations Depending on the design of primary winding , current transformers are divided into various types. This basically depends on the application (high or low voltage).High voltage transformers are as a rule designed with oil-paper or SF6 insulation.

Instrument transformers for switchgear installations

Instrument transformers for switchgear installations

Instrument transformers for switchgear installations

Instrument transformers for switchgear installations Voltage transformers can fundamentally be divided into two groups: inductive and capacitive voltage transformers. Inductive voltage transformers are the most economical solution for voltages up to 145 KV and above that level capacitive transformers have advantages. High voltage transformers are generally designed as oil-paper insulated transformers. Apart from inductive voltage transformers, capacitive voltage transformers ara available for higher system voltages up to 765 KV. They fundamentally consist of a capacitive divider and an inductive voltage transformer.

Instrument transformers for switchgear installations

Instrument transformers for switchgear installations

Instrument transformers for switchgear installations

Instrument transformers for switchgear installations Optical current transformers use the Faraday effect in crystalline structures for passive measurement of currents. Monochromatic light is sent polarized into a solid body of glass, which surrounds the current carrying conductor. Reflection from the bewelled corners of the glass container directs the light beam around the conducting line before it exits again on one side. The magnetic field around the conductor rotates the polarization plane of the light, whose phase difference is proportional to the magnetic field intensity H. The phase difference at the end of the path in the glass body is directly proportional to the current.

Instrument transformers for switchgear installations

Surge arresters Surge arresters are used for protection of important equipment, particularly transformers, from atmospheric overvoltages and switching overvoltages. Arresters are primarily selected on the basis of two basic requirements: -the arrester must be designed for stable continuous operation -it must provide sufficient protection for the protected equipment. Today surge arresters are based on metal oxide (MO) resistors, which have an extremely nonlinear U/I characteristic and a high energy absorption capability. They are known as metal oxide surge arresters. The metal oxide arrester is characterized electrically by a current/voltage curve. The current range is specified from the continuous operating range (range A of the curve, order of magnitude 10-3 A) to a minimum of the double value of the rated discharge current (order of magnitude 103 A). The MO arrester corresponding to the characteristic is transferred from the high resistance to the low resistance range at rising voltage without delay. When the voltage returns to the continuous operating voltage or below, the arrester becomes high ohmic.

Surge arresters

Surge arresters Surge arresters are preferably installed parallel to the object to be protected between phase and earth.Because of the limited protection distance with steep lightning voltages, the arresters must be installed adjacent to the equipment that is to be protected as much as possible. Monitoring systems (surge counters) may be used to monitor surge arresters. They are installed in the ground conductor of the arrester.

Surge arresters

Surge arresters

Transformers

Transformers

Oil Immersed Type Distribution Transformers

Hermetic

Iınside view

With conservator

Dry Type Distribution Transformers With tap changer

Inside view

In metal encase

1.Core limbs 2.LV winding 3.HV winding

4.Tapping winding 5.Conductors 6.LV bushings 7.HV bushings 8.Pressing equipment 9. On-Load tap changer 10.Motor-drive mechanism 11.Oil conservator 12.Radiators

Stacking of core laminations

Lifting up of the core with special apparatus.Three limbed transformer

A transformer core with five limbs Step-lapped core

The difference between Transformers and Reactors ; Reactors have only primary winding and their core has air-gaps as shown below.(But their periodical test and maintenance are the same as transformers except turn ratio and magnetizing current measurings)

Single phase reactor core

Winding apparatus for layer winding

Winding apparatus for disc winding

Winding apparatus for layer winding

Vertical winding apparatus

Pressing equipment for layer winding

INTRODUCTION Upper clamping ring Active part of a transformer

Bottom plate for the windings

INTRODUCTION Active part with on-load tap changer Due to the voltage variations in the networks or in the substations, transformers are normally equiped with tapping windings having necessary taps to accomplish the requested voltage level. The connections of these taps are either made with no-load tap changer(off-load tap changer) when the transformer is deenergized or with on-load tap changer when the transformer is under operating conditions. The motor drive mechanism is used for the, control of on-load tap changer.This control can either be made locally on the transformer or remotely from the control room.The operation of off-load tap changers can either be made on the cover or on the sidewall of the transformer by manual drive mechanism.Upon request, motor drive mechanism can be provided to operate the off-load tap changers.

Active part with off-load tap changer

INTRODUCTION Protection and control equipment

Bucholz relay It is mounted on the pipe connection from transformer tank to conservator.The gasses which occur in transformer for any reason are collected here and depending on the volume of gas it gives an alarm or tripping signal.

Pressure relief device It is mounted on the transformer cover.It replies to the sudden pressure increase that may occur by an arc in the oil in the transformer and gives tripping signal by the contacts on itself.

Oil level indicator It is mounted onto the sidewall of the conservator. Depending on the oil temperature variations, it indicates the oil level in conservator and gives too low or too high indications by the contacts on itself.

INTRODUCTION Dehydrating breather It is mounted onto the conservator.It takes the moisture and dust in the air that enters the conservator and increases service security of the transformer, the amount of silicagel particles in it varies with the amount of the oil in the transformer.

Oil thermometer

It controls the temperature of the oil in the transformer tank and gives alarm and trip signal at the adjusted temperature limits.It gives start and stop signal for the fans used at forced cooling.If remote control is required,Pt 100 resistance or 4-20 mA output is added to it.

Winding thermometer

It controls the temperature of the windings with its monitoring circuit and gives alarm and trip signal at the adjusted temperature limits.Like the oil temperature,it is used for the controls of fans and pumps and if reqired Pt 100 resistance or 4-20 mA output is added to it.

Oil flow indicator

It controls the oil flow at forced oil cooled transformers.It is mounted on the pipe connection in which the oil flows through.It gives alarm signal if the oil does not flow for any reason.

CF101 air cell alarm relay

CL064 oil level OLTC

CL060oil level

CF 050 BUCHHOZ

CP096 pressure relief valve for OLTC

AT005 OLTC breathing AT001 aircell breathing

Main Tank

OLTC bucholz relayCF 061

CP081 pressure relief valve for main tank

HV Bushing turret CT033 winding temp. indicator

CT031 oil temp. indicator

BQ011Thermometer pocket for wind. Temp.

BQ010 Thermometer pocket

RADIATOR

Air Cell

SECTION .2 - CONSTRUCTION RADIATORS • Butterfly valve

Air ejecting plug (vent screw)

•O-ring

•Lifting eye

Transformer Tank

•Radiators (cooling elements)

•Oil Drain plug

Radiators are important part of the cooling of the transformers.Radiators have two ducts for connection to transformers. On upper and bottom connection pipes ,there are butterfly valves. On upper side there is a ventilation plug. On bottom side there is a draining plug. On top of it, there is a lifting eye.

SECTION .2 - CONSTRUCTION

Ø The Fans and their Connections

RADIATOR

CONTROL

CUBICLE

FAN

FAN TANK

Transformer Power Efficiency can be increased by adding fans. They are built under radiators to blow air upwards for cooling the oil inside the radiators. They are operated automatically / manually when the oil temperature rise. The basically cooling operations; ONAN (Oil Natural Air Natural) (without fan or pumps) ONAF (Oil Natural Air Forced) (air forced with fan) OFAF (Oil Forced Air Forced) (air forced with fan or oil forced with pumps)

OLTC - MR Type

SECTION .2 - CONSTRUCTION

Transformers

Transformers

Transformers

Transformers

Transformers

Transformers

Transformers

Transformers

Transformers

Transformers

Transformers