skt-maintenance of electro-mechanicl equipment of shp

8/9/2019 Skt-maintenance of Electro-mechanicl Equipment of Shp

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MAINTENANCE OF ELECTRO-MECHANICL

EQUIPMENT OF SHP

S.K.TYAGI, CONSULTANT, AHEC,IIT, ROORKEE


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INTRODUCTION

Experience of running hydropower station reveals that even after detailed project planning/quality control measures taken at various stagesfrom inception to commissioning several unforeseen problems do take placeduring the operation and maintenance resulting in forced outages/lowgeneration and load shedding etc. causing misery to the consumers andundesired set back to the overall economy.

The main reasons which can be attributed to these undesiredphenomenon/events (during operation), are that the hydro power stationequipments are custom built in construction and tailor made at eachdiscipline viz. design ,manufacturing, erection, commissioning, operation andmaintenance etc.

The equipment cannot be fully assembled or tested at ManufacturersShop. Maintenance exercise at predetermined time interval is therefore,planned to ensure the following objective:


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Q uality and reliable operation of equipment on long term basisthrough identified periodic inspection /checking of componentsand subsequent replacement /rectification parts, wherever required.

Maximum availability of equipment with least number of shut downs by ensuring that the rate of deterioration of anycomponent does not exceed the life expectancy of theequipment at any stage. Periodic /planned shut downs shouldbe arranged to avoid long term forced shutdowns.

Eradication /non-repetition of operational problems bytimely analysis of the cause of faults/problems and replacementof short term solutions by long lasting and permanent ones.


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REQUIREMENT OF EFFECTIVE MAINTENANCE

In addition to planning maintenance and allotting suitable time interval onthe basis of water supply availability following items also require closewatch otherwise it may become difficult to adhere to the schedules.

Man power planning and arrangement is most essential as withoutexperienced / skilled staff any maintenance program may fail.

Planning and arrangement of spares and consumable in advance so thattime is not lost in arrangement of the same after taking shut down.

The maintenance engineers should have in his possession all theerection and commissioning log sheets, document to establish a record of installed clearances, parameters, alignment results, test characteristics of

all the power plant equipment.

These may be required at the time of diagnosis of the operationalproblems as well as defined maintenance purpose .


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Log sheets of the previous maintenance exercise carried out onthe machines. These may be required to compare with theclearances/ settings/characteristics achieved during presentmaintenance.

History registers of various machines duly recorded with all theabnormalities observed on the machine and details of actiontaken to provide a guide line for future maintenance exercisemust be maintained at the power station.

Logging of the performance characteristics of the power plant ondaily basis recording all the abnormalities and misbehaviors (if

any) of the total plant observed during its operation from onemaintenance exercise to another .


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G UIDELINES FOR MAINTENANCE OF SMALLHYDROPOWER STATIONSIn most of small hydro plants preventivemaintenance approach is preferred over other approaches. Following inspection checks are donein this type of maintenance:

Daily checks Weekly checks

Monthly checks Quarterly checks

Half yearly checks Annual inspection and maintenance Capital Maintenance


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PREVENTIVE MAINTENANCE OF HYDRO TURBINE &AUXILIARIES1.1 Daily Checks1 .Foundation parts and Expansion Joints:

C heck for any leakage in draft tube manholes, spiral casingmanhole, expansion joint.

2.Vacuum Breaking Valve / A ir A dmission ValveC heck the working of both vacuum breaking valve and see

that there is no abnormality in the springs, seats etc.

3. W ater Seal and A ir Seal:i) C heck the position of water leakage of the water seals and

see that there is no excessive splashing and water level donot rise in top cover ii) Note water pressure of water sealing /under sealing.


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4 .Turbine Guide Bearing:i)C hecks the oil level(stand still machine /running

machine)ii)Note the temperature of bearing and check that the

temperature of oil and guide bearing pads are withinlimits.

iii)Note the maximum and minimum temperature andcompare with readings of the previous day.

iv)C hecks for any oil leakage from the bearinghousing and check that oil is flowing above the bearingpads.

5.Guide Apparatus:C heck any leakage from GV servomotor and its

piping


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6 .Oil Leakage Unit:i) C heck any leakage from pipe line jointsii) C heck its satisfactory running on Auto.

7.Top C over D rain System:i) Main supply of ON for D PM.ii) Vibration, noise in the pump motor.

iii) Any leakage form the water pipingiv) W orking and water pressure of the ejector.

8. C entralized Grease Lubrication System:i) C heck for any leakage from grease pipes,

unions and nipples.ii) C heck grease container is filled with grease


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9 .Oil H eader: (For Kaplan)i)C heck from Perspex sheet manhole any splashing of oil fromtop and bottom bush.

ii)C heck any oil leakage from the jointsiii)Note the pressure difference of opening and closing side of

runner.10 .Oil Pressure System:

i)C heck if there is any abnormal sound in the runningof the motor and pump unit of OPU.

ii)C heck the oil level in pressure accumulator.iii)C heck any oil leakage from oil piping and its valve.iv)C heck for over heating of motor.v) Note the timing of OPU pumps running and

compare with previous day running hour


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Weekly Maintenance ChecksGreasing of guide vanes and servomotor with centralized

grease lubrication system and manually.-Grease in the container shall be checked.-C heck for any leakage-W orking of end pressure relay and solenoid valves, if defective, should be reported.

Cleaning of throttle filters in the governor mechanical cabinet.Cleaning of governor compressor air filters and checking of

oil levels.Checking physically oil of OPU of the running machine, after

taking sample through the sampling cock, do the crackle testfor detecting presence of water. Take remedial measures.

Check oil level of all the bearingsCheck wobbling of shaft at coupling flange and at oil header

servo tube.


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Monthly Maintenance Checks A ll the checks covered in weeklymaintenance as above are carried outmonthly also. But while carrying out

these checks more attention is paidand short shutdowns, if required, for rectification are taken.


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Annual Inspection and Maintenance of Hydro Turbine

A fter successful running of plant for about one year few weeks are required tobe allotted to inspect rotating parts, control equipment and measuringinstruments etc. and analyze cause of change in the performancecharacteristics, if any. Modify / repair / replace (wherever required) the worn outparts in order to prevent forced outages of machine at later date.

After every five years it is necessary to inspect the machine more critically for abnormalities like fatigue defects for excessive wear and tear of some parts or

any change in original parameters / clearances etc. This exercise becomesvery essential in cases where performance level has been observed to havegone down in 5 years operation.

Following checks and inspections should be carried out during annual and fiveyearly maintenance:


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Following checks and inspections should be carried out duringannual and five yearly maintenance:Foundation Parts:

1 .C heck condition of water path system. The damage due tocavitation and wear to be rectified2. C heck painting of spiral casing.

Runner:1 .C heck the condition of the surfaces of the runner hub andthe blades. The damage due to cavitations & wear to berectified by welding and grinding. It is, however, to be ensuredthat hydraulic profile of blades is not disturbed.2. C heck the runner blade seals by pressurizing the system.C hange seals if necessary. No oil leakage is to be allowed(Kaplan only).3. C heck the runner sealing for hermetic tightness, leakages of water in the runner hub is not to be permitted (Kaplan only).


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Guide Apparatus:1 .C heck the presence of rubber sealing cords and the tightness of therubber sealing between the adjacent guide vanes in fully dosed position of guide apparatus.2. C hange oil in the regulating ring.3. R eplace damaged shear pins.4 .C heck cup sealing of guide vane journals and replace, if necessary.5. C heck the bushes of guide vanes and change the worn out bushes of guide vanes journals.6

.Inspect the servomotor and change the seals, if these are worn out.Guide Bearing:

1 .C heck the condition of rubbing surfaces of guide bearing . C lean thesurface and polish it with the help of chalk powder.2. Adjust the clearances by moving the segments with the help of adjustingbolts.

3.Thorough cleaning of housing is necessary.4 .C heck all the R TD s and TS D s, replace damaged one.Shaft Gland Seal and A ir Seal:

1 .C heck the condition of rubbing surface of sealing rings. In case founddamaged change the same.2. C heck pipe lines and piping joints for leakage, if any, attend the same.


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Emergency Slide Valve:1 .C heck the functioning of emergency slide valve and thecondition of inner surfaces.2.Swift return of the valve in its original position after emergency operation should also be checked.

Centralized Grease Lubrication System:i) C heck satisfactory working of C GLS system.ii) A ttend wherever fault is located.

OPU:1 .C heck and attend leakage from any valve or flanged jointsetc.2.Provide proper lubrication to the bearings of pump motor.3. C heck filter and repair, if required.4 .C lean oil sump, refill with centrifuged oil.5. C heck setting of the float relays for proper sequence of operation of pumps.

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Oil H eader(Kaplan only)1 .Measure clearances of upper and lower bushes, if found increased getthe bushes replaced.2. C lean the oil bath.3. C heck the rubber cord fixed below the oil guide to check any oil dippingon the exciter winding.

Oil Leakage Unit:1 .C heck satisfactory working on Auto as well as manual.2. C lean the tank.3. C heck the pipeline joints and valve for leakage, attend wherever necessary.

Oil C ooling Unit:1 .C heck all the oil and water pipe lines for leakage and attend if necessary.2. C heck satisfactory working of all cooling unit.

Governor Mechanical C abinet(if applicable):1

.C heck filter and throttle, if found damaged replace the same.2. A ttend leakage of oil through pipe line joints and valves.3. C heck auto rod setting, if found disturbed; set the same.4 .C heck alignment of feedback wire rope pulleys


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Capital Maintenance of Hydro Turbine

Overhauling or capital maintenance of hydro set is usually recommended after about 10 years of operation services. The whole unit is to be stripped off during capital

maintenance and all the defective/worn out parts/components repaired /replaced withnew ones.

Then the unit re-commissioned as per originally established commissioning practice of the power station.

A fter capital maintenance the units are subjected to all periodic maintenance exercisesoutlined above before it reach the next cycle of capital maintenance.

Following checks are to be exercised during capital maintenance of a hydro set:

Turbine Bearing:1 .D isassembly, inspection, cleaning, measurement of clearances, polishing of guide

pads, centering of shaft, reassembly, setting of clearances, filling of oil sump withfiltered water.2. C heck the temperature sensing device, if necessary, replace with new ones.

Gland Seals and Isolating A ir Inflated Seals:D ismantling, inspection, cleaning and reassembly. R eplacing of worn

out rubber flaps or carbon segments, if necessary.


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Clean W ater System:C lean water pipes are dismantled, cleaned,

reassembled with new gaskets; allthe valves are attended for any leakage etc.Guide Vane Servomotor:

D ismantling for inspection and cleaning.R eassembling and replacing the seals with new ones,if necessary.Guide Vanes Bush H ousing :

1 .R emoving, cleaning and inspecting for wear andtear replacing with new ones if found necessary.R eplace seals, if necessary.2.Guide vanes are reconditioned and proper beddingin closed position is ensured.


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Governor:1 .C leaning and checking OPU pumps. R eplace bushes, bearings etc. if found worn out. A lso attend pump motors.2. C leaning OPU sump and pressure accumulator and refill with filtered oil.3. A ttend oil pipeline flanges and valves for leakages.4 .C heck setting of pressure switches installed for Auto operation for OPUpumps.5. A ttend Governor Mechanical cabinet for leakages, loose links. C leanmain and pilot slide valves. Set Auto rod as per designs A lpha Beta settingmay also be checked in case of Kaplan turbine.6 .C heck electrical circuit. Tightening of all the connections should be done.

Under W ater Parts1 .Inspect condition of welded seams of penstock, spiral casing and drafttube, rectify defects by welding and grinding. Penstock filling line valve,spiral drain valve, draft tube drain valve should also be checked and

repaired.2. C leaning and painting of penstock, spiral casing and draft tube liner.


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Runner 1 .D ewatering of draft tube and fabrication of platform in the draft tube for inspection of runner.2. If it is a Kaplan R unner test the same after applying full governor pressurefor leakage of oil.3. R eplace blade seals, if necessary.4 .Inspect blades of the runner and make up profile of the blades bywelding. D ue to erosion, abrasion and cavitations, material of the bladewashes away with passage of time. A fter weld repair heat treatment anddynamic balancing is must before installation.5. In case the runner is found to be irreparable arrange to replace the samewith new one.6 .In case of Kaplan runner hydraulic test is also required to be done.

Turbine AuxiliariesDPM

i) Inspect top cover drain system; overhaul the ejector and drainage pumps.ii) C heck pipe lines and valves. R eplace gaskets and other parts, if necessary.


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Oil C ooling Unit1 .Overhaul cooling pumps2. A ttend all the valves and pipe line for leakage

Centralized Grease lubrication System1 .Overhaul greasing pump.2. C heck whole greasing lines. R eplace worn outvalves and gaskets etc.3. C heck all the nylon pipes connected with the guidevane bushes. R eplace damaged pipes.4 .C heck that all the guide vanes are receiving greaseproperly.

Oil Leakage Uniti) C heck the oil leakage unit overhauls the pumps.

ii)C lean tank and check that float is properly workingiii)C hecking all the pipe liens and valves for leakages.


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Preventive maintenance of the generator Preventive maintenance ensures a long trouble free operation of the generator.

Given in the following table are the recommended daily, monthly, quarterly, half yearly & yearly maintenance checks to be conducted on the generator.


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Capital Maintenance of Hydro generator Dismantling:

Decouple generator shaft and turbine shaft after recording guide

bearing clearances air gaps between stator & rotor air gaps of main, pilot exciter & PMG etc if mounted on shaft.

Dismantling other components one by one in proper sequence tillrotor is free to be lifted.

Rotor should be taken out very carefully and kept in rotor assembly pit duly bolted with base plate. R otor rim to besupported by block and jacks all around the circumference.

All stator air coolers are to be dismantled and kept for testing andrepair.Braking & jacking units to be dismantledAll cares are to be taken during dismantling to ensure safety of all

components, fasteners, pins etc.Prior arrangement of proper T&P, special T&P, slings, D -shackles

etc, is also necessary.


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Maintenance of R otor -The rotor is to be thoroughly cleaned with dry compressed air.-C heck general condition of coil and pole, clean with dry

compressed air.-C heck the coil joints for any cracks due to overheating etc.-C heck field coils and rotor leads for inter turn fault. Measureimpedance of coils by applying 60 to 100 V AC , 5 0 C /s. If impedance of some coil is very low (< 4% ) they must bechecked for possible inter turn faults.-Shaft is to be checked specially at G.B. journals for any marksroughness etc. R emedial measures are to be taken if marks,roughness is found.-C heck top and bottom rotor fans, if found damaged replacethe same.


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-C heck tightness of all the joints of rotor spider andextension arms-C heck tightness of rotor rims, pole key rim keys etc.- A fter rectification of all defects and thoroughcleaning, spray paint the rotor with insulating red gelpaint.-Keep the rotor covered with asbestos cloth toprevent deposit of dust and fire safety.- A ll safety precautions for external damage, fire etcare to be taken in the service.

Maintenance of brush gears and slip rings-C heck if there are any grooves, roughness highpoints use oil stone for rectification-C heck brush gear connections clean all the insulatedparts with dry compressed air.


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Maintenance of BearingGuide bearings

-C heck condition of H ousing-C heck condition of Pads, if required, bedding is to bedone-In case babbit material found damaged or thinned,rebabbit pads with proper grade of white metal.-C heck insulation of pads, if found damaged replacethe same. C heck IR value-C heck all R TD s & T S D s

Thrust Bearing-C heck condition of pads, if found some damage tobabbit material, get rebabbiting done-Bedding of pads to ensure removal of high pointsand having desired contact area.


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-C heck bearing insulation by measuring IR value.R eplace insulation if found damaged.-C heck insulation of vapor seal also and replace, if found damaged-C heck condition of housing, pivot points of thrustbearing.-C heck all pressure gauges, level indicator.-C heck all R TD s & T S D s

Maintenance of A ir C oolers-C lean inside and outside of air cooler tubes-C heck for any tube leakage by pressurizing to apressure slightly more than max. expected workingpressure-If more than 10% tubes are leaking change full set of tubes or change only leaking tubes

- A fter repair paint the body of coolers.


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Maintenance of Oil C oolers-C lean inside and outside of cooling tubes-C heck for any tube leakage by pressurizing to a pressure

slightly more than maximum expected working-R eplace full set of tubes if more than 10% of total tubes areleaking.

Maintenance of H .S. Lube system-Inspect bearing and grease, if necessary-C heck the condition of hoses, if necessary replace-C heck for any leakages and take remedial measures.-C heck pressure gauges etc.

Maintenance of Flow relays, visual flow indicators and flow meter:-Inspect, clean water passages remove silt.- A ll defective meters are to be replaced.


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Braking and jacking system:-C heck brake units and clean inside outside of theunit-C hange seals-C arry out hydraulic test-C lean the filters, bowl of lubricator -C heck brake track, tighten dog clamps-C heck working of brake limit switches.-R eplace brake lining

General checks-C heck condition of current carrying leads.-C heck all water & oil valves for their proper working-C heck general operational healthiness of allauxiliaries-C heck proper working of overspeed device.


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PREVENTIVE MAINTENANCE OF POWER TRANSFORMERSThe maintenance of transformer is an ongoing process and stress should be onpreventive maintenance rather than acting when a fault occurs. A schedule of maintenance activities is drawn and tabulated below. This is applicable to Main, A

uxiliary, Station & distribution transformers.


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NOTEI) As there is continuous deterioration of oil and insulation in a transformer,

it is preferable that the core and windings and the inside surfaces of tank bethoroughly cleaned for any deposits etc. at regular intervals. This can bedone while the transformer is in position. C lose all valves connecting thecooler circuit/ radiators to the tank. D rain oil from the tank while letting thedry air to go inside. C lean core and winding by hosing down clean dry oilthrough the inspection cover. R emove dirty oil from the tank and wipe off this oil from the tank bottom. Let there be a continuous entry of dry air intothe tank while the cleaning activity is on so that there is a minimum contactof the transformer core and windings with the atmospheric air. Similarlydrain oil from cooling circuit and radiators and fill dry clean oil.

W henever transformer windings are to be taken out due to any reason such

as to repair a damage, thorough washing due to sludge formation or for thorough inspection to locate a fault as a result of D G A or some other tests,after carrying out the necessary work for which the transformer wasopened, do the following also:


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Tighten all coil clamping screws to remove looseness from the windings, if any.

Tighten all nuts and bolts whether metallic or made of insulating material onmechanical and electrical joints.

Tighten core yoke bolts, core-clamping screws etc.

Under the normal operating condition transformer has a useful life of about 25-3 0 years. This may vary considerably depending upon the overloads it has carried andthe temperature at which it has worked during its span of operation.

Therefore, for any future planning it may be worth while to know well in advance theremnant life of the transformer in service.

This can be done by assessing extent of degradation of cellulosic paper throughfuran content in transformer oil or / and degree of polymerization ( D P) of paper. It isproposed to carry out this study after a period of 2 0 years of service.

A fter knowing the remnant life in a transformer, the action can be planned inconjunction with life assessment studies on generating unit.

As these are comparatively new studies, the data are still being built and oneshould go by the re-commendation of the Test Laboratory.


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skt-maintenance of electro-mechanicl equipment of shp

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