R, M&U OF GENERATING UNITS OF NPH. A Case Study

Transcription

1 R, M&U OF GENERATING UNITS OF NPH A Case Study

2 KARNATAKA POWER CORPORATION LIMITED(KPCL) HYDRO THERMAL SOLAR WIND STATE OWNED PUBLIC LIMITED COMPANY IN THE BUSINESS OF GENERATION OF ELECTRIC POWER. THE COMPANY HAS A WORK FORCE EXCEEDING 5000 PEOPLE INCLUDING ABOUT 1800 ENGINEERS. THE CUSTOMERS OF KPCL ARE HESCOM, BESCOM, GESCOM, CHESCOM AND MESCOM FOR SALE OF ENERGY. KPCL HAS A TOTAL INSTALLED CAPACITY OF ABOUT MW CONSISTING OF HYDRO- ELECTRIC STATIONS, THERMAL POWER PLANTS, WINDMILLS AND SOLAR PV PLANTS.

3 HYDRO MW THERMAL 3528 MW SOLAR 24 MW WIND MW Thermal Units at Yermarus are at final stages of commissioning TOTAL KPCL MW RES Hydro Thermal Solar Wind

4 KPCL has 21 Hydro Power Stations: Shivasamudram years Shimsha - 76 years MGHE - 68 years SGS - 52 years Bhadra - 54 years Munirabad - 54 years NPH - 38 years Linganamakki - 38 years Supa - 31 years Varahi - 27 years Mani - 23 years Kadra - 19 years Kodasalli - 18 years Gerusoppa - 15 years Almatti - 12 years Shivasamudram Power House

5 Kalinadhi Hydro Electric Scheme was developed in stages. First stage- 6x135MW at Nagjhari Power House. 2x50MW Supa dam power house. Second Stage: 3x40MW at Kodasalli Power House 3x50MW Kadra Power House. NPH -Commissioned during Turbine: Vertical Francis. Rated rpm: 375 Rated Net head : 347m First time 375 rpm units with Francis turbine installed. Very few units with 375rpm Francis type turbines were in operation at that time. Design energy of the project was 4082 MU.

6 Performance of the units Generating units were prone to vibration since commissioning Detailed analyses to find the cause of vibration were carried out Various experts were involved in analyzing the problems Tests conducted by Dr. Mahern Holtz of Hamberg University during 1984 showed that critical speed is in the vicinity of rated speed of 375 RPM

7 Analysis of the results The analyses by various experts indicates that transient vibrations are basically due to following reasons: Periodical residual mechanical and magnetic unbalanced pulls causing excitation and resonance to the rotor system at sub-synchronous speeds Unacceptable Stator and rotor form, resulting in very high UMP (unbalanced magnetic pull) Resonance close to normal speed due to insufficient stiffness of bearing support structure Drawal of higher than designed/rated excitation current at 135MW. Excitation current was exceeding 1250 Amp as against rated 1140 Amp for 135 MW The stiffness of present bearing brackets are as follows: Upper Bracket 0.2x 109 N/m Lower Bracket 0.5x109N/m Recommendations: Stiffness of both upper and lower brackets have to be higher than 1.0x109 N/m and UMP to be reduced by improving the circularity of stator and rotor

8 Expert committee consisting of members from CEA, OEM and KPCL recommended to take up Renovation, Modernization & Uprating of one unit on a pilot basis and carry out the modifications based on the results of analyses. R, M&U OF U#1,2&3 Subsequently, Contract was awarded to the OEM for R, M & U of one unit at NPH on Since, Unit-2 was under shut down due to stator coil failure, it was taken up for R, M & U works on at a cost of Rs Lakhs and re-commissioned on (16months) Major works carried out includes replacement of stator, modification of top bracket housing and arm assembly, guide bearing support ring for bottom guide bearings, slip rings, etc

9 Based on the results of R, M & U of Unit-2, R, M & U of units 1& 3 was taken up in the second phase and OEM was awarded the Contract through competitive bidding at a total cost of Rs.1639 Lakhs for two units. Scope of work mainly covers only generator portion as done for unit-2. Turbine: Self lubricated bushed were provided. No major works on turbine carried out. Additional HP lubrication system provided which would operate whenever thrust bearing temperature shows raising tendencies. The performance of the Units after R, M & U is generally satisfactory.

10 R, M&U OF U#4,5&6 Based on the experience of the R, M & U of Units-1, 2 & 3, R, M & U of Unit-4, 5 & 6 was taken up in the next phase in 2003 Contract was awarded to a Non-OEM through an ICB Modernization of Governors and Static Excitation systems were also taken up. Total cost for lakhs of supply was Rs.2430Lakhs and Rs. 790 lakhs for erection, testing and commissioning of equipment Delivery period was 33 months (Staggered deliver period for three units) and erection period was 8 months from handing over of each unit It was planned to take up works on one unit at a time so that other units are available to support the grid and optimum utilization of water

11 New technologies adopted for R, M&U of U#4,5&6 Floating rim technology used instead of the earlier floating Rim technology for rotor spider. Stator frame supplied in 3 segments and built as joint less ring at site to eliminate core sector joints and to improve rigidity of stator core The stator core supplied of silicon alloy sheet steel(low loss material) On line monitoring system used to monitor the Air gap, vibration and partial discharge of the units Epoxy insulation Disc between thrust collar and runner disc provided to avoid entry of leakage current to runner disc Over-speed device with latest technology Digital excitation system Digital Governor system Flow measuring device

12 R, M&U of unit-4 Dynamic Shaft Analysis was conducted at NPH during December Contractor recommended to have modified rotor structure with rigid rim technology instead of existing floating rim technology for improving performance and reducing vibrations. The subject was discussed with experts in the field including experts in IITs. Based on the studies, it rotor spider. was decided to retain the exist

13 R, M&U of unit-4 Erection works on Unit-4 was taken up from After dismantling, ND tests on rotor spider showed 40 Nos of weld cracks Considering need for long term performance, detailed review to reduce vibrations, modification of rotor structure was taken up and it was decided to provide new modified rotor spider for shrunk fitting on rotor shaft. Price of Rs.837 Lakhs for supply and Rs. 93 Lakhs for erection for all 3 units during June 2006 Delivery period for 4th unit was 9 months Unit No.4 commissioned on after completion of R, M & U works NEW MODIFIED ROTOR SPIDER

14 Various stages during Rotor Rim Building 1 Rotor Rim Building 3 Pre-heating of Rotor Spider 2 Lifting of Rotor Spider 4 Shrink Fitting of Rotor Spider with Generator Shaft

15 R, M&U of unit-4 Performance of unit was satisfactory with Vibration levels within limits. But oil splashing problem from UGB oil sleeve noticed. Modifications carried out on thrust collar assembly and other accessories in the Bearing Housing to solve the problem. Total time period taken for R, M&U works is 35 months. Main reasons for delay : Major defects noticed after opening of the unit. Non-availability of machine drawing, Time taken for reverse engineering, Manufacturing of equipment after opening of unit for supply of new modified rotor spider as cracks were noticed only after opening unit, etc.

16 R, M & U of unit-5 U#5 was handed over from for erection and commissioning works. Problems in U#5 After opening of the unit, the following observations were made: Generator Shaft was found with varying diameter from DE side to NDE side During inspection, undercuts found due to welding of plates near aeration holes at 4 places on NDE side flange of turbine shaft (rotor shaft coupling side) Pitting in Lower Labyrinth Welded Region of Turbine Shaft Generator Shaft

17 R, M & U of unit-5 The inner diameter of the MIV Main seal found corroded, ovality (2 to 2.5 mm) and found in damaged condition Eccentric and Concentric Pin for GV Lever and Regulating Ring were found eroded Coupling Bolts Coupling bolts and nuts between Turbine and Generator Shaft Coupling were found damaged Eroded Central Part of Gland Seal Assembly of MIV Main seal

18 R, M & U of unit-5 It was necessary to repair Labyrinth rings, replace housing of shaft gland seal, eccentric pins for guide vane lever and regulating rings, rotor rim studs, etc. Additional price of Rs.99.9 Lakhs with a delivery period of 6 months for supply and erection period of 3 months there after Unit 5 was synchronized with the grid after the completion of R, M&U works on

19 R, M & U of unit-6 Based on experience of unit 4 & 5 and inspection of Unit-6 carried out in dewatered condition(without dismantling). Additional orders were placed for supply of pivot ring based on inspection for unit-6 to save time Unit-6 was handed over on After opening of the unit, ND tests were carried out ND test results showed presence of crack in turbine shaft, erosion beyond permissible limits in top cover, high erosion and corrosion in runner and other under water parts

20 NDT test results DP test on turbine shaft Damages observed in poles Runner under DP test before refurbishment Cracks observed during MP test on pole end plates

21 Some of the Eroded/Damaged parts after opening of unit 6 Regulating ring Shaft Sleeve plate assembly Labyrinth ring Base metal erosion near labyrinth and liner plate area

22 List of Eroded/Damaged parts after opening of unit 6 GV body pitting Guide Vane Levers Pivot Ring Turbine Shaft

23 List of Eroded/Damaged parts after opening of unit 6 Regulation Ring Metal chipped out from vane exit area of Runner. Top Cover Top Cover Shaft gland housing Base metal erosion near labyrinth and liner plate area Eroded top cover

24 Additional orders placed for U#6 after inspection of components and discussions with OEM: OEM Repairs to turbine shaft and supply of modified shaft sleeve in August 2013 Supply of new top cover in October Top cover has been supplied in 6 months Contractor Refurbishment of runner Refurbishment of labyrinth ring Supply of new epoxy runner insulation disc Line boring works for assembly of top cover and pivot ring

25 Components after refurbishmentt Regulating ring MIV Guide Vane Levers New top Cover supplied by OEM New Pivot Ring

26 Pivot ring Order placed on Contractor for supply of pivot ring Noticed difference in flange thickness by 4.5mm during inspection Contractor proposed to provide additional plate of 4.5mm thickness of stainless steel-304 with rigid counter shank screw locking Contractor informed that they would fillet weld the SS plate with the base of pivot ring on the whole periphery Old Pivot Ring New Pivot Ring

27 Top Cover It was observed that the base metal has eroded more than 75% at critical areas and most of the eroded areas were beyond refurbish/repair. Contractor and OEM recommended for replacement of top cover. Old Top Cover Both recommended for replacement of top cover. The offer obtained from OEM was less and also time period offered was also less. Top Cover was supplied in six months New Top Cover

28 Turbine Shaft 2 Nos. cracks of size 170mm and 42mm found in Shaft at shaft seal machining area during DP test Around 7mm deep penetration of crack observed through traverse length of 50 60mm at Shaft sleeve seating area through Ultrasonic test OEM was consulted in the matter OEM informed that the defective portion of turbine shaft would be machined and diameter of the shaft shall be reduced in the entire portion where the shaft sleeve is to be fitted New SS shaft sleeve with reduced ID shall be fitted on the shaft & its OD machined Additional order placed on OEM for refurbishment of turbine shaft along with new SS shaft sleeve Time taken was about 4 months Turbine shaft under DP test

29 Runner After opening of unit 6, the following observations were made: Multiple pitting on runner vanes Metal chipped out 30 to 50mm from Runner vane exit area After NDT tests at factory, it was observed that runner had 236 indications on outside of 4-30mm and inside 85nos. indications of 4-20mm Both OEM and Contractor recommended for replacement of runner After detailed studies and need to put back the unit at the earliest, additional order for refurbishment of runner was placed on the Contractor. Metal Chipped out Turbine shaft under DP test Runner after refurbishment

30 Line boring Works Challenges: Stay ring refurbished in site. New Pivot ring with tolerance for line boring 0.25mm Machined in separate CNC machine. New top cover with tolerance of 2 mm for line boring Machined in separate CNC machine. Refurbished runner Observed that dia of top cover at regulating ring seating area was excess by 6mm. Pilot holes were provided for doweling. It was necessary to have proper matching for concentricity of holes with different parts and matching of dimensions of holes with close tolerances 0.05 mm/ m. An additional order placed for line boring works order value 24 Lakhs. Delivery period 45 days.

31 Matching of top cover and pivot ring at site This is a rare case of matching different components to achieve required results Top cover and pivot ring were manufactured by two different machines. Re-engineering took considerable amount of time The clearance between Labyrinth ring and top cover was maintained by 4 dowels and complete load of static labyrinth taken by bolts and transferred to top cover Unit 6 was synchronized to grid after completion of R, M&U works on Main reason for delay is non-availability of as built drawings and surprises noticed after opening of the unit Higher capacity oil coolers provided to bring down thrust bearing temperature and its performance after commissioning is satisfactory

32 Benefits Derived after R,M&U Works: Addition of 90 MW peaking capacity to the grid Life extension of 10 to 15 years Problem of over drawal of field current has been resolved by achieving circularity in stator and rotor forms Performance of the unit with respect to vibration and temperature rise of thrust bearing is generally satisfactory and is under observation Online monitoring of vibration levels and PD Analyser has become a safety tool to monitor the units at any instant of time

33 CONCLUSION R, M & U of the units provide opportunity for correcting some of the inherent problems and adopting new technology Challenging considering the requirement to match with many old parts for which neither machine drawings nor design calculations are available Undertaking timely RM&U & Life extension programme, life of generators has been extended Major works has been carried out only in Generator portion and higher output is achieved through higher guide vane opening utilizing the margins available in old machines It is clear from the experience of R, M & U that extent of refurbishment/replacement required in respect of turbine could not be assessed before opening of the unit

34 CONCLUSION After opening of the unit, reverse engineering will take considerable time which will affect the schedule of erection and commissioning OEM will have the advantage of having the initial designs and hence has the advantages with respect to manufacturing and delivery of new components NON-OEM manufacture may have a different solution for solving the problems. It may be difficult to bench mark the prices especially with respect to refurbishment works and with two differing technologies. These aspects have to be factored while executing the works to adhere to planned schedule

35 CONCLUSION We have taken up preparation of DPR for R&M works of turbine of Unit-1,2 & 3 in association with IIT Roorkee. DPR prepared and submitted to Hon ble KERC.

36 Rotor Turbine shaft Runner

37 Cross section of turbine with location of runner and top cover Top Cover Pivot ring Runner

38 THANK YOU