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

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