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

COMMISSIONING

Carry out functional checks to prove the operation of interlocks/inter-tripping between the 415 Volts incoming and bus coupler breakers in each switchboard & MCC.

Carry out functional checks to prove the operation of interlock and inter tripping between the 11 KV upstream and 415 Volts circuit breaker wherever required.

GENERAL CHECKS:

Inspect any physical damage in the bus bar, insulation, panel doors, power & sliding contacts etc. And to be rectified if found and make individual unit ready for commissioning.

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

Checking the tightness alignment & clearance of bus bars ,smooth ness in racking in & racking out of modules, proper making of sliding contacts, tightness of input power cables and module power control o/ps & control internal wire connection.

Inspect all contacts , relays and make sure that any blocking used for shipping purpose is removed. This is a must check before commissioning .

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

Check door interlock mechanism.

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)

Test the insulation of boards with 500 v dc megger & the value should be as per the relevant is specification (more than 5 mega ohms)

Check closing & tripping interlocks , overload release setting of all air circuit breakers in the panel.

Check the protection circuit wiring connections by conducting primary injection current

Check the input power cable terminations from transformer secondary

Ensure the phase sequence and ct links are proper before charging the panel.

check closing & tripping mechanism operates smoothly both manually and electrically

Space heaters & thermostat shall be in good and running condition.

Energising checks

Check that communications have been established between 11 KV

switchgear,415 Volts switchgear and the UCB. Also check the safety

clearance available before charging.

Ensure that the 11 KV and 415 Volts circuit breakers for charging are in isolated position. Also tie breakers between Emergency switchboard No-1 and bus coupler breaker at unit service switchboard No-1 are OFF and isolated.

Ensure that the 415 volts V.T.s for Section A & B are in position and fuses in service.

Ensure that all the outgoing feeder breakers, contactors and Isolators of 415 Volts switchgear are off and isolated.

Ensure that the control circuit fuses for 11 KV and 415 volts circuit breakers for the power transformers and those for the 415 volts buscoupler breaker of switchboard are put on.

Ensure that protection relay settings are correct for feeder VCBs at HT switchgear and incomers at LT switchgear.

ENERGISING PROCEDURE:

Energise the 415 volts switchgear control circuit bus from its normal source of supply.

Put the 415 volts circuit breaker(Incomer 1) in test position with selector switch in LOCAL.

Close and open the breaker from local and check that the status indications are correct.

Carry out the tests for the next Incomer and buscoupler for the same LT Switchgear.

Put the 11 KV breaker for power transformer - A in test position with the selector switch to interlock ‘OUT” position.

Close and open the 11 KV breaker from local and check status indications are correct.

Put the selector switch to interlock IN and close and open the breaker from UCB and check that status indications are correct.

Carry out the tests for 11 KV breaker Transformer – B.

Put the 11 KV breaker transformer A in service position with the selector switch to interlock ‘IN’ position.

Close the 11 KV breaker from UCB to first energise the Power Transformer A.

Open and close the 11 KV breaker

Note the ammeter for the transformer H.V side for any abnormal current. Check the transformer externally for any abnormality.

If 8.3.13 ( bus coupler breakers )is O.K.,put the 415 Volts breaker (Incomer 1) for Transformer A in SERVICE position with the selector switch in REMOTE.

Close the 415 Volts Incomer 1 breaker from UCB to first energise the section A of LT switchboard.

Check the ammeter and voltmeter reading and noted in the register.

voltage relays are in picked up(energised) condition. Check phase rotation.

Check externally for any abnormality with the 415 Volts LT switchboard.

Initiate tripping through overcurrent relay on the 11 KV side and check that both the 11 KV and 415 Volts breakers of the power transformer A trip.

Put the 415 Volts bus coupler breaker for LT switchgear in SERVICE position with the selector switch in ‘REMOTE’

Close the 11 KV and 415 Volts breakers(Incomer 2) for power transformer B in “TEST” position

Close the 415 volts bus coupler breaker from UCB to first energise the section B of the LT switchgear

Note the ammeter in incomer-A panel for any abnormal current. Also note the voltmeter in bus section B for correct bus voltages.

Check that the under voltage relays in section B are in energised condition.

Check externally for any abnormality with the 415 Volts in bus section B

Switch off the bus coupler breaker

Put the 11 KV breaker for power transformer B in ‘SERVICE’ position with its selector switch to interlock ‘IN’.

Close the 11 KV breaker for power transformer B from UCB to first energise the transformer.

Open and reclose the 11 KV breaker

Note the ammeter on the 11 KV side of the transformer for any abnormal current

Check externally for any abnormality with the transformer.

Put the 415 Volts breaker(Incomer 2) for Transformer B in SERVICE position with its selector switches in ‘REMOTE’

Close the 415 volts breaker for the transformer to energise the bus section B

Note the ammeter and voltmeter in bus section B for any abnormal current and voltage.

Check phase rotation of B section and phase in & phase out between section A & B

If everything with the transformers and the LT switchgear are O.K. keep the transformers and the 415 volts bus energised for 24 hours.

After 24 hours check that there is no abnormality with the transformers and the 415 Volts LT switchgear. Also check periodically bucholtz relay for any chapped gas on in.

For MCCs & Aux. Control panels ,Upstream breakers and interconnecting cables will come into picture in stead of 11 KV outgoing feeder and power transformers.