ELECTRICAL SYSTEM (LT) INSTALLATION , PRE-COMMISSIONING , COMMISSIONING OF DIFFERENT LTMCC -ABC OF THERMAL POWER PLANT

Besides HT cubicles other common electrical items are transformer , LTMCC ( Low tension Motor eontrol center ) , Different Power distribution board coming under lighting packages etc. In this dispatch we will discuss only about LTMCC. There are numbers of LTMCC in a power station which can be classified as LTMCC or the name of the system like soot Blower MCC, Valves MCC etc. LTMCC is having operating voltage of  415 V.

To appreciate the construction feature of LTMCC one must study the IS ( Indian standard ) codes  for items . Few  of them is listed below for ready reference.

375         Specification for Marking & Gen Arrangement of Swgr, Busbars, Main Connection & Aux. Wiring

513         Cold Rolled Low Carbon Steel Sheet & Strips

722         Specification for A. C. Electricity Meters. (Integrity Meters)

1248       Specification for Direct Acting Electrical Instruments.

1822       AC Motor Starters of Voltages not exceeding 1000

1841       Specification for EC grade Aluminium Rod Produced By Rolling

1897       Specification for Copper Strips for Electrical Purposes

1901       Visual Indicator Lamps.

2147       Degree of Protection provided by Enclosure for Low Voltage Switchgear

2208       Specification for HRC Fuse Links up to 650 Volts

2516       A.C. Ckt Breaker Requirement for Voltages not Exceeding 1000 V (Part - I, Sec - I + Part - II, Sec-II)

2705       Specification for Current Transformers.

3231       Electrical Relays for Power System Protection.

3247       Switchgear General Requirements

3427       Metal Enclosed Switchgear & Control gear

4064       Specs for Heavy Duty Air Break Switches Fuses for Voltages not exceeding 1000 V.

4237       General Requirement for Switchgears & Control gear for Voltage not exceeding 1000 V

6875       Control Switches / Push Buttons

8623       Factory Built Assemblies of Switchgears & Control Gear.

8828       Miniature Circuit Breaker

13947    LV Switchgear and Control Gear.

General Information on LT MCC  ( only a few ones  to understand the construction features.)

-the enclosure shall provide a degree of protection of not less than IP-52. The height of all the panels shall not exceed more than 2200 mm & depth shall not be more than 500 mm for Single Front & 800 mm for Double Front, except for the Circuit Breaker panel, where the depth could be 1000 mm.

- CRSP (t=1.4mm and above) ,  angle , channels are used for cubicle construction.

-The Panel shall be fully compartmentalized with all doors on the front only.

  The panel should have cable entry point , Bus bar mounting system , shrouding of bus bar etc

- There will three live bus bar and one neutral bus bar running horizontally and vertically .

-Earth bus bar will run all around the panel . The size will be same as neutral . Earth will be ultimately connected with station earth at the end of the panel.

-Bus bars shall be of high conductivity Aluminum with current density of 800 A Inch² .

- As per requirement and to facilitate easy transportation panels are sent as per transportation size which are then assembled at site .

WARNING: MAJOR CONTRACTOR ( LIKE l&t ML12,10 ML 8 ETC) ARE HAVING MOVING CONTACTS WHICH CAN BE EASILY REMOVED WITH SPECIAL TOOLS . AT SITE THEFT OF MOVING CONTACT IS VERY COMMON THEREFORE YOU SHOULD BE VERY CAREFUL IN THIS ASPECT OTHERWISE DURING CHARGING YOU WILL FIND INSPITE OF ALL  REQUIRED CONDITIONS YOUR PANEL IS NOT GETTING CHARGED. MOVING COST MORE THAN 60% OF THE MAIN CONTRACTOR COST.

CONTINUED TO PART-II 

PRE CHARGING TEST AND COMMISSIONING OF HT SWITCH GEAR (TYPICAL) ( photoes) -ABC OF THERMAL POWER STATION

HT switchgear getting erected in the power plant.

A portion of single line diagram of HT line at thermal power station.

PRE CHARGING TEST AND COMMISSIONING OF HT SWITCH GEAR (TYPICAL) -ABC OF THERMAL POWER STATION

CONCLUDING PART

PRE – ENERGISING CHECKS & TESTS

-Inspect any physical damage in the busbar, insulation, panel doors, power & sliding contacts etc. and to be rectified if found. Special attention to be given on porcelain insulators holding the live line

-Making the panel inside dust free & free from foreign materials

-Checking the tightness alignment & clearance of bus bars ,smoothness in racking in & racking

out of modules, proper making of limit switch contacts(test and service), tightness of input power cables and outgoing  power & control internal wirings.

-Inspect all relays and make sure that any blocking used for shipping purpose is removed and the

armature  moves freely.

-Check all doors for proper mounting with respect to the switch handle.

-Check door interlock mechanism and connection.

-Test the pts,cts & relays involved. keep the recommended settings for the relays like over

current,  under voltage & overload protections, calibrate the meters (ammeters, voltmeters, power

meters & energy meters etc) and keep proper records for future reference.

-  Test the insulation of boards with 5000 v dc megger & the value should be as per the relevant

is specification (more than 50 mega ohms).

-Check closing & tripping interlocks ,overload relay setting in the panel.

-Measure busbar resistance , vcbs contact resistance (should be less than 50 milli ohms), closing

& tripping time if test report is not available at site.

-Check the protection circuit wiring connection by conducting primary injection current.

-Carry out high pot test for 75% of voltage mentioned in the test report for ht buses,100 % for ht

incoming power cables and find out the leakage current.

-Check  the input power cable terminations from transformer secondary

-Ensure  the phase sequence of incoming pt wirings and circuit closing of cts are proper before

charging the panel.

-Check closing & tripping mechanism operates smoothly both manually and electrically.

-Space heaters & thermostat shall be in good condition Space heaters to be ON a day before charging.

-Ensure all covers are provided and no conducting part is earthed. All the gland holes are covered

and temporarily sealed to minimize the short circuit of live terminal through rodents.

CHARGING PROCEDURE:

-Ensure tie breaker in associated station switchgear is in withdrawn position.

-Ensure all feeder breakers of unit  Swtichgear  are in withdrawn position.

-Check and record the final IR of supply cables for the DC control bus and the AC heater supplies :

-Energise both the supply cables for DC control bus and AC heater supplies.

-Put the tie breaker  in Test position.

-Put  all control fuses for the Tie breaker in position and switch on its control supply.

-Select LOCAL/REMOTE selector switch to local and close and trip the tie breaker once check  its operation.

-Check  tie isolator.  Interlock  in  closing circuit of tie breaker.

-Check that tripping relays for Tie breaker and main incomer breaker are not operated and are reset.

-Select Tie breaker Local / Remote switch to REMOTE.

-Give closing impulse to Tie breaker from UCB and check that the breaker closes.

-Short Terminals (tripping contact of E/F and O/C Relay) and check that tripping relay energises and tie breaker trips.

-Switch off the control supply and reset the tripping relay and remove the shorts  as detailed earlier.

-Put the incomer breaker  in Test position.

-Put control fuses of Incomer breaker in position and switch on control supply.

-Select Local/Remote switch of Incomer breaker to local and close and trip the incomer breaker once to check its operation.

-Short the terminals  in Incomer breaker cubicle to bypass the “Generator Breaker closed permissive”.

-Select Incomer breaker Local/Remote switch to Remote.

-Give closing command by control switch in UCB and check that the breaker closes.

-Switch on the control supply to tie breaker.

-Short terminals  in incomer breaker and check that :

a.            Incomer breaker trips

b.            Tie breaker closes automatically

-Reset all alarms and relays and remove shorts.

-Give trip command to incomer breaker control switch in UCB to bring switch position corresponding to breaker position.

-Put check/manual switch for incomer breaker in UCB in MANUAL position.

-Give closing command to incomer breaker and check  that :

a.            Incomer breaker closes.

b.            Tie breaker trips automatically.

-Reset all alarms and relays.

-Give trip command to tie breaker control switch in UCB to bring switch position corresponding to

breaker position.

-With incomer breaker ON and check/manual switch in manual position, give closing command to the tie breaker and check  that :

a.            Tie breaker closes;

b.            Incomer breaker trips.

-Reset all alarms and relays.

-Trip the Tie breaker.

-Switch off the control supplies to both incomer and tie breakers.

-Remove all test connections and check that any disconnections made for the purposes of testing have been correctly reinstated in tie and incomer panels.

-Keep  incomer breaker in withdrawn position (It will remain in withdrawn position till unit auxiliary

transformers are commissioned).

-Check ‘danger/warning notices’ are fixed at relevant points to ensure safety.

-Ensure effective communications between  UCB and switch board room are established.

-Check and record the final IR value of the following equipments :

a Isolator/Tie breaker of associated station switchgear.

b.Tie breaker of  Unit switchgear

c. Unit switchgear bus bar

d.Tie bus duct/cable megger used ___________ KV

-Ensure VT is  in service position with all its fuses put on.

-Check all the relay settings in TIE breaker panel are as per their protection schedule.

ENERGIZING PROCEDURE

-Put the Tie breaker of associated station switchgear in service position and close the tie breaker to charge the Tie cable.

-Observe the cable for any abnormality.

-Put the tie breaker in service position.

-Switch on the control supply to the tie breaker.

-Inform all concerned parties about the intention of charging the unit switch board.

-Put local/remote switch of tie breaker in REMOTE position.

-Give closing command from the UCB to tie breaker to charge the unit switch board.

-Check and record the unit bus bar voltage for all the three phases.

-Observe the unit switch board for any abnormality.

-Put the synch. Check/manual selector switch to CHECK.

-Check permissive contact in synchronising check relay closes.

-Check the phase sequence at  unit bus VT secondary terminals as detailed in following table.  (It shall be  same as that of associated station board).

MEASUREMENT IN VT CUBICLE

-Do the phasing out between VT secondaries of station and unit board.

-Keep the board charged for 24 Hours and  observe it for any abnormality.

-Inspect all equipment externally for  any sign of abnormality after being charged for 24 Hrs.

-It will  be the duty of the testing team leader to ensure that when the system is operating under load conditions that all equipment are externally inspected for any sign of stress or abnormality. 

Few photographs of drawing is given below

balance phographs in final part

HT SWITCHGEAR ERECTION ,TESTING AND COMMISSIONING (PART-II) -ABC OF THERMAL POWER PLANT

In my last dispatch I have indicated the number of panels required to be installed for HT connection .A picture of the same was also attached. Numbers of panels are erected aligned on line. Incoming and outgoing cables are laid through spreader room . These panels are erected by the side of the service bay through an opening kept for this purpose only. Once these panels are and aligned then pre-commissioning activity starts.

Opening has been kept at service bay side to lift panels as shown in the above picture.

Cable spreader room  erection of cable trays under progress. This is below the Panel room

This is the panel room ..civil works under progress.

Following testing are being carried on HT panel after erection.

 a. Insulation resistance measurement of bus bar (power ,control ),vcb

b. Busbar,contact resistance measurement

c. High voltage test – bus.

d. Primary injection test  - vts & cts.

e. Protection, interlocks and metering circuits .

Following instruments (calibrated)  , systems , qualified testing personnel  ( Accident while testing is very common, this may be fatal at HT lines) etc are required to be lined up.

5000v insulation tester (motorized) ; 3 phase 415  ac 50 hz system with variac (3 ph and  1 ph)

Dc control supply (preferably from permanent DC source;  Hi pot ac/dc source

 Measurement kit ; Current injection kit ; Micro ohm meter; Milliseconds timer ; Multimeter ( 4 and half digit ) digital ; Ananlog Multimeter ; Volt and Ampere meter for measurement; Tong tester;  Number of long testing leads with end connectors ; Supplier’s tools for the panel etc.

Safety precaution is paramount before and after testing a few points are given below:-

The Engineer-In-Charge of the testing  team will inform each member of his team as to the exact nature and extent of his contribution and responsibilities towards the tests carried out.

 Only nominated person will take part in the tests. 

All persons must acquaint themselves with the use and location of fire  extinguishers and first aid posts.

Adequate lighting facilities will be provided at all times.

Each test will be carried out under the control of the test team leader.

A strict and safe method of applying test leads shall be practiced.  Bare wires shall not be inserted into sockets.

A record of any alternation made during the test such as shorts or disconnections, shall be made and annexed to relevant test procedures .

Adequate number of poster ,signboard are placed strategic location for safety.

All procedures are recorded and checked with the drawings . A single line diagram or conditions to energise the particular panel and also for tripping may be made before testing .This will be immense help. This is not a must condition but helps during testing as ready reference.

CHECKLIST FOR THE FOLLOWING PANELS ARE CHECKED

i. Incomer panels (1 & 2) ;ii. Outgoing feeders; iii. Bus coupler; iv. Tie breaker

- All incoming and outgoing cables to incomer panels are completed.

-Interlocks for closing and protection for tripping are to be checked as per standard check list.

-11KV Bus Duct/Cable erection from station switch gear to unit switch gear complete in all respects.

-The Tie Breakers at station switchgear end of tie is tested and in withdrawn position with shutters locked.

All circuit breakers contained in 11KV unit switch gear in withdrawn position.

Clearance from Erection Department for carrying out tests on 11KV unit   switchgear and 11KV Bus duct/cable from unit to station switchgear obtained.

-11KV station switchgear associated with the energising of this unit switchgear is live.

-Safety Clearance notification issued  and effective for 11KV unit switchgear and 11KV tie bus duct/cable.

-The associated DAS/Annunciation scheme is complete, tested and in service.

-The control supplies are available.

COMMISSIONING PROCEDURE :

-Check and test all the panels of 11 KV unit switch board and associated equipments as per their standard check list.  Record in a format for future use.

Check and test the unit switchgear bus bars and the Tie bus duct/cable to the station switchgear as per their standard check lists and record.

Check and test supply cables for the DC control bus and the AC heater supplies as per their connection diagram and record.

Continued to PART-III --PRE ENERGISING TESTING ,AND COMMISSIONING

ELECTRICAL SYSTEM ( HT ) PANEL 11KV FOR EQUIPMENTS AND SYSTEM (PART -I)- ABC OF THERMAL POWER

Till last dispatch basics electrical system discussed which are essential for the erection and commissioning of the Power system. Earthling rods and flats are laid at different places when civil works under progress. Riser are kept at different places to get it connected. Slowly it becomes like a grid. There value etc are precisely monitored time to time. After that main plant DC system are getting erected .As it was told no AC system will run without  the DC input.

Two more systems are coming after that one is HT ( 11kv/6.6 KV /3.3KV system ). It allows to distribute power in power plant as bulk and also the source running equipment like BFP , ID ,FD PA etc motors . Higher rating equipments are connected with HT ac voltage and this will reduce the cable size considerably and easy handle at site.

Here is brief description of panel in a 500 MW power station. There will be variation site to site but more or less these feeders will be there. This will give a good idea of number of HT panel to be commissioned. Viewers comments /value addition  will be appreciated.

11 KV Switchgear

Generally a few companies supplied these panels and they are BHEL . ABB , C&G ETC . these panels are installed in service bay near unit one side at an elevation of 8.5m .

1.         PLANT DETAILS :

       THIS SYSTEM CONSISTS OF  11 KV AND 3.3 KV HT SWITCHGEARS (UNIT SWITCH BOARD BA,BB,CA,CB FOR UNIT #1 AND UNIT #2 AND STATION SWITCH BOARD 0BA,OCA FOR 11 KV/3.3 KV  STANDBY SWITCHBOARD  SUPPLY IN CASE OF BOTH GENERATORS OUT OF SERVICE) .

MAKE: BHEL,BHOPAL

RATINGS VOLTAGE : 11 KV & 3.3 KV 3PHASE 50 HZ AC , CURRENT:2750 A

11 KV SWITCHGEARS

I.The 1BA Board consists of the following HT Panels :

1.Incomer Panel ( incomer from UT A )

2.PT PANELS ( line /feeder PT  and Bus PT )

3.         Tie breaker from standby switchboard (0BA)

4 .        OUTGOING FEEDERS    

            3240 KW Cooling Water Pumps 1 & 2

2450 KW Primary Air fan        A (Unit #1)

            16MVA Unit Aux. Transformer A

            16MVA Misc. service Transformer()

            2MVA  Unit service transformer A

            3MVA VFD transformer (ID Fan 1A Channel 1&2)

            1.25MVA Bunker area service transformer

            1.6 MVA ESP Service transformers

            1.25 MVA CHP transformer 1A

            0.75 MVA Track Hopper Service Transformer

            1.6MVA Fuel oil service transformer

            7.5 MVA Station  aux. Transformer.

            2 MVA Station Service Transformer

            6.3 MVA CHP Aux.

             5. Spare feeders

            a) 3240 KW Motor feeder

            b)2 MVA Transformer feeder

II.The 2BA Board consists of the following HT Panels :

1.         INCOMER PANEL

            Incomer Panel ( incomer from UT A ) (Unit #2)

2.         PT PANELS ( line /feeder PT  and Bus PT )

3.         Tie breaker from standby switchboard (0BA)

4.         OUTGOING FEEDERS    

            3240 KW Cooling Water Pump 4

            2450 KW Primary Air fan        A (Unit # 2)

16MVA Unit Aux. Transformer A

            16MVA Misc. service Transformer

            2MVA  Unit service transformer A

            3MVA VFD transformer (ID Fan 2A Channel 1&2)

            1.25MVA Bunker area service transformer

            1.6 MVA ESP Service transformers

            1.25 MVA CHP transformer 1B

            0.75 MVA Track Hopper Service Transformer

            1.6MVA Fuel oil service transformer

            7.5 MVA Station  aux. Transformer.

            2 MVA Station Service Transformer

            6.3 MVA CHP Aux.

            5.  Spare feeders

            3240 KW Motor feeder

            2 MVA Transformer feeder

III. The 1BB Board consists of the following HT Panels :

1.         INCOMER PANEL

            Incomer Panel ( incomer from UT B ) (Unit #1)

2.         PT PANELS ( line /feeder PT  and Bus PT )

3.        Tie breaker from standby switchboard (0BA)

4. OUTGOING FEEDERS    

            10000 KW MD BFP (Unit # 1)

            3240 KW Cooling Water Pump 3

            2450 KW Primary Air fanB (Unit # 1)

16MVA Unit Aux. Transformer B

            2MVA  Unit service transformer A

            3MVA VFD transformer (ID Fan 1B Channel 1&2)

            1.6 MVA ESP Service transformers

            1 MVA Switchyard Service Transformer

            2 MVA Ash Sys Compressor Plant Transformer

            1 MVA Ash Water Power House Service Transformer

            2 MVA Off Side Plant Service Transformer

            2 MVA WTP Area Service  Transformer

            2 MVA Station Service Transformer

            0.5 MVA Raw Water Pump House Service Transformer

            1.6 MVA Administration Building Service Transformer

5. Spare feeders

            2450 KW Motor feeder

            1 MVA Transformer feeder

IV.The 2BB Board consists of the following HT Panels :

1. INCOMER PANEL   

            Incomer Panel ( incomer from UT B )  (Unit #2)

2. PT PANELS ( line /feeder PT  and Bus PT )

3. Tie breaker from standby switchboard (0BA)

4. OUTGOING FEEDERS    

            10000 KW MD BFP (Unit # 2)

            3240 KW Cooling Water Pump 5

            2450 KW Primary Air fanB (Unit # 2)

16MVA Unit Aux. Transformer B

            2MVA  Unit service transformer A

            3MVA VFD transformer (ID Fan 2B Channel 1&2)

            1.6 MVA ESP Service transformer

            1 MVA Switchyard Service Transformer

            2 MVA Ash Sys Compressor Plant Transformer

            1 MVA Ash Water Power House Service Transformer

            2 MVA Off Side Plant Service Transformer

            2 MVA WTP Area Service  Transformer

            2 MVA Station Service Transformer

            0.5 MVA Raw Water Pump House Service Transformer

            1.6 MVA Administration Building Service Transformer

5. Spare feeders

            2450 KW Motor feeder

            1 MVA Transformer feeder

Above description is typical of coal based super thermal power station feeder list. There may be variation site to site and of uses. But this will given an idea of HT drives and transformer required for HT drives.

Recently i was visiting a super thermal power station and there HT panel erection is going on. Some other picture on this will be on next dispatch.

continued to pat -ii

220 VOLT DC SYSTEM-BATTERY CHARGER -COMMISSIONING PART -I I-ABC OF THERMAL POWER PLANT.

COMMISSIONING PROCEDURE:

     TESTING OF BATTERY CHARGERS:

The insulation value shall be checked with 500 V DC Megger. During this test, all low voltage circuits  & Relays etc, shall be  bypassed ( shorting)

The panel shall be switched on at no load. For this, first make input switch ON & check the voltages at all phases indicated by lamps  & voltmeter by selector switch . Now the voltage is connected to the primary of the Main transformer which steps the voltage down as required for the specific DC output Voltage & isolates AC Input line from Battery circuits. The transformer's secondary is connected to the Full wave rectifier assembly.

The bridge is standard  three phase full wave half controlled silicon bridge. The voltage control is accomplished by the application of a positive pulse to the gate terminals of the SCR at the desired time. Before the pulse is applied , the SCR is open  and no current flows in the circuit.  As soon as SCR is fired, it operates as a standard silicon rectifier until the forward current is reduced to almost zero.

Check the no load output voltage at the output terminals.

Ensure the output voltage is steady without any trouble for 15 minutes.

Check for annunciation interlocks  etc.

If load is available, the equipment shall be loaded progreesively upto rated value

Check for voltage regulation, free from oscillation, ripple etc.

Check for dropping characteristics at higher loads.

Run the equipment for 4 hours and observe of stability and check for local heating.  When unit is loaded the ripple voltage level (peak to peak) may be observed . Follow the advice of Service engineer.

II          FIRST CHARGING OF BATTERY:

 Thumb rule says DC  Voltage needed for battery charging will be 2 times the no of cells in battery bank. The initial charging will take approximately 16 to 24 hours since the batteries are already charged and sent as maintenance free ones.

k board is firmly coIt is of utmost importance that the terminal of the battery is connected to +ve load of charging source. So polarity should be ascertained.

Commence charging not later than 24 hours after connecting all battery cells.

Give the first portion of charge at a rate of 100 Amps for 10 Hours

Discharge it using Water resistance or halogen lamps as recommended by supplier

Give the second charging at the rate of approximately 20 Amps till the signs of completion  of charge observed.

Select any one cell (except the end cell or regulating cell) as pilot cell out of every rack as given in the layout of the battery bank.

Voltage and specific gravity reading from pilot cells will indicate the state of charging of the whole battery system. Follow supplier’s recommendation

All cell terminals & connections are to be applied with pertroleum jelly to reduce contact resistance. No adjustment should be made which will disturb charging.

When all the cells have been greasing freely and when voltage and specific gravity of pilot cell has been constant over 3 successive hour readings, the cells can be deemed to be fully charged and the charging may be terminated. Then wipe down outside of all cells and clean the floor.

Put the battery system on trickle charging when charging completes.

The trickle charge should be adjusted to give optimum battery voltage of 1.53 - 1.67 volts per cell.

III         ENERGISING OF DISTRIBUTION BOARD:

Take final I.R. value of the board. Check ea
ethi ected with earth through wire or strip as shown in the drawing.

Ensure that all outgoing circuits are locked in OFF position.

Ensure that all safety procedures have been observed.

Check that polarities of D.C switch board battery charger and battery are matching.

Close the incomer switch of board to charge it.

Measure D.C Voltage at the Input.

Observe D.C board for any abnormality.

If board condition is satisfactory, check that all remote end fuses of outgoing circuits are removed.

Switch ON outgoing feeders one by one. Record the following for each circuit.

i.)         Polarity  at both ends of circuit

ii.)        Voltage at both ends of circuit.

IV       EARTHFAULT RELAY ON LOAD TEST:

To carry  out on load test for the Battery E/F relay, connect variable resistance box of the range of 15 to 150 K Ohms between +ve  pole of the board and earth

Keep selectivity setting plug of E/F relay  at 3 ms setting.

Cut out resistance slowly to simulate an E/F  and observe the current in milli ammeter when the relay operates.

Record resistance and current in mA

Carry out this test on each available setting on relay.

While doing test observe and record the direction of deflection in the ammeter. Check whether it confirms the pole on which the fault is simulated.

Repeat  once a again on -ve pole of the board.

The test is satisfactory if the operation of the relay confirms with the setting.

Note : Electrical commissioning demands cool approach not rushed to wards the job. Any mistake may cause permanent damage and that was witnessed many a time.

All instrument need to calibrated so that during dispute you can rely. This is also a common problem.

All hand tool should be insulated one and value checked before using.

Electrical signboard /safety signboard should be displayed .

220 VOLT DC SYSTEM-BATTERY CHARGER PRE-COMMISSIONING PART -I -ABC OF THERMAL POWER PLANT.

220 volt dc system with battery charger commissioning

Till last dispatch I have discussed about the basic requirement of electrical system in apower plant . In continuation with that commissioning of DC 220v system will be described briefly.

The system consist of :-

i.          Battery Bank

ii.         Battery Charger - Main and Standby

iii.        DC Distribution board.

The battery is installed in the battery room in the HT switchgear room.  This provides a 220 V DC supply to the relay and control circuits in the Generator. Generator transformer and Unit transformer protection and control panels, 11KV  and 3.3 KV HT switchgear and 4.5 V LT switchgears Unit and station service boards and aux. Control panels. As told you earlier 220 volt DC system is backbone of the electrical system .To energise AC system you need DC system.

Battery Cells - Data Sheet ( Typical 500 MW power plant

            Guaranteed AH Capacity at 10 Hrs.discharge

            Rate 1 Volt / Cell at 27 C                                -           990 AH

            Designation                                                     -           KPH 990 P

            Recommended range of floating/trickle

            Charging voltage                                            -           1.4 -- 1.42 V/Cell

            Recommended range of boost charging

            Voltage                                                            -           1.53 -- 1.67 V/Cell

            Trickle charging current                                 -           1 to 2 MA /AH

            Boost charging current                                   -           198 A

             Open circuit voltage of cell when completely

            Discharged at 27 C at 5 hrs discharge rage   -            1.0 V

            Dimension (mm)                                           -            522 L x 192 W x 405 H

            Amount of specific gravity or electrolyte

            Per cell  required for first filling at 27 C         -          18 Lit / cell, 1.19 +- 0.01

            Specific gravity of cell when fully charged                1.19+- 0.01

            Max. electrolyte temp. that cell can withstand

            Continuously                                                  -           50 C

            Net dry cell weight                                        -           45 Kg

            With electrolyte                                             -           68 Kg

            Cell container material                                  -           Polypropylene

            No of cells / Bank                                         -           169

             Charger - I & II

            Input Voltage                                                  -           415 V+- 10%

            Output Voltage                                               -           220 V DC

            Float Voltage                                                   -           236 V DC

            Boost Voltage                                                  -           287.3 V  DC

            Rectifier current limit                                     -           400 A

            Battery current limit                                       -           198 A

            Auto charge over current                               -           40 A

            Steady state output voltage Regulation (For +- 10% I/P

            Voltage variation                                            -           +-1%

            0 - 100 % load variation

            at a time).

The above data was given from a data sheet of particular power station but this may vary marginally  power station to power station depending on system design and integration for which I am not expert.

Pre -commissioning  

- Battery,  battery charger and distribution boards are installed as per drawing.

- Cabling between the battery / battery charger and the distribution boards completed .

-     

      Basic testing .quality checks of components like insulation testing ,continuity testing , dimension checking etc are over. Charge the distribution board live at 220 V DC in  a safe and orderly manner without load and keep it charged for 24 hours.

- To carry tests and checks to ensure that all the components on the boards are operating satisfactorily including cables to all the remote points in the 400 KV substation and control room.

-  AC distribution board for input supply to be charged and commissioned.

-  Each module will be checked individually

-  Each outgoing supply will be tested up to the fuses at the remote end.

-  Battery E/F will be simulated for both the poles and E/F relay sensitivity will be

    checked.

-  Following  services will be  required during ,testing and pre –commissioning

 - 415 V,  3 Phases, 50 Hz supply ,Adequate running water, Suitable voltmeter, ammeter,

  

   thermometer and hydrometer,Variable resistance or water load for discharging the battery.

    Electrolyte for cells as per IS-266, Pure battery grade distilled water, Variable resistance box

    of 15 to 150 K Ohms, 1 No.  500 VDC megger, Multimeter , hand tools etc.

-Standard safety equipment for handling acid and battery .  Also fire prevention equipment like

extinguishsers , Exhaust fans to take out fumes if any , etc should be made available. Different

precautionary sign board in and around the panel battery room etc.

continued part -II battery charger commissioning.