Group14-P1-V1

EH2741- Communication & Control in Electric Power Systems Project Assignment Part 1 – Substation Automation Systems

By Andrius Maneikis HannanAfifi MdShahinur Islam Pratik Sonthalia

Contents EH2741- Communication & Control in Electric Power Systems Project Assignment. . .1 Part 1 – Substation Automation Systems.................................................................1 1.1 Theory Part: Design a substation automation systems.....................................3 1.1.1 Detailed Substation Design.........................................................................3 1.1.2 Circuit Breaker Maintenance.......................................................................6 1.1.3 Substation protection zones......................................................................12 1.1.4 Protection in Substation............................................................................ 14 1.1.5 Example of Logical Nodes interaction for over-current protection.............17 References................................................................................................................ 20 Appendix.................................................................................................................. 21 List of Figures........................................................................................................ 21 List of Tables.......................................................................................................... 21

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1.1 Theory Part: Design a substation automation systems Requirements of the substation: 1. 2 incoming Lines with a transformer each 2. 3 feeders for power supply to downstream The required topology has been described in the diagram below.

Figure 1 Substation Topology Overview

1.1.1 Detailed Substation Design The substation design is required to comply with the following:  Reliability: Single component failure in the substation should not interrupt feeder power supply.  Flexibility of maintenance: When you do the maintenance, no power supply to any feeder should be interrupted.  Cost: Try to minimize the component to reduce the cost of substation.  Measurements: Place the necessary measurements in the system to fulfill the requirements of the functions you proposed in question c Various factors shall affect the above requirements of the substation design, one of which is the arrangement of the buses and switching devices. In an airinsulated substation, the commonly used types of substation bus/ switching arrangements are [1]: a. b. c. d. e. f.

Single Bus Double bus, double breaker Main and transfer bus Double Bus, single breaker Ring Bus Breaker and a half Reliability

Flexibi

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Cost

Single Bus Double Bus, double breaker

No Yes

lity No Yes

Main and Transfer Bus Double Bus, single breaker Ring Bus

No

No

Moderate Cost (1.76)

No

No

Moderate Cost (1.78)

No- single failure isolates the component

Yes

Moderate Cost (1.56)more components

Breaker and a Half

Yes- single failure isolates the component, the failure does not affect the circuit

Yes

Moderate Cost (1.57)breaker and a half for each configuration

Least High Cost- duplicated components

Table 1: Bus Bar Configurations comparison study

A double-bus, single breaker was initially proposed. However, based on specific requirements of reliability (single component failure in the substation should not interrupt feeder power supply), it was rejected and a breaker and a half was suggested.

Figure 2 Single Line Diagram of a double-bus single breaker system

A double-bus, single breaker would require 6 CB. However,afailure in any of the circuit breaker shall lead to an interruption in the supply to the feeder or the generation. Though the component requirement is less for double bus single breaker and least cost, it does not meet the reliability requirements. Similarly, other breaker configurations do not completely fulfill the requirements. A comparative study has been included in the table 1. Instead, a hybrid solution with a breaker and a half configuration is proposed.

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The detailed design of the hybrid configuration is done on HELINKS and is shown in Figure 1. For protection, the design contains 10 circuit breakers and 16disconnecters, 7 current transformers and 2 voltage transformers. The entire system has been divided into 6 bays. The measurement components used in the substation have been compiled in the table 1. Component Type

Circuit Breakers

Protecti on

Disconnectors

Component Label CB1 CB2 CB3 CB4 CB5 CB6 CB7 CB8 CB9 CB10 CB11 CB12 CB13 DS1, DS2 DS3, DS4 DS5, DS6 DS7, DS8 DS9, DS10 DS11, DS12 DS13, DS14 DS15, DS16

Bay Number Bay1 Bay2 Bay3 Bay4 Bay4 Bay4 Bay6 Bay5 Bay6 Bay6 Bay1 Bay2 Bay3 Bay1 Bay2 Bay3 Bay4 Bay4 Bay4 Bay5 Bay6

Table 2 Protection Components in the substation

Bus Bars System

Line Transformer

Bus Bar1 Bus Bar 2 Line 2 Line 1 Line 3 T1 T2

Bay1 Bay2 Bay6 Bay3 Bay5

Table 3 System components in the substation design

Measurem ent

Current Transformer

CT6 CT5 CT2 CT1

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Bay1 Bay2 Bay3 Bay3

Voltage Transformer

CT3 CT4 CT7 VT1 VT2

Bay5 Bay5 Bay6

Table 4 Measurement components in the substation design

The diagram for the division of the bay has been shown below:

Figure 3Single Line Diagram depicting the bays

1.1.2 Circuit Breaker Maintenance In the above system, suppose CB1 has reached its lifecycle and needs maintenance. The assumption is made that the circuit breaker has reached its Page 6 of 22

lifetime and can be still operated. Generally, in a breaker and a half configuration, all the circuit breakers are kept closed normally to increase the redundancy.The maintenance process will have to be done ensuring that the supply to none of the feeders is disrupted. The detailed steps have been described below: 1. Initial condition is shown in the figure below. The current flows into Line2 through both CB1 and CB4.

Figure 4Normal Operating Condition for the substation

2. Open CB1. Upon tripping the circuit breaker CB1, the current stops flowing into Line2 through the circuit breaker CB1. However, it is still being fed through the circuit breaker CB4 ensuring supply and reliability.

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Figure 5Open CB1- First step for circuit breaker maintenance

3. Once the circuit breaker is open, the disconnectersDS1 and DS2 can be safely opened.

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Figure 6Open the disconnecters- Step 2 for CB maintenance

4. Remove the circuit breaker CB1 requiring maintenance.

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Figure 7Remove CB1 -Third step for CB maintenance

5. Place the new circuit breaker CB1new in place of CB1.

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Figure 8Place new CB1 -Fourth step for CB maintenance

6. Close the disconnecters DS1, DS2 and then circuit breaker CB1 new. Now the current flows into the feeder from both the circuit breakers CB1 new and CB4.

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Figure 9Close the disconnecters and CB1newSixth step for CB maintenance

Thus circuit breaker that has reached its lifetime can be replaced without disrupting the supply. 1.1.3 Substation protection zones To denote the protection type, the entire design has been divided into a number of zones. The diagram depicting the zones is shown in the figure.

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Figure 10 Zones in the substation design

Each of the above zones deploys its own protection mechanism which has been summarized in the table below and described the following section. Page 13 of 22

Protection Zones Zone 1 Zone 2 Zone 3 Zone Zone Zone Zone Zone

4 5 6 7 8

Zone 9

Protection Types Over-current Over-current Protection Under voltage &Differential Protection Differential Protection Over-current Over-current Protection Over-current Protection Under voltage & Differential Protection Differential Protection

Table 5 Protection zones and the corresponding protection type

1.1.4 Protection in Substation 1. Over-current protection Basic of over-current protection devices are circuit breaker and fuse. Overcurrent protection is widely used in protection of distribution feeders [12. Overcurrent protection is principally used to protect expensive equipment, feeders and also lines from the enormous/excess current flow. This can be done by setting threshold current of the relay. Threshold current normally is set above nominal value to avoid unwanted trip due to high load. Only if current measured by CT (Current Transformer) is higher than threshold value, over-current relay will send signal to circuit breaker to trip. There are several types of over-current relay: Instantaneous over-current, define time over-current, inverse time over-current relay (IDMT) and also directional over-current relay. Instantaneous over-current will react in a definite time when current excess its setting without time delay. Define time over-current has constant time operation and independent from magnitude of current above the setting. Inverse time over-current relay (IDMT) operates time-inversely from current magnitude which means higher current will operate faster than low current. Moreover IDMT relay also has three additional types: standard inverse, very inverse and extremely inverse. Directional over-current operates in direction of current flow and blocks the opposite direction [5]. Figure 11Instantaneous over-current, definite time over-current and IDMT relays

In our substation design, over-current protection is implemented to protect the incoming and outcoming feeder. As depicted in figure 10, there are 3 outcoming load (line 1, 2 and 3) and 2 incoming feeders. For incoming load, one of the CT in Page 14 of 22

input of transformer is used for both differential protection for transformer and also over-current protection for the line. For outcoming load, each has CT to measure current flowing. In this case, we assume that all outcoming feeders are identical. Therefore the settings of the over-current protection are similar for those lines. In figure x, we take zone protection 7 as an example of over-current protection. Since we are using half and breaker configuration, we assume each of the outcoming feeder receive power from both bus bar (bus 1 & bus 2). Therefore, line 2 is supplied directly from incoming feeder of zone protection 1 and bus bar 1. If fault is occurred in line2, relay will send signal to CB 1 and CB 4 to trip to isolate only line 2 (faulted feeder).

Figure 12Substation protection zone 7

2. Differential protection Differential protection is principally based on comparison between current flowing into and out from the equipment, either in magnitude or phase. During normal condition, ideally the current entering and leaving equipment should be the same. However, fault condition in apparatus will cause significant difference between entering and leaving current. Differential protection is implemented for protecting power transformer and busbars in our substation design. Power transformer, as one of main and expensive instrument in substation, has to be protected properly to prevent any further damage when fault occurred in it. The use differential protection provide advantages in potential transformer such as helping Buccholz relay to detect any internal fault in transformer outside insulating oil quickly and also protecting faults outside transformer but inside the differential protection zone of transformer [3]

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To implement differential protection in power transformer, two Current Transformer is assembled in input and output of power transformer to measure current of low voltage and high voltage side. As can be seen in figure 10, CT 1 and CT 2 are placed in the middle of T1 and CT 3 and CT 4 are placed in the middle of T2. The solution of differential relay is given by

¿ I P−I S ∨≥ I T IT

Where

is threshold setting current of differential relay. In that case if the

difference between input and output current of transformer equal or bigger than threshold current, relay will active and send trip signal to trip the transformer.

Figure 13Differential protection of Power Transformer (Source: 7 )

In

bus

bar protection, differential relay is implemented by assembling three CT’s connected in parallel in the line which is connected to the bus bar as input of the relay. Principally, bus bar should be protected as bus bar availability will determine performance of substation. If we take example bus bar 1 in zone protection 8, we can see that there are three CT’s (CT 11, CT 12 and CT 13) connected to bus bar 1. According to KCL (Kirchoff Current Law), during normal condition the current flowing to relay should be

I 1 +I 2+ I 3=0 Which means no current will flow to relay protection. However, if fault happens inside protection of zone 8, current flowing to relay will no longer zero and relay will send trip signal to CB which is connected faulted line.

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Figure 14Differential protection in Bus bar 1

3. Undervoltage protection Undervoltage relay is type of relay that operates when input voltage drops below limit value. Undervoltage relays are typically device which measure instantaneous value. Therefore, every time the input voltage drops below set point, instantaneous undervoltage relay should react immediately. Setting of Instantaneous undervoltage relay depends on the drop voltage and also VT ratio. [4] In our design, undervoltage relay is implemented to protect bus bar. As mentioned earlier, availability of bus bar will effect on operation of entire substation. Hence we use undervoltage protection as backup of differential protection for protecting bus bar. However, as undervoltage is defined as backup, time delay and block settings should be set to allow differential relay to operate first. In implementation of undervoltage protection, each bus baris installed with VT as input of undervoltage relay (VT 1 for bus bar 1 and VT 2 for bus bar 2). If fault happens in bus bar, and differential protection fails to operate, undervoltage will send signal to trip all the feeders connected to the relevant bus bar.

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Figure 15Implementation of undervoltage protection in bus bar 2 by placing VT 2

1.1.5 Example of Logical Nodes interaction for over-current protection For the chosen over-current protection Logical Nodes (LN) are implemented according to the scheme below. In case there is a short circuit in either of the feeder lines, two nearby circuit breakers (LN XCBR1 and LN XCBR2) shall open in order to isolate the fault location from the source lines. The over-current protection LN PTOC receives sampled values from LN TCTR. LN CSWI is used to control all switching conditions and check the interlocking from LN CILO1 in bay level and LN CILO3 in station level. For local/remote control Human Machine Interface (LN IHMI) is used. [6]

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Figure 16Over-current protection scheme

Source Logical Node

Information Attribute

Destination Logical Node

TCTR

TCTR.Amp.instMag

PTOC1

TCTR

TCTR. Amp.instMag CSWI1.OpOpn.general CSWI1.OpCls.general

PTOC2

CSWI1

CSWI1.Pos.origin CSWI1.OpOpn.general CSWI1.OpCls.general

XCBR1

CSWI1

CSWI1.Pos.origin CSWI1.OpOpn.general CSWI1.OpCls.general

XSWI1

CSWI1

CSWI1.Pos.origin CILO1.EnaOpn.stVal

XSWI2

CILO1

COLO1.EnaCls.stVal CILO1.EnaOpn.stVal

CSWI1

CILO1

COLO1.EnaCls.stVal PTOC1.Str.general

CILO3

PTOC1

PTOC1.Op.general PTOC1.Str.general

IHMI

PTOC1

PTOC1.Op.general PTOC1.Str.general

CSWI1

PTOC1

PTOC1.Op.general

CSWI2

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CSWI2.OpOpn.general CSWI2.OpCls.general CSWI2

CSWI2.Pos.origin CSWI2.OpOpn.general CSWI2.OpCls.general

XCBR2

CSWI2

CSWI2.Pos.origin CSWI2.OpOpn.general CSWI2.OpCls.general

XSWI3

CSWI2

CSWI2.Pos.origin CILO2.EnaOpn.stVal

XSWI4

CILO2

COLO2.EnaCls.stVal CILO2.EnaOpn.stVal

CSWI2

CILO2

COLO2.EnaCls.stVal XCBR1.Loc.stVal XCBR1.Op.Cnt.stVal XCBR1.Pos.origin XCBR1.BlkOpn.origin XCBR1.BlkCls.origin

CILO3

XCBR1

XCBR1.CBOpCap.origin XCBR2.Loc.stVal XCBR2.Op.Cnt.stVal XCBR2.Pos.origin XCBR2.BlkOpn.origin XCBR2.BlkCls.origin

CILO1

XCBR2

CILO2

XCBR2.CBOpCap.origin CILO3.EnaOpn.stVal CILO3

COLO3.EnaCls.stVal CILO3.EnaOpn.stVal

CSWI1

CILO3

COLO3.EnaCls.stVal

CSWI2

IHMI

IHMI

CSWI1

IHMI

CSWI2

IHMI

Table 6 Logical nodes for the over current protection

References [1] McDonald, John D, Electric Power Substations Engineering, Third Edition, CRC Press, 2012 [2] Chen, Wai-Kai (eds), The Electrical Engineering Hand Book, Academic Press, 2004

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[3] http://www.electrical4u.com/differential-protection-of-transformer-differentialrelays/, accessed 22 Nov 2014 [4] Sleva, Anthony, Protective Relay Principle, CRC Press, 2009 [5] http://electrical-engineering-portal.com/types-and-applications-of-over-current -relay-1, accessed 22 Nov 2014 [6] IEC-62850-5, Communication Network System in Substation, IEC, 2003 [7] Aktaibi et al, Digital Differential Protection of Power Transformer Using Matlab, Intech, 2012

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Appendix List of Figures Figure 1 Substation Topology Overview......................................................................3 Figure 2 Single Line Diagram of a double-bus single breaker system.........................4 Figure 3Single Line Diagram depicting the bays.........................................................6 Figure 4 Normal Operating Condition for the substation............................................7 Figure 5 Open CB1- First step for circuit breaker maintenance...................................8 Figure 6 Open the disconnecters- Step 2 for CB maintenance...................................9 Figure 7 Remove CB1 -Third step for CB maintenance.............................................10 Figure 8 Place new CB1 -Fourth step for CB maintenance........................................11 Figure 9 Close the disconnecters and CB1new Sixth step for CB maintenance...........12 Figure 10 Zones in the substation design.................................................................13 Figure 11 Instantaneous over-current, definite time over-current and IDMT relays. .14 Figure 12 Substation protection zone 7....................................................................15 Figure 14 Differential protection in Bus bar 1..........................................................16 Figure 13 Differential protection of Power Transformer (Source: Adel Aktaibi et al, 2 ) ................................................................................................................................. 16 Figure 15 Implementation of undervoltage protection in bus bar 2 by placing VT 2 17 Figure 16 Over-current protection scheme...............................................................18

List of Tables Table Table Table Table Table

1: Bus Bar Configurations comparison study.....................................................4 2 Protection Components in the substation.......................................................5 3 System components in the substation design................................................5 4 Measurement components in the substation design......................................5 5 Protection zones and the corresponding protection type.............................14

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