Summer Internship Report -By Rahul Mehra

1 SUMMER TRAINING REPORT

A

Report On

Practical Training

Taken At

400/220 KV SCADA CONTROLLED SUBSTATION

OPERATED BY : POWER GRID CORPORATION OF INDIA LIMITED

(A Government of India Enterprise )

Submitted in the Month of July, 2015 by Under the Guidance of

Rahul Mehra Mr. Lokesh Singh Chundawat Batch: 2012 – 2016 ( Sr. Engineer)

As part of Bachelor of Technology (Electrical Engineering) Curriculum of

Rajasthan Technical University, Kota (Raj.)


ACKNOWLEDGEMENT

It is often said that life is a mixture of achievements, failures, experiences, exposures and

efforts to make your dream come true. There are people around you who help you realize

your dream. I acquire this opportunity with much pleasure to acknowledge the invaluable

assistance of all the people who have helped me through the course of my journey in successful completion of this project. I would like to express my deep gratitude to Mr. Lokesh Singh Chundawat, Sr. Engineer

PGCIL Kankroli Substation for their active support and continuous guidance without which it

would have been difficult for me to complete this project. They were generous enough to take

time out of their regular work to lend a helping hand whenever I needed one and enabling me to complete this project. I would also like to mention the generous guidance of Mr. H. H. Mahto, Chief Manager,

Kankroli Substation, Mr. Chandra Shekhar, Technician, Mr. Rameshwar Lal Balai,

Technician, whose guidance helped me settle down in the organization and successfully

complete the project within the relatively short time frame of 8 weeks, from 15th May, 2015

to 15 July, 2015. They were supporting enough to give me an opportunity to be a part of such a prestigious organization for 2 months and learn the day to day functioning.

Last but by no means the least, I am grateful to the of Mr. Rohit Aheer (Assistant

Professor, Electrical Engineering Department, SITE Nathdwara) for providing a quick

turnaround time for all the requests.


EXECUTIVE SUMMARY

As a student of B.Tech – Rajasthan Technical University, Kota (Raj.), I got an opportunity to

do my summer internship in Power grid Corporation of India Limited, India’s Central

Transmission Utility.

Though my reporting office was the PGCIL Kankroli 400/220 KV Sub-Station situated in

Kankroli (Raj.), the authorities were generous enough to allocate me a working project that

Dealt with the study of existing infrastructure at the 400/220 KV substation which supplies

Power to Bhilwara (TEXTILE INDUSTRIES), to Kankroli (MARBLE FACTORIES), to

Debari, it also has important link between Southern and western Rajasthan (Jodhpur link),

Inter-Regional Tie between NR-I and WR-II (Zerda and Bhinmal Link), It is linked with

Rajasthan Atomic Power Project (Generation Link RAPP –I, II) The initial part of the project

Consisted of a thorough study of the equipments used in the transmission substation. The

study of existing infrastructure showed the advantage is its easy compatibility with the

Supervisory Control And Data Acquisition (SCADA) system which provide easy mechanism

for access and control.

The next phase of the project was about study of proposed plan of Static Var Compensator

(SVC) and NTAMC with an existing facility. The main advantage of SVCs over simple

mechanically switched compensation schemes is their near-instantaneous response to change

in the system Voltage. Static Var Compensator (SVC) provides fast acting dynamic reactive

compensation for voltage support during contingency events which would otherwise depress

the voltage for a significant length of time. SVC also dampens power swings and reduces system losses by optimized reactive power control.


The emphasis on the power sector to ensure the growth in GDP has brought in many changes

in the business environment of Power Sector. The transmission sector being the integral part

of, is also facing multiple challenges like competitive bidding for transmission project,

stringent demands by the regulator etc. Thus, state of the art computerized control centers

NTAMC & RTAMC with associated telecommunication system and adapted substation for

enabling remote centralized operation, monitoring and control of POWERGRID

Transmission system has been proposed. The aim is to have completely unmanned substation except security personnel.


Table of Content

1 Introduction..........................................................................................................................8

2 Why we need a Sub-Station? ............................................................................................ 8

3 About PGCIL Kankroli 400/220 KV Sub-Station...................................................................9

4 SLD Of PGCIL Kankroli 400/220KV Sub-Station...............................................................….10

5 Detail of erected equipments in 400/220kv kankroli sub-station…………………….……….11

6 Classification of Sub-station........................................................................................…….13

6.1 According to service requirement……………………………………………………………..…..……….13

6.2 According to constructional features ………………………………………………………………………14

6.3 According to nature of duties…………………………………………………………………………………..14

6.4 According to operating voltage……………………………………………………………………….………15

7 Sub-station site selection ………………………………………………………………………………….………15

8 Main equipments in a sub-station .................................................................................15

8.1 Power Transformer .........................................................................................................16

8.2 Instrument Transformer……………………………………………………………………………..…….…....18

8.3 Bus Bar…………………………………………………………………………………………………….………..……19

8.3.1Typical Bus Configurations……………………………………………………………………….…….…….19

8.3.1.A Single Bus……………………………………………………………………………………………………..…19

8.3.1.B Sectionalized Bus………………………………………………………………………………………..……20

8.3.1.C Main and Transfer Bus……………………………………………………………………………………..20

8.3.1.D Ring Bus…………………………………………………………………………………………………….…….21

8.3.1.E Breaker-and-a-Half……………………………………………………………………………………..…..22


8.3.1.F Double Breaker-Double Bus…………………………………………………………………………....…..23

9 Isolator…………………………………………………………………………………………………………………………24

10 Relay……………………………………………………………………………………………………..…………………….25

11 Circuit Breaker………………………………………………………………………………………..……..…………….25

11.1 SF6 Circuit Breaker………………………………………………………………….……………………….…………26

12 Wave-trap…………………………………………………………………………………………………………………….26

13 Reactor………………………………………………………………………………………………………….……...….…26

14 Lightning Arrestor…………………………………………………………………………………..……………..……..27

15 Sub-station Protection…………………………………………………………………………….………..……..…..29

16 Transformer and reactor protections…………………………………………………………….……………33

17 Circuit breaker auxiliary relays……………………………………………………………………………….37

17 Transmission line protection………………………………………………………………………..………………39

19 Bus bar protection…………………………………….………………………………….……………...………………41

20 Supervisory Control And Data Acquisition (SCADA)………………………………………..……...42

20.1 Parts of a SCADA System…………………………………………………………………….…………...……43

21 National Transmission-Asset Management Centre (NTMC) ......................................44

21.1 Operational Philosophy……………………………………………………………………………….…………..…46

21.2 Structure of NTMC..…………………………………………………………………..………..………….46

22 Static VAR compensator (SVC) ………………………………………………………………………...48

22.1 Control Concept of SVC…………………….………………………………………..……………………..…...49

22.2 The Thyristor Controlled Reactor ………………………………………………………….…………..…50

23 Conclusion…………………………………………………………………………………………….……………………52


List of Figures Figure 1: View of Kankroli sub-station................................................................................... 9

Figure 2: Single line diagram Kankroli Sub-Station……….......................................................10

Figure 3: Strategic Presentation of Associated transmission lines with sub-station………….13

Figure 4: 315 MVA interconnected transformer (ICT).......................................................... 16

Figure 5: Bushing of transformer......................................................................................... 17

Figure 6: Silica gel in a cylinder............................................................................................. 17

Figure 7: Single Bus............................................................................................................... 19

Figure 8: Sectionalized Bus ................................................................................................... 20

Figure 9: Main and Transfer Bus............................................................................................ 21

Figure 10: Ring Bus………………………………………………………………………………………………….21

Figure 11: Breaker-and-a-Half………………………………………………………………………………….22

Figure 12: Double Breaker-Double Bus…………………………………………………………………....23

Figure 13: Isolator in a sub-station…………………………………………………………………………24

Figure 14: Circuit Breaker in a substation………………………………………………………………..25

Figure 15: wavetrap in a sub-station………………………………………………………….……………27

Figure 16: lightning arrester in a sub-station………………………………………………………….28

Figure 17: Step Potential and Touch Potential…………………………………………………………30

Figure 18: earth wire…………………………………………………………………………………………….32

Figure 19: Buchholz Relay………………………………………………………………………………………………….33

Figure 20: Location of buchholz relay on transformer………………………………………………………34

Figure 21: Structure of NTMC ……………………………………………………………………………46

Figure 22: Evolution of voltage level in India…………………………………………………………...47

Figure 23: Network Management System in India……………………………………………………47


Figure 24: SVC with control concept………………………………………………………………..………..50

Figure 25: Elementary thyristor-controlled reactor (TCR)…………………………………………….51

List of Tables

Table 1: Detail of erected equipments in 400/220kv kankroli sub-station............................ 11

Table 2: 400/220kv kankroli sub-station at a glance............................................………….……12

Table 3: Associated transmission lines with 400/220kv kankroli sub-station...................... .12


1: Introduction Electric power is produced at the power generating stations, which are generally located far away from the load centers. High voltage transmission lines are used to transmit the electric power from the generating stations to the load centers. Between the power generating station and consumers a number of transformations and switching stations are required. These are generally known as substations. Substations are important part of power system and form a link between generating stations, transmission systems and distribution systems. It is an assembly of electrical components such as bus-bars, switchgear apparatus, power transformers etc. Their main functions are to receive power transmitted at high voltage from the generating stations and reduce the voltage to a value suitable for distribution. Some substations provide facilities for switching operations of transmission lines, others are converting stations. Substations are provided with safety devices to disconnect equipment or circuit at the time of faults. Substations are the convenient place for installing synchronous condensers for the purpose of improving power factor and it provide facilities for making measurements to monitor the operation of the various parts of the power system. The substations may be classified in according to service requirements and constructional features. According to service requirements it is classified in to transformer substations, switching substations and converting substations. The present day electrical power system is a.c. i.e. electric power is generated, transmitted and distributed in the form of Alternating current. The electric power is produce at the power station, which are located at favorable places, generally quite away from the consumers. It is delivered to the consumer through a large network of transmission and distribution. At many place in the line of power system, it may be desirable and necessary to change some characteristic (e.g. Voltage, ac to dc, frequency p.f. etc.) of electric supply. This is accomplished by suitable apparatus called sub-station for example, generation voltage (11KV or 6.6KV) at the power station is stepped up to high voltage (Say 765KV to 400KV) for transmission of electric power. Similarly near the consumer’s localities, the voltage may have to be stepped down to utilization level. This job is again accomplished by suitable apparatus called sub-station. 2: Why we need a Sub-Station?

Sub-Station forms an important link between Transmission network and Distribution network. It has a vital influence of reliability of service. Apart from ensuring efficient transmission and Distribution of power, the sub-station configuration should be such that it enables easy maintenance of equipment and minimum interruptions in power supply.


3: About the PGCIL Kankroli Sub-Station

� Kankroli sub-station is situated 12 km milestone on Kankroli-Bhilwara highway. It is constructed in a piece of 45.0 acres of land.

� Mavli is nearest railway station which is 60 km away from sub-station and nearest

airport is Maharana Pratap Airport in (Udaipur). � The sub-station was commissioned in March 2008 with the total transformation

capcity:3x3 15 MVA= 945 MVA.

� The Sub-Station acts as an inter-regional link between NR-I and WR-II plays an important role in power system strengthening of south-western Rajasthan.

� It mainly evacuates power from RAJSTHAN ATOMIC POWER PROJECT and supply it to South-Western Rajasthan.

� Double main and transfer bus scheme has been employed in 220 KV S/Y and one and

� half breaker scheme (I-TYPE) has been employed in 400 KV S/Y in this Sub-Station.

Figure 1: View of Kankroli sub-station


4: Single line diagram (SLD) PGCIL, Kankroli Sub-Station

Figure 2: Single line diagram

A Single Line Diagram (SLD) of an Electrical System is the Line Diagram of the concerned Electrical System which includes all the required ELECTRICAL EQUIPMENT connection sequence wise from the point of entrance of Power up to the end of the scope of the mentioned Work. As these feeders enter the station they are to pass through various instruments. The instruments have their usual functioning.


5: DETAIL OF ERECTED EQUIPMNTS

DETAIL OF ERECTED EQUIPMNTS IN 400/220KV KANKROLI SUB-STATION

AS ON DATE-15.07.2015

S.No

CB(3 PHASE) CT CVT LA ISOLATOR EARTH SWITCH

MAKE QTY MAKE QTY MAKE QTY MAKE QTY MAKE QTY MAKE QTY

400 KV SYSTEM

1) AREVA 10 TELK 30 AREVA 12 AREVA 30 ELPRO 108 ELPRO 114

2) ABB 4 ABB 12 ABB 09 CGL 15 HIVELM 18 HIVELM 18

3) SIEMENS 1 CGL 3 0 0 CGL 3 SIEMENS 2 SIEMENS 2

TOTAL 15 45 21 48 128 134

220 KV SYSTEM

1) SIEMENS 11 TELK 33 AREVA 18 AREVA 27 ELPRO 123 ELPRO 57

2)

TOTAL 11 33 18 27 123 57

S.No Name of the Equipment Make Rating Qty.

1) ICT-I BHEL 315 MVA 1

2) ICT-II CGL 315 MVA 1

3) ICT-III BHEL 315 MVA 1

4) BUS RACTOR CGL 50 MVAR 1

5) BUS REACTOR CGL 125 MVAR 1

6) LINE REACTOR BHEL 50 MVAR 2

7) LINE REACTOR CGL 50 MVAR 2

Table 1: Detail of erected equipments in 400/220kv kankroli sub-station


SUB-STATION AT A GLANCE

S No. EQUIPMENT 400 KV SYSTEM

220 KV SYSTEM

1 CB 15 11 2 CT 45 33 3 CVT 21 18 4 LA 48 27 5 ISOLATOR 132 123 7 EARTH SWITCH 138 57 8 ICT 3 9 BUS REACTOR 2

10 LINE REACTOR 4

Table 2: 400/220kv kankroli sub-station at a glance

Associated Transmission Lines

S No. Name of the Line Type Line length

1) 400 KV Kankroli-RAPP-I Line S/C 199 Kms

2) 400 KV Kankroli- RAPP-II Line S/C 199 Kms

3) 400 KV Kankroli - Zerda line S/C 235 Kms

4) 400 KV Kankroli – Bhinmal Line S/C 202 Kms

5) 400 KV Kankroli – Jodhpur Line S/C 188 Kms

6) 220 KV Kankroli – Bhilwara Line S/C 82 Kms

7) 220 KV Kankroli- Kankroli Ckt-I S/C 11 Kms

8) 220 KV Kankroli- Kankroli Ckt-II S/C 8 Kms

9) 220 KV Kankroli- Debari S/C 63 Kms

Table 3: Associated transmission lines with 400/220kv kankroli sub-station


Strategic Presentation 400kv D/C 400kv D/C 220kv S/C 220kv S/C 220kv S/C 220kv S/C

Figure 3: Strategic Presentation of Associated transmission lines with 400/220kv kankroli sub-station

6: CLASSIFICATION OF SUBSTATION 6.1: According to service requirement a) Transformer sub-station: Those sub-station which change the voltage level of electrical supply is called Transformer sub-station. b) Switching sub-station: This sub-station simply perform the switching operation of power line. c) Power factor correction S/S: This sub-station which improves the p.f. of the system are called p.f. correction s/s. these are generally located at receiving end s/s.

400/220KV Kankroli Sub-

Station.

RAPP Generation Link

(RAPP –I,II)

Important link between

Southern and western

Rajasthan (Jodhpur link)

Inter-Regional Tie between

NR-I and WR-II ( Zerda and

Bhinmal link)

SOURCE TO BHILWARA

(TEXTILE INDUSTRIES)

SOURCE TO KANKROLI

(MARBLE FACTORIES

SOURCE TO DEBARI


d) Frequency changer S/S: Those sub-stations, which change the supply frequency, are known as frequency changer s/s. Such s/s may be required for industrial utilization e) Converting sub-station: That sub-station which change A.C power into D.C. power are called converting s/s ignition is used to convert AC to dc power for traction, electroplating, electrical welding etc. f) Industrial sub-station: Those sub-stations, which supply power to individual industrial concerns, are known as industrial sub-station. 6.2: According to constructional features a) Outdoor Sub-Station: For voltage beyond 66KV, equipment is invariably installed outdoor. It is because for such Voltage the clearances between conductor and the space required for switches, C.B. and other equipment becomes so great that it is not economical to install the equipment indoor. 23

b) Indoor Sub-station: For voltage up to 11KV, the equipment of the s/s is installed indoor because of economic consideration. However, when the atmosphere is contaminated with impurities, these sub-stations can be erected for voltage up to 66KV Figure 6 24

c) Underground sub-station: In thickly populated areas, the space available for equipment and building is limited and the cost of the land is high. Under such situations, the sub-station is created underground. The design of underground s/s requires more careful consideration.

� The size of the s/s should be as small as possible.

� There should be reasonable access for both equipment & personal.

� There should be provision for emergency lighting and protection against fire.

� There should be good ventilation 6.3: According to nature of duties a) Step-up or Primary Substations- Where from power is transmitted to various load centers in the system network and are generally associated with generating stations. b) Step-up and Step-down or Secondary Substations- may be located at generating points where from power is fed directly to the loads and balance power generated is transmitted to the network for transmission to other load centers. c) Step-down or Distribution Substations- receives power from secondary substations at extra high voltage (above 66 kV) and step down its voltage for secondary distribution.


6.4: According to operating voltage a) High Voltage Substations (HV Substations) - involving voltages between 11 kV and 66 kV. b) Extra high voltage substations (EHV Substations) - involving voltages between 132 kV and 400 kV and c) Ultra high voltage substations (UHV Substations) - operating on voltage above 400 kV

7: Sub-station site selection The aspects necessary to be considered for site selection are:

� Fairly level ground

� Right of way around the substation yard for incoming & outgoing transmission & distribution lines.

� Preferably of soil strata having low earth resistance values

� Easy approach & accessibility from main roads for Heavy equipment transportation and routine O & M of substation.

� Economy / Cost 8: MAIN EQUIPMENTS USED IN A SUBSTATION A substation is an assembly of various electrical equipments connected to step down electric power at higher voltages and to clear faults in the system. The various electrical equipments used in the substation are as follows:-

1. Power Transformers (ICT)

2. Instrument Transformers i.e. CT and CVT

3. Bus Bars

4. Isolators

5. Relays

6. Circuit Breakers

7. Lightening Arrestors

8. Wavetrap 9. Reactor


8.1: POWER TRANSFORMERS (Inter Connected Transformer I.C.T) This is the costliest equipment of substation. ICT is used to step down the EHV transmission Voltage (400kv) to HV transmission voltage (220kv). Normally 315 MVA auto transformers are being used. The secondary winding provides 220 KV voltages and other 33 KV voltage (tertiary winding). Usually tertiary winding is connected in closed delta formation and can be used for auxiliary station supply purpose. In practice, it is preferred to installed three phase ICT as far as possible however in case of hilly terrain, where due to transportation limitations, three single phase units are installed. A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core, and thus a varying magnetic field through the secondary winding. With transformers, however, the high cost of repair or replacement, and the possibility of a violent failure or fire involving adjacent equipment, may make limiting the damage a major objective. The protection aspects of relays should be considered carefully when protecting transformers. Faults internal to the transformer quite often involve a few turns. While the currents in the shorted turns are large in magnitude, the changes of the currents at the terminals of the transformer are low compared to the rating of the transformer.

Figure 4: 315 MVA interconnected transformer ICT


There are different parts of a transformer given below:

i. Bushing: This maintains the incoming and outgoing connection of a transformer.

Figure 5: Bushing of transformer

ii. Radiator: This is used to radiate the heat of a transformer when transformer is heated up at a certain level.

iii. Oil temperature meter: This meter indicates the temperature of transformer oil. If temperature crosses a certain level then it makes an alarm.

iv. Temperature meter: This meter indicates the temperature of transformer windings. If temperature crosses a certain level then it starts the winding fans.

v. Oil level meter: This meter indicates the oil level of transformer. If oil is low than a certain amount it makes an alarm that means that transformer have to feed oil.

vi. Silica gel: It works like breathing. There have a little amount oil under the silica gel which suck the moisture of air and further sends this air to silica gel which further sucks the rest of the moisture of the air.

Figure 6: Silica gel in a cylinder


vii. Exchanger: Regulate voltage through winding selection between primary & secondary side.

viii. PRD (Pressure relief device): release the oil pressure by releasing oil when oil pressure is high.

8.2: Instrument Transformer: They are devices used to transform voltage and current in the primary system to values suitable for measuring instruments, meters, protective relays etc. They are basically the current transformers and voltage transformers. Current transformers : Current transformer is similar in construction to single phase power transformer and obeys the same fundamentals laws but primary current of CT is not controlled by the connected load in secondary circuit. In facts it is governed by the current in the main circuit viz. line/transformer to which is connected. A typical 400/220 KV CT has five cores which is used for following functions:-

� Core 1: Busbar I protection � Core 2: Busbar II protection � Core 3: Metering � Core 4: Main I Protection � Core 5: Main II Protection

The metering core of CT is of accuracy class of 0.5 whereas the other cores having accuracy of PS class which is a special protection class for which Knee point Voltage and max. exciting current is specified.

Capacitive Voltage Transformer (CVT’s): It is used for providing small representative voltage of primary system for metering and protection applications. CVT consists of coupling capacitors, intermediate voltage transformer, High frequency coupling terminal. The H.F terminal is used for PLCC purpose. The CVT has three cores which are utilized as follows.

� Core 1: Main I protection � Core 2: Main II protection � Core 3: Metering.

The accuracy class of protection core is 3P and metering core is 0.5.


8.3: BUS-BAR

In electrical power distribution, a bus bar is a thick strip of copper or aluminum that conducts electricity within a switchboard, distribution board, substation or other electrical apparatus. Bus bars are used to carry very large currents, or to distribute current to multiple devices within switchgear or equipment. Bus bars are typically either flat strips or hollow tubes as these shapes allow heat to dissipate more efficiently due to their high surface area to cross sectional area ratio. The size of the bus bar is important in determining the maximum amount of current that can be safely carried. Bus bar may either be supported on insulators, or else insulation may completely surround it. Bus bars are protected from accidental contact either by a metal enclosure or by elevation out of normal reach. Bus bars may be connected to each other and to electrical apparatus by bolted or clamp connections.

8.3.1: Typical Bus Configurations

8.3.1.A: Single Bus Figure shows the one-line diagram of a single bus substation configuration. This is the simplest of the configurations, but is also the least reliable. It can be constructed in either of low profile or high-profile arrangement depending on the amount of space available. In the arrangement shown, the circuit must be de-energized to perform breaker maintenance, which can be overcome by the addition of breaker bypass switches, but this may then disable protection systems.

Figure 7: Single Bus

Single Bus Advantages:

� Lowest cost � Small land area � Easily expandable � Simple in concept and operation � Relatively simple for the application of protective relaying


Single Bus Disadvantages:

� Single bus arrangement has the lowest reliability � Failure of a circuit breaker or a bus fault causes loss of entire substation � Maintenance switching can complicate and disable some of the protection schemes

and overall relay coordination 8.3.1.B: Sectionalized Bus Figure 3 shows the layout of a sectionalized bus, which is merely an extension of the single bus layout. The single bus arrangements are now connected together with a center circuit breaker that may be normally open or closed. Now, in the event of a breaker failure or bus bar fault, the entire station is not shut down. Breaker bypass operation can also be included in the sectionalized bus configuration.

Figure 8: Sectionalized Bus Sectionalized Bus Advantages:

� Flexible operation � Isolation of bus sections for maintenance � Loss of only part of the substation for a breaker failure or bus fault

Sectionalized Bus Disadvantages:

� Additional circuit breakers needed for sectionalizing, thus higher cost Sectionalizing � may cause interruption of non-faulted circuits

8.3.1.C: Main and Transfer Bus A main and transfer bus configuration is shown in Figure 4. There are two separate and independent buses; a main and a transfer. Normally, all circuits, incoming and outgoing, are connection the main bus. If maintenance or repair is required on a circuit breaker, the associated circuit can be then fed and protected from the transfer bus, while the original breaker is isolated from the system.


Figure 9: Main and Transfer Bus Main and Transfer Bus Advantages:

� Maintain service and protection during circuit breaker maintenance � Reasonable in cost � Fairly small land area � Easily expandable

Main and Transfer Bus Disadvantages:

� Additional circuit breaker needed for bus tie � Protection and relaying may become complicated � Bus fault causes loss of the entire substation

8.3.1.D: Ring Bus Figure 5 depicts the layout of a ring bus configuration, which is an extension of the sectionalized bus. In the ring bus a sectionalizing breaker has been added between the two open bus ends. Now there is a closed loop on the bus with each section separated by a circuit breaker. This provides greater reliability and allows for flexible operation. The ring bus can easily adapt to a breaker-and-a-half scheme, which will be looked at next.

Figure 10: Ring Bus


Ring Bus Advantages:

� Flexible operation High reliability � Double feed to each circuit � No main buses Expandable to breaker-and-a-half configuration � Isolation of bus sections and circuit breakers for maintenance without circuit

disruption Ring Bus Disadvantages:

� During fault, splitting of the ring may leave undesirable circuit combinations � Each circuit has to have its own potential source for relaying � Usually limited to 4 circuit positions, although larger sizes up to 10 are in service. 6 is

usually the maximum terminals for a ring bus

8.3.1.E: Breaker-and-a-Half A breaker-and-a-half configuration has two buses but unlike the main and transfer scheme, both busses are energized during normal operation. This configuration is shown in Figure 6. For every 2 circuits there are 3 circuit breakers with each circuit sharing a common center breaker. Any breaker can be removed for maintenance without affecting the service on the corresponding exiting feeder, and a fault on either bus can be isolated without interrupting service to the outgoing lines. If a center breaker should fail, this will cause the loss of 2 circuits, while the loss of an outside breaker would disrupt only one. The breaker-and-a-half scheme is a popular choice when upgrading a ring bus to provide more terminals.

Figure 11: Breaker-and-a-Half


Breaker-and-a-Half Advantages:

� Flexible operation and high reliability � Isolation of either bus without service disruption � Isolation of any breaker for maintenance without service disruption � Double feed to each circuit � Bus fault does not interrupt service to any circuits � All switching is done with circuit breakers

Breaker-and-a-Half Disadvantages:

� One-and-a-half breakers needed for each circuit � More complicated relaying as the center breaker has to act on faults for either of the 2

circuits it is associated with � Each circuit should have its own potential source for relaying Substation

Configuration Reliability 8.3.1.F: Double Breaker-Double Bus The final configuration shown is the double breaker – double bus scheme in figure 7. Like the breaker-and-a-half, the double breaker-double bus configuration has two main buses that are both normally energized. Here though, each circuit requires two breakers, not one-and-a-half. With the addition of the extra breaker per circuit, any of the breakers can fail and only affect one circuit. This added reliability comes at the cost of additional breakers, and thus is usually only used at large generating stations.

Figure 12: Double Breaker-Double Bus


Double Breaker-Double Bus Advantages:

� Flexible operation and very high reliability � Isolation of either bus, or any breaker without disrupting service � Double feed to each circuit � No interruption of service to any circuit from a bus fault � Loss of one circuit per breaker failure � All switching with circuit breakers

Double Breaker-Double Bus Disadvantages:

� Very high cost – 2 breakers per circuit

9: ISOLATOR In electrical systems, an isolator switch is used to make sure that an electrical circuit is completely de-energized for service or maintenance. Such switches are often found in electrical distribution and industrial applications where machinery must have its source of driving power removed for adjustment or repair. High-voltage isolation switches are used in electrical substations to allow isolation of apparatus such as circuit breakers and transformers, and transmission lines, for maintenance. An isolator can open or close the circuit when either a negligible current has to be broken or made or when no significant voltage change across the terminals of each pole of isolator occurs. It can carry current under normal conditions and can carry short circuit current for a specified time. They can transfer load from one bus to another and also isolate equipments for maintenance. Isolators guarantee safety for the people working on the high voltage network, providing visible and reliable air gap isolation of line sections and equipment. They are basically motorized i.e. motor does the closing and opening of the isolator. Isolators are distinguished as “off load” and “on load” isolator.

Figure 13: Isolator in a sub-station


10: RELAYS

A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. Relays are used where it is necessary to control a circuit by a low-power signal (with complete electrical isolation between control and controlled circuits), or where several circuits must be controlled by one signal. Relays with calibrated operating characteristics and sometimes multiple operating coils are used to protect electrical circuits from overload or faults; in modern electric power systems these functions are performed by digital instruments still called "protective relays".

Types of relays:

� Electromagnetic attraction relay

� Electromagnetic induction relay

� Thermal relay

� Buchholz relay

� Numerical relay

� Over current relay

11: CIRCUIT BREAKER A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow. Unlike a fuse, which operates once and then has to be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation. Circuit breakers are made in varying sizes, from small devices that protect an individual household appliance up to large switchgear designed to protect high voltage circuits feeding an entire city.

Figure 14: Circuit Breaker in a substation


The type of the Circuit Breaker is usually identified according to the medium of arc extinction. The classification of the Circuit Breakers based on the medium of arc extinction is as follows:

� Air break Circuit Breaker. � Oil Circuit Breaker (tank type of bulk oil) � Minimum oil Circuit Breaker. � Air blast Circuit Breaker. � Vacuum Circuit Breaker. � Sulphur hexafluoride Circuit Breaker. (Single pressure or Double Pressure).

11.1: SF6 circuit breaker SF6 is inert gas the property of this gas the higher pressure and temperature its dielectric strength will be SF6has two gas chamber when contract is close the pressure is two chamber have the same pressure but when the contract is open then one of the chamber get totally close and other remain open ,there is a narrow channel between two chamber and when contract open the SF6 flow a plane of high pressure region to the low pressure region there will be turbulence of SF6.At zero current the turbulence of SF6 absorb all the ions and since it is flowing from a narrow region hence it provide high dielectric strength but there is problem that the pressure of SF6 is not always remain fixed due to leakage in the cylinder of SF6 so there is pressure gauge as well as alarm attached with it. Whenever pressure decreases the alarm ringing and the gas is refilled to increase pressure. 12: Reactor It is similar in appearance and used for absorbing the reactive power from the system. When the system voltage is high. It has air core, oil filled ONAN type. Generally 50 and 63 MVAR shunt reactor are used with both the LINE/BUS both non-switchable/ switchable type shunt reactors are in use.

13: Wavetrap It is an inductor having tuned LC circuit, which is mainly used for PLCC purpose. It offers very high impedance to high frequency PLCC signals does not allow them to enter in S/Y and offers very low impedance for frequency currents.


Figure 15: wavetrap in a sub-station

14: Lightening arrestors A lightning arrester is a device used on electrical power systems and telecommunications systems to protect the insulation and conductors of the system from the damaging effects of lightning. The typical lightning arrester has a high-voltage terminal and a ground terminal. When a lightning surge (or switching surge, which is very similar) travels along the power line to the arrester, the current from the surge is diverted through the arrestor, in most cases to earth. In telegraphy and telephony, a lightning arrestor is placed where wires enter a structure, preventing damage to electronic instruments within and ensuring the safety of individuals near them. Smaller versions of lightning arresters, also called surge protectors, are devices that are connected between each electrical conductor in power and communications systems and the Earth. These prevent the flow of the normal power or signal currents to ground, but provide a path over which high-voltage lightning current flows, bypassing the connected equipment. Their purpose is to limit the rise in voltage when a communications or power line is struck by lightning or is near to a lightning strike. If protection fails or is absent, lightning that strikes the electrical system introduces thousands of kilovolts that may damage the transmission lines, and can also cause severe damage to transformers and other electrical or electronic devices. Lightning-produced extreme voltage spikes in incoming power lines can damage electrical home appliances.


Figure 16: lightning arrester in a sub-station

15: SUBSTATION PROTECTION Substation Grounding/Earthing The sole purpose of substation grounding/earthing is to protect the equipment from surges and lightning strikes and to protect the operating persons in the substation. Hence intentional earthing system is created by laying earthing rod of mild steel in the soil of substation area. All equipments/structures which are not meant to carry the currents for normal operating system are connected with main earth mat .The substation earthing system is necessary for connecting neutral points of transformers and generators to ground and also for connecting the non current carrying metal parts such as structures, overhead shielding wires, tanks, frames, etc to earth. Earthing of surge arresters is through the earthing system. The function of substation earthing system is to provide a grounding mat below the earth surface in and around the substation which will have uniformly zero potential with respect to ground and low earth resistance.


The earthing system in a substation:

� Protects the life and property from over-voltage.

� To limit step & touch potential to the working staff in substation. Provides low impedance path to fault currents to ensure prompt and consistent operation of protective device.

� Stabilizes the circuit potentials with respect to ground and limit the overall potential rise.

� Keeps the maximum voltage gradients within safe limit during ground fault condition inside and around substation.

Earth Resistance:

Earth Resistance is the resistance offered by the earth electrode to the flow of current in to the ground. To provide a sufficiently low resistance path to the earth to minimize the rise in earth potential with respect to a remote earth fault. Persons touching any of the non current carrying grounded parts shall not receive a dangerous shock during an earth fault. Each structure, transformer tank, body of equipment, etc, should be connected to earthing mat by their own earth connection. Generally lower earth resistance is preferable but for certain applications following earth resistance are satisfactory

Large Power Stations – 0.5 Ohm

Major Power Stations - 1.0 Ohm

Small Substation – 2.0 Ohm

In all Other Cases – 8.0 Ohm Step Potential and Touch Potential Grounding system in a electrical system is designed to achieve low earth resistance and also to achieve safe ‘Step Potential ‘and ‘Touch Potential’. Step Potential: Step potential is the potential difference between the feet of a person standing on the floor of the substation, with 0.5 m spacing between the feet (one step), through the flow of earth fault current through the grounding system.

Touch Potential: Touch potential is a potential difference between the fingers of raised hand touching the faulted structure and the feet of the person standing on the substation floor. The person


should not get a shock even if the grounded structure is carrying fault current, i.e. The Touch Potential should be very small. Usually, In a substation a surface layer of 150 mm of rock (Gravel) of 15 mm to 20 mm size shall be used for the following reasons:

� To provide high resistivity for working personnel.

� To minimize hazards from reptiles.

� To discourage growth of weed.

� To maintain the resistivity of soil at lower value by retaining moisture in the under laying soil.

� To prevent substation surface muddy and water logged.

Figure 17: Step Potential and Touch Potential

FORMATION OF SUBSTATION EARTHING:

The main earth mat shall be laid horizontally at a regular spacing in both X & Y direction(9m) based upon soil resistivity value and substation layout arrangement .The main earth mat shall be laid at a depth of 600 mm from ground. The earth mat shall be connected to the following in substation


i. Lightning down conductor, peak of lightning mast ii. Earth point of S A, CVT iii. Neutral point of power Transformer and Reactor iv. Equipment framework and other non-current carrying parts. v. Metallic frames not associated with equipments vi. Cable racks, cable trays and cable armor. LIGHTNING PROTECTION

The protection from the lightning is done with the help of shield wire and lightning mast (high lattice structure with a spike on top).

Shield wire Shield wire lightning protection system will be generally used in smaller sub stations of: Lower voltage class, where number of bays is less, area of the substation is small, & height of the main structures is of normal height. The major disadvantage of shield wire type lightning protection is, that it causes short circuit in the substation or may even damage the costly equipments in case of its failure (snapping ). Earth wire Overhead power lines are often equipped with a ground conductor (shield wire or overhead earth wire). A ground conductor is a conductor that is usually grounded (earthed) at the top of the supporting structure to minimize the likelihood of direct lightning strikes to the phase conductors. The ground wire is also a parallel path with the earth for fault currents in earthed neutral circuits. Very high-voltage transmission lines may have two ground conductors. These are either at the outermost ends of the highest cross beam, at two V-shaped mast points, or at a separate cross arm. By protecting the line from lightning, the design of apparatus in substations is simplified due to lower stress on insulation. Shield wires on transmission lines may include optical fibers (OPGW), used for communication and control of the power system. 7/3.66 mm wire is used for providing earthing in lightning mast and towers. The main function of Earth wire/Ground wire is to provide protection against direct lightening strokes to the line conductors or towers.


In addition Ground wire reduces the induced voltage on parallel telecom lines under fault condition Ground wire must meet the following requirements:

� It must be able to carry the maximum lightening current without undue overheating.

� It must be strong mechanically.

� It must be high enough to afford protection to all the line conductors. This function is called shielding.

� It must have enough clearance above the line conductors at mid-span to prevent a side flashover to a line conductor.

� Tower footing resistance should be low.

Figure 18: earth wire


16: TRANSFORMER AND REACTOR PROTECTIONS

Buchholz Relay:

� This relay is located in pipe between Trf. tank and conservator and protects/warns for incipient faults internal to the Trf. Main faults in this group are core insulation failure, loss of oil and wdg. Turn to turn short.

� The relay has two elements; upper one is a float with a mercury switch. lower elements consists of baffle plate and a mercury switch. Due to incipient minor faults gas is produced which in turn reduces oil level in relay and upper float sinks causing its mercury switch to close and alarm is initiated.

� In case of severe fault likes phase to earth or ph˗ph short circuit or faults in OLTC a surge of oil results and it strikes a baffle plate which causes second mercury switch to close and trip command to Trf. CB is initiated .

Figure 19: Buchholz Relay


Figure 20: location of buchholz relay on transformer

PRV (Pressure Relief Valve) protection:

� On transformer tank two pressure relieving valves are provided which opens whenever the pressure inside the trf .Tank increases beyond designed value.

� The operation of PRV involves loss of substantial trf . oil and this protection operates whenever heavy gas is generated inside the transformer tank because of severe insulation failure in core or transformer windings.

� A Micro switch closes on PRV operation which energizes an aux. relay whose N/O contact closes and trips the trf. HV & LV CBs.

� Inter –tripping of HV & LV CB is incorporated.

Differential protection:

� Low impedance type static percentage biased restraint differential relay MBCH13 is provided for detecting Phase to earth fault and phase to phase fault internal to trf. and terminal faults.

� The relay has an operating time of 10-25 sec. and provides high stability against heavy thorough faults, magnetizing inrush current and over fluxing conditions.

� The setting range of differential current is 10-50% of in .generally relay diff. current is set at 20% in. The relay also has a high -set ranging feature and varies from 4 in at normal load condition to 8 In at heavy thorough faults .

� Inter -tripping of HV & LV CB is incorporated.


Back up O/C and E/F protection:

� Directional O/C and E/F backup protection against external/internal short circuits and excessive O/L is provided by CDD31 IDMT relay.

Restricted E/F protection:

� CAG14 high impedance relay is employed to provide restricted to E/F protection for transformer windings.

� This is also a differential protection where 3 line CT output are paralleled and balanced against neutral CT output .The differential current setting is kept at minimum i.e.10% In .

� Inter -tripping of HV & LV CB is incorporated.

Over fluxing protection:

� GTTM relay operating of V/F ration is used to protect Transformer against over fluxing condition. this occurs when large quantum of trf. Load is disconnected which results in the rise of transformer Primary voltage and its exciting current.

Oil temperature alarm/trip:

• Oil temperature is measured and indicated by oil temperature indicator When temperature reaches 85degree C alarm is initiated .If left unattended and reaches 95 degree C trip command to HV & LV CBs is given.

Winding temperature alarm/trip:

� Winding temp. is indirectly measured by adding equivalent temperature generated by flow of load current in transformer.

� For this a turret CT is used to supply load current to a thermister whose resistance changes according to temperature rise due to current flow .

� Generally an aux. relay contacts are used for initiating winding temp. alarm /trip . � When temperature reaches 90degree C first aux . relay operates and its N/O contact closes

the supply ckt . of cooler fans start them. � When temperature reaches 95 degree C second aux. relay operates and its N/O contact

close the supply ckt .of cooler oil pump and pump starts. � When temperature reaches 100 degree C third aux. relay operates and its N/O contact

closes the alarm ckt. � When temperature reaches 110 degree C fourth aux. relay operates and its N/O contact

closes the trip ckt to the trf. HV & LV CBs.


� Low oil level alarm:

� Whenever oil level in the transformer drops below designed /specified safe operation level an alarm is initiated through a micro switch connected with MOG installed at transformer main tank which operates an aux. relay to initiate alarm in the control room.

� The relay has stepped time distance characteristics for three independent measuring zones, having quadrilateral shaped mho characteristics.

� The max operating time of the relay for zone -1 fault is 40 ms for all types of 30-75 degrees.

� The relay schemes include timers for zone -2&3 are having continuously variable setting of 0-3&0-5 seconds respectively.

� It is suitable for carrier aided tripping. � It is having power swing blocking protection for blocking the tripping in zone 2&3 but

tripping can be permitted in zone -1, if desired. � The relay has memory circuit to ensure correct operation during close 3-phase fault or

switch on to fault feature (SOFT). � The relay also provides Distance to fault measurement.

Auto –reclose Relay:

� VARM relay is provided which is suitable for 1/3 phase auto -reclosing. � The relay has continuously variable Dead time setting range of 0.1-2 sec. � The relay scheme has reclaim timer setting of 25secs. � The relay scheme is of single shot type. � The scheme has provision for assigning priority in both CBs in case of 11/2 breaker

scheme to allow closing of main CB first. � The relay scheme has facility for selecting check synchronizing or dead line charging

feature for which SKD and VAG type relays provided respectively. � SKD relay have response time of 200 ms and a continuously variable timer with range

0.5-5 seconds. The max. phase angle setting is 35 degrees and max. voltage difference setting is 10%.

� VAG type relay have two sets of relay and each set is able to monitor the 3-phase voltage where one set is connected to line CVTs with fixed setting of 20% of rated voltage and other set is connected to bus CVTs with a fixed setting of 80% of rated voltage.

Over Voltage Relay:

� 3 VTU type relays provided with two stages. � 1st stage has IDMT characteristics and adjustable setting of 100-170% of rated voltage

with a timer of 1-60 seconds. � 2nd stage has instantaneous characteristics and adjustable setting of 100-170% of rated

voltage with a timer of 0-200ms. � Voltage setting of 110% &150% and Timer setting of 4 seconds & 30 ms are kept for 1st

& 2nd stage respectively.


� The relay has separate flags for operation indication of each stage.

17: CIRCUIT BREAKER AUXILIARY RELAYS

Local Breaker Back up relay:

� MCTI type solid state relay is provided. � It is a fast operating relay with op. & resetting time less than 15 ms. � It has 3 O/C elements with setting range of 20-80% of rated current .The E/F elements

are set at 20%. � It incorporates timer with continuously adjustable setting range 0.1-1 sec. The timer

setting is kept as 0.2 sec. � In the event of non-operation of any CB on receipt of tripping command and

availability of 20% current through feeder CT secondary, the O/C elements of this scheme operates and after timing bus zone CBs through B/B protection and all the ckts connected on that particular bus are disconnected to clear the bus.

Trip Circuit Supervision Relay:

� VAX type relay provided which are capable of monitoring the healthiness of each phase trip coil and associated circuit of circuit breaker during ON and OFF conditions.

� The relay initiates alarm in case of fault in trip circuit. � The relay has a time delay on drop off-of 200 ms at least and provided with flags for each

phase.

D.C. Supervision Relay:

� VAA type aux relay is provided for supervising each D.C. Supply. � The relay monitors the failure of DC supply and initiates an alarm. � The relay has flag for indicating its operation. � The relay has a time delay on drop-off of 100 ms at least.

A/R Lock out (Z2&3) /Distance operated relay:

� This operation of this aux .relay indicates that distance relay has operated in Zone 2/3 and auto-reclosure feature is locked out.


Fuse failure relay:

� This relay monitors all the three fuses of CVT s and its secondary cables (from S/Y to C&R panels) for any open circuit condition.

� In the event of CVT fuse failure /open circuiting of its cables, the relay operates and inhabits trip ckts of CBs and initiates alarm.

� This relay is of very fast acting type and its operating time is only 7ms. � This relay remains inoperative for system earth faults.

For Carrier aided protection following aux. relay are provided:

� Carrier receive relay � Carrier healthy relay � Carrier send /aided trip relay � Direct trip received ch-1 relay � Direct trip received ch-2 relay

Pole Discrepancy Relay:

� This relay is provided in Circuit Breaker. in the event of mismatch in the closing of all three phases CB is more than 2.5 sec the relay operates and trips the closed CB and locks out the A/R feature.

Low SF6 gas pressure protection:

� SF6 pressure in the CB is kept at 7 kg /sq.cm. � When this pressure comes down due to leakage of gas an alarm is initiated at 6.5 Kg /sq.

cm. � When gas pressure comes down to 6.0kg/sq. the CB operation is locked out.

Low Air pressure protection

� Air pressure in the CB is kept at 16 kg/sq. cm. � When this pressure is comes down to 14 Kg/sq.cm (due to non –functioning of

compressor) an alarm is initiated. � When this pressure comes down to 13kg/sq. cm the CB operation as well as A/R feature

are locked out.


18: TRANSMISSION LINE PROTECTION

Introduction:

All relay are electrically isolated from main power system and receive measuring quantities from CT, CVT etc. The following basic properties are desired of any relay/protection scheme:

- Selectivity - also known as discrimination means relay should chose correctly which portion to isolate and trip nearest CB only.

- Stability- means relay should remain unaffected by load conditions and external faults.

- Speed- means relay should operate quickly for minimizing the damage due to fault. - Sensitivity- relay should have minimum operating current/voltage to operate.

Distance Relay:

� Normally this relay scheme is employed for line protection. Since impedance of line is proportional to its length, therefore relay measures impedance and based on this decides whether faults lies within its zone or not. Accordingly relay either operates or restrain.

� To ensure correct co-ordination between distance relay in a system it is customary to choose a relay setting of 80% of line impedance for Zone-1 setting. In Zone-2 setting reach of relay is extended to 1st line +50% of next shortest line.

� Zone-3 setting is kept as 1st line +2nd longest 25% of third shortest line.

Main-I Protection:

� In 400KV line this protection is provided by a numerical distance scheme such as EPAC3000.

� This relay is self monitoring type, non-switched scheme with separate measurements for all ph-ph and ph-earth faults.


� The relay has self diagnostic features.

� The relay is having stepped time distance characteristics for three independent measuring zones, having quadrilateral shaped Mho characteristics. The max. Operating time of the relay for zone-1 fault is 40 ms for all types of faults. The relay has independent R/X settings and adjustable characteristics angle of 30-75 degrees.

� The relay scheme has timers for Zone-2&3 are having continuously variable setting of 0-3 & 0-5 seconds respectively.

� It also has an off-set feature with 10-20% of Zone-3 to cover backward zone faults between relay and busbar.

� The relay has memory circuits to ensure correct operation during close 3-phase fault or switch on to fault feature (SOTF).

� It is suitable for carrier aided tripping.

� It is having power swing blocking protection for blocking the tripping in zone 2&3 but tripping can be permitted in zone-1, if desired.

� The relay also provides distance to fault measurement.

Main-II protection:

� In 400KV line this protection is provided by static modular type distance scheme such as OPTIMHO.

� This relay is non-switched scheme with separate measurements for all ph-ph and ph-earth faults.


19: BUS BAR PROTECTION

� The bus bar faults generally involve one phase and earth and large no. of bus bar faults result from human error when safety earthing done for maintenance work is not removed before charging the bus.

� The requirement of bus bar protection is high speed of operation (of the order of one cycle) to limit the consequential damage and maintain system stability.

� The other important requirement of bus bar protection is that it should be completely stable.

� To achieve this 2 independent measurement are taken by two differential relay systems being energized from separate cores of CTs. One relay is applied to each busbar/bus section and second relay is applied to both buses/sections and called check system.

� The tripping of busbar/section is only initiated if both i.e. its busbar/section relay has operated and check busbar relay has also operated.

� The busbar protection is based on circulating differential current measurement principle. The CT output of all the zone/section feeders/ckts are connected in parallel and relay measuring element is connected between phase and neutral.

� The busbar protection covers phase as well as earth faults in that zone and setting for operation is kept same for both.

� The selective tripping of bus zone/bus section involved with fault is achieved through the position of aux. contact of bus isolators of faulted feeder.

� For 400KV busbar two identical low impedance biased differential protection scheme MBCZ are employed.

� It is a modular solid state relay having very fast operating time of less than 20ms. Separate modules for feeders, tie, Bus coupler, zone measuring and bus selection isolators are assembled to make the scheme functional.


20: Supervisory Control and Data Acquisition (SCADA) The task of supervision of machinery and industrial processes on a routine basis can be an

Excruciatingly tiresome job. Always being by the side a machine or being on a 24x7 patrol

duty around the assembly line equipment checking the temperature levels, water levels, oil

level and performing other checks would be considered a wastage of the expertise of the

technician on trivial tasks. But, to get rid of this burdensome task, the engineers devised

equipments and sensors that would prevent or at least reduce the frequency of these routine

checks. As a result of that, control systems and it’s various off springs like SCADA systems

were formed. Supervisory Control and Data Acquisition (SCADA) offers the ease of

monitoring of sensors placed at distances, from one central location.

SCADA systems are used to monitor and control a plant or equipment in industries such as

telecommunications, water and waste control, energy, oil and gas refining and transportation.

A SCADA system gathers information, such as where a leak on a pipeline has occurred,

transfers the information back to a central site, alerting the home station that the leak has

occurred, carrying out necessary analysis and control, such as determining if the leak is

critical, and displaying the information in a logical and organized fashion. SCADA systems

can be relatively simple, such as one that monitors environmental conditions of a small office

building, or incredibly complex, such as a system that monitors all the activity in a nuclear

power plant or the activity of a municipal water system. SCADA systems were first used in

the 1960s.


20.1: Parts of a SCADA System There are many parts of a working SCADA system. A SCADA system includes signal

hardware (input and output), controllers, networks, user interface (HMI), communications

equipment and software. All together, the term SCADA refers to the entire central system.

The central system monitors data from various sensors that are either in close proximity or

off site (sometimes miles away).

For the most part, the brains of a SCADA system are performed by the Remote Terminal

Units (sometimes referred to as the RTU). The Remote Terminal Units consists of a

programmable logic controller. The RTU are set to specific requirements, however, most

RTU allow human intervention, for instance, in a factory setting, the RTU might control the

setting of a conveyer belt, and the speed can be changed or overridden at any time by human

intervention. In addition, any changes or errors are automatically logged for and/or displayed.

Most often, a SCADA system will monitor and make slight changes to function optimally;

SCADA systems are considered closed loop systems and run with relatively little human

intervention.

One of key processes of SCADA is the ability to monitor an entire system in real time. This

is facilitated by data acquisitions including meter reading, checking statuses of sensors, etc

that are communicated at regular intervals depending on the system. Besides the data being

used by the RTU, it is also displayed to a human that is able to interface with the system to

override settings or make changes when necessary.

SCADA can be seen as a system with many data elements called points. Each point is a

monitor or sensor. Points can be either hard or soft. A hard data point can be an actual

monitor; a soft point can be seen as an application or software calculation. Data elements

from hard and soft points are always recorded and logged to create a time stamp or history.


21: NTMC & RTMC: THE NEXT LEVEL

NATIONAL TRANSMISSION- ASSET MANAGEMENT CENTRE (NTM C) WHAT IS NTMC? “Centralized control of entire transmission system from single point with fully automated remote controlled sub-stations”.

The emphasis on the power sector to ensure the growth in GDP has brought in many changes

in the business environment of Power Sector. The transmission sector being the integral part

of, is also facing multiple challenges like competitive bidding for transmission project,

stringent demands by the regulator etc.

The technological development couple with falling prices of communication system and

information technology provides us the opportunity for virtual manning of Substation thereby

optimizing the requirement of skilled manpower and managing the asset with the available

skilled workforce. Thus, state of the art computerized control centers NTAMC & RTAMC

with associated telecommunication system and adapted substation for enabling remote

centralized operation, monitoring and control of POWERGRID Transmission system has

been proposed.

The aim is to have completely unmanned substation except security personnel. The

operations of the substations will be done from a remote centralized location i.e. NTAMC.

The RTAMC will co-ordinate the maintenance aspect of the substation from a centralized

location and will act as a backup to the NTACM for operation. The maintenance activities

would be carried out by maintenance service hub (MSH). One MSH will cater to the

requirements of 3-4 substations in its vicinity in coordination with the respective RTAMCs.

The substations and various control centers will be connected by redundant broadband


communication network through POWERGRID (Telecom) communication links. Telecom

Department to provide high speed communication links between NTAMC, RTAMCs and

Sub-stations. The Connectivity Status has been finalized in association with LD&C

department and NTAMC group. More links have to be planned by LD&C for total

protection. Bandwidth requirement and Connectivity Scheme finalized. At stations where this

connectivity is not possible, leased lines will be hired from other telecom operators up to the nearest connection point.

WHY NTMC ?

TECHNICAL • With merging grids (N-E-W) & S, inter-regional power flow needs more coordination • Long delays in layered system of manual operation.

• Delays in gathering & evaluating intelligence in standalone s/s.

ECONOMIC

• Huge Manpower Cost in Manned system • No requirement of manning S/S operation in today’s digital, automated control system • Low technology cost in Automation & Remote Control • Gearing up for competitive bidding regime of transmission assets

• Stringent demands by the regulator etc.

47

21.1: OPERATIONAL PHILOSOPHY

� NTMC shall carry out Remote Operations of all theDesks.

� RTMC will co-ordinate maintenance aspect of substations

will act as backup to NTMC for

� MSH (Maintenance Service Hub) shall carry out

also catering to the requirements of 3in coordination with RTMC

21.2:

SUMMER TRAINING REPORT

OPERATIONAL PHILOSOPHY

NTMC shall carry out Remote Operations of all the substations from its own regional

ordinate maintenance aspect of substations from a Regional HQ and will act as backup to NTMC for Operation.

MSH (Maintenance Service Hub) shall carry out maintenance from one central S/S requirements of 3-4 satellite substations in vicinity (100

in coordination with RTMC.

.2: STRUCTURE OF NTMC

Figure 21: Structure of NTMC


substations from its own regional

from a Regional HQ and

maintenance from one central S/S satellite substations in vicinity (100- 150 KM)

48

Figure 22

Figure 23


22: Evolution of Voltage level in indian grid

23: Network Management System in India



22: STATIC VAR COMPENSATOR

A static VAR compensator (SVC) is an electrical device for providing fast-acting reactive

power compensation on high voltage transmission networks and it can contribute to improve

the voltages profile in the transient state and therefore, in improving the quality performances

of the electric services. A SVC is one of FACTS controllers, which can control one or more

variables in a power system. The dynamic nature of the SVC lies in the use of thyristor

devices (e.g. GTO, IGCT) . The thyristor, usually located indoors in a “valve house”, can

switch capacitors or inductors in and out of the circuit on a per-cycle basis, allowing for very

rapid superior control of system voltage. The compensator studied in the present work is

made up of a fixed reactance connected in series to a thyristor controlled reactor (TRC) based

on bi-directional valves- and a fixed bank of capacitors in parallel with the combination

reactance-TRC. The thyristors are turned on by a suitable control that regulates the magnitude

of the current.

Configuration of SVC

SVC provides an excellent source of rapidly controllable reactive shunt compensation for

dynamic voltage control through its utilization of high-speed thyristor switching/controlled

devices . A SVC is typically made up of coupling transformer, thyristor valves, reactors,

capacitance (often tuned for harmonic filtering). Advantages of SVC The main advantage of SVCs over simple mechanically switched compensation schemes is

their near-instantaneous response to change in the system voltage. For this reason they are

often operated at close to their zero-point in order to maximize the reactive power correction.

They are in general cheaper, higher-capacity, faster, and more reliable than dynamic

Compensation schemes such as synchronous compensators (condensers). In a word:


1) Improved system steady-state stability. 2) Improved system transient stability. 3) Better load division on parallel circuits. 4) Reduced voltage drops in load areas during severe disturbances. 5) Reduced transmission losses. 6) Better adjustment of line loadings.

22.1: Control Concept of SVC An SVC is a controlled shunt susceptance as defined by control settings that injects reactive

power into the system based on the square of its terminal voltage. Fig illustrates a TCR SVC,

including the operational concept. The control objective of the SVC is to maintain a desired

voltage at the high-voltage bus. In the steady-state, the SVC will provide some steady-state

control of the voltage to maintain it the high-voltage bus at a pre-defined level. If the high-

voltage bus begins to fall below its set point range, the SVC will inject reactive power Into

thereby increasing the bus voltage back to its net desired voltage level.

If bus voltage increases, the SVC will inject less (or TCR will absorb more) reactive power,

and the result will be to achieve the desired bus voltage. From Fig. 1, +Q cap is a fixed

capacitance value, therefore the magnitude of reactive power injected into the system, Q net,

is controlled by the magnitude of reactive power absorbed by the TCR. The fundamental

operation of the thyristor valve that controls the TCR is described here. The thyristor is self

commutates at every current zero, therefore the current through the reactor is achieved by

gating or firing the thyristor at a desired conduction or firing angle with respect to the voltage waveform.


Figure 24: SVC with control concept. 22.2: The Thyristor Controlled Reactor The basis of the thyristor-controlled reactor (TCR) is shown in Fig. The controlling element

is the thyristor controller, shown here as two oppositely poled thyristors which conduct on

alternate half-cycles of the supply frequency. If the thyristors are gated into conduction

precisely at the peaks of the supply voltage, full conduction results in the reactor, and the

current is the same as though the thyristor controller were short circuited.


Principle of Operation

The current is essentially reactive, lagging the voltage by nearly 900. It contains a small in-

phase component due to the power losses in the reactor, which may be of the order of 0.5-2%

of the reactive power. Full conduction is shown by the current waveform. If the gating is

delayed by equal amounts on both thyristors, a series of current waveforms is obtained. Each

of these corresponds to a particular value of the gating angle α, which is measured from a

zero-crossing of the voltage. Full conduction is obtained with a gating angle of 900. Partial

conduction is obtained with gating angles between 900 and 1800. The effect of increasing the

gating angle is to reduce the fundamental harmonic component of the current. This is

equivalent to an increase in the inductance of the reactor, reducing its reactive power as well

as its current. So far as the fundamental component of current is concerned, the thyristor-

controlled reactor is a controllable susceptance, and can therefore be applied as a static compensator.

Figure 25: Elementary thyristor-controlled reactor (TCR).


23: CONCLUSION

The past months of my training have been very instructive for me. POWER GRID

CORPORATION OF INDIA LIMITED has given me opportunities to learn and develop

myself in many areas. I gained a lot of experience, especially in the substation switchgears,

equipment and protection field. A lot of the tasks and activities that I have worked on during

my internship are familiar with what I’m studying at the moment. I worked in many areas where I did different work. As a bonus, I got to experience the recent projects of power grid i.e. NATIONAL

TRANSMISSION- ASSET MANAGEMENT CENTRE (NTMC) and STATIC VAR

COMPENSATOR. I learned how these projects transform existing infrastructure of the

400/220 KV substation kankroli. There is a big difference in the college projects and the

tasks and activities during the actual work. In college we learn how to describe the work in

projects, where in work you learn how to implement them in reality. This internship was definitely an introduction to the actual work field for me. I learned a lot from the different interns that I have been working with during my internship.

Each intern had a different educational background and that made it interesting for me. By

working with them I got to learn from them and become aware educational background.

My mentor during my internship was Mr. Lokesh Singh Chundawat (Sr. Engineer) whom

I have also learned a lot from during my internship. As a sr. engineer, he has lots of

knowledge of the working area . he was very helpful and always willing to give me advice

and feedback which I appreciate. he had always time to answer all my questions concerning

my internship.

Summer Internship Report -By Rahul Mehra

Technology

Transcript of Summer Internship Report -By Rahul Mehra