Operational description of 400kv switchyard NTPC Ramagundam RSTPS

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
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
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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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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:
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
Installed Capacity 2600MW
Stage-I: 3 x 200
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Unit Sizes 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.
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.
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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
Transmission Lines: 15 Outgoing feeders
• Hyderabad ------------------ 4
• Nagarjuna Sagar ------------------- 2
• Chandrapur ------------------ 2
• Warangal ----------------- 1
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• Dichipally ------------------ 1
• AP Transco ------------------ 5
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
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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.
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
5.1 220 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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1. NTPC AP Transco line 1 Through 400 /220 KV 250MVA
AT # 3 & 4
2. NTPC AP Transco line 2
3. NTPC AP Transco line 3 Through 400 /220KV
315MVA AT # 5
5.2 132 KV TRANSMISSION LINES
6. TRANSFORMERS & REACTORS
1. NTPC AP Transco line 1 Through 400 Kv/132KV 200MVA
AT # 1 & 2
2. NTPC AP Transco line 2
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6.1 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
20

switches are commonly fitted to domestic extractor fans when used in bathrooms in the UK.
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
21

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
22

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.
23

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
27

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 phase
3. Reactive power (MVAR) meter
4. Watt (MW) meter
5. 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.
29

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
30

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 TRIP
All 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.
PLAN OF ACTION
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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.
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
35

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.
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.
36

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.
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.
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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.
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.
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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.
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.
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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.
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.
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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.
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.
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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.
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.
42

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.
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 3
3. Charge 400 /220 kv Auto Transformer 3/4/5
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4. 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/S
3. Charge 220 kv substation at Warangal.
4. Charge 20 kv Warangal Malyalapally line at Warangal S/S
5. charge 220 kv Malyalapally substation.
6. Take start-up power supply from Malyalapally substation.
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.
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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.
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.
45

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.
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
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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 TRIP
All 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.
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
47

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.
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
48

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
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
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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.
CONCLUSION
We 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.
50

REFERENCES
From electrical dairy of Ramagundam thermal plant.
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Operational description of 400kv switchyard NTPC Ramagundam RSTPS

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Operational description of 400kv switchyard NTPC Ramagundam RSTPS