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.

Few  portion of SLD are given to understand the flow of power to different LTMCC.

wish all my readers happy new year 2017.

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

415 Volts LT switch gear consists of two bus sections A&B with a bus coupler between them. The two sections are fed from two individual power transformers 1A and 1B in case of switchboard & up stream breakers in case of MCCs & ACPs.The Transformers get their supplies from 11 KV unit switchgear feeders TRF1 & TRF2.  415 Volts Unit service switchboard feeds the boilers and turbine auxiliaries,(MCCS) Soot blower MCCs,Battery chargers(220 V ,24 V DC) Emergency switch gear and other unit auxiliaries.The single line diagram of the Unit service switchboard is given below :

LT SWITCHGEARS in typical 500 mw Project:     

I.SWITCHBOARDS

1.  Unit emergency switchboard

2.  Unit Service Switchboard

3.  ESP-1 to 4 LT Main switchboard

4.  Station service switchboard

5.  Ash system compressor switchboard

6.  Ash water Power House switchboard

7.  Off side plant services switchboard

8.  Switch yard Service Switchboard

9.  CHP Switchboard-1

10.    CHP Switchboard-3

11.    CWPH Switchboard

12.    ADM Bldg. Switchboard

13.    Raw Water Pump House Switchboard

14.    Ash Water Re circulation Service switchboard

15.    Sea Water Power House switchboard

16.    Bunker service switchboard

17.    Sweet Water Makeup Power House switchboard

II Motor Control Centres

1.  Turbine MCC

2.  Turbine valves MCC

3.  Coal mill MCC

4.  Boiler MCC

5.  Boiler Valve MCC

6.  Boiler Damper MCC

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7.  Boiler AC Distribution Board

8.  Track Hopper MCC

9.  PT MCC

10.    DM Plant MCC

11.    CMB MCC

12.    ETP MCC

13.    Hydraulic Generation Plant MCC

14.    Chimney lighting MCC

15.    Emergency Chimney board

16.    ESP Area MCC

17.    ESP A/C & Vent MCC

18.    Ash SILO MCC ()

19.    Air Washer MCC

20.    AC & Vent MCC (

21.    Aux. Boiler MCC

22.Station AC Distribution Board

III.Aux Control Panels:

ESP – 1 to 4 Aux Control Panels 

FOUNDATION OF MCC ROOM WHERE PANEL WILL BE INSTALLED . PANELS ARE BEING SHIFTED FOR ERECTION. TRAYS FOR CABLE IS RUNNING BELOW THE  PANEL.

LOCATION OF MCC ROOM IN THE POWER HOUSE 

PANEL LINED UP FOR ERECTION.

Every 415 V LT  switch gear consists  of a number of equipment and it is proposed that these will be checked individually using standard check lists and test procedures which will be recorded in the testing schedule. Items like transformers (LT and HT side) , Breaker and its circuit, different type of relays and their settings , Bus bars etc. If these equipments are checked individually then commissioning of the particular system will take very less time. All organisation prepared detailed documentation for checking the same . Some of the organisation also outlined about the IMTE required for the testing and also tools are required to do testing work.

STATUS OF THE PLANT.

All panels are erected , aligned and individually tested for any mechanical damage . Also check all the power contractors ( a waring was issued in last despatch.

Testing equipment required.

1. Variable 03 phase 415 v AC supply and also 220 v DC supply.

2. Insulation tester (megger) hand operated / electronically operated 500V

3 Digital multimeter ( 3 and half digit).

4. Analogue multimeter , Ampere meter , voltmeter 

5. Phase sequense meter.

6. Injection test kit for injecting current /voltage to relays for testing cut in and cut out

7. Micro ohm meter 

8. Battery operated continuity tester .

9. Hand tools of standard size and make.

All IMTE must calibrated and certificate should be available with leader .Cross reference to be mentioned in the testing report.

continued to PART -III

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