ELECTRICAL SYSTEM OF A THERMAL PLANT CONCLUDING PART- ABC OF THERMAL POWER PLANT.

     Earth pit checking

Each earth pit is checked as mentioned in the standard check list of 

Switch yard earthing system

Check that the depth of the earth pit is 3.5 Mtr in case of pipe 

electrode 3 Mtr incase of rod electrode.

Incase of pipe electrode, earth pit must be having the layers of sand, gravel, salt, and coal with the thickness  as mentioned in the separate detail.

Thickness of the gravel must be 150mm  and the gravel must be spread over the switch yard area.

Main earthing and subsidiary conductors are to be ensured that 40/50 mm dia rod is used for the same.

GENERAL CHECKS :

Minimum spacing between electrodes shall be 6 Mtrs.

Earthing conductor shall be laid at least 300 mm below cable trenches and under ground service ducts, pipes, tunnels, railway tracks etc., if crossed.

Risers of 40/50 mm  dia MS rod shall be brought nearby equipment foundations :  1.  2 Nos. for each equipment earthing.  2.  1 No. for each structural earthing.

Risers end near the foundation shall be brought 300 mm above the ground level near foundation.

Earthing conductors along their run on cable trench ladder columns, beams, walls, etc. shall be supported by suitable welding/cleat fixation at intervals of 750mm .

Galvanized iron sleeves shall be provided for the passage of the conductors where ever it passes through the walls. Both ends of the sleeves shall be sealed to prevent the passage of water through the sleeve.

Earthing conductor embedded in concrete shall have approximately 50 mm concrete cover.

Auxiliary mesh of 1500 x 1500 mm size shall be laid at spacing of 300 mm below operating boxes of circuit breakers, isolators-main switches and earth switches.

All joints  shall be welded as per the drawing and IS code.

LAs, CVTs, and Earth wire down conductor shall be connected to the main earth mat through rod electrodes, rod electrodes shall be made out of 40 dia MS rods at site.

Lightning Masts down conductor shall be connected to earth mat through 1 NO. pipe electrode.

Transformer neutral shall be connected to earth mat through 2  nos. pipe electrodes.

Earth mat shall extend 2 mtrs outside the switch yard fence through rod electrode.

All equipment shall be earthed to at least two points on opposite side which shall be connected to different conductors of the earth mat.

Testing of earth pits  :  Earth pit resistance is measured with earth megger and it should be in the range of 1 to 1.5 ohms. The continuity between two earth pits connected together is checked using a multimeter and it should show exact continuity.

Earth resistance of earth mat is measured and it should be in the range of  0 to 0.05 ohms.

Check overlapping of joints are welded with no gap between two joints.

The connection of earthing network is checked according to the layout drawing. 

We will discuss 220V DC System  as this system is required to start AC system breaker. Therefore  a little knowledge on DC system will help to understand the electrical system.

 continued

ELECTRICAL SYSTEM OF A THERMAL PLANT - ABC OF THERMAL POWER PLANT.

In my earlier post erection of heaters ,de aerators  were discussed . beside that in Turbine package there are other auxiliaries both static and rotary such as different coolers , CEP ( condensate extraction pump ) , vacuum pumps , CPU ( condensate polishing unit) etc. Except CEP erection of other auxiliaries need not require any special strategy. For CEP erection foundation checking and canister erection is slightly crtical. CEP is a vertical pump therefore canister is to be erected before erection of CEP. It is sometimes noticed that CEP foundation is full of water at bottom most area and prevent  canister erection . It is recommended to repair the foundation so that leakage can be stopped or draining the pit before erection.

It was decided that next topics will be steam blowing as we have covered all the major equipment . However i received mails from young engineers to cover electrical system erection and commissioning . I am an electrical engineer but did not work with the system. Therefore what i have seen at site is written down. Value addition is to be done by individual. 
Earthing system is the mother of electrical system. You can not run an electrical machine without earthing.

The  earthing system consists of  following. Earthing is the basic requirement of any  Good electrical system. This is essential to protect human lives and also help us to detect fault in the system . Good earthing  provides smooth electrical operation  and avoid spurious tripping.

i.              Earth Pit

ii.             Subsidiary conductors

iii.            GI Flats

1.            EARTH PIT :   Each earth pit must be made as per their design normally that will be either pipe or rod electrode type earth pits.  In pipe electrode earth pit the depth will be 3.5 Mtr . Where as in rod electrode the depth will be 3 Mtr only.  In pipe electrode,  the earth pit must be made with different layers of  sand, coal, salt  and gravel  whereas in rod electrode, the rod will be inserted into the earth soil. BTG area earth mat was laid after  doing the PCC of the area. Risers were raised along the column foundation from two sides. Rods are welded at least 250 mm overlap so that firm contact is made.  Special earth pits are made for electronic panels and skids which are separated from electrical earthing. 

2.            SUBSIDIARY CONDUCTORS :  The conductors connects between earth pit and various equipments are subsidiary conductors.  They are connected with main earth mat  which is  600 mm depth by means of   raiser  and will be connected to each earth pit through test links.  The other end of the earth pit will be connected to the equipment.

3.            GI FLATS :  All the test links and equipment connections of the switch yard are  done with GI flats of 75 x 12 mm .  Inside the control building, the earthing connection is provided by 50x6 mm GI flats. 

Testing

-             To test the individual earth pits of 400 KV switch yard

-              To test the continuity of the earth mat

-             To measure the resistance of  total earth mat.

Testing Equipment

-          Earth  Megger calibrated.

 -     Calibrated digital multimeter.

State  of the plant

Erection of 400 KV Switch yard earthing network completed.

Test links and connections to various equipments disconnected for test.

Clearance from erection department for carrying out various tests obtained.

continued part -ii

HEATERS, DEAERATORS , PLATE TYPE EXCHANGERS , COOLERS ETC PART II _ ABC OF THERMAL POWER PLANT

Part I  i have discussed about the heaters ,coolers heat exchangers etc. In this blog I will discuss about the erection of  

DE AERATOR .

On erection point of view erection of  De aerator needs detail planning and equipment for erection .De aerator consist of  de aerator and FEED STORAGE TANK. De aerator is in one assembled unit and FST consist of three units pre fabricated but 

not assembled. Once assembled it becomes a very big round shaped

drum/ tank .There are other accessories also like platform around de aerator , saddle at the bottom of FST as such FST rests on it , stand pipes for level measurement ,misc pipe connection, misc structural items etc. Two dished ends are welded with respective pieces. This De aerator need to be lifted on 37M floor CD bay structure.

Approach to CD can be achieved from end only. If there is one unit then approach any one end will serve the purpose. If there is two unit then approach will be required from both the sides. If there is 03 units the approach from middle is required.

Minimum crane capacity required is 250 MT with adequate length of boom. You may have to remove a few member of roof structure

to accommodate the boom length and the angle. 

If you are having luxury 600MT/1200 MT cranes then you place your crane away from CD bay end but still you may have to remove some of the  roof structure for lifting FST and De aerator.

But having 600MT/1200MT will cost you more.

A 5T electric winch and 50 M pair of rail CR100 will be required to lay on the floor for dragging of FST. One end of the FST is lifted first and placed on the rail then dragged it to its position . Middle piece and de aerators are trial assembled at he bottom and then dismantled .This is done to avoid any mismatching during lifting at a height.2nd piece then lifted and locked temporarily on the floor . De aerator is then lifted and placed on the 2nd piece and bolted securely. Assembly was dragged into position by winch. Then third pieces were lifted.  

Different stages of FST erection shown in the above pictures.

HEATERS, DEAERATORS , PLATE TYPE EXCHANGERS , COOLERS ETC_ ABC OF THERMAL POWER PLANT

I have detailed major equipment of Turbine Package and their method of erection generally followed in India. There may be some differences during execution due project specifics but base is the same.

Already I have discussed main turbine , Generator and MDBFP and TDBFP.

In this article I will cover HP Heaters , LP Heaters , Deaerator , Plate type Heat exchangers ,coolers etc.

Erection Method of static equipment.

< All coolers are erected as soon as foundation is available.

   Normal foundation checking i.e level ,co ordinate w.r.t. turbine axis is checked before placement . Coolers are placed after checking the orientation. 30 mm to 50 mm packer plates are required for placement and subsequent secondary Grouting. Front piping opens after that as one end is fixed now. Same method is also followed for other heat exchangers. All the coolers are coming AB bay structures i.e Turbine hall.

HP heaters and LP Heaters

< In earlier days and upto 500MW plant all the heaters are erected vertically with the help of the TG hall EOT crane. An erection device is supplied with HP heaters for erection as clearance between EOT crane hook bottom and 10 M Turbine floor is minimal.Therefore erection device is necessary. 

Higher capacity unit like 660 MW and above heaters are placed Horizontally at BC bay of 17 M floor. Counter flanges for the connection of pipes to be checked .

Structural members for vertical heaters erection are to be checked , Specially welding between the members. It has been experienced that some of the members are not welded . Those are to checked and welded before erection. Also Level and co ordination are to be  checked and mark it in nearest column. This will help during piping erection for drawing reference. Vertical heaters are erected by EOT crane with a few packer plate in the bottom .As no grouting is involved therefore leveling and alignment is done through packer plate of different thickness.Once alignment is over then the heat is locked with temporary structure and release for piping.

Heaters require to be erected horizontally requires pre planning . All the heaters are erected one by one ,one after another side by side . Therefore pre planning is required to push heaters one by one . Heaters floor is concrete floor therefore guide rail is a must. Sequential erection is must otherwise there will not be enough space on the floor for overtaking . Location of heaters on 17 M floor such that approach is not available by EOT Crane. Heaters are unloaded on 17M floor at designated place.Dragging on rollers are carried out. Heaters are heavy weight items dragging to be done through particular place otherwise it can damage the concrete floor.

Picture shows horizontal heaters and Plate type heat exchanger . Erected and piping under progress from one end. 

continued to Part II

DISASTER AT KOLKATA / SHAME ON CONSTRUCTION INDUSTRY

Twenty six person lost their lives and around  one hundred are injured in this accident .Newspaper is full of stories , photographes ,weird theories about construction is going on endlessly. As a professional of construction industry a few statements need to be cleared in the mind of common man who does not understand construction industry

aa. Chief Minister is well within her rights for expediting its completion within March'16. One should  thankful to CM for taking interest on delayed project.I have seen and worked in different projects of national interest but never seen CM taking such interest for completion of the project. Ground rule is, series of meeting prior to CM meeting will be held for finalisation of dates and CM may take that or further squeeze the schedule and that becomes final for all the authorities.Therefore blaming CM for expediting is ridiculous.

bb. As reported in the newspaper span of this section is more than others . There will be engineering checks but experience says that there will be no problem in engineering as we are good in engineering and there may be three to four layers of check and such calculation is done through specialised software where in margin of error is minimum. The only area left is construction supervision ,methodlogy  and material etc. Civil construction does not require much items. Now all the major contracts contains a clause of cement procurement ( at five companies are mentioned with iS requirement). Therefore technically there will not be any problem in cement. Same procedure is follwed for TMT Bar and plates. These are modern procedures. Manufacturers are certified buy ultimate client , reputed consultant  etc. Major item left is HSFG bolts/HTC bolts which will be subject to scrutiny. \

cc. Therefore construction method is the kyt area to be looked into. KMDA is company which is more than fifty years old therefore their outlook is orthodox and may not fit for executing such time bound big project wherein the rquirement of decision and method /process is must . One need to look into DMRC execution as they follow most modern methods to carry out the project and KMDA may be found wanting . Old orthodox companies are averse to change their outlook. Therefore KMDA may not have a laid down procedure of quality management and safety management.. In spite of excellant management of DMRC they also faced the collapse of girder and number of cranes. All the root causes are construction supervison .

dd. IVRCL was awarded contract on 2009 that time company's performance was good . It is detoriated from 2013 onwards . Therefore awarding is wrong should not be a point to ponder.

Any company got a contract in a GOVT or PSU is very difficult to change in the midway whatever be the cause . It  may take more than a year to do so . Therefore official take softer root and compromise with quality and safety. This type of companies compromise with quality manpower ,try to bypass system etc. Therefore results into such happening.. If they had quality supervisor engineer at site during concreting then caution raised by workers should have been checked and accident can be avoided.

ee. Enquiry will be done for all aspect of labor supply the result will not come to the public. labor supply contractor cannot be blamed for this mishap as their role is limited to manpower supply and supervision of their manpower .

There will be number of state Govt agency will jump into this mishap to find out the cause but as it has been earlier only enquiry report will be bulky but the construction worker will not be benefited.

All arrest etc will not bring the dead man alive neither it will prevent recurrence of such incidents because we follow wrong procedure of vendor selection * based on finanacial value rather than qualitative value(*. we do not follow modern techniques of evolution of vendor..we do not follow basic labor laws and try offload the responsibility to incompetent people. This is a picture of construction industry. Only construction worker,supervisor and engineers are scapegoat.

There are many other aspect like insurance , compensation , minimum wages , PF , etc . All this aspect will come into play time to time. Whatever i saw in earlier cases this remain unsolved and political influence comes into play. Construction worker remain deprived of benenfit.

We request to CM to take immediate steps for improvement of process and monitoring the same otherwise this type accident will happen time and again.  

TURBINE DRIVEN BOILER FEED PUMP COMMNG CONCLUDING PART ABC OF THERMAL POWER PLANT

Steam rolling and actual overspeeding of Turbine (solo run of turbine) of Boiler Feed Pump

Check that Gear box and main pump are disconnected from the turbine.

Check  turbo -visory system is working properly (i.e calibration is over).

Check proper clearance at the holding down bolts of turbine casing and front bearing pedestal.

Check tightness of flanges in the turbine casing and exhaust line.

Check that all the temporary supports are removed from turbine casing, steam lines, oil lines etc.(i.e turbine is free from any restraints ).

Ensure that the TD BFP foundation is separated from the main turbine foundation all around and the support spring assembly of TD BFP is properly placed.

Start oil system. Keep the turbine on hydraulic barring. Record the measurements of oil system and turbovisory.

Install dial gauges for checking even expansion of the casing and pedestal as a precautionary measure ( back up of turbovisory specially during over speed test).

Warm up gland sealing steam supply header ensure measurement of sealing steam supply temperature.

Keep open casing drain and balance piston loop drain valves.

Observe vacuum created in turbine casing and exhaust line. Check for tightness of exhaust line and casing joints.

Keep the gland steam controller on auto and observe that it maintains properly.

Gradually open the exhaust butterfly valve in steps, keeping a watch on the vacuum in the condenser.

Check the protections of the turbine as given in the control scheme.

Keep open all drain valves  ( steam) associated with  TDBFP under commissioning.

Ensure governing oil system charged and ESV in close Condition.

Warm up the steam inlet line to turbine (Steam supply can be taken from any one of the available sources)

Ensure steam inlet pressure, temperature and flow measurements are healthy.

Reset the turbine and observe the trip oil pressure is available.

Ensure steam purity as recommended in O & M manual.

Ensure isolating valve in the steam supply source to turbine is opened full and all the drain lines are hot( important).

Ensure steam parameters are achieved as per O&M manual

Open emergency stop valve.

Raise the speed of the turbine gradually to 1500 RPM, keeping a close watch on bearing metal temperature, shaft vibrations, casing expansions and for any rubbing noise.

Check whether JOP is switching off and turning gear valve closes at speed of 500 RPM.

Soak the turbine at 1500 rpm for about 30 minutes observe the parameters are stablised.

Raise the speed of the turbine gradually to rated speed as per start up curve, given in O & M manual.

Monitor the behaviour of control valve during warming up speed and at rated speed for any hunting.

At rated speed soak the machine for 15 minutes, observe for all parameters. Adjust lube oil flow to bearings if required.

Carry out oil injection test of overspeed governor for few times to check repeatability of the action.

Keep exhaust hood spray system on auto. Ensure its operation.

Carryout actual overspeeding test of the turbine if the parameters such as vibration ,temperatures ,expansion within limits

If actual overspeed trip does not occur at required value, hand trip the turbine and adjustment to be done at emergency governor.

Keep the hot turbine on hydraulic barring, ensuring gradual cooling down.

Commissioning of Turbine Driven Boiler Feed Pump.

Ensure alignment readings are logged and cleared for coupling.

Couple turbine with BFP and Gearbox. Couple gearbox with booster pump.

Crack open feed water suction isolating valve and vent out air in all the vents.

Flush and shut the booster pump casing drain and BFP drain and interconnecting pipe drain.

Check all the instrument tapping point isolating valves are open and that all drain and equalizing valves are shut.

Gradually open suction isolating valve keeping watch on the trend of differential temperature of top and bottom of the main pump casing.

Check mechanical seal water control isolating valves are open for Booster pump and BFP.

Check magnetic separator isolating valves for BFP seal water are open.

Ensure cooling water flow through all coolers.

Ensure isolating valves in re-circulation line and leak off line are open.

Ensure all c&I points are healthy and available at  DCS/local.

Ensure proper clearance at the holding down bolts of the booster pump and main pump.

Check the booster pump and main pump.

Ensure oil system in service. Start jacking oil pump.

Engage the main pump with turbine.

Check the freeness of Turbine rotor along with booster pump and main pump by hand barring.

Disengage the main pump and keep the turbine on hydraulic barring and prepare the turbine for steam rolling.

When the turbine is ready for steam rolling, stop the turbine and engage the main pump with turbine.

Keep the turbine along with main pump and booster pump on hydraulic barring.

Raise the speed of the TDBFP to rated speed as per start up curve.

Keep the pump on recirculation flow of approximately 250 T/hr for 8 hours to observe and record performance.

Check the speed control and pressure variations during operation of BFP for drum level control.

During trial operation feed water suction strainers of Booster pump and BFP should be closely monitored.

Stop TDBFP after trial run, put turbine on hydraulic barring .

TURBINE DRIVEN BOILER FEED PUMP COMMNG PART-III ABC OF THERMAL POWER PLANT

Commissioning of Governing System of BFP Turbine

Check that the oil lines from governing rack to governing elements and at the governing rack are as per drawing with proper slope.

Ensure main and auxiliary control valves lift reference indicator is fixed and set to zero position.

Check the damping valve in HP and LP secondary oil lines are kept open by few turns.

Check the filter elements at the control rack of the duplex filter are clean and healthy.

Ensure emergency stop valve open / close limit switches mounted and wired.

Switch off the supply to the following solenoids.

a)         Trip solenoid valves,

b)         Remote reset of trip lever solenoid valve.

c)         Power supply off to the I/H convertors.

Ensure lube oil pump in service and charge governing oil to the governing system.

Ensure all pressure switches and pressure gauges in governing rack are charged and their drain valves are closed.

Reset the turbine locally and ensure following:

a)         Trip oil pressure more than 5.0 kg/cm2.

b)         Stop and control valves in closed condition.

c)         HP and LP secondary oil pressures less than 1.0 kg/cm2

Ensure oil temperature of 45-50 deg C during governing system adjustment.

Opening / closing of emergency stop valve.

Ensure power supply for solenoids (It will be normally in deenergised condition)

Ensure no steam available ahead of ESV and live steam isolating valve in closed condition.

Give open command to ESV and observe the following sequential  operation of solenoid valves .

a)         Both solenoids energises. Oil pressure above piston more than 5 kg/cm2 and below disc 0 kg/cm2 

b)         Solenoid  deenergises oil pressure above piston more than 5 kg/cm2  and below disc more than 5 kg/cm2  .

c)         Solenoid   also deenergises. Oil from above piston starts draining gradually through orifice and ESV opens.

d)         When ESV full open oil pressure below disc is more than 5 kg/cm2  and above piston ‘0’ kg/cm2 . Adjust open limit switch and check feed back available in control room.

By tripping turbine trip lever, ensure tripping/closing of ESV. Check close feed back available in control room.

Reset the turbine from remote by energising corresponding  solenoid  Ensure the same solenoid gets automatically deenergised when trip oil pressure raises more than 4.5 kg/cm2  through pressure switch.

Switch on power supply to HP and LP I/H convertors.

Give 4 mA current to HP I/H convertor with external source or through governor panel.

Ensure HP sec. Oil pressure of 1.5 kg/cm2. If not set the pressure to 1.5 kg/cm2  by adjusting potentiometer in I/H convertor.        

Check that the control valve servomotor pilot is rotating freely and having a slight up and down movements.

Check the main control valve servomotor is just opened, by 0.2 mm. The start of opening can be measured by fixing dial guage on servomotor.

If the start of opening is not correct adjust the adjustment screw of the pilot slide to achieve the start of opening.

Raise the current to I/H conventor to 20 mA. Observe HP sec oil pressure increases to 4.5 kg/cm2 . If not adjust the potentiometer of I/H convertor to achieve the pressure.

Check the main control valve servomotor lift is maximum. If the lift is not correct adjust feed back angle to obtain the full lift.

Check and adjust auxiliary control valve servomotor similarly as done for main control valve .

Record control valve characteristics (from 4 mA to 20 mA to I/H convertor)

1.         Current  mA Vs HP sec oil pressure Vs main control valve lift.

2.         Current to LP I/H convertor mA Vs LP sec-oil pressure Vs Auxiliary control valve lift.

Compare the characteristics and ensure these are in line with governing adjustment diagram/ shop floor test protocol.

Operate the tester for ESV and ensure partial closing of ESV and put back the tester in normal position, ESV opens back to full open position.

Energise the remote trip solenoid  and ensure the following.

a)         ESV closed.

b)         Main control valve is closed

c)         Auxiliary control valve is closed.

d)         Trip oil pressure is zero.

continued - PART-IV