Operation and maintenance of hydropower stations planning and management – an Indian perspective CONTENTS
1
INTRODUCTION
1
2
PREVENTIVE MAINTENANCE OF HYDRO TURBINE
1
3
REQUIREMENT OF EFFECTIVE MAINTENANCE
2
4
MAJOR MAINTENANCE PROBLEMS OF WATER TURBINES
2
4.1 RUNNER 4.1.1 EROSION DUE TO SILT 4.1.2 CAVITATION RELATED CRACKING AND WEAR OF THE RUNNER 4.1.3 PRECAUTION IN WELDING OF RUNNERS 4.2 TURBINE GUIDE BEADINGS 4.3 GLAND SEALS 4.3.1 CARBON OR FERROBESTOS SEGMENT TYPE 4.3.2 RUBBER FLAP TYPE 4.4 GUIDE VANE SERVOMOTOR 4.5 GOVERNOR 4.6 GOVERNING OIL SYSTEM 4.7 HEADER
2 2 2 2 2 2 2 2 2 2 2 2
5
2
PREVENTIVE MAINTENANCE OF HYDRO GENERATORS
1 Introduction Experience of running hydropower stations in India has shown that even after careful project planning and good quality control measures from construction to commissioning, unforeseen problems do occur in service resulting in unplanned outages / low generation and load shedding etc. This causes disruption to consumers and reduced cash generation for the operator. A contributing factor to these operational problems is the fact that hydro power equipment and plant is custom built. The equipment cannot be fully assembled or tested in a factory before sending it to site. Maintenance activities at predetermined time intervals are necessary to ensure the following: 1.
2. 3.
Quality and reliable operation of equipment in the service environment through planned, periodic inspection and checking of components and systems. Together with replacement or rectification of parts wherever required. Maximum availability of equipment and a minimum of unplanned shut downs by using planned / periodic shutdowns to inspect all equipment (serviceable and non-servicable). Eradication of operational problems by a timely analysis of the cause of faults / problems and replacement of short term solutions by long lasting and permanent ones.
2 Preventive maintenance of Hydro turbine In order to achieve above objectives of maintenance, time has to be allotted every year for each machine. Normally the periodicity and the procedure for maintenance is recommended by the manufacturer of the equipment. However, experience of operators of Hydro Power Stations in India has shown that the maintenance is required according to the following guidelines. Routine Maintenance Normally there will be daily, weekly, monthly and quarterly checks as per the maintenance schedules are done. These checks are necessary for controlling any change in the installed clearances, commissioning characteristics etc. connected with the performance of equipment. Rectification and adjustment wherever required should be carried out in order to arrest any deterioration of the equipment. The daily, weekly and monthly check schedules designed for Chilla Hydro Power Station are used to illustrate the kind of maintenance schedule that will be needed: 2.1.1.
Daily Maintenance Checks
1. Foundation Parts and Expansion Joints: Check for any leakage in draft tube manholes, spiral casing manhole, expansion joint. 2. Vacuum Breaking Valve: Check the working of both vacuum breaking valve and see that there is no abnormality in the springs, seats etc. 3. Water Seal and Air Seal: SKT-S7-RevB.doc
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• •
Check the position of water leakage around the water seal and check that there is no excessive splashing and water level do not rise in top cover. Note water pressure of water sealing/under sealing.
4. Turbine Guide Bearing: • • • •
Check the oil level (stand still machine/running machine). Note the temperature of bearing and check that the temperature of oil and guide bearing pads are within limits. Note the maximum and minimum temperature of the previous day. Check for any oil leakage from the bearing housing and check that oil is flowing above the bearing pads.
5. Guide Apparatus: Check any leakage from GV servomotor and its piping. Oil Leakage Unit: • •
Check any leakage from pipe line joints. Check its satisfactory running on `Auto’.
Top Cover Drain System: • • • •
Main supply of `ON’ for DPM. Vibration noise in the pump motor. Any leakage from the water piping. Working and water pressure of the ejector.
Centralised Grease Lubrication System: • •
Check for any leakage from grease pipes, unions and nipples. Check grease container and fill grease, if required.
Oil Header: • • •
Check from perspex sheet manhole any splashing of oil from top and bottom bush. Check any oil leakage from the joints. Note the pressure difference of opening and closing side of runner.
Oil Pressure System: • • • • •
Check if there is any abnormal sound in the running of the motor and pump unit of OPU. Check the oil level in pressure accumulator. Check any oil leakage from oil piping and its valve. Check for over heating of motor. Note the timing of OPU pumps running.
Mechanical Cabinet of Governor: SKT-S7-RevB.doc
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• •
Pressure in transducer. Check any oil leakage from joints of piping.
2.1.2.
Weekly Maintenance Checks:
1.
Greasing of guide vanes and servomotor with centralized grease lubrication system and manually. i) Oil in the gear box shall be checked. ii) Check for any leakage iii) Working of end pressure relay and solenoid valves, if defective, should be reported.
2. 3. 4. 5.
6.
Cleaning of OPU filters 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 sample taking through the sampling cock and do the crackle test for detecting presence of water. Take remedial measures. Check oil level of all the bearings.
Check wobbling of shaft at coupling flange and at oil header servo-tube. 2.1.3.
Monthly Maintenance Checks
All the checks covered as part of the weekly maintenance are also carried out as part of the monthly check. In addition to these checks, more attention is paid and short shutdowns, if required, for rectification are taken. 2.1.4.
Annual Preventive maintenance of Hydro Turbines
After successful running of plant for about one year, a few weeks are required to inspect rotating parts, control equipment and measuring instruments and to analyze the cause of changes in the performance characteristics, if any. Modify, repair or replace (wherever required) worn out parts in order to prevent unplanned outages of plant at later date. After every five years it is necessary to inspect the machine more critically for abnormalities like fatigue defects or excessive wear and tear of some parts or any change in original parameters/clearances etc. This exercise becomes very essential in cases where performance level has been observed to have gone down in 5 years operation. The checks for annual and five yearly maintenance specified for Chilla Power Station are enlisted below: 1.
Foundation Parts: i) ii)
2.
Check condition of water path system. The damage due to cavitation and wear to be rectified. Check painting of spiral casing.
Runner:
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i) ii) iii)
3.
Guide Apparatus: i)
ii) iii) iv) v) vi) 4.
ii) iii) iv)
ii)
ii)
Check the functioning of emergency slide valve and the condition of inner surfaces. Swift return of the valve in its original position after emergency operation should also be checked.
Centralised Grease Lubrication System: i) ii)
8.
Check the condition of rubbing surface of sealing rings. In case found damaged change the same. Check pipe lines and piping joints for any leakage if any, attend the same.
Emergency Slide Valve: i)
7.
Check the condition of rubbing surfaces of guide bearing. Clean the surface and polish it with the help of chalk powder. Adjust the clearances by moving the segments with the help of adjusting bolts. Thorough cleaning of housing if necessary. Check all the RTDs and TSDs replace damaged one.
Shaft Gland Seal and Air Seal: i)
6.
Check the presence of rubber sealing cords and the tightness of the rubber sealing between the adjacent guide vanes in fully dosed position of guide apparatus. Change oil in the regulating ring. Replace damaged shear pins. Check cup sealing of guide vane journals and replace, if necessary. Check the bushes of guide vanes and change the worn out bushes of guide vanes journals. Inspect the servomotor and change the seals, if these are worn out.
Guide Bearing: i)
5.
Check the condition of the surfaces of the runner hub and the blades. The damage due to cavitations & wear to be rectified by welding and grinding. Check the runner blade seals by pressurizing the system. Change seals if necessary. No oil leakage is to be allowed. Check the runner sealing for hermetic tightness, leakages of water in the runner hub is not to be permitted.
Check satisfactory working of CGLS system. Attend wherever fault is located.
OPU: i) ii) iii) iv) v)
Check and attend leakage from any valve or flanged joints etc. Provide proper lubrication to the bearings of pump motor. Check filter and repair, if required. Clean oil sump, refill with centrifuged oil. Check setting of the float relays for proper sequence of operation of pumps.
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9.
Oil Header: i) ii) iii)
10.
Oil Leakage Unit: i) ii) iii)
11.
Check satisfactory working on Auto as well as manual. Clean the tank. Check the pipeline joints and valves for leakage, attend wherever necessary.
Oil Cooling Unit: i) ii)
12.
Measure clearances of upper and lower bushes, if found increased get the bushes replaced. Clean the oil bath. Check the rubber cord fixed below the guide to check any oil dipping on the exciter winding.
Check all the oil and water pipe lines for leakage and attend if necessary. Check satisfactory working of all cooling unit.
Governor Mechanical Cabinet: i) Check filter and throttle if found damaged replace the same. ii) Attend leakage of oil through pipe line joints and valves. iii) Check auto rod setting, if found disturbed; set the same. iv) Check (Alpha – Beta) characteristic, if found disturbed set the same. Alignment of feed back wire rope pulleys.
2.1.5.
Capital Maintenance
Overhauling or capital maintenance of hydro plant 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 with new ones. Then the unit is re-commissioned as per originally established commissioning practice of the power station. After capital maintenance the units are subjected to all maintenance exercise outlined above before it reach the next cycle of capital maintenance. Following checks are to be exercised during capital maintenance of a hydro set: 1.
Turbine Bearing: i)
ii) 2.
Dismantling, inspection, cleaning, measurement of clearances, polishing of guide pads, centering of shaft, reassembly, setting of clearances, filling of oil sump with filtered water. Check the temperature sensing device, if necessary, replace with new ones.
Gland Seals and Isolating Air Inflated Seals:
Dismantling, inspection, cleaning and reassembly. Replacing of worn out rubber flaps or carbon segments, if necessary. SKT-S7-RevB.doc
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3.
Clean Water System:
Clean water pipes are dismantled, cleaned, reassembled with new gasket all the valves are attended for any leakage etc. 4.
Guide Vane Servomotor:
Dismantling for inspection and cleaning. Reassembling and replacing the seals with new ones, if necessary. 5.
Guide Vanes Bush Housing: i) ii)
6.
Governor: i) ii) iii) iv) v)
vi) 7.
Cleaning and checking OPU pumps. Replace bushes, bearings etc. if found worn out. Also attend pump motors. Cleaning OPU sump and pressure accumulator and refill with filtered oil. Attend oil pipeline flanges and valves for leakages. Check setting of pressure switches installed for Auto Operation for OPU pumps. Attend Governor Mechanical cabinet for leakages, loose links. Clean main and pilot slide valves. Set Auto rod as per designs Alpha Beta setting may also be checked. Check electrical circuit. Tightening of all the connections should be done.
Submerged Parts i) ii)
8.
Removing, cleaning and inspecting for wear and tear replacing with new ones if found necessary. Replace seals, if necessary. Guide vanes are reconditioned.
Cleaning and painting of spiral casing and draft tube liner. Overhauling of spiral drain valve and draft tube drain valve.
Runner i) ii) iii) iv)
v)
De-watering of draft tube and fabrication of platform in the draft tube for inspection of runner. If it is a Kaplan Runner test the same after applying full governor pressure for leakage of oil. Replace blade seals, if necessary. Inspect blades of the runner and make up profile of the blades by welding. Due to erosion, abrasion and cavitations, material of the blade washes away with passage of time. In case the runner is found to be irreparable arrange to replace the same with new one.
Turbine Auxiliaries 1.
DPM i) Inspect top cover drain system, overhaul the ejector and drainage pumps.
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ii)
Check pipe lines and valves. Replace gaskets and other parts, if necessary.
2.
Oil Cooling Unit i) Overhaul cooling pumps ii) Attend all the valves and pipe lines for leakage.
3.
Centralised Grease Lubrication System i) Overhaul greasing pumps ii) Check whole greasing lines. Replace worn out valves and gaskets etc. iii) Check all the nylon pipes connected with the guide vane bushes. Replace damaged pipes. iv) Check that all the guide vanes are receiving grease properly.
4.
Oil Leakage Unit i) ii) iii)
Check the oil leakage unit overhaul the pumps. Clean tank and check that float is properly working. Checking all the pipe liens and valves for leakages.
3 Requirement of effective maintenance In addition to planning maintenance and implementing a suitable schedule (on the basis of seasonal water availability perhaps), the following items also require attention otherwise it may be difficult to keep to the schedules in practice: 1. 2. 3.
4.
5.
6.
4
Man Power Planning and arrangement is essential as without experienced and skilled staff any maintenance programme may fall. Planning and arrangement of spares and consumable in advance so that time is not lost in re-commissioning the plant after the shut down. The maintenance engineers should have in his possession all the erection and commissioning log sheets documents 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 operational problems as well as defined maintenance purpose. Log sheets of the previous maintenance exercise carried out on the machines. These may be required to compare with the clearances / settings / characteristics achieved during present maintenance. History registers of all plant should be kept with records of all the abnormalities observed on the machine and details of action taken. This data can be used to as a guideline for future maintenance work at the power station. Logging of the performance characteristics of the power plants on daily basis recording all the abnormalities and misbehaviours (if any) of the total plant observed during its generation programme from one maintenance exercise to another.
Major maintenance problems of water turbines
Some of the major problems encountered in the hydro turbines are damage in runners due to erosion, cracking and cavitation due pressure pulsation in draft tube, instability of operation at partial gate opening. Other serious issues include failure of turbine guide bearings, leakages of SKT-S7-RevB.doc
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water through turbine guide bearings, leakage of water through guide vane seals and turbine gland seals. These problems are discussed in detailed in the following section. 4.1
Runner
4.1.1 Erosion due to silt Erosion of turbine runners, guide vanes and other under water parts is a serious service problem especially in run-of-river schemes. The rivers in the Northern region of India carry significant silt loads especially during monsoon period so much so that hydro power stations are often closed down to prevent serious damage to the turbines parts and water passage. Greater attention should, therefore, be paid to effective de-silting arrangements. Excessive wear and damage often occurs on the runner labyrinths, seals, guide vanes, butterfly valves, shaft seals and draft tube cone. Wear due to silt occurs so fast that the turbine units have to be taken out for repair every few months in some stations. The solution lies in the original specification of effective de-silting civil works however, this is of little practical help in the service environment. In the service environment the use of turbine parts coated with or made from material with harder and erosion resistant properties is the most practical option to be pursued. At Chilla Project following measures of de-silting have been taken: i) Silt extruders have been provided near under sluice gates of the barrage. ii) Half a kilometre downstream of the head regulator, a silt ejector has been constructed in the bed of the power channel. 4.1.2 Cavitation related cracking and wear of the runner The problem of cracks in turbine rotors and Pelton buckets has been reported in few power stations. This can be due to following reasons. i) Faulty design ii) Poor metallurgy iii) Metal fatigue The phenomenon of cavitation occurs due to the vaporization of water in a zone of excessive low pressure. Cavitation damage can occur if the turbine has to operate at part flow. Limits of structural wear (metal removal) are normally specified beyond which repair of the plant is needed. To minimize the effects of cavitation, the following steps are recommended: i)
Periodically (annual) inspection of the runner and other turbine parts to judge when repair is necessary. ii) Operation of the turbine plant according to the manufacturers guidelines. Specifically, a turbine unit should not be run below the minimum load (discharge), recommended by the manufacturer. iii) At design stage, ensure i) proper submergence of the turbine ii) correct specifications of cavitation resistant materials and iii) specification of the runner profile based on model tests for cavitation onset. iv) As a result of draft tube pulsation and surges at no load or part gate opening excessive noise, vibrations and cavitation is experienced. To minimise pulsations of draft tube following measures must be taken: -
Air admission through air admission/ vacuum breaking valve installed at top cover.
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-
Provision of fins or flow splitter in draft tube to break the vortex flow. Provision of a bypass arrangement for releasing the pressure built up below the top cover.
Normally the discharge side surface of buckets or blades, areas on the crown on the throat ring and the tip of the blades and the upper portion of the draft tube liner are affected by the action of cavitation. In rare cases, there may be pitting on the pressure faces of the buckets or blades due to an unusual amount of over hung of the guide vanes improper design or unusual operating conditions. Hydro Power plant operators have, over the years, gained expertise of ways of repairing and welding of the runner at site, but it becomes a regular maintenance problem as wear and cracking occurs quickly. 4.1.3 Precaution in welding of runners Some general remarks about the welding repair of turbine runners are given below. It should be noted that different materials will require specific (often proprietary) welding processing. 1. 2. 3. 4.
5. 6. 7. 8. 9.
Surface of the parent material should be prepared by chipping or grinding. To locate cracks, inclusions and the like, a die penetration test must be carried. Preheating of the blade to about 60oC is necessary Avoid any localized excessive heating. This is achieved by welding for a short time in any one particular area and then moving to a diametrically opposite area to continue with the work. The parent material should be about 70 to 75 mm from the weld and should not be allowed to get too hot to be touched with bare hand. Plenty of time should be allowed for the welded area to cool down since forced cooling may cause distortion due to locked in stresses. Hot peening is also required. A close check should be made at least two to three times per day during the repair for runner to runner chamber clearances. After welding all the welded areas should be properly ground to match with the desired profiled. Die penetration tests should once again be carried out to ensure crack free welding. Rectification if necessary should be done.
If extensive welding on the runner is required, it will be necessary re-balance statically and possibly dynamically all rotating parts and stress relieving before recommissioning otherwise. 4.2 Turbine Guide Beadings A number of turbine guide bearing designs are in use. These may be classified as follows: i) ii) iii) iv) v)
Plain water cooled bearing Bath type with circular cooling turbines Bath type with cooling water tubes embedded in the pads. Rotating bath type. Grease lubrication bearing.
In the case of plain water cooled bearings, either ferrobestos or rubber lined pads are used against a welded shaft sleeve. The ferrobestos lined bearing have given considerable trouble at one of the power station and these had to be replaced by rubber lined pads. SKT-S7-RevB.doc
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Small diameter cooling pipes embedded in bearing pads have a tendency to clog especially at the time of high silt contents resulting water starvation. Complaints of excessive oil splashing have been received about the rotating bath type bearing. Grease lubrication bearings have a tendency to clog when in contact with the water and it is very essential to use grease with the right type of properties. A number of cases of turbine guide bearing failures have come to notice. These are: i) Starvation of oil in the bath ii) Failure of cooling water due to clogging of pipe. iii) Mal-functioning of instruments like RTDs, TSDs, oil level relay and flow relays etc. To avoid failure of bearing due to cooling water tube, a new design of turbine guide bearing has been developed by BHEL, Hardwar. Two separate oil sumps are located in the top cover in diametrically opposite locations. These sumps, through pipe lines are connected to the oil bath of the bearing. The oil is circulated between sumps and the bath. Top cover being stationed just above the draft tube, separate to cooling water arrangement for bearing oil is not required. The bearing temperatures with this arrangement never go beyond 40oC to 42oC and this design is effectively working at Chila Power Station. 4.3
Gland Seals
Normally two types of shaft gland seals are in use in different power stations: i) Carbon or ferrobestos segment. ii) Rubber flap type 4.3.1 Carbon or Ferrobestos Segment Type The seal segments are housed in the stuffing box. Stuffing box being always in touch with the shaft is subjected to excessive wear and tear. The overhauling of the stuffing box becomes necessary when it is observed that consumption of cooling water has considerably increased or excessive water in top cover appears to be coming. In general maintenance of the seal is required to be done annually. In the event of breakage or damage to a carbon segment it is advisable to replace the whole set of carbon segments. In very rare case only the damaged segment is replaced care must be taken to ensure that the axial thickness of the new segments falls within the limit size to ± 0.002” of the existing ring to which it is to be fitted. All carbon segments and spacers are fitted to place and match marked on assembly. Whenever any part is replaced, matching marks / indents should be made after final assembly is satisfactorily completed. Whenever reassembly of the gland seal with existing gland ring or new ring is done it is important to ensure: 1. 2. 3. 4.
All carbon/ ferrobestos segments are carefully examined for any chipping or damage. All stainless steel facings are flat and square with the gland sleeve and there are not steps at the facing joints. Stainless steel facing and sleeve are completely free from grease. Ensure proper bedding of segments with shaft sleeve.
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5. 6. 7.
All segments to segment and segment to stainless steel mating surface are completely free from grease. All garter springs are assembled to obtain even tension all around. Alignment of segments in the lower assembly is carefully checked with a hard wood peg for similar device before fitting retaining pins.
4.3.2 Rubber flap type Maintenance of rubber flap type gland seal is comparatively simpler and easier. Only precaution during assembly of rubber gland is jointing of the rubber seal in the proper way. The quality of rubber used plays a very important role for satisfactory performance of the rubber gland. In one of the recently commissioned power stations rubber gland seal used to fail very frequently. The cause of frequent failure was discussed and analysed to be lying in the quality of rubber. The problem after selection and use of proper quality of rubber is now over. 4.4 Guide vane servomotor Normally main source of trouble is rubber seals which need to be replaced after a few years. Rubber seals should be replaced during annual maintenance. It is important that all the parts are match marked before dismantling so that reassembly is correctly done. 4.5 Governor Different types of governors are in use in different hydro power stations: a)
b) c)
Mechanical governor can be classified as follows i) Fly ball type ii) Accelero technometric type Governor employing magnetic amplifier. Governor employing electro hydraulic amplifier. The governor may require maintenance because of the following reasons: i) Chocking of oil parts and throttles ii) Wearing out of throttles due to which oil leakage becomes more and readjustment of governor becomes essential. In this case governor should be opened and all the throttles etc. should be cleared. Filters should also be cleaned, and after cleaning and reassembly governor parameters and characteristics should be readjusted so that there is no hunting of the governor.
4.6 Governing Oil System The oil sump should be well cleaned and filled with filtered oil. The oil samples should be got tested for verification of the desired properties. Regular centrifuging of oil with the help of De-Laval type oil purifying machine would go a long way in enhancing the life of the oil. In certain cases oil retained its properties even up to 15 to 20 years of continuous use. During annual overhauling OPU sump and pressure accumulator should be completely emptied and cleaned. The strainers should be inspected and repaired of necessary. The OPU pumps require maintenance when they develop excessive noise or vibrations. This may be due to some worn out bearing of the pump which would be replaced. Another problem which has been faced in different power station is entry of water in the governing oil system. This problem was analysed in detail and remedial measures were taken SKT-S7-RevB.doc
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at Chila Power Station. From following two sources the water can enter in the governing oil system: 1.
2.
From top cover, through oil leakage pumps which caters leakage of servo motor oil. Its sump being located well below the level of servo motors in the top cover may not be properly sealed, thus providing access to the top cover water which may ultimately be pumped in to the OPU sump. In case of Kaplan turbine water may enter into the runner hub through cup seals.
To eliminate first possibility the oil leakage unit delivery was isolated from the OPU sump and connected to a separate tank. But for the second possibility there is no way except replacing blade seals if excessive water found in the Governor oil. Daily check of the OPU sump oil sample and test of the sample is necessary to keep training of such possibilities. 4.7 Header In Kaplan turbine the oil header is required to supply governing oil to the runner servomotor and return oil to the OPU sump. Oil header has an oil guide connected with the rotating and servo tube. The servo tube has ports to receive return oil to the pipes coming from OPU sump. This tube is guided by three sets of bushes in the oil. Due to run out of the shaft these bushes had to press the servo tube. Failure of these had been very frequent in one of the recently commissioned power station. Monitoring of wobbling of the servo tube with help of dial indicator may provide a guide line and save the bushes from further wearing. Remedial measures to reduce run out of the servo tube must be taken at this stage. At the time of assembly of various parts of header proper match marking and dowelling is essential so that reassembly may be correctly done. Due to failure of these bushes oil splashing occur which may drench the PMG, main & Pilot exciter and reduce the life expectancy of the windings and brush as such all out efforts should be made to prevent such happenings.
5
Preventive maintenance of Hydro Generators
Preventive maintenance ensures a long trouble free operation of the generator. Given in the following Table are the recommended daily, monthly, once in 3 months, half yearly & yearly maintenance checks to be conducted on the generator. While it is appreciated that it is not always possible to rigidly follow this schedule due to generator loading constraints, the recommendation given may be taken as a guide line and these may be altered slightly, based on his experience. After the first 600 hours operation of the unit, the checks having periodicity of half yearly and yearly in the following schedule should be carried out.
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Sl. No. 1.00 1.01
1.02 1.03
1.04
1.05
1.06 1.07
1.08 1.09 1.10 1.11
1.12 1.13
2.00 2.01
Description
Periodicity
Stator: Temperature record on log sheet for core and winding, hot and cold air temperature Visual inspection of the overhang parts of the stator winding. Checking the fixing of winding, condition of winding joints with bus bars etc. Clean the winding with dry & clean compressed air (2 to 3 kg/ cm2). Check overhang parts of stator winding, bus bars, inner periphery of stator core (if possible), parts of stator winding in slots (specially at sector joint) binding & spacers between the winding bars/ bandage rings. Check looseness of overhang, bus bars, slot wedges etc. Check the fixing of stator active iron with the frame body in all possible places. If it is necessary, tighten the studs of pressing plates. Check pins &fixing of stator with foundations. Check D.C. resistance, IR & PI value. Check functioning of RTDs of stator. Blow the winding, active iron and bandage rings etc. with dry & clean compressed air (2 to 3 kg/cm2). After cleaning apply Red-gel coat on the overhang. In case of excessive wetting of stator winding during conditions such as flooding, drying of winding by passing current is not allowed initially as hydrolysis of water may take place. This is harmful to the winding. ROTOR: Check rotor winding and insulation details of current carrying leads.
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Remarks
Hourly
Once in 3 months Once in 3 months
Once in 3 months
Cleaning to be done such that the dust does not collect in side machine
Yearly
Yearly Yearly
Yearly Yearly
Record to be maintained
Yearly
-do-
Yearly
Yearly As per requirement
Not required during 600 hours inspection. External heating arrangement is to be provided till wetness is removed.
Once in 3 months
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Sl. No. 2.02 2.03 2.04
2.05
2.06 2.07 2.08
2.09 2.10 3.00 3.01 3.02
3.03
3.04
Description
Periodicity
Check the condition of inter polar connections Check the condition of damper winding. Check the locking of pole wedges. If required carryout additional wedging. Check locking of rim wedges.
Once in 3 months
Check the gaps of spider arms, brake track. Check tightening & proper locking of all fasteners. Clean rotor from dust by blowing compressed air free from moisture (2 to 3 kg/ cm2). Measure D.C. resistance and IR value of rotor winding. Check the pole coils for inter turn fault. Slip ring and Brush Rocker Check sparking. Check pitting & Grooving of slip ring
Yearly
Check IR value slip rings before slip rings. Clean the brush slip rings and areas.
Once in 3 months Yearly
Yearly
Yearly
Yearly
Keep a record
Yearly
Not required during 600 hours inspection.
Every shift Monthly
rocker, Brushes, Monthly the surrounding
3.05
Check brush tension
3.06
Check for absence of oil or oil Every shift. vapour slip ring area. Check distance of brush holder Monthly from slip ring and keep it as specified in the drawing. New brushes to be used after While replacing
3.07
3.08
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&
spring Monthly
Section 7
In case the wedges are loose contact manufacturer before attempting any rectification.
Yearly
of rotor through Once in 3 months & after cleaning
wear
Remarks
In case of excessive grooving rectify by grinding. Keep record
Special care must be taken to clear carbon dust from ‘V’ shaped insulation pieces fitted between slip rings. Use a precision spring balance for adjusting spring tension. The carbon brushes can be used till it is not possible to measure/ adjust spring tension. Oil leakages, if any, to be removed
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Sl. No.
3.09
3.10
3.11
Description
Periodicity
bedding the brushes. The brush should not be too tight/ loose inside the holder. Ensure use of same & recommended grade of carbon brushes on one machine. Check all fasteners of slip rings, Once in 3 months brush rocker & current carrying lead. Check carbon brushes for absence Monthly of splits, cracks and severe wear.
3.12
Inter change polarity of slip rings.
3.13
Carryout thorough cleaning of slip Half yearly ring area. Stop oil leakages in this area. In case the original insulating Yearly enamel unit is peeling off remove the balance payment and apply free enamel IE –82 dry Check wobbling at slip rings. At the time of installation/ during major overhauling Thrust Bearing Measurement of temperatures of Hourly T.B. Pad & Oil by RTD & TSD and record on log sheet. Check & record reading of oil Once in a shift. level relay. Analysis of oil from oil bath. Half yearly Change of oil in T.B. oil bath When centrifuging doesn’t help in improving its quality up to acceptable values. Check level of oil from the gauge Once in every shift. glass. Any increase in level may be due to leakage of water in the oil bath from coolers.
3.14
3.15
4.00 4.01
4.02 4.03 4.04
4.05
4.06 4.07 4.08
Half yearly
Measures insulation resistance of Yearly T.B. disc. Check calibration of the TSD’s & Yearly RTD’s of thrust bearing. Check the working surface of Yearly thrust bearing pads, scrapping, if required, should be carried out
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Remarks
In case the damage is excessive, replace complete set. Not required during 600 hrs. inspection
While cleaning avoid using insulating paint removers.
Record to be kept.
Unit should be stopped in case of leakage from cooling tube. Plugging of cooling tubes up to 10% can be done depending upon bearing temperature. Not required during 600 hours inspection. Not required during 600 hours inspection. Not required during 600 hrs. inspection
Page 15
Sl. No.
4.09
4.10
4.11
4.12 4.13
4.14 4.15
4.16
4.17 4.18 5.00 5.01
5.02 5.03 5.04
Description
Periodicity
with respect to T.B. disc after apply lard (animal fat) on the pads & giving rotation to the unit. Load sharing on T.B. pads and the verticality of the unit is to be checked thereafter. Check the condition of mirror During capital surface of T.B. Disc. Polishing of maintenance the surface can be done to remove minor scratches. Clean all inner surfaces of oil bath Once in Two years. from dust, wash them with Kerosene and dry with clean cloth. Check the condition of weld seam of oil bath & oil pipe lines for leakages visually. Check the condition of insulation of RTD leads. Check if excessive foaming is taking place in oil through gauge glass. This is normally due to mixing of water leaking from oil coolers. If oil level is not rising, the oil may need changing. Oil sample to be checked. Check if any insulating segment over T.B. Disc is displaced. Check (in case of problem) the intactness of spherical surface of thrust bolt In case of uneven wear of pad, check that the pad eccentricity is correct. Check for proper seating of pads during each Change rubber seals & woolen felts GUIDE BEARINGS Measurement of temperatures of G.B. pads, oil by RTD & TSD & record on log sheets Check & note reading of level relay Analysis of oil from oil bath Change of oil in T.B. oil bath
SKT-S7-RevB.doc
Section 7
Remarks
This will require partial dismantling of unit.
Oil bath is to be finally flushed with fresh turbine oil; to be discarded after use.
Yearly
Yearly As required.
Watch carefully for rise in water level to confirm leakage and attend accordingly.
During capital maintenance As per requirement.
As per requirement
As required As required
Hourly
Once in every shift Once in 3 months Record to be kept. When centrifuging doesn’t help in improving its quality up to acceptable values Page 16
Sl. No. 5.05 5.06 5.07
5.08
5.09
5.10
5.11
5.12
5.13
5.14 5.15 5.16 5.17 5.18 5.19
6.00 6.01
Description
Periodicity
Measures insulation resistance of G.B. pads. Check calibration of TSD’s & RTDs of G.B. Prior to removal of pads, measure and record guide bearing clearances. Check each pad for: i) Absence of scratch marks. Scrapping to be done with respect to the journal, if required ii) Heavy damage on Babbit surface of pads – full set must be replaced with genuine spares. The spare set to be scrapped with respect to its respective journal surface by giving rotation to the unit. Check the centering of the unit vis-à-vis the labyrinth/runner chamber of turbine. Check the friction surface of the bearing journal. Clean and polish if necessary. Wash pads & journal with aviation petrol and then carryout assembly of the guide bearing. Check the condition of welding seams of oil bath & leakages from them and oil pipe liens. Clean all inner surfaces of oil bath from dust, wash them with Kerosene and dry with clean cloth.
Yearly
Change rubber seals and woolen felts Check operation of the level relay and its calibrations. Check welding of pad support block with oil bath. Check looseness of pad and pad support bolts. Check condition of pad insulation. Check looseness of bolts holding ‘Z’ clamps (in wedge type construction of guide bearings. Air/Oil Coolers Check water boxes for clogging by
As required
SKT-S7-RevB.doc
Section 7
Yearly As per requirement
Yearly
Yearly as requirement.
Remarks
Not required during 600 hrs. inspection To be readjusted if required, during reinstallation Not required during 600 hrs. inspection
per Not required during 600 hours inspection.
Yearly
Yearly
Not required during 600 hrs. inspection
Yearly
Once in tow years
Oil bath is to be finally flushed with fresh turbine oil; to be discarded after use.
Yearly Yearly Yearly Yearly Yearly
Yearly
This checking may be Page 17
Sl. No.
6.02
6.03
6.04
Description
Periodicity
opening them. In case of clogging clean tubes water boxes with wire/ nylon brush. Remove all dirt etc & finally clean with fresh water & dry. Check the gasket between oil Yearly cooler & oil bath & between air cooler & stator frame. Gaskets to be replaced if required. When the shutdown exceeds 10 As required days, water from coolers is to be drained and the coolers kept dry. Coolers are to be immediately On flooding of the unit. attended to as given above at 6.03
6.05
Normally up to 10% of the cooling As required tubes of coolers can be plugged, if required.
7.00
UPPER DRACKET/ LOWER BRACKET External inspection & tightening of the lock nuts in the radial jacks, if required. Check fixing of the generator cover plate Check all fasteners of Upper and lower air baffles. Check the value of air gap between air baffles and rotor.
7.01
7.02 7.03 7.04
Yearly
7.06
Check fastening between upper bracket & stator and stator and foundation plates. Check foundation bolts tightening for stator & lower bracket. Check all fasteners for locking/ tightness Brake pipe line Record air pressure available at brake panel. Check thickness of brake pad
Yearly
8.02
SKT-S7-RevB.doc
Section 7
Not required during 600 hrs. inspection
This is to safe guard failure on subsequent commissioning of the unit. Temperature of the bearing pads/ stator winding to be taken in view while plugging tubes of the coolers.
Once in 3 months
Yearly
8.00 8.01
if
Once in 3 months
Clean the brackets of dirt & dust.
7.08
done frequently clogging is more.
Once in 3 months
7.05
7.07
Remarks
Theses gaps are to be compared with original values during erection and maintained as such, if required. Cleaning can be done more often if possible.
Yearly Yearly
Every shift
Record on log sheet
As required
Record to be maintained along with number of Page 18
Sl. No.
Description
Periodicity
8.03
Measure: i) Time for unit to come braking speed from rated speed after signaling the unit to stop.
8.04
Check if excessive brake dust is generated and find its cause. During jacking operation lifting of the rotor is to be limited to the specified value (7.0 mm) Keep the unit on jacks which are mechanically locked during each shut-down of the unit After each jacking operation ensure cleaning of pipe with air under pressure as provided in the system. Check no oil leaks from return line during jacking operation Check function of the braking system on manual and automatic and the operation of the limit switches of brake. Check leakage through pipelines during braking/ jacking. Check all fasteners of brakes and brake pipe lines & gaskets wherever provided. Check the condition of brake track and its holding with the rotor Open brake cum jack assembly. Clean the inner surface of dust with kerosene & reassemble.
8.05
8.06
8.07
8.08 8.09
8.10
8.11 8.12
9.00 9.01 9.02
9.03
Remarks
braking in the period with Air pressure used for braking. During first spinning/ Record by kept. In case yearly if this time has increased abnormal then look for increased guide vanes clearances. Presence of oil on brake track or reduction in air pressure, defective gauge etc. Yearly Clean the affected areas periodically as required During jacking Limit switch to be suitably mounted to check the rotor lift. As required
As required
As required Yearly
Yearly
Yearly Yearly
Record must be maintained. In case of any problem brake panel & brakes are to be checked & rectified as required. Not required during 600 hours inspection. Not required during 600 hrs. inspection Replace the gas if required. Not required during 600 hours inspection.
GENERAL External examination of parts of Once in each shift generator which are accessible. External inspection of air coolers, Once in each shift oil coolers, pipe lines, sealing & control etc. for leakages. Ensure cleanliness of all external Once in each shift accessible parts of the generator & wipe with clean & dry cloth.
SKT-S7-RevB.doc
Section 7
Page 19
Sl. No. 9.04 9.05 9.06
9.07 9.08 9.09 9.10
9.11
9.12
9.13
9.14
9.15
10.00
10.01
10.02
Description
Periodicity
Check wobbling of the shaft at turbine generator flange/ TGB Blow with compressed air the internal surface of the generator External inspection of current carrying leads PMG, Bus Bars, Terminal Blocks, Panels etc. Check the condition of lighting inside the barrel Check the recordings of lighting inside original results. Check for proper cleaning of slip rings. Check the vibrations at TGB, UGB & LBG predetermined points. Check connections of current carrying leads & cables. Tighten the bolts, if required, after removing the insulation. Check the calibration of Electrical measuring instruments i.e. voltmeter, ammeter, Active/ Reactive Power meter. Frequency meter, P.F. meter for Stator output, Voltmeter & Ammeter in Field winding circuit, energy meter etc. Check the Sensitivity & Stability of Generator Electrical Protection scheme. Check the working of Fire Extinguishing (CO2) system without actually releasing the CO2 gas on manual and on auto operation as per the instructions provided in O&M manual of the Fire Extinguishing System provided by its supplier Check the characteristics of Static Excitation system in both auto & manual mode and sensitivity of various limits. OIL PIPE LINE/ EXTERNAL OIL COOLING SYSTEM (if applicable) Check oil pressure at the pump across the filter & point of entry to the bearing. Check the operation of the
Daily
SKT-S7-RevB.doc
Section 7
Remarks
Monthly Monthly
To be necessary
cleaned
if
Monthly Daily
Reasons for variance to be investigated
As per requirements Yearly
Yearly
Yearly
As specified supplier.
by
its
Yearly
As specified in its O&M manual.
Every shift
Record is maintained.
Monthly Page 20
to
be
Sl. No. 10.03
10.04
10.05 10.06 10.07 10.08 10.09 10.10 10.11
10.12
Description
Periodicity
Remarks
electrical contact pressure gauge. Check temperature of bearings of Daily the Pump-motor set.
Check conditions of gland packing of the pump and see that air is not being sucked from here into the system. Completely clean the oil tank & T.B. oil bath Clean the oil pipe line after disconnecting it Check the operation of the valves of the pipe line. Check the Operation of D.C. pump motor set (if provided) Remove sludge from oil tank. Check the temperature of cold & hot oil. Check the air ventilation cocks of the oil tank are open during. Operation of the unit. Check pipe line for leakage of oil.
This temperature is not to exceed the specified limits. If the temperature is excessive, check if lubricating grease is filled as required. These are holes in pipes which feed oil in between the pads.
Monthly
Yearly
Not required during 600 hours inspection. Not required during 600 hours inspection. Not required during 600 hours inspection.
Yearly Yearly Monthly Monthly Hourly
Keep record in the log sheet
During start of the unit/ during each shift. Once in each shift
10.13
Check oil sample for acidity, Once in 3 months viscosity, moisture content, foreign material & sludge. Formations.
10.14
Clean holes for oil entry into the Yearly T.B. housing
Separate oil sample from each bearing should be sent for chemical analysis & record to be kept. Not required during 600 hrs. inspection
HYDRO GENERATORS DAILY CHECKS Sl. No. 1.
Assembly
Item
Check Point
Method
Stator Core
Core Noise
Abnormal noise around stator
Periodic listening
SKT-S7-RevB.doc
Section 7
Remark & Remedial Measures Checking for core looseness especially at frame joints If abnormal add additional Page 21
2.
Wound stator
Stator core and coils Bear pads
Core & winding temp. Bear. Temp.
3.
Guide & thrust bear
4.
Temp. scanners RTDs.
Bear oil
Oil level
Level gauge
Visual
5. 6.
Air coolers Collector
Cooler tubes Brushes
Visual Visual
7.
Brake & Jack
Air Pr.
Water leakage Sparking, Mix of CDust/ Oil Pr. Gauge
8.
D.C. Exciter
Commutator brush gear
Commutation
Visual
Pr. Gauge
paramax paper in core joints Check cooled air & cooling system Abnormal Vibrations, Balancing of rotor, dirty oil coolers, cooling water flow contaminated oil, bearing clearances High- Due to Water Leakage Low- Leakage of Oil From Housing Plug the leaking tubes Cleaning Check for leakage, pipeline, joints
MONTHLY/ WEEKLY CHECKS Sl. No.
Assembly
Item
Check Point
Method
Remark & Measures
1.
Weekly Collector ring
Cleaning
Visual
Clean compare, IR value
2.
Brushes
Accumulation of Dirt Sparking, chattering wear & clearance
3.
Brake
Lining
Air leakage, excessive wear
Visual
4.
Brake
Track
Visual
5.
Dc. Exciter
Commutator Brush Gear
Clean liners & Oil Sludge/ Moisture Trap Commutation
Visual
Brushes are not sticking in their boxes, rough or high spot on commutator smooth surface.
1.
Monthly Stator core
Back of core
Visual
Adjust core packing of jack screws, insert paramax paper
2.
Field wind
Field coil top
Visual Feeler Gauge Visual
Clean Comp. Air
3.
DC Exciter
Commutator, Brush Gear, Air Filter
Rusting, flatness of core lamination looseness of punch top and bottom Gen. Condition Tightness Deformation Abnormal wear of Brushes, accumulation of dust.
Visual
Replace brushes, clean com., Risers, clean with detergent sol. Dry.
SKT-S7-RevB.doc
Section 7
Remedial
Smoothen collector surface clean adjust brush (5 to 8 mm for 1000 R-hour) Attend leakages More than 4 to 5 mm Per 50 OP Reduce application, speed & PR. Check air PR, Clean Track, Change Lining Clean Drain Trap & Clean Brake Track
Page 22
ANNUAL INSPECTION Sl. No. 1.
2.
Assembly
Item
Check Point
Method
Stator
(i) Frame
Hammering
(ii) Core
Joint bolt tightness & Dowel Pins Tightness of Core
Core Duct
Contamination
Visual
Stator winding
Cleanliness & general condition
Visual
Field winding
Field coil & rotor
General condition of coil, Pole & cleanliness
Field coil & rotor leads
Inter turn faults
General Conditions & Cleanliness
3.
Brush gear and Slip rings
Brushes & Slip rings
4.
DC exciter
Core & Winding
Measure values cleaning Visual
Remark & Remedial Measures Retighten if Necessary Check the tightness of core especially at the top & bottom most packets. Any local looseness between stampings can be filled up with asbestos of paramax paper glued with epoxy varnish & core bolts retightened. After repairs spray the top & bottom three packets (both from I.D. & O.D.) with loctite – 290 Marketed By M/s Fit Tite Chemicals Ltd. Clean with Dry compressed air Clean the end windings. IR after
Measure impedance field coils applying 60 100 V AC, 50 supply Visual
Dry out if IR Value is low Clean the field coil with compressed air
of by to Hz
Check the coil joints for any cracks overheating etc. If impedance of some coils is very Low (say less than 40%) they must be checked for possible inter-turn faults The slip ring is running out, correct it, any groves etc to be removed by oil stone for excessive sparking For cleaning the exciter
Accumulation of Visual dust Note: For cleaning stator ducts, stator winding, field coils, rotor leads, brush gear, PMG and DC Exciter, Use cleaning agents as recommended by manufacturer 5. Bearings Top & Bottom Clearance Feeler Gauge Check guide bearing Guide Bearing pad clearance. If pad Pads clearances have to be reset the shaft must be centered first. Examine the condition of guide pads and any slight scouring marks can be attended by water emery paper (GR400) 6. Air coolers Coolers tubes Clean inside and outside SKT-S7-RevB.doc
Section 7
Page 23
7.
Oil coolers
Coolers tubes
8.
HS Lubrication System
HS Lubrication Motor HP Hose Assembly
9.
PMG
Air gap winding
10.
Shaft run out, centering and rotor level Water flow relays, visual flow indicators & flow meters Oil level indicator Braking & Jacking system
11.
12. 13.
14.
15.
Thrust & top guide bearing
Electrical Connections
General condition & cleanliness
Inspect, clean water passages, if necessary to remove silt etc.
Clean rod probe • Combinatory unit and air supply pipe line,
• Brake fixing • Brake switch Bearing
track limit Bearing insulation
IR value
Oil vapour seal of top bearing
Vapour insulation
IR value
Pole to pole connections
Electrical joints
Brush gear connection RTD terminal connection heater SKT-S7-RevB.doc
of air cooler tubes Check for any tube leakage by pressurizing to a pressure slightly more than maximum expected working pressure. Clean inside & outside of oil Check for any tube leakage by pressurizing to a pressure slightly more than maximum expected working pressure. Inspect bearing & Grease if necessary check the condition of the hoses & if necessary replace them. Check air gap Clean the stator & field windings check the open circuit voltage and if less than 100 V remagnetise Readjustment statement, if necessary.
seal
Tightness
Clean the filter element and bowl of filter, similarly clean the bowl of lubricator also, cessation of oil dripping through that sight glass is an indication that cleaning is done Tightness of Dog clamps Proper Operation & Cleaning Check IR value of bearing Insulation & replace insulation if damaged Check IR value of vapour seal insulation and replace, if damaged Tighten all electrical joints
Tighten joints Section 7
all
Page 24
electrical
16.
Brush gear
terminal connection Cleaning
17.
Rotor assembly
Tightening fasteners
18.
Rotor
Shaft vibration
Insulated parts of
Looseness fasteners
Slip ring coupling
Visual of
and
Bracket vibration Vibration
19.
Rotor pole
20.
Top shaft
21.
Generator Auxiliaries
22.
Cooling water valves Over speed device
23.
SKT-S7-RevB.doc
Damper system
Current carrying leads
Visual
Dial gauge Balancing equipment
Interconnection between poles
Visual
Supporting structure for proper tightness
By tapping By shaking
Insulation provide on supporting structure Tightness of clamps General condition General operational healthiness
Visual
Check for proper operation Plunger & contact mechanism
Visual As per supplier’s recommended actions
Clean the insulated parts by compressed air Tighten all the approachable fasters on rotor assembly including tightening pole and rim keys & lock all of them. Check for run out at slip ring and turbine coupling and readjust if found more than the specified value. Rebalance if necessary Tighten and lock properly if supporting structure found loose
Rectify damaged
if
found
Repair insulation if found damaged Ensure that these are in good working condition Clean & replace glands where needed Proper operation
Section 7
Page 25
