A

PROJECT REPORT ON

“OPERATIONAL DESCRIPTION OF 400KV SWITCH YARD”

AT

UNDER THE GUIDANCE OF

Sri.B.SAKRU

DY.MANAGER (EM)

A Dissertation report submitted to the

Sindhura College of Engineering and Technology

In partial fulfillment of the degree of

VOCATIONAL TRAINING IN

ELECTRICAL & ELECTRONICS ENGINEERING

SUBMITTED BY

A.PRADEEP (11B71A0244)

B.LAKSHMAN NAYAK (11B71A0242)

L.VENKATESH (11B71A0255)

B.SAITEJA (11B71A0232)

DEPARTMENT OF ELECTRICAL AND ELECTRONIC ENGINEERING

SINDHURA COLLEGE OF ENGINEERING AND TECHNOLOGY

(Approved by AICTE, Accredited by NBA and Affiliated to JNTUH)

Medipally, Godavarikani (NTPC)Ramagundam, Dist.Karimnagar (TS).

CERTIFICATE

This is to certify that the project entitled

“OPERATIONAL DESCRIPTION 400KV SWITCH YARD”

By

A.PRADEEP (11B71A0244)

B.LAKSHMAN NAYAK (11B71A0242)

L.VENKATESH (11B71A0255)

B.SAITEJA (11B71A0232)

Students of Electrical & Electronics Engineering SINDHURA COLLEGE OF ENGINEERING AND TECHNOLOGY (Approved by AICTE, Accredited by NBA and Affiliated to JNTUH) has done “OPERATIONAL DESCRIPTION 400KV SWITCH YARD” at NPTC Ramagundam and gained valuable knowledge along with industrial experience.

Project Guide: Project In charge:

Sri.B.Sakru Sri. B.V.Subramanyam

DY.MANAGER (EM) ADDL.GENERAL MANAGER (EM)

N.T.P.C. LTD N.T.P.C. LTD

RAMAGUNDAM RAMAGUNDAM

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ACKNOWLEDGEMENT

We take this opportunity to record our gratitude to all those who helped us in successful completion of the project.

We take immense pleasure in thanking our Head of the Department (Electrical & Electronics Engineering) Prof. J.Madhukar Reddy and Principal Dr. M.Sushanth Babu, for permitting us to carry out this project.

Successful completion of our project is indeed practically incomplete without support from Sri.B.V.Subramanyam, Sri.B.Sakru Dy. Manager (EM) and Sri.B.Krishnamurthy Asst.Manager (O) helped us constantly with their support and guidance in learning the practices with hands on experience.

We are thankful to Sri.E.Nandakishore AGM (HR-EDC), Sri.P.M.G.V.Srinivas DGM (HR-EDC) for assigning this project and extending co-operation and encouragement. We wish to regard our gratitude to Sri.M.V.R.Sarma asst.manager (HR-EDC) and Sri.C.Keshavulu, Staff asst. (EDC) for providing us an opportunity to do this project work in this organization.

Finally, we wish to express our profound thanks to all the employees, in charges and workmen without their support, completion of this project would have been impossible.

BY

A.PRADEEP (11B71A0244)

B.LAKSHMAN NAYAK (11B71A0242)

L.VENKATESH (11B71A0255)

B.SAITEJA (11B71A0232)

3

INDEX

S.NO TOPIC PAGE NO

1 Introduction of NTPC 5-7

2 Salient Features of RSTPS 8-10

3 Abstract of RSTPS 400KV Switchyard 11

4 Line diagram of 400kv switch yard 12

5 About 400kv switch yard 13-14

6 Auto, Tie T/F, Shunt reactor, Bus reactor 15-18

7 Switchyard protection activities 19

8 Switchyard equipment 20-25

9 Relay panels 26-28

10 Relays and protection schemes 29-31

11 Switchyard emergencies and action 32-42

12 Synchronizing Transformer 43-46

13 Tripping action 47-50

14 Conclusion & references 51

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1. INTRODUCTION

“To be the world’s largest and best power producer, powering India’s growth.”

- Vision Statement of NTPC

National Thermal Power Corporation Ltd. is one of the Maharatna companies.

Incorporated in 1975, NTPC is India’s largest power generation companies in India. It is the

sixth largest thermal power generating company in the world. Its core business is

Engineering, Construction & Operation of power-generation plants. It also provides

consultancy to power utilities in India and abroad. It has 15 coal-based and 7 gas-based

Power stations, across the nation. Almost 25 % of total power needs in India are met by

NTPC. Presently, it has an installed capacity of about 41,184 MW. Its target is to achieve

128,000 MW by 2032.

‘Forbes Global 2000’ ranking of the world’s biggest companies ranked NTPC at 337 in the

year 2012.

National thermal power corporation is a major power generation

corporation in the country. It generating one-third of the total power consumed in the country.

This organization made an impeccable record by consistently generating reliable and quality

power since three decades. The mission of NTPC has been to construct commission and

operate power projects most economically and efficiently.

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Vision of Operation Department

“To achieve operational excellence through systematic practices,

Innovation and Team work with strong commitment towards safety, Environment, Quality, and Human excellence”. NTPC has 17 Coal-fired stations, 8 coal based jv & 8 Gas-based stations spread across India as follows:

Coal-fired stations:

S.NO STATION STATE CAPACITY(MW)

1 Singarauli Uttar Pradesh 2000

2 Korba Chattisgarh 2600

3 Ramagundam Andhra Pradesh 2600

4 Farakka West Bengal 2100

5 Vindyachal Madhya Pradesh 4260

6 Rihand Uttar Pradesh 3000

7 Kahalgon Bihar 2340

8 Dadri Uttar Pradesh 1820

9 Talcher Kaniha Orissa 3000

10 Unchahar Uttar Pradesh 1050

11 Talcher Thermal Orissa 460

12 Simhadri Andhra Pradesh 2000

13 Tanda Uttar Pradesh 440

14 Badarpur Delhi 705

15 Sipat Chattisgarh 2980

16 Mauda Maharashta 1000

17 Barh Bihar 3300

Total 35,655

Coal-based joint ventures of NTPC:

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S.NO STATION STATE CAPACITY(MW)

1 Durgapur West Bengal 120

2 Rourkela Orissa 120

3 Kanti Bihar 110

4 IGSTPP, Jhajjar Haryana 1500

5 Aurangabad Bihar 1980

6 Chennai Tamilnadu 1500

7 Nabinagar Bihar 1000

8 Bhilai Chattisgarh 574

Total 6904

Gas-based stations:

S.NO STATION STATE CAPACITY(MW)

1 Anta Rajasthan 413

2 Auraiya Uttar Pradesh 652

3 Kawas Gujrat 645

4 Dadri Uttar Pradesh 817

5 Jhanor Gandhar Gujrat 648

6 Kayankulam Kerala 350

7 Faridabad Haryana 430

8 RGPPL(JV) Maharashtra 1940

Total 5895

2. SALIENT FEATURES OF RSTPS

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Installed Capacity 2600MW

Unit Sizes

Stage-I: 3 x 200

Stage-II: 3 x 500

Stage-III: 1 x 500

Location Karimnagar (dist), Telangana

Source of Coal (i) South Godavari Coal Fields of Singrani Collieries for Stage I & II

(ii) Korba Coal Fields of SECL for Stage III

Water Source Pochampadu reservoir

Coal Consumption 40,000 tons per day (approx.) 14.6 million tons per annum

Water Consumption 250 cu secs per annum

Total Transmission System 2475 km of 400 kv lines

Total Plant Area 10,000 Acres

Reservoir Area 5000 Acres

Coal Transportation System Merry Go Round(MGR) System of 27 kms

Total Investment 3475 crores

Man Power Requirement 1560(0.6 per MW)

Height of Chimney Stage-I: 225 meters

Stage-II: 250 meters

Stage-III: 275 meters

Length of Earthen Dam 8.5 km

Beneficiary States Andhra Pradesh, Tamilnadu, Goa, Kerala, Pondicherry, Karnataka.

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Foundation:

Ramagundam Super Thermal Power Station is third in the series of super thermal power station set up by NTPC. Late Sri. Morarji Desai, the former Prime Minister of India, laid foundation stone for this project on 14th November 1975. This station consists of 3X200 MW units regarded as Stage-1 and 3X500 MW units as Stage-2 and 1X500 MW units as Stage-3, making a total capacity of 2600MW.

Distribution of Electricity:

Total Capacity of Ramagundam NTPC is 2600MW of stage 1, 2&3(i.e. 1, 2, 3&4, 5,&7 units) distributing electricity to following states in MEGA WATT

STATE MW PERCENTAGE (%)

ANDHRA PRADESH 838MW 32%

TAMILNADU 666MW 26%

KERALA 388MW 15%

GOA 75MW 3%

PONDICHERRY 108MW 4%

UNITS COMMISSIONED:-

Unit 1 -------------- 200MW --------------------- Nov 1983

Unit 2 -------------- 200MW --------------------- May 1984

Unit 3 -------------- 200MW --------------------- Dec 1984

Unit 4 -------------- 500MW --------------------- June 1988

Unit 5 -------------- 500MW --------------------- Mar 1989

Unit 6 -------------- 500MW --------------------- Oct 1989

Unit 7 -------------- 500MW --------------------- Aug 2004

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Transmission Lines: 15 Outgoing feeders

Hyderabad ------------------ 4

Nagarjuna Sagar ------------------- 2

Chandrapur ------------------ 2

Warangal ----------------- 1

Dichipally ------------------ 1

AP Transco ------------------ 5

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3. ABSTRACT OF 400KV SWITCH YARD

400 KV Switchyard of Ramagundam Super Thermal Power Station is the most vital switching station in the southern Grid. 2600 MW of Bulk Power generated by three 200 MW Units and four 500 MW Units of NTPC Ramagundam is evacuated for supplying to the southern states.

Switchyard consists of four 400 KV busbars fed by 7 Nos. of generators, 10 Nos. of 400 KV feeders, 3 Nos of 220 KV feeders and two nos. of 132 Kv feeders as shown in the single line diagram of 400 Kv switch yard.

In addition to the above, four nos. of Tie Transformers, five nos. of Auto transformers, two nos. of Shunt Reactors and one Bus reactor are provided.

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4. LINE DIAGRAM OF 400KV SWITCH YARD

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5. ABOUT LINE DIAGRAM OF SWITCH YARD OF RSTPS

It is four busbar system with one & half and two circuit breaker system. It consists of 15 outgoing lines which transmit the power to various regions in the southern and western region of India.

400 KV TRANSMISSION LINES

1. Ramagundam Nagarjunasagar Circuit 1 Double Circuit lines (267 Km length)

2. Ramagundam Nagarjunasagar Circuit 2

3. Ramagundam Hyderabad Circuit (LILO at

Gajwel)

1 Independent lines (189 Km length)

4. Ramagundam Hyderabad Circuit (LILO at

Malkaram)

2

5 Ramagundam Hyderabad Circuit 3

6 Ramagundam Hyderabad Circuit 4

7. Ramagundam Khammam Circuit (LILO at

Warangal)

1 Single line (202 Km length)

8. Ramagundam Chandrapur Circuit(HVDC

Bhadravati)

1 HVDC back to back intergrid

connecting double circuit lines (180

Km length)9. Ramagundam Chandrapur Circuit (HVDC

Bhadravati)

2

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5.1 220 KV TRANSMISSION LINES

1. NTPC AP Transco line 1 Through 400 /220 KV 250MVA

AT # 3 & 42. NTPC AP Transco line 2

3. NTPC AP Transco line 3 Through 400 /220KV

315MVA AT # 5

5.2 132 KV TRANSMISSION LINES

1. NTPC AP Transco line 1 Through 400 Kv/132KV 200MVA

AT # 1 & 2

2. NTPC AP Transco line 2

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6. TRANSFORMERS & REACTORS

6.1 AUTO TRANSFORMERS

What is Autotransformer……?

An autotransformer is a transformer that uses a common winding for both the primary and secondary windings. Essentially an inductor with a center-tap, an autotransformer is often used in power-supply boost-converter applications to achieve a higher output voltage, while limiting the peak fly back voltage seen by power switch.

Five Auto Transformers with on Load Tap Changers are provided to interconnect the 400 Kv system of NTPC and 220/132 Kv system of AP Transco, Malyalapally sub station situated 1.8 Km away from the RSTPS switchyard.

1. 400/132 Kv 200 MVA (TELK make) 2 Nos

2. 400/220 Kv 250 MVA (TELK make) 2 Nos

3. 400/220 Kv 315 MVA (Crompton Greaves Ltd. make) 2 Nos

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6.2 TIE TRANSFORMER

It is a step down transformer which is used to supply the electrical power to the station utilities and the town ship.

Four nos. of Tie Transformers are provided for feeding power to station auxiliaries like Cooling water & Raw water pumps, Coal Handling & water treatment Plants, Ash & Fuel Handling pumps, Cooling towers and lighting requirements of station & township.

6.3 SHUNT REACTOR

A reactor that has a relatively high inductance and is wound on a magnetic core containing an air gap; used to neutralize the charging current of the line to which it is connected.

Long lines when lightly loaded, the receiving end voltage raises, due to Ferranti effect. Shunt Reactors produce lagging MVAR there by control the receiving end voltages during lightly loaded conditions. Shunt reactors also limit the short circuit fault levels. Therefore, Shunt reactors are provided on both the ends of Nagarjuna Sagar lines 1 & 2, the length of these lines being about 267 km.

6.4 BUS REACTOR

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Reason for high grid voltage in southern grid during off peak period-As per CEA report

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Effect of high grid voltage

High over voltage cause

Difficulty in regulating load flow in HVDC line

Difficulty in synchronization with inter grid transmission line

Instability in generator due to operation in underexcitation zone near pole slip region

Increase in line loss

RECOMMENDED LOCATION FOR ADDITIONAL 25 Nos REACTORS

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7. SWITCHYARD OPERATION ACTIVITIES

As mentioned elsewhere, RSTPS switchyard is handling bulk power and its operation and Maintenance has become critical. Any ambiguity in the operation of the switchyard may lead to such disasters like grid failure, station outages crippling not only the normal life of people but also the very economy of the country. Even in less serious situations such as cascade tripping of Auto Transformers due to unplanned over loading has caused under utilization of our generating capacity many times. The operation of switchyard calls for a very alert staff that shall have to sense the abnormalities in time and prompt to concern timely to enable normalcy of the system. The following are some of the identified activities of 400 KV switchyard operations.

1. Identifying of faulty equipment, safe isolation of equipment without disturbing other system as much as possible, raising job cards, arranging shutdowns, trial charging and normalization of 400 KV SWYD. And 132KV Swyd, associated equipment like CBs, Isolators, A/Ts, T/Ts, Shunt Reactors, ACDBs, DCDBs, Battery, Charges PLCC equipment, Swyd. Compressors and lighting.

2. Daily inspection of indoor/outdoor swyd equipment, checking of oil leakages, temperatures and any other abnormalities like sparks etc. SF6 gas pressures, compressed air pressures, running period of compressors, availability status of mulsifier system, swyd. And station P.A. system and PLCC communication system etc. monitoring of physical conditions of swyd equipment.

3. Analyzing and locating of fault leading to feeder/Transformer trip, reporting emergencies to the higher authorities, coordinating with other agencies like AP Transco/Genco, PGCIL in clearing faults and normalization of system.

4. Close monitoring of grid parameters, coordinating with CPCC, SRLDC, OS (SR), OS (ED), LDC (APSEB), Shift charge Engineer & Desk Engineers for smooth operation of grid system, timely action to ensure continuity of power supply.

5. Quick arrangement of startup power supply in case of grid failures, station outages.

6. Continuous monitoring of system parameters like voltage, frequency, line and Transformer, loading unit generations, MVAR and MW net exports etc. recording and corrective action where the abnormality found.

7. Preparing of daily power generation / export/import energy reports, exchanging data with CPCC, OS (ED), OS (SR), collection of generation details from other power projects and storing.

8. Assisting the shift in charge in transmitting the flash report, availability report, unit trip/synchronization messages, shutdown messages, generation back down messages, modification of availability declarations, feed back to shift in charge, the deviation if any in total generation with respect to the declaration.

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8. SWITCHYARD EQUIPMENT

To perform switchyard operation activities perfectly, operation staff should have good knowledge about the equipment provided in switchyard as well as in control room. They should be familiar with the control system adopted here and a good understanding about the procedures to be followed during the emergencies, outage requirements and

charging. Brief description about switchyard equipment is given below.

8.1 BUS BAR:

In electrical power distribution, a busbar is a thick strip of copper or aluminum that conducts electricity within a switchboard, distribution board, substation or other electrical apparatus.

Busbars are used to carry very large currents, or to distribute current to multiple devices

within switchgear or equipment.

Busbar is an Aluminium tube of 4” IPS having wall thickness of 0.4”, where all incoming and outgoing feeders are connected in a schematic way to enable smooth operation and Maintenance of equipment without any interruption to the system. At RSTPS one and half breaker scheme is provided for 200 MW generator feeders and 400 KV outgoing lines, Two-breaker scheme is provided for 500 MW generator feeders.

8.2 ISOLATORS:

In electrical engineering, a disconnector or isolator switch is used to make sure that an electrical circuit can be 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. Isolating switches are commonly fitted to domestic extractor fans when used in bathrooms in the UK.

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Often the isolation switch is not intended for normal control of the circuit and is only used for isolation.

Isolator is an off load device provided in conjunction with circuit breaker to disconnect the equipment or the section, which is to be isolated from all other live parts. The isolators provided in the switchyard are of central break type. The operation of Isolators can be done from control room (remote) or local. Motorized operation for opening & closing of Isolator is provided, however Isolators can also be opened & closed manually in the even of non-availability of motorized operation.

8.3 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

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It is an automatic device capable of making and breaking an Electrical Circuit under normal and abnormal conditions such as short circuits. SF6 is the arc quenching media for all the 400 KV and 220 KV breakers installed in the switchyard. Pneumatic operating system is provided in AEG, ABB, AREVA and NGEF make breakers and Hydraulic operating system is provided in BHEL make breakers. 132KV breakers provided in 132 KV

lines are of Minimum oil type operating on spring charge mechanism.

8.4 SURGE/LIGHTINING ARRESTER : A lightning arrester is a device used on electrical power systems to protect the insulation on the system from the damaging effect of lightning. Metal Oxide Varistors (MOVs) have been used for power system protection since the mid 1970s. The typical lightning arrester also known as surge arrester has a high voltage terminal and a ground terminal. When a lightning surge or switching surge travels down the power system to the arrester, the current from the surge is diverted around the protected insulation in most cases to earth.

Surge Arresters are provided to ground the over voltage surges caused by switching and lighting surges. Surge Arresters provide leakage path to the ground whenever the system

Voltage rises above the specified value. They are equipped with surge monitors, which measure the leakage currents and a counter to record the number of surges taken place.

8.5 EARTH SWITCH:

In electricity supply systems, an earthing system defines the electrical potential of the conductors relative to that of the Earth's conductive surface. The choice of earthing system has implications for the safety and electromagnetic compatibility of the power supply.

Earth switch is mounted on the isolator base on the line side or breaker side depending upon the position of the isolator. The earth switch usually comprises of a vertical

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break switch arm with the contact, which engages with the isolator contact on the line side. Earth switch is required to discharge the trapped charges on the line or equipment (under shut own) to earth for maintaining safety. Earth switch can be operated only from local either by electrical operation or manually.

8.6 CURRENT TRANSFORMER (CT):

Current transformer (CT) is used for measurement of electric currents. Current transformers, together with voltage transformers (VT) (potential transformers (PT)), are

known as instrument transformers. When current in a circuit is too high to directly apply to

measuring instruments, a current transformer produces a reduced current accurately proportional to the current in the circuit, which can be conveniently connected to measuring

and recording instruments. A current transformer also isolates the measuring instruments from what may be very high voltage in the monitored circuit. Current the electrical power industry.

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Current Transformers are provided to step down the current to low values suitable for measuring protection and control instruments. Current Transformers also isolate measuring and protective devices from high system voltage. CTs in the switchyard consist of five secondary cores. Core 1&2 are used for busbar protection, 4 & 5 are for main 1&2 protection and core 3 is for measuring instruments.

8.7 CAPACITIVE VOLTAGE TRANSFORMER (CVT):

CVTs step-down the system voltage to sufficiently low value (110 V) for measuring, protection and synchronizing circuits. CVT has a H.F. terminal point for receiving & transmitting the high frequency signals for carrier protection and communication.

8.8 WAVE TRAP:

Wave Trap is a parallel resonant circuit tuned to the carrier frequency connected in series with the line conductor at each end of the protected transmission line section. Wave trap offers high impedance path for high frequency signals and low impedance path for power frequency current. This keeps carrier signal confined to the protected line section and does not allow the carrier signals to flow into the neighboring sections.

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8.9 SWITCH YARD CONTROL ROOM EQUIPMENT

The control room is the place where the conditions of the system are monitored, controls

initiated and operations are integrated. Control room consists of the following equipment.

8.9.1 CONTROL PANELS:

Corridor type flat control panels are provided in U shape with doors at both the end panels. Between the front and rear panels, there is adequate space for inspection of interior wiring. The controlling knobs are provided on front panel for opening & closing of breakers and isolators. The close/open position of the breakers / isolators / earth switches is indicated through lamps or semaphore indicators. The relative position of each equipment is shown in the mimic single line diagram that is painted on front side of the control panels. The indicating instruments (MW, MVAR, voltage, current etc.) and annunciation windows are provided on the top of front panel for monitoring of the equipment. Breaker monitoring and protective relays such as LBB, Auto reclosure, check synchronization, Trip circuit monitoring, Annunciation relays and energy meters are mounted on the rear side of the

panel.

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9. RELAY PANELS

Relay panels are of cubicle type, flat independent boxes with a door at backside. All the protective relay units related to one bay are divided into two groups viz. Main 1 protection, stub protection, O/V protection and their auxiliary & trip relays as group 1 and Main 2 protection, U/v protection and their auxiliary & trip relays as group 2 relays. Group 1 & group 2 relays are mounted on front side of two separate panels side by side. Fault locator and disturbance recorder of the corresponding bay mounted on front side of the third panel. A separate glass door is provided front side of all the panels to cover the relays from dust.

9.1 EVENT LOGGER:

Even Logger recognizes the changes in signal-input states, plus time data allocation for sequential recording of events. It displays the events in a time sequential of 1/ sec, such as opening/closing of breaker poles, Isolator poles, E/S etc. pressure high/low of air, SF6, N2 Oil etc. Alarm Appeared/reset of all protection / trip relays, it also displays the status of equipment, in service/ out of service in a regular period say 8 hrs. This is one of the important diagnostic equipment available to operation staff to understand the type of emergency in a flick of a second.

9.2 GENERATION DATA ACQUISITION AND MONITORING SYSTEM (GDAMS):

At large switchyard control rooms like RSTPS it is essential to record and continuously monitor the parameters of the Generation & transmission system. NTPC is the largest power utility of the country generating power from 20 thermal/ gas power stations at various places of the country. Many more power stations are ye to come. To manage all these power stations efficiently and effectively NTPC has established an operational services control room at corporate office in New Delhi, where generation data from all the stations is to be monitored continuously. To facilitate the above function, Generation Data acquisition and Monitoring system is provide at all NTPC switchyard control rooms. CMC Ltd. has supplied the necessary software on

Micro Soft Windows NT environment and installed the PC based GDAMS network in Server Client configuration. GDAMS scans automatically the real time measurements like load on units, load flows on feeders. Bus voltage, grid frequency, MVR loads, etc. for every second through RTUs and record it. The Acquired data is linked up to OS control room though satellite communication channel. The types of data displays available in GDAMS are given below.

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9.3 TYPES OF DISPLAYS

1 Alpha Numeric Display Displays direct of measured parameter along with name of the parameter in a tabular form

2 Mimic Diagram Display In this Display the single line diagram of the circuit with position of the breakers along with real time power flow is indicated.

3 Graphical Display This displays the graph of quantities

4 Threshold Display In threshold blackout Display the threshold (border) values of quantity are Displayed.

5 Alarm Displays Alarms are Displayed to draw the attention of operator.

6 Trend display In this display the trend of the quantity real time values in a specified time blocks are shown

The data Acquisition by GDAMS is more vital in analyzing the faults, forecasting the local trends, impact of the line and unit outages, estimation of variations in frequency and voltages in different seasons, generating reports etc.

9.4 DISTURBANCE RECORDER

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All 400 KV lines connected to this switchyard are provide by the Disturbance Recorders (D/R), D/R is a PC based or Microprocessor based on line monitoring equipment D/R is the most vital diagnostic equipment in analysis of post fault trappings.

9.5 FAULT LOCATOR

When a line tripped on fault, the Fault Locator provided in the Relay panel indicates the approximate distance of the fault location so that Maintenance group easily tract the fault and clear it. When F.L. indicates zero or very less distance, operation staff should assume that the fault is in the switchyard equipment, and check for all equipment connected to the concerned bay, which was tripped on fault.

9.6 INDICATING & RECORDING INSTRUMENT

The following measuring instruments were providing on control panels of all bays.

a) At the top of the control panel.

1. Ammeters in three phases. 2. Volt (KV) meters in three phase3. Reactive power (MVAR) meter4. Watt (MW) meter5. Winding Temperature indicating meter (for only Transformer bays)6. Tap position indicating meter (do)

b) Rear side of the each bay control panel

1. Main energy meter (export)2. Check Energy meter (do)3. Main energy meter (import) 4. Check Energy meter (do)

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10. RELAYS AND PROTECTION SCHEMES

Every power system element is subjected t a fault or a short circuit. The cause of fault is any of the following.

1. Healthy insulation in the equipment subjected to either transient over voltages of small time duration due to switching and lighting strokes, direct or indirect.

1. Aging of insulation. 2. An external object, such as a tree branch, bird, kite, rodent etc. spanning either two

power conductors or a power conductor and ground.

EFFECTS OF FAULTS

1. Equipment is likely damage due to over heating and sudden mechanical force developed.

2. Arcing faults invariably are a fire hazard and damage the equipment.

3. A frequency drop may lead instability among interconnected system.

4. Unsymmetrical faults result in voltage imbalance and negative sequence currents, which lead to overheating.

10.1 PROTECTIVE RELAYS

A relay detects the faulty element in the integrated power system and removes it, with the help of the circuit breaker, from the remaining healthy system as quickly as possible to avoid damage and maintain security or reliability of supply in the healthy system. The quality of relaying depends on its sensitivity, selectivity, speed and reliability. Varieties of protection relays are provided to protect EHV lines and Transformers. A brief Description is given below about the relays used for protection of Transformers and lines connected to

switchyard.

10.2 OVER CURRENT RELAY

There are basically three types of OC relays

1. Instantaneous OC relay

As the name signifies instantaneous OC relay operates without any intentional time delay as and when the input current exceeds the pickup value or the plug setting.

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2. Definite time OC relay (DTOC Relay)

The DTOC Relay has two settings; the first one is the pick value in amperes (plug setting.). Another setting is the constant or definite operating time of the relay. The relay delivers trip output only when the current exceeds the pickup value and that after a specified time delay.

3. Inverse Definite Minimum Time OC Relay (IDMT OC Relay)

The operating time of IDMT relay is inversely proportional to the square o the relay input current (plug setting) and the travel time of the disk to close the NO contacts. The travel time of the disk to close the NO contact can be changed by moving the backstop of the relay (Time multiplier setting).

10.3 DIRECTIONAL RELAYS

Conventional over current relays are non-directional, which means the relay operates on current magnitude and not on its direction or phase shift. The Directional over current

relay comprises two elements, a directional element and OC relay element. The OC element is inhibited for operating until the directional element has operated. The directional element is a watt metric device, which measures the direction of power flow.

10.4 EARTH FAULT RELAY

Earth fault relay is a sensitive protection against earth faults, which responds only to residual current of the system, since a residual component that exists only when fault current flow to earth. The residual component is extracted by connecting the line CTs in parallel.

10.5 DIFFERENTIAL PROTECTION

The differential relay checks the difference between the input and output currents for any power system element, either in amplitude or in phase or both, to determine whether the state of the power system is healthy or faulty. In the event of a substantial difference, the element is assumed to be faulty and trip the concerned breakers.

10.6 PILOT WIRE PROTECTION:

Pilot wire protection scheme can be used for protection of transmission lines of 220 KV and below voltages. Similar current Transformers at each end of the protected zone are interconnected through pilot wires. Current transmitted through the zone causes secondary current to circulate round the pilot circuit without producing any current flow in relay. A fault within the protected zone will cause secondary current flow in to protection relay.

10.7 PHASE COMPARISON RELAY

The basic principle of the phase comparison relay is to check the phase difference of current at both ends of the protected line. The carrier channel is used to convey the phase angle of

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the current at one relaying point to another for comparison with the phase angle of the current at that point.

10.8 DISTANCE RELAY

Distance relay is of the high speed class can provide both primary and back up facilities in a single scheme. Distance relay operate only for faults occurring between the relay location and the selected reach point, thus giving discrimination for faults that may occur between different line sections. The basic principle is comparing of the fault current ‘seen’ by the relay with voltage at the relaying point; by comparing these two quantities sit is

possible to determine whether the impedance of the line up to the point of the fault is greater

than or less than the predetermined reach point independence.

For EHV, line where fast fault clearance and high reliability vital ‘full scheme of distance relays are provided. Full distance scheme uses six measuring units per zone, three for phase faults and three for earth faults. All 18 measuring units in three zones operate independently to protect the line and provide backup to the adjacent lines.

10.9 POWER SWING BLOCKING

Power swings are variations in power flow which occur when the voltage of generators at different points of the power system slip relative to ach other to cater changes of load magnitude and direction or as a result of faults and their subsequent clearance. In the case of a transient power swing, it is important that the Distance relay should not trip and should allow the power system to return to a stable condition. For this reason Distance, protection scheme has an optional power swing-blocking feature.

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11. SWITCHYARD EMERGENCIES AND PLAN OF ACTION

11.1 CONDITION MONITORING

The abnormalities in equipment or system are continuously monitored by the relays, pressure/level switches etc. and initiate a trip/alarm followed by an annunciation. The Alarm alerts the operator and annunciation flashes give the first information of the type of breakdown. Event logger provides the sequence of events taken place along with time. This does allow some assessment in relation to failure of equipment. Basing on this information operator has to start quick remedial action.

11.2 BREAKDOWN ANALYSIS

The details break down analysis can be done after checking the relays, protections operated at relay panels. Disturbance recorder provides the voltage and current graph with respect to time of pre and post incident of fault conditions. D/R also provides the sequence

of protections operated.

11.3 ANNUNCIATIONS AND ALARM SCHEME

Annunciation and alarm scheme is provided to call attention of the operation staff against any abnormality in the switchyard equipment and control system, so the quick preventive measures can be initiated. The annunciation flashes along with an alarm on the control panel until it is acknowledged. The annunciation is reset only after normalization of the system. The operation staff upon receiving an alarm has to comprehend the nature of the problem to take appropriate steps at the earliest, thus saving the equipment system from failing further. The various annunciations are provided for 400 KV lines and Auto Transformers at RSTPS switchyard control room are shown in the following tables.

11.4 TYPES OF ANNOUNCIATIONS

Annunciations are grouped into four categories.

A) Annunciations initiated by the Circuit Breaker condition monitoring relays.

B) Annunciations initiated by the protective relays provided to monitor the healthiness of line and its related equipment.

C) Annunciations initiated by the protective relays provide to monitor the healthiness of Transformers and its accessories.

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A brief description about the annunciations provided, and the plan of action to be taken by the operation staff is as follows.

11.5. C.B. AUTO TRIP

This annunciations appears whenever circuit breaker trips on a protection or on intertrip signal (Other than manual trip)

PLAN OF ACTION

1. Confirm the opening of the other end breaker if it is a line feeder or opening of the LT

side breaker if it is a Transformer.

2. Check for the protective Relay operations if any.

3. Check for the event logger and D/R printouts for various relay operations and events taken place.

4. If CB auto trip indication appears during the closing operation of the breaker, check for closing interlocks.

5. Reset the CB auto trip indication by giving the trip impulse with the breaker close/open handle at control panel.

11.6 CB POLE DISCREPANCY TRIPAll the three poles of a circuit breaker must open or close at a time when a trip or

close command initiated. If one of the pole fails or delayed to open or close within a specified (0.02 secs) time, circuit breaker trips immediately followed by C.B. pole discrepancy alarm.

PLAN OF ACTION

1 Check the flag indication for operation of pole discrepancy relay (62x) in relay panel.

2 Confirm from local, the opening of all the three poles of breaker. If not immediate action to be taken to open the poles.

3 Breaker tripped on pole discrepancy protection shall be charged only after checking and rectifying the problem.

11.7 LBB PROTECTION OPERATED

This is operated when the breaker in the fault circuit fails to open due to breaker fault or trip circuit fault. Then this relay gives trip signals to the breakers which are connected to the bus which is connected to faulty breaker.

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PLAN OF ACTION

1 Check for the protection relay, which caused operation of Group A/B trip relays.

2 Check for the busbar protection trip relay (96) for Main/tie breaker whichever LBB has operated.

3 Check for physical opening of breakers for which LBB relay operated.

4 Inform Maintenance group for attending the problem.

5 Restore the normalcy through the other breaker (Tie breaker) in case of Main breaker failed to trip and vice versa.

11.8. TRIP COILS 1/2 CKT. FAULTY

All the circuit breakers are provided with two trip coils to facilitate breaking operation reliability. This annunciation appears whenever either of the trip circuit gets open circuited. As the failure of one of the trip circuit reduces the reliability of the tripping operation of the breaker in the vent of fault.

PLAN OF ACTION

1 Check for operation of relays 195AR, 195BR/195AY, 195BY/195AB, 195BB Or combination of these relays and identify fault is in T.C. 1 and respective pole.

2 Check for operation of relays 295AR, 295BR/295AY, 295BY 295AB, 295BB or combination of these relays and identify fault is in TC. 2 and respective pole.

3 This annunciation appears in case of operation lockout, failure of DC or actual failure of trip coil. Verify the actual cause.

4 In case of failure of both the trip coils of the breaker, the breaker shall be isolated from the system by making the load flow zero and opening of both sides of isolators of breaker

5 Inform to the Maintenance staff for attending the problem.

11.9. C.B. SF6 DENSITY LOW/ AIR PRESSURE LOW

This annunciation appears whenever SF6 gas pressure/ Air pressure falls below the specified value.

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PLAN OF ACTION

1 Check the SF6 pressure / Air pressure locally, and asses the rate of leakage.

2 If the rate of leakage is high, after obtaining necessary clearance trip and isolate the breaker as early as possible. Otherwise the breaker may go into lockout state, which is to be avoided as much as possible.

3 If leakage rate is low inform Maintenance group for attending the problem.

11.10. CB OPERATION LOCKOUT

This annunciation appears whenever either air pressure (oil pressure in case of hydraulic operated breakers) or SF6 gas pressure falls below specified values. In operation lockout state circuit breaker will not operate. This feature is very much required to prevent the breaker operation in adverse conditions of operating system and/or arc quenching media (SF6 gas).

The settings for this annunciation are given below for reference.

AIR / OIL PRESSURE SF6 PRESSURE

AEG MAKE (pneumatic operation) <30.0 bar <6.5 bar

ABB “” <23.0 bar <6.5 bar

NGEF “” <31.5 bar <6.5 bar

BHEL (hydraulic operation) <253 bar <6.0 bar

PLAN OF ACTION

A) FOR PNEUMATIC OPERATED BREAKER

1 Check for the air pressure and SF6 gas pressure locally.

2 Identify the problem. If heavy leakage is observed in SF6 gas/ AIR system, then sough permission from IOCC for isolates the breaker from connecting bus.

3 Isolate the breaker by opening the both the side isolators after making the load flow zero.

4 If leakage is minute, Inform Maintenance staff to attend the problem. After normalizing SF6/Air parameters the reset alarm.

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11.11 AUTO RECLOSURE LOCKOUT (186 A/B)

Auto reclosure feature is provided to ensure availability of feeder during transient faults. In the event of a feeder fault, protection relay detect the fault and trips the line. Auto reclosure relay operate and close the breaker after a specified time (0.5m sec). If the fault is still persisting, the breaker trips again on protection relay operation. Auto reclosure relay locks out on its own after one reclosure effect.

11.12 TRANSFORMER BUCHHOLZ ALARM/ TRIP

Buchholz relay is a gas-operated relay. When a slight or incipient fault occurs in the Transformer, the gas generated will collect in the top of the buchholz relay. A pre set volume of gas collection in the relay causes the buchholz annunciation / trip contacts to operate.

PLAN OF ACTION (ALARM)

1 Confirm the flag indication for the operation of the relay

2 Check for the gas accumulation in Buchholz relay

3 If gas collection is found, Transformer shall be hand tripped

After getting clearance from SCE, DGM (EM), IOCC and AP TRANSCO

PLAN OF ACTION (TRIP)

1 The Transformer can be charged only after carrying out tests including DGA and obtaining clearance in writing from EM dept.

2 In case the gas is not found in buchholz relay, the reason shall be established for operation of buchholz relay and then the Transformer should charged.

3 In case of air accumulated in Buchholz relay, the Transformer can be charged after releasing the air.

11.13 TRANSFORMER OVER LOADED

The load (current) on Transformer exceeds its rated (or set) value for more than a specified time, and then Transformer over loaded annunciation appears.

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PLAN OF ACTION

1 Check the current readings of the Transformer, in case the current is more than the

set value, request LDC to reduce load.

2 Check the system voltage and frequency. Also check voltage and frequency

recorders for any sudden change.

3 Request IOCC to coordinate with SREB and AP LDC to bring the system parameters

with in the limits.

11.14 ISOLATION OF 400 KV TRANSMISSION LINE BAY

1. Physically check at breaker for open indications in 3 poles and ensure that the breaker is absolutely in open position.

2. Open the 400 KV side (HT) isolator from remote or local mode.

3. Open the 220kv/132kv side (LT) isolator either from remote or from local position.

4. Ensure physically all the three poles of isolators opened.

5. Close the 400 kV side isolator earth switch and 220 kv/132 kV side earth switches and lock them.

6. Keep the danger tags at breakers on/off handle giving the details of the permit being issued.

7. Note down on the permit card the isolations done along with the precautions to be taken further by the recipient at time of work carrying the work and issue the permit card to the applicant.

11.15 NORMALIZATION & CHARGING OFLINES AND TRANSFORMERS

For normalizing and charging the transmission lines and Transformers, certain preconditions are required to be met so as to safely normalize and charge the feeder or Transformer. As the transmission lines in 400 KV net works are so long and Transformer is of large capacities, certain conditions like enough capacity of the system to absorb the line MVAR to be ensured. Safety of personnel to be ensured. While synchronizing the feeder, enough precautions to be taken to ensure that the grid system is compatible and within limits so that there should not be power swings owing to a synchronism.

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11.16 COMMON INSTRUCTIONS FOR CHARGING THE LINE AND TRANSFORMERS

a) Lines or Transformers shall be charged always from the strong source end, where there is a facility to absorb reactive power and synchronization shall be done from the other end in normal conditions.

b) Generally, voltage at charging end bus shall be kept below 400 kv before charging of the line.

C) When a line or a Transformer is charging after completion of Maintenance works trips on a fault, second attempt shall not be made until it is thoroughly investigated and

reasons for tripping should be established.

d) If the frequency and voltage are not in synchronism limits. Line / Transformer shall not synchronies to Grid. A synchronous inter connection may lead to unwarranted power swings that may cause not only grid disturbances but also accidents SRLDC shall coordinate with SEBs to bring the parameters within the limits.

11.17 CHECKS BEFORE NORMALIZATION

a) Ensure that all permits issued on Line equipment / the authorized area Maintenance engineer canceled Transformer. Also, ensure that any NBFC issued to the other end substation was returned back in writing.

b) Check physically the work area for removal of men and Material.

c) Take clearance from IOCC, if the line is connected to PGCIL substations or from LDC, if the line is connected to AP Transco substations and take clearance from shift in charge.

d) Ensure that all switchyard equipment associated with the line or Transformer under shutdown is in operating condition.

e) Check for SF6 gas and air/ oil pressure of main/ tiebreakers.

f) Ensure that the Local / Remote switches of the Main/ Tie breakers are kept on remote position.

g) Check physically for the removal of all the temporary earthlings done at the work site.

h) Check physically for the healthiness of line shunt reactor or the Transformer going to be charged.

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i) Ensure that all relay flags are reset.

j) Check that no window indication is persisting and ensure that annunciation lamp test OK.

k) Ensure that disturbance recorder, fault recorder, and event logger are in service.

l) Check the communication book for remarks if any on the equipment associated to the shutdown bay. Remarks if any found take written clearance for charging the bay form the concerned area Maintenance engineer.

m) Return back the NBFC obtained from the other end substation through written message and take clearance in writing for charging the line.

11.18 NORMALIZATION OF A TRANSMISSION LINE BAY EQUIPOTENT

a) Open the earth switch of the line isolator. Also open the earth switches of main and tie bay isolators if any closed position.

b) Close the line isolator of the line under shut down.

c) Close the Bus 1 / Bus 2 connecting isolators in main bay, if permits are not pending on the concerned bay equipment.

d) Close the tie bay isolators I the permits are not pending on Tie bay equipment.

e) Close the shunt reactor isolator if shunt reactor available for the line and it is in isolated condition.

f) If isolators are closed in remote mode, check physically to confirm all the three poles closed properly.

11.19 CHARGING OF TRANSMISSION LINES

In case of IOCC instructed to charge the line from this end and to synchronize from the remote substation.

a) Inform IOCC that the line is ready for charging and take the final clearance for charging the line.

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b) Inform orally to the other end substation operator that the line is ready for charging and hold him on line.

c) Give announcement in swyd PA system regarding line charging to aware the Maintenance group any body working in swyd.

d) Give announcement in station PA system for alerting the unit desk operation engineers to face abnormality if any arises during process of line charging.

e) Keep heck synchronizing selector switch in bypass position (switch available in control panel no.12) and plug-in the synchroscope into the concerned breaker synchronizing socket Keep the synchroscope in on mode.

f) Close main/ tiebreaker which ever bay is made ready for charging the line (dead line charging). Subsequently close the other breaker also If the bay equipment not under permit.

g) Inform the remote end operator on telephone that the line is charged and give clearance for synchronizing to the grid.

11.20 SYNCHRONIZING THE LINE AFTER CHARGING AT REMOTE END

In case, IOCC instructed to charge the line at remote end and synchronize the line this end.

a) Inform IOCC that the line is ready for synchronizing and take the final clearance for synchronizing and take the final clearance for synchronizing the line.

b) Ensure that check synchronizing selector switch is on position and plug in synchronic scope into the concerned breaker-synchronizing socket. Make synchroscope on and check for syncro in limit indication. If it is not in limits inform to IOCC which parameter (Voltage/ frequency) is not matching and request them to coordinate in bringing the voltage/ frequency within limits i.e. 0.4% in respect of frequency and 10% in respect of voltage.

c) Once again, ascertain that the voltage and the frequency are within synchronizing limits.

d) Inform orally to the other end substation operator that the line is going to be synchronized and let him hold on line.

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e) Give announcement in switchyard PA system regarding closing of the beaker to aware the persons any body working in switchyard.

f) Given announcement in station PA system regarding line charging to alert the unit desk operation engineers to face any abnormality if arises during the process of line charging.

g) Close Main/ tiebreaker whichever bay is made ready for charging the line. Subsequently close the other breaker also if the bay equipment not under permits.

11.21 NORMALIZATION OF TRANSFORMER BAY EQUIPMENT

a) Inspect the Transformer physically and check the following.

1. Conservator oil level of main tank and OLTC is maintained

2. Breather silica gel color is blue.

3. Check for heavy oil leaks if any from tank, radiator, pipes and bushings.

4. Check the availability of cooler supply and healthiness of fans and pumps by running in manual mode.

5. Note down the WTI and OTI readings, confirm they are working.

6. Check the cleanliness of Transformer & surround area.

7. Check any removal of HT/LT connections and fuses in marshaling box.

8. Check the emulsifier system operation.

b) Open the earth switches of the 400 KV Bus side Isolator (HT) and 220 kv line side isolator (LT) . Also open the earth

switches of main and tie-bay isolators if any found in close position.

c) Check for any portable earthlings on bay equipment. If

found any, request Maintenance staff to remove the same.

d) Close 220 kv side isolators and 400 kv side main and tie bay isolators provided the permits are not pending.

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e) If isolators are closed in remote mode, check physically to confirm all the three poles closed properly.

11.22 CHARGING OF TRANSFORMER FEEDER

In case, AP Transco requested to change the 220 KV line from this end and to synchronize at their substation.

a) Inform LDC that the 220 KV line is ready for charging and take the final clearance for charging the line.

b) Inform orally to the AP Transco substation Engineer that Auto Transformer is going to be charged at our end.

c) Give announcement in swyd & station PA system regarding charging of Transformer.

d) Keep check synchronizing selector switch in by pass position and plug in the

synchroscope into concerned breaker synchronizing socket. Keep the

synchroscope in on mode.

e) Close Main/ Tie breaker which ever bay is made ready for charging the

Transformer. Subsequently close the other breaker also if the bay equipment not

under permits.

f) Inform to the AP Transco Engineer on telephone that 20 kv line is going to

charge and hold him on line.

g) Keep Auto recolor switch in NLA mode. Close the line breaker of the feeder to

be charged.

h) Inform AP TRANSCO ENGINEER that feeder is charged and check for voltage

at their end. Give clearance to synchronize the feeder at their end.

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12. SYNCHRONIZING THE TRANSFORMER FEEDER

In case, AP LDC requested to charge the Transformer feeder at remote end and synchronize at this end.

a) Give clearance to AP Transco Engineer to charge the 220 Kv line at their end.

b) After getting information from AP Transco Engineer regarding the closing of 220 KV line breakers at their end, check for the line voltage at control panel meter and confirm.

c) Keep check synchronizing selector switch in bypass position and plugin the synchroscope into the concerned Auto Transformer breaker-synchronizing socket. Keep the synchroscope in on mode.

d) Close Main/ Tie breaker which ever bay is made ready for charging the Auto Transformer. Subsequently close the other breaker also if the bay equipment is not under permit.

e) Auto Transformer is in idle charge condition. Check the current in three phases to ascertain the healthiness of the Transformer.

f) Normalize the check-synchronizing switch from by pass position.

g) Inform the AP Transco Engineer on telephone that 220 KV line is going to synchronies and hold him on line.

h) Keep the check synchronizing selector switch in on position and plug-in the synchroscope into the concerned line breaker-synchronizing socket. Make the synchroscope on. Ascertain that the voltage and the frequency are within synchronizing limits.

i) Give announcement in switchyard & station PA system regarding closing of breaker

j) Close the 220 kv line breaker (LT breaker of Auto Transformer). k) Inform to AP Transco S/S & APLDC that the line is synchronized.

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12.1QUICK RESTORATION OF STARTUP POWER IN BLACKOUT CONDITION

I. IN THE EVENT OF TRIPPING OF ALL UNITS OF STATION WITH SURVIVAL OF RAMAGUNDAM THERMAL POWER STATION (R.T.S ‘B’ STATION AP GENCO).

Request AP LDC / AP GENCO / AP TRANSCO to

1. Charge 132 kV RTS B station Malyalapally substation line. 2. Charge 220 kv Malyalapally NTPC line 1, 2 or 33. Charge 400 /220 kv Auto Transformer 3/4/54. Charge 400 kV Bus ½ at RSTPS Switchyard. 5. Charge 400/33 KV tie Transformer 1 or 2 or 3.6. Charge 33 kv Bus of 33 kv switchgear

II. IN CASE OF PARTIAL BLACKOUT OF REGION WITH SURVIVAL OF KOTHATUDEM 5TH STAGE OF AP GENCO

Request AP LDC/IOCC/SRLDC/PGCIL to change.

1. 220 KV Khammam lines at Kothagudem substation.2. 315 MVA ICT’s of 220/400 kV at Khammam sub station. 3. 400 KV Khammam switchyard. 4. 400 KV Khammam Ramagundam line. 5. Charge Bus1/2 of RSTPS switchyard and inform to SCE that startup power is

available.

III. IN CASE OF PARTIAL BLACKOUT OF REGION WITH SURVIVAL OF KOTHAGUDEM 1ST OR 2ND STATE OF AP GENCO

Request AP LDC / AP GENCO / AP TRANSCO to

1. Charge 132 kv Kothagudem Warangal line at Kothagudem S/S 2. Charge 100 MVA ICT’s 132/220 kv at Warangal S/S3. Charge 220 kv substation at Warangal.4. Charge 20 kv Warangal Malyalapally line at Warangal S/S5. charge 220 kv Malyalapally substation.6. Take start-up power supply from Malyalapally substation.

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IV. IN CASE OF PARTIAL BLACKOUT OF REGION WITH SURVIVAL OF VIJAYAWADA THERMAL POWER STATION OF AP GENCO

Request AP LDC/IOCC/ SRLDC/PGCIL t charge

1. 220 kv VTPS Nunnalines at VTPS substation 2. 315 MVA ICT’S OF 220/400 KV AT Nunna substations.3. 400 KV Nunna (PGCIL) switchyard. 4. 400 kV Nunna Khammam line. 5. 400 kV Khammam (PGCIL) Switchyard. 6. 400 KV Khammam Ramagundam line 7. Charge Bus ½ of RSTPS switchyard inform t SCE that start up power is

available.

V. IN CASE OF TOTAL BLACKOUT (GRID FAILURE) IN THE REGION WITH TRIPPING OF ALL HYDEL, THERMAL AND NUCLEAR POWER STATIONS

Request to AP LDC/ AP TRANSCO / AP GENCO to

1. Startup Nagarjuna sagar or Srisailam Hydel units. 2. Charge Thallapally 220 Kv substation 3. Charge any one of the 3 x 3 315 MVA ICT’s at Thallapally. 4. Charge 400 kV bus at Nagarjunasagar (PGCIL) switchyard.5. Charge 400 kV Nagarjunasagar Ramagundam line. 6. Charge 400 kV Bus 1 or 2 at RSTPS switch yard.

12.2 ACTIVITIES AFTER OBTAINING STARTUP POWER

a) Close 400 KV breakers pertaining to above set feeder and thus charge 400 kV buses 1 or 2

b) Charge 400/33 kV Tie Transformer 1 or 2 or 3.

c) Charge 33 kV bus 1 and / r 2 and / or 3.

d) Depending on the quantum of power available and units to be brought on bar; seek shift charge engineer instructions regarding charging of CW Transformers, WTP Transformers, Station Transformers and act accordingly.

e) Charge switchyard service Transformers and extend supply to switchyard MCC and lighting panel

f) After normal supply is resumed, switch off DC lights.

g) Due to lack of power, battery chargers had tripped and the entire DC Batteries supplied load.

i) Check the condition of batteries and accordingly keep the chargers in service.

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j) See that air compressor, providing compressed air for breaker operations, have started and developing adequate pressure.

k) Now situation is normal. Once units are ready for synchronization seek instructions from IOCC and LDC, accordingly take lines in service and synchronize

the units.

Types of Annunciation

Annunciations are grouped into four categories.

A) Annunciations initiated by the Circuit Breaker condition monitoring relays.

B) Annunciations initiated by the protective relays provided to monitor the healthiness of line and its related equipment.

C) Annunciations initiated by the protective relays provide to monitor the healthiness of Transformers and its accessories.

A brief description about the annunciations provided, and the plan of action to be taken by the operation staff is as follows.

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13. TRIPPING ACTIONS

13.1 C.B. AUTO TRIP

This annunciations appears whenever circuit breaker trips on a protection or on intertrip signal (Other than manual trip)

PLAN OF ACTION

1. Confirm the opening of the other end breaker if it is a line feeder or opening of the LT side breaker if it is a Transformer.

2. Check for the protective Relay operations if any.

3. Check for the event logger and D/R printouts for various relay operations and events taken place.

4. If CB auto trip indication appears during the closing operation of the breaker, check for closing interlocks.

5. Reset the CB auto trip indication by giving the trip impulse with the breaker close/open handle at control panel.

13.2 CB POLE DISCREPANCY TRIPAll the three poles of a circuit breaker must open or close at a time when a trip or

close command initiated. If one of the pole fails or delayed to open or close within a specified (0.02 secs) time, circuit breaker trips immediately followed by C.B. pole discrepancy alarm.

PLAN OF ACTION

1 Check the flag indication for operation of pole discrepancy relay (62x) in relay panel.

2 Confirm from local, the opening of all the three poles of breaker. If not immediate action to be taken to open the poles.

3 Breaker tripped on pole discrepancy protection shall be charged only after checking and rectifying the problem.

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13.3 LBB PROTECTION OPERATED This annunciation appears when the master trip relay (86) operates in response to a

fault but the concerned circuit breaker fails to trip. Local Breaker Breakup relay (50Z) acts and initiates the busbar protection of the respective bus, which trips all other circuit breakers connected to the bus.

PLAN OF ACTION

1 Check for the protection relay, which caused operation of Group A/B trip relays.

2 Check for the busbar protection trip relay (96) for Main/tie breaker whichever LBB has operated.

3 Check for physical opening of breakers for which LBB relay operated.

4 Inform Maintenance group for attending the problem.

5 Restore the normalcy through the other breaker (Tie breaker) in case of Main breaker failed to trip and vice versa.

13.4 TRIP COILS 1/2 CKT. FAULTY

All the circuit breakers are provided with two trip coils to facilitate breaking operation reliability. This annunciation appears whenever either of the trip circuit gets open circuited. As the failure of one of the trip circuit reduces the reliability of the tripping operation of the breaker in the vent of fault.

PLAN OF ACTION

1 Check for operation of relays 195AR, 195BR/195AY, 195BY/195AB, 195BB Or combination of these relays and identify fault is in T.C. 1 and respective pole.

2 Check for operation of relays 295AR, 295BR/295AY, 295BY 295AB, 295BB or combination of these relays and identify fault is in TC. 2 and respective pole.

3 This annunciation appears in case of operation lockout, failure of DC or actual failure of trip coil. Verify the actual cause.

4 In case of failure of both the trip coils of the breaker, the breaker shall be isolated from the system by making the load flow zero and opening of both sides of isolators of breaker.

5 Inform to the Maintenance staff for attending the problem.

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13.5 C.B. SF6 DENSITY LOW/ AIR PRESSURE LOW

This annunciation appears whenever SF6 gas pressure/ Air pressure falls below the specified value.

PLAN OF ACTION

1 Check the SF6 pressure / Air pressure locally, and asses the rate of leakage.

2 If the rate of leakage is high, after obtaining necessary clearance trip and isolate the breaker as early as possible. Otherwise the breaker may go into lockout state, which is to be avoided as much as possible.

3 If leakage rate is low inform Maintenance group for attending the problem.

13.6 CB OPERATION LOCKOUT

This annunciation appears whenever either air pressure (oil pressure in case of hydraulic operated breakers) or SF6 gas pressure falls below specified values. In operation lockout state circuit breaker will not operate. This feature is very much required to prevent the breaker operation in adverse conditions of operating system and/or arc quenching media (SF6 gas)

The settings for this annunciation are given below for reference.

AIR / OIL PRESSURE SF6 PRESSURE

AEG MAKE (pneumatic operation) <30.0 bar <6.5 bar

ABB “”” <23.0 bar <6.5 bar

NGEF “” <31.5 bar <6.5 bar

BHEL (hydraulic operation) <253 bar <6.0 bar

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PLAN OF ACTION

A) FOR PNEUMATIC OPERATED BREAKER

1 Check for the air pressure and SF6 gas pressure locally.

2 Identify the problem. If heavy leakage is observed in SF6 gas/ AIR system, then sough permission from IOCC for isolates the breaker from connecting bus.

3 Isolate the breaker by opening the both the side isolators after making the load flow zero.

4 If leakage is minute, Inform Maintenance staff to attend the problem. After normalizing SF6/Air parameters the reset alarm.

B) FOR HYDRAULIC OPERATED BREAKERS

1 Check for the loss of oil/N2 gas pressure /SF6 gas pressure locally and also AC supply to the pump.

2 Conform the running of the pump if oil pressure is low.

3 Identify the problem. If leakage is observed in SF6 gas line, sought permission from IOCC to isolate the breaker.

4 If leakage is minute, inform the Maintenance staff to attend the problem. After normalizing SF6/Oil parameters rest the alarm.

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CONCLUSIONWe have studied the over view of NTPC Ltd, Ramagundam unit

switch yard and its auxiliary equipments , bus-bar system circuit breaker arrangement system. The major role of “OPERATION OF 400KV SWITCH YARD OF NTPC Ltd, RAMAGUNDAM” is to transmit the power to various parts of southern India like Chandrapur, Khammam, Nagarjunasagar, Hyderabad, Dichipally, Warangal, Gajwel, Malkaram and AP Transco.

REFERENCES

From electrical dairy of Ramagundam thermal plant.

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