Switch Yard

1. ABOUT RSTPS 400 KV 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 two 400 KV busbar systems fed by 7 Nos. of generator feeders, 9 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 and two nos. of Shunt Reactors are provided as shown in the switchyard line diagram.

1.1. 400 KV TRANSMISSION LINES

1. Ramagundam Nagarjunasagar Circuit 1 Double Circuit lines

(267 Km length)2. Ramagundam Nagarjunasagar Circuit 2

3. Ramagundam Hyderabad Circuit 1 Independent lines

(189 Km length)4. Ramagundam Hyderabad Circuit 2

5 Ramagundam Hyderabad Circuit 3

6 Ramagundam Hyderabad Circuit 3

7. Ramagundam Khammam Circuit 1 Single line (202 Km length)

8. Ramagundam Chandrapur Circuit 1 HVDC back to back inter-grid

connecting double circuit lines

(180 Km length)

9. Ramagundam Chandrapur Circuit 2

1.2. 220 KV TRANSMISSION LINES

1. NTPC AP Transco line 1 Through 400 Kv/220KV

250MVA A.T # 3 & 42. NTPC AP Transco line 2

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

250MVA A.T # 5

1.3. 132 KV TRANSMISSION LINES

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

200MVA A.T # 1 & 22. NTPC AP Transco line 2

1.4. AUTO TRANSFORMERS

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 Tranco, 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 Greevs Ltd. make)

2 Nos

1.5 TIE TRANSFORMER

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 & colony.

1.6 SHUNT REACTORS

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.

2. SWITCHYARD OPERATION ACTIVITIES

As mentioned else where, 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, Ats, TTS, Shunt Reactors, ACDBs, DCDBs, Battery Plant, 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 IOCC, 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 IOCC, 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.

3. 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.

3.1 CIRCUIT BREAKER

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 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.

3.2 ISOLATORS

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.

3.3 EARTH SWITCH

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 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.

3.4 BUSBAR

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.

3.5 SURGE / LIGHTING ARRESTERS

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.

3.6 CURRENT TRANSFORMER (CT)

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.

3.7 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.

3.8. 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.

4. 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.

4.1 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 re-closure, check synchronization, Trip circuit monitoring, Annunciation relays and energy meters are mounted on the rear side of the panel.

4.2 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.

4.3 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.

4.4 MASTER CLOCK

One maser clock (make Keltron) is provide in switchyard control room to synchronize the timings of all the Event loggers, DAS (Data Acquisition system of units), Disturbance Recorders, clocks provided in control rooms, etc., to maintain a uniform time, so that the sequence of events can be recorded and analyzed to know the cause of disturbance.

4.5-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.

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.

4.6 DISTURBANCE RECORDER

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.

4.7 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.

4.8 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)

4.9 PLCC ( power line carrier communication )In order to achieve fast clearance and correct discrimination for faults in 400 KV transmission network, it is necessary to signal between the points at which protection relays are connected. PLCC is high frequency signal transmission along with actual overhead power line. IT is robust and therefore reliable, constituting a low loss transmission path that is fully controlled by the power authority. PLCC is required for the following cases.

a) Inter tripping

In inter trip (direct or indirect trip) applications; if the command is unmonitored by a protective relay at the receiving end, reception of the command causes circuit breaker operation.

b) Permissive tripping

Permissive trip commands are always monitored by a protection relay. The circuit breaker can be operated only when reception of the command coincides with operation of protective relay responding to a system fault.

c) Blocking

Blocking commands are always monitored by a protection relay. The circuit breaker can be operated only if the command is absent when the protection relay is operated by a fault.

d) Telemetry

Telemetry refers to science of measurement from remote location. The various measurements obtained from transducers converts into signals and these signals transmit to remote control rooms through PLCC ex. All lines and generators of RSTPS parameters like MW, MVAR, etc linked up to IOCC through PLCC.

e) Telephone

PLCC can be used as a speech channel. All substations connected to RSTPS are providing by one direct telephone (hot line) for speedy communication.

Communication is also available for all PGCIL S/S through PLCC telephone exchanges.

4.10. 220 V DCDB & BATTERY PLANT

220 VDC supply is required mainly for the following applications.

a) Control supply for 400, 220, 132, 33 KV breakers, and associated equipment.

b) Control supply for relaying and protection circuits.

c) Annunciation & indication circuits.

d) Emergency lighting.

5. 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.

2. Aging of insulation.

3. An external object, such as a tree branch, bird, kite, rodent etc. spanning either two power conductors or a power conductor and ground.

5.2. 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.

5.3 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.

5.4 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.

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).

5.5 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.

5.6 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.

5.7 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.

5.8 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.

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

5.10 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.

5.11 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.

SWITCHYARD EMERGENCIES AND PLAN OF ACTION

6.1 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.

6.2 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 provide the sequence of protections operated.

6.3 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.

6.4 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.

A) CIRCUIT BREAKER CONDITION MONITORING ANNUNCIATIONS

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.

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.

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.

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.

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.

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

AGEG MAKE (pneumatic oprn) <30.0 bar <6.5 bar

ABB “”” <23.0 bar <6.5 bar

NGEF “” <31.5 bar <6.5 bar

BHEL (hydraulic oprn) <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.

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.

B. ALARMS RELATED TO TRANSMISSION LINE FEEDER PROTECTION

1. MAIN 1/2 PROTECTION OPERATED Two main protection relays are providing for the protection of each EHV transmission line against phase to phase and phase to earth faults. Two distance relays or combination of one distance relay and one phase comparison relay are provided as main protection relays in each line. Main 1/2 operated alarm appears when one of the main protection relays operates.

PLAN OF ACTION

1 Check the operation of protection relays.

2 Check the phase and the zone of operation.

3 Confirm the breaker tripping at both ends.

4 Collect the other end relay operations and fault locator reading and correlate with the relay operations this end.

5 Take the prints of D/R And E/L prints and analyze the cause of tripping.

6 Check the Auto reclosures switch position and confirm from D/R and E/L the auto reclosure operation. In case the auto reclosure operation taken place, do not attempt to change the line until Maintenance group gives clearance.

7 In case the Auto reclosure switch is in non-auto position or line tripped other than line fault, an attempt may be made to test charge the line.

2. OVER VOLTAGE PROTECTION OPERATED (86 O/V)

Over voltage relay operate when the line voltage rises above a specified value. Instantaneous and definite time over voltage relay is provided for each line. If the voltage exceeds 40% of the rated voltage (400 kv) instantaneous relay

picks up and trip the line. If voltage exceeds 10% of rated value for duration of more than 5 sec. the time delay relay picks up and trip the line.

PLAN OF ACTION

1 Check whether time delayed or instantaneous element has picked up.

2 Confirm the relay operations/ breaker tripping at the other end.

3 Check the D/R and voltage recorder printouts.

4 Check the CVT physically for any damage of equipment.

5 Find out there is any system disturbance at other end.

6 Line is to be charged only after testing CVT secondary voltages and obtaining clearance from Maintenance group.

3. MAIN 1/2 PROTECTION UNHEALTHY (97XY)

This alarm appears when one of the main protections becomes unhealthy due to D.C. supply failure for relay unit or some in built problem in the relay.

PLAN OF ACTION

1 Identify the faulty relay

2 Check for the DC fail indication

3 Inform to Maintenance staff for rectification

4. PROTECTION PANEL D.C. SUPPLY FAIL (80 MT/80MZ)

All protection relays work on 220 volts DC supply; Protection panels are provided with two separate sources of 220 volts DC supply. This alarm appears whenever one or both D.C. supply sources fails.

PLAN OF ACTION

1 Check the operation of the DC supply supervision relays 80MI/80M2

and identify which source of DC supply failed.

2 If both the sources of DC supply failed, immediate action to be taken to

restore the supply with the help of Maintenance group.

5. VT FUSE FAIL (97RX/XX)

6 Nos of fuses are provided for the three secondary cores of a CVT. VT fuse

fail annunciation appears in case of one of the fuse fails.

PLAN OF ACTION

1 Check for the flag indication for the operation of the relay indication.

2 Inform Maintenance group for replacing the CVT fuse/rectifying the problem.

3 In case the rectification of problem takes more time. The voltage inputs to the over fluxing relay, directional over current relay and VT fuse failure relay shall be shifted to other 400 KV bus.

6. INTERTRIP SIGNAL RECEIVED (PERMISSIVE INTERTRIPPING 85XY)

In carrier aided distance schemes carrier signal is used in connection with distance relays to speed up fault clearance, falling in delayed zone 2, from

both ends. The delay inherent in the second zone may be overcome by transmitting an intertrip signal to the relay at the remote terminal via a carrier channel, transmission being initiated by local zone 1 relay operation. The intertrip signal thereby allows simultaneous and fast tripping at both ends of the line and also permits application of auto re closure schemes.

PLAN OF ACTION

1 Confirm the breakers tripping at both ends.

2 Collect the other end relay operations and analyze the fault

3 After getting the clearance from the other end operator and IOCC charge the line.

7. GROUP 1/2 PROTECTION OPERATED (95CA/95CB)

The protection scheme provided for the bay equipment are divided into two groups and connected separately to two trip relays. Operation of any protection relay will operate the trip relay connected to that group. The operation of any one of the two trip relays initiates the above annunciation.

PLAN OF ACTION

1 Check for protection relays in the group operated.

2 Confirm the breaker opening at both the ends.

8. CARRIER L/O RELAY OPERATED 85 LO DIRECT INTERTRIP)

Carrier L/O relay operates through remote end carrier signal and give direct trip command to the local breaker during the following conditions.

1. Voltage high protection operated.

2. LBB protection operated.

3. Bus bar protection operated with other (main/tie) breaker is in open condition.

4. Reactor protection operated.

5. Hand trip with other breaker open condition.

PLAN OF ACTION

1 Check the protection relays operated if any.

2 Collect the remote end relay operations and the cause of trip.

9. 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.

PLAN OF ACTION

1 Collect the other end relay and breaker operation and correlate with the operations of this end.

2 Do not charge the line until Maintenance clearance obtained.

10. CARRIER CH I/II FAILS (30X1 /Y1 30X2/Y2)

The carrier aided distance schemes (Micromho, LZ 96, RAZFE) and phase comparison scheme (P 40 contra phase relay) use signaling to convey a single Command, usually in the form of a contact closure, from a remote relaying point to a local relaying point, where the additional information is used to aid or speed up clearance of faults within a protected zone or to prevent tripping for faults outside a protected zone. For more reliability in EHV protection schemes the carrier signals send/receive in two channels. If one of the channels fails this alarm appears.

PLAN OF ACTION

1 Check for supervision relay flag indication for CH 1/2

2 Identify the faulty PLCC panel in PLCC room

3 Check the 50V DC supply system

4 Check whether MCB in panel supply module of ETI 21/21 is off.

5 Witch on the panel if it is off. If it trips again inform Maintenance staff.

11. FAULT LOCATOR FAULTY (CS57)

This alarm appears whenever power supply unit of fault locator fails (power switch off position etc) or some in built problem in the unit arises.

PLAN OF ACTION

1 Check for DC supply fuse for F/L

2 Check the selector switch in/out

3 Check the 50VDC supply system

4 Check whether MCB in panel supply modules of EIT 21/21 is off.

5 Witch on the panel if it is off. If it trips again inform Maintenance staff.

11. FAULT LOCATOR FAULTY (CS57)

This alarm appears whenever power supply unit of fault locator fails (power switch off position etc.) or some in built problem in the unit arises.

PLAN OF ACTION

1 Check for D.C. Supply fuse for F/L

2 Check the selector switch in/out

3 Inform Maintenance group to attend.

12. DISTURBANCE RECORDER FAULTY (DRX) / 86B CIRCUIT FAULTY

This alarm appears whenever power supply unit of D/R fails (power switch off position etc.) Or some in built problem in the unit arises.

PLAN OF ACTION

1 Check for the DC supervision relay flag indication.

2 Inform Maintenance group to attend.

13. REACTOR TROUBLE (30 L/M/O/R/G/H/J/K)

Reactor trouble Annunciation indicates the unhealthiness of the reactor or NGR (Neutral Grounding reactor) Generally neutral point of a reactor is grounded through a reactor. This annunciation appears when one or more of the following events taken place.

1. Reactor Buchholz alarm

2. Reactor wdg. Temp. High alarm

3. Reactor oil temp. High alarm

4. Reactor oil level low alarm

5. NGR Buchholz alarm

6. NGR wdg. Temp. High alarm

7. NGR oil temp. High alarm

8. NGR oil level low alarm

PLAN OF ACTION

1 Check for the protection relay operations of the reactor and identify the fault.

2 Check physically reactor and its NGR (Neutral grounding reactor) observe any oil spillage in the surroundings, oil leakages, gas accumulation in buchholz relay.

3 If any abnormality observed take permission from IOCC and trip the line.

4 Inform to Maintenance group to attend the problem.

C. ALARMS RELATED TO TRANSFORMER PROTECTIONS

1. TRANSFORMER COOLER TROUBLE

Cooler trouble alarm appears when one or more of the following conditions.

1. Failure of cooler supply

2. Cooling fan failure

3. Cooling pump failure

PLAN OF ACTION

1 Check for the cooling fans and pumps operation.

2 In case of a group of fans or pumps not in service check their overload relay operation and reset.

3 Check for availability of two sources of power supply

2. 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

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

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.

3. TRANSFORMER WDG. TEMP/OIL TEMP. HIGH

This alarm appears when the wdg. Temp/oil temp of the Transformer goesbeyond the set value.

PLAN OF ACTION

1 Confirm from local the actual winding/ oil Temperature

2 Confirm the running of all the cooling fans and oil pumps

3 If the fans and pumps are not running, start them in manual mode. In case not possible to start inform Maintenance group.

4 Request IOCC and LDC to reduce the local on Transform

4. TRANSFORMER OIL LEVEL LOW

The magnetic oil level gauge fitted on the main conservator initiates annunciation / trip in the event of the oil level falling below the preset levels due to any reason.

PLAN OF ACTION

1 Confirm from the local the actual level of oil.

2 Check for any heavy leakage of oil from the Transformer if found then

take immediate action to trip the Transformer

3 Inform Maintenance group to attend the problem

5. TRANSFORMER OVER LOADED

The load (current) on Transformer exceeds its rated (or set) value for more than a specified time, 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.

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.

7. PRESSURE RELIEF DEVICE OPERATED

Pressure release device allows for the rapid release of excessive pressure that may be generated in the event of a serious fault in the Transformer. A bright colour coded Mechanical indicator pin in the cover moves with the valve disc during operation of PRD and is held in position by an in the pin bushing. This pin is clearly visible from the ground level indicating that the device is operated.

PLAN OF ACTION

1 Check for any other protection relays operated to identify the problem.

2 Check for both LT and HT side breaker tripping. If any one of the

breaker in service hand trip the same.

3 Check for any gas accumulation in Buchholz relay

4 Transformer may be charged only after thorough investigation for the

reason of PRD operation and obtaining clearance from Maintenance

group.

7.DEENERGISATION AND ISOLATION OF SWITCHYARD EQUIPMENT

De energisation of equipment isolation from live parts, normalization of the equipment after completion of Maintenance jobs trail charging and taking in to service are the important day-to-day operation activities.

7.1 IMPORTANCE OF SAFETY IN SWITCHYARD OPERATION

Isolation and charging of high voltage equipment have great potential for hazardous occurrences and need to consider safety at each juncture. Safety in electrical system concerns three different areas; protection of life, protection of equipment, protection of uninterrupted productive output. The protection of human life is paramount. Equipment can be replaced lost production can be made up. However, human life can never be recovered nor human sufferings compensated. Therefore, only qualified and authorised persons shall be allowed to operate switchyard equipment.

7.2 GENERAL PRECAUTIONS

a) All apparatus should be legibly marked for identification. These makings should not be placed on removable part.

b) There must be checks and cross checks to confirm that you are at right apparatus for the particular operation.

c) NO part of the body should touch any part of the equipment under charging during isolation or normalization.

d) Proper illumination should be there to avoid poor visibility in any part.

e) All control knobs and indicative lamps should be in working condition.

f) Operation staff for their own safety should use the personal protective equipment like safety shoe, hand gloves etc. at work.

g) Always put DANGER TAGS after isolating the equipment and remove the danger ages after and normalization of the equipment.

h) Operation staff they must understand operations to be done and be completely familiar with every details of his part of operation.

i) Should not start a switching sequence until it is correct in every respect.

j) Once begum the switching sequence keeps total attention on what is doing, ignoring distractions, until the job is completed. If attention is diverted to another tasks while executing a switching operation, then should not continue the operation before carefully checking what has already been done.

7.3 DE- ENERGIZATION & ISOLATION OF EQUIPMENT

De energisation and Isolation of equipment required during the following situations.

1. When carrying out preventive or breakdown Maintenance it is essential to isolate reliably the equipment or section on which the work is to be done, from all other live parts on the installation in order to ensure complete safety of working staff.

2. When some abnormality observed in a section of the system, t The faulty section should be isolated from the main system to safe guard the rest of the system.

3. When the equipment found defective while in service, isolation of defective equipment or section is necessary to stop further damage to that equipment or surrounding equipment.

7.4 PLANNING OF SHUTDOWN PF EQUIPMENT

If it is a planned shutdown, to attend a preventive or break down Maintenance job, the problem will be discussed in daily planning meeting in the presence of operation and Maintenance representatives and the shutdown schedule of equipment will be planned.

If it is an emergency shutdown, Maintenance and operation HOD’s discuss the emergency and decide the plan of shutdown of the equipment.

If the required shutdown is going to affect the power flow in the tie lines connected to PGCIL substations, then shutdown concurrence must be obtained from IOCC. For the line belongs to AP Transco, shutdown concurrence must be obtained from LDC.

7.5 REQUESTS FOR PERMIT TO WORK (PTW)

The concerned authorized area Maintenance Engineer requests for a permit to work (PTA) on the shutdown-planned equipment in a specified form to the authorized operation engineer of the location. Operation Engineer takes the responsibility of de energizing and isolating the equipment for which shutdown is required with the help of the controllers and operators.

7.6 PRE REQUISITES BEFORE DE ENERGISAITON

a) Take clearance from the shift in charge for de energisation of the equipment.

b) Inform the Maintenance group before de energisation.

c) If the de energisation is for a tie line or auto Transformer inform the other end substation operator and take clearance.

d) Check the line loads and ensure that the shutdown of the equipment should not make over loading the other lines or Transformers.

e) Identify the correct bay and concerned main and tie breakers to be tripped for de energisation of the line/ Transformer.

f) Keep the Auto Reclosure switches of the main and tie breakers in N.A. position.

g) Give announcement in swyd. PA system, the name and the number of the breaker, which is going to hand, trip to aware the personnel working in swyd.

h) Give announcement in station PA system, the name of the line or Transformer that is going to hand trip, to alert the unit desk operation engineers to face any abnormality arises during line de energisation.

i) Inform orally to the other end substation shift in charge regarding the de energisation of line/Transformer and hold him on line.

7.7 PROCEDURE OF DE ENERGISATION

A) DE ENERGISATION OF 400 KV TRANSMISSION LINES

1. Hand trip Main/ Tie breaker whichever bay is to be energized. Subsequently trip the other breaker if the bay equipment is not under PTW.

2. Confirm from the other end operator on telephone that the breaker at their end tripped on inter-trip signal.

B) DE ENERGISATION OF 220 KV/132 KV LINES

1. Hand trip the main breaker of the line to be de energized if the line is connected to main bus or the transfer bay breaker if the line is connected to transfer bus.

2. Confirm from the other end operator on telephone that the breaker at their end tripped on inter-trip signal.

C. DE-ENERGISATION OF 400 KV/220KV AUTO TRANSFORMERS

1. Hand trip Main/ Tie breaker (400 KV SIDE) whichever bay is to be de energized. Subsequently trip the other breaker also if the bay equipment is not under PTW.

2. Hand trip line breaker (220 KV side) and inform the other end shift in charge on phone that the Transformer is de energized and ensure that the other end breaker tripped on inter-trip signal.

D. DE ENERGISATION OF 400KV/132 KV AUTO TRANSFORMERS

1. Hand trip Main/ Tie breaker (400 KV SIDE) whichever bay is to be de energized. Subsequently trip the other breaker also if the bay equipment is not under PTW.

2. Hand trip the LT breaker (220 KV SIDE) of the Transformer is on main bus or hand trip the transfer bus breaker if the Transformer is on transfer bay. Inform the other end operator on telephone that the Transformer is de energized.

7.8 POST DE ENERGISATION CHECKS

1. Check for any window annunciation or alarms appeared.

2. Check for the breaker open events in event logger.

3. Check for the semaphore indication of breakers in open position.

4. Check the breaker on/off indication lamp and ensure the breaker is in off position.

5. Check for the fall of flags in three phase of the trip relay.

7.9 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 been 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.

NOTE:

FOR DETAILS OF BREAKER AND ISOLATOR NUMBERS TO BE OPENED FOR ISOLATION OF TRANSFORMER AND LINE FEEDERS, READERS MAY PLEASE REFER THE BOOK SHARPENING SKILLS VOLUME NO. 4 “ STANDARD ISOLATION PROCEDURES FOR SYSTEMS AND EQUIPMENT”.

8.NORMALIZATION AND CHARGING OF LINES 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 network are so long and Transformers are 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.

8.1 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 charged 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 be synchronised 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.

8.2 CHECKS BEFORE NORMALIZATION

a) Ensure that all permits issued on Line equipment / the authorised 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.

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.

8.3 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 if 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.

8.4 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.

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 check synchronising 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 is not under permit.

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

8.5 SYNCHRONISING THE LINE AFTER CHARGING AT EMOTE 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.

8.6 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 colour 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.

8.7 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.

8.8 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 breaker 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 sysnchroscope 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 plugin the synchroscope into the concerned line breaker-synchronizing socket. Make the syncrhoscope on.

i) Ascertain that the voltage and the frequency are within synchronizing limits.

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

k) Close the 220 kv line breaker (LT breaker of Auto Transformer).

l) Inform to AP Transco S/S & APLDC that the line is synchronized.

9. BLACKOUT OF STATION AND BLACK START PROCEDURES

Despite of all precautions and protective measures, the integrity of the power system is occasionally at risk owing to human error, malfunction of equipment, lack of complete information, and natural disasters. The emergency like grid failure/ partial grid failure may lead to total loss of power supply in the region / station, which is called the blackout condition.

In case of total Blackout of station / region due to grid failure or partial grid failure, operation staff are responsible.

1. To analyse and locate the fault leading to the situation

2. To inform all the authorities and units about the problem.

3. To arrange startup power at the earliest to bring back the units.

9.1 PLAN OF ACTION DURING STATION BLACKOUT

1. See and ensure DC lighting has come in auto.

2. Have a broad lock on the panel, see whether any unit has survived on house load and / or any line feeding on house load has survived.

3. Inform shift charge engineer and all units about the status on emergency PA system through group call.

4. Specifically inform shift charge engineer, Sr. supdt. (Operation) DGM (O), DGM (EM), AGM (O&M), and GM (R) about grid failure.

5. Check and not down the relays operated, ascertain the reasons of cause leading to grid failure also whether it is from station side or switchyard side or substation side.

6. See that all outgoing feeder breakers have opened out, if not, open them manually.

7. Normal sources of startup power are Chandrapur HVDC S/S and Nagarjuna sagar Hydro power station (AP GENCO). Find out how much startup power can be made available.

8. Inform shift charge engineer about the amount of startup power available and quantum thereof. This I necessary to decide further course of action regarding bringing back the units.

9. As per recommendations of IOCC/LDC, Hyderabad startup power is to be availed through respective feeder.

9.2 BLACK START FACILITIES AT RSTPS

In general at least one of the 400 KV Chandrapur Ramagundam HVDC back-to-back lines is always in service. With the consent of SRLDC, startup power supply can be taken immediately from Western region by passing HVDC back to back like at Chandrapur.

In case of startup power not available form CHANDRAPUR S/S due to outage of equipment or any other, reason the following alternate arrangements to be made.

9.3 QUICK 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

III. 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.

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

9.4 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 D 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.

OPERATION GUIDELINES OF 400 KV SWITCH YARD

Contents

S.NO.

Description Page Nos.

1 ABOUT RSTPS 400 KV SWITCH YARD

2 SWITCHYARD OPERATION ACTIVITIES

3 SWITCHYARD EQUIPMENT

4 SWITCHYARD CONTROL ROOM EQUIPMENT

5 RELAYS & PROTECTION SCHEMES

6 SWITCHYARD EMERGENCIES AND PLAN OF ACTION

7 DE ENERGISATION AND ISOLATION OF SWITCHYARD EQUIPMENT

8 NORMALISATION & CHARGING OF LINES & TRANSFORMERS

9 BLACKOUT OF STATION AND BLACKSTART PROCEDURES