DURGAP UR PRESENTATION ON PREVENTIVE PREDICTIVE MAINTENANCE A

DURGAP UR PRESENTATION ON PREVENTIVE & PREDICTIVE MAINTENANCE. . A CASE STUDY S. BASU - Sr. Manager(EMD) A. SINGH-Asst. Manager(EMD) NSPCL-DURGAPUR WE WELCOME ALL

SYNOPSIS Ø Ø Ø Ø DURGAP UR Plant Overview. Case Study-1: Preventive Maintenance of GT-2 Case Study-2: Predictive Maintenance of GT-1 Identification of Problem Root Cause Analysis Implementation & Solution to the Problem Cost Analysis Conclusion

DURGAP UR v. NSPCL is a Joint Venture Company of captive power utility with 50: 50 equity share between NTPC & SAIL, two of India’s largest Maharatna PSUs. v. NSPCL is more process industry than a generator- performance evaluation on no of tripping with PLF or PAF. v At NSPCL Durgapur stresses more upon predictive and preventive maintenance instead of breakdown maintenance approach.

PLANT OVERVIEW DURGAP UR v. NSPCL is a Joint Venture Company of captive power utility with 50: 50 equity share between NTPC & SAIL, two of India’s largest Maharatna PSUs. NSPCL Durgapur is a captive power plant of 2 x 60 MW generating capacity for DSP/SAIL at Durgapur & both the units have been commissioned in 1986 and 1987 respectively. The entire power evacuation system is through 2 nos. of 75 MVA Generator Transformers 11. 5 k. V/33 k. V. v At NSPCL Durgapur, Electrical Maintenance Department stresses more upon pro-active and preventive maintenance instead of breakdown maintenance. v. NSPCL Durgapur is a captive power plant of 2 x 60 MW generating capacity for DSP/SAIL at Durgapur & both the units have been commissioned in 1986 and 1987 respectively. v. The entire power evacuation system is through 2 nos. of 75 MVA Generator Transformers 11. 5 k. V/33 k. V

DURGAP UR CASE STUDY-1: PREVENTIVE MAINTENANCE OF GENERATOR TRANSFORMER-2 Preventive maintenance involves time based systematic maintenance of equipment to lessen the likelihood of its failing. It is performed while the equipment is still working so that it does not break down unexpectedly. The problems are detected and corrected to enhance the life of the equipments. PM covers checking of oil level, thermography, silica gel replacement & performance of cooling system checking. At NSPCL Durgapur Transformer DGA analysis was carried out by NETRA.

BHEL GT-2 RATING-75 MVA KV-11. 5/33 HV AMPS-1312 LV AMPS-3765 OCTC: NO. OF TAPS-5 DURGAP UR

NETRA DIAGNOSIS DURGAP UR DGA ANALYSIS SAMPLING DATE H 2 100 CH 4 120 CO 350 CO 2 2500 C 2 H 4 50 C 2 H 6 65 C 2 H 2 1 TDCG 10. 09. 2018 10 2 153 1939 4 1 0 180 10. 12. 2018 35 56 147 2234 180 25 2 445 15. 12. 2018 32 63 113 1943 210 32 2 452 22. 12. 2018 63 123 155 2287 323 55 2 721 01. 2019 90 175 160 2478 514 82 5 1026 19. 01. 2019 127 255 123 1568 777 118 7 1407 27. 01. 2019 124 274 100 1769 876 136 8 1518 TABLE-1: DGA ANALYSIS OF GT-2 PRIOR TO SHUTDOWN

DGA ANALYSIS DURGAP UR As it can be observed that TDCG value of GT-2 has increased up to 1518, which indicates violation of Condition 1 & entering Condition-2 & would have entered the status of condition 3 also if corrective action had not been taken at right time. The values are greater than normal combustible gas level.

DECISION MAKING DURGAP UR ØValuable inputs received from NTPC-OS. ØGT replacement was a probable option. ØAccordingly shutdown planned after discussion. ØIt was also decided to check for any defects in the transformer through testing after shutdown during the replacement process. ØMeasurement of winding resistance. ØThrough checking if any abnormality found.

DURGAP UR INHOUSE REPAIRING, RECTIFICATION & IMPROVEMENT TEST RESULTS WINDING RESISTANCE OF HV SIDE TAP NO 1 U-1 N(mΩ) 1 V-1 N(mΩ) 1 W-1 N(mΩ) ERROR % 1 24. 60 28. 65 24. 90 14. 1% The contact resistance value in Y phase (14. 1%) is beyond IS tolerance limit (5%). Immediately stage inspection started & oil drained up to bushing level & found no abnormality in bushing.

OVERVIEW: OCTC OF BHEL GT DURGAP UR FIXED CONTACTS MOVING CONTACT

INTERNAL INSPECTION DURGAP UR Afterwards the entire oil was drained out and thorough internal inspection was carried out. The root cause of the problem was identified. In HV side Y phase tap-1 fixed contact, sparking and carbon deposition was found. The same was replaced by spare contact. CORRODED FIXED CONTACT

DURGAP UR REPAIRING UNDER PROCESS The entire job has been executed departmentally.

DURGAP UR After contact replacement winding resistance measurement was done and following results were obtained TEST RESULTS WINDING RESISTANCE OF HV SIDE AFTER RECTIFICATION TAP NO 1 U-1 N(mΩ) 1 V-1 N(mΩ) 1 W-1 N(mΩ) 1 24. 60 24. 65 24. 80 ERROR % 0. 8% The results were found satisfactory and charging clearance has been given after oil filling & filtration of oil

DURGAP UR DGA RESULT AFTER RECTIFICATION TEST SEQUENCE SAMPLING DATE H 2 100 CH 4 120 CO 350 CO 2 2500 C 2 H 4 50 C 2 H 6 65 C 2 H 2 1 AFTER FILTRATION BEFORE CHARGING 29. 01. 2019 8 23 7 323 141 28 1 AFTER 7 DAYS OF CHARGING 07. 02. 2019 7 24 8 350 138 29 1 1 MONTH AFTER CHARGING 25. 02. 2019 10 17 13 381 105 19 1 3 MONTHS AFTER CHARGING 22. 04. 2019 8 12 23 501 87 18 0 On 29. 01. 2019, the transformer was charged. DGA analysis was carried out after 1 month & 3 months and TDCG value was 165 & 148 respectively, which indicates no increase in all key fault gases. From DGA Table it can be inferred that TDCG values are within limit which means transformer operation was normal.

DURGAP UR COST ANALYSIS FOR GENERATOR TRANSFORMER-2 REPLACEMENT ØIn event of replacement of transformer time required will be approx 4 days Ø Generation loss of four days will be Rs: 92, 16, 000/(approx considering fixed cost as Rs 1. 60/kwh)…A ØDue to in-house repairing at site by Department, same transformer(GT-2) has been brought back to service with in 50 Hrs & running satisfactorily till date. ØHence generation loss of 50 Hrs will be Rs: 46, 08, 000/(approx considering fixed cost as Rs 1. 60/kwh)---B Hence total minimum savings : (A-B)=Rs 46, 08, 000/-

DURGAP UR CASE STUDY-2: PREDICTIVE MAINTENANCE OF GENERATOR TRANSFORMER-1 Predictive maintenance is a technique to predict the future failure point of a machine component, so that the component can be replaced, based on a plan/opportunity, just before it fails. Thus, equipment downtime is minimized and the component lifetime is maximized. This approach promises cost savings over routine or time-based preventive maintenance, because tasks are performed only when warranted.

ABB GT-1 RATING-75 MVA KV-11. 5/33 HV AMPS-1312 LV AMPS-3765 OCTC: NO. OF TAPS-5 DURGAP UR

DURGAP UR NETRA DIAGNOSIS SAMPLING DATE H 2 100 CH 4 120 DGA ANALYSIS CO 350 CO 2 2500 C 2 H 4 50 C 2 H 6 65 C 2 H 2 1 TDCG 14. 02. 2018 14 26 162 1632 71 11 0 284 13. 05. 2018 11 27 221 2363 74 12 0 345 12. 08. 2018 8 22 147 1858 41 9 0 227 10. 11. 2018 8 26 265 2271 67 14 0 380 01. 2019 7 23 231 2212 71 15 0 347 11. 03. 2019 4 17 157 1745 53 11 0 242 From DGA ANALYSIS it can be observed that although TDCG values are within limit & indicates no significant fault, but the ethylene component is greater than permissible limit for a long period.

DURGAP UR INHOUSE REPAIRING, RECTIFICATION & IMPROVEMENT During U#1 overhauling, GT-1 contact resistance measurement was done immediately after shutdown TEST RESULTS WINDING RESISTANCE OF HV SIDE TAP NO 1 U-1 N(mΩ) 1 V-1 N(mΩ) 1 21. 67 21. 26 1 W-1 N(mΩ) ERROR % 28. 46 25. 2% The contact resistance value in B phase (25. 2%) is beyond IS tolerance limit (5%). The transformer requires further checking in details. Inspection of bushings.

OVERVIEW: OCTC OF ABB GT TAP CONTACTS PHASE SIDE FIXED CONTACTS NEUTRAL SIDE DURGAP UR

IDENTIFICATION OF PROBLEMS DURGAP UR Entire oil was drained & thorough internal inspection was carried out through inspection chamber. The root cause of the problem was identified. In B phase tap both phase & neutral side moving contact & fixed contact, sparking and carbon deposition was found & the same was replaced by spare contacts. Carbonised fixed contact B-phase neutral side. Damaged Moving contact B-phase side Damaged fixed contact B-phase neutral side.

IDENTIFICATION OF PROBLEMS DURGAP UR Traces of carbon growth in tap contacts were also observed in R & Y phases. Pyrolytic carbon around the point of contact which would increasingly raise the contact resistance to a high value and overheating would become progressively more severe. Damaged Moving contact Bphase side Pyrolytic Carbon Growth

ROOT CAUSE ANALYSIS DURGAP UR Following actions were taken for all the phases: 1) Spring pin was replaced with 95 mm to 80 mm length for better spring pressure after consulting with tap changer OEM. 2) The Damaged tap contacts were replaced. Spring pin

DURGAP UR TEST RESULTS WINDING RESISTANCE OF HV SIDE AFTER RECTIFICATION TAP NO 1 U 1 N(mΩ) 1 V-1 N(mΩ) 1 W 1 N(mΩ) ERROR % 1 21. 03 21. 07 21. 09 0. 2% The results were found satisfactory and charging clearance has been given after oil filling & filtration of oil.

DURGAP UR DGA RESULT AFTER RECTIFICATION TEST SEQUENCE SAMPLING DATE H 2 100 CH 4 120 CO 350 CO 2 2500 C 2 H 4 50 C 2 H 6 65 C 2 H 2 1 LAST RESULT BEFORE S/D 11. 03. 2019 4 17 157 1745 53 11 0 AFTER FILTRATION BEFORE CHARGING 22. 04. 2019 1 2 11 290 8 2 0 AFTER 7 DAYS OF CHARGING 06. 05. 2019 1 1 18 252 6 2 0 AFTER 2 MONTHS OF CHARGING 01. 07. 2019 2 1 24 267 4 1 0 From DGA Table it can be inferred that all components including ethylene is within permissible limit. Thus the transformer was charged and is running smoothly

DURGAP UR COST ANALYSIS FOR GENERATOR TRANSFORMER-1 ØIn event of replacement of transformer time required will be approx 4 days Ø Generation loss of four days will be Rs. 92, 16, 000/(approx considering fixed cost as Rs 1. 60/kwh) Ø Cost of Replacement Rs. 10, 000/ØCost of Repairing Rs. 30, 000/Hence total savings =Rs. 1, 32, 16, 000/-

TANGIBLE BENEFITS DURGAP UR ØPredictive measure is a tool by which we can prevent any sort of forced outage & may not call for preventive maintenance also. We should stress upon predictive maintenance to achieve ØUnwanted long forced outage ØEquipment breakdown ØMaximize equipment life ØIncreased safety ØLower overall maintenance cost to a huge extent.

INTANGIBLE BENEFITS DURGAP UR ØOur team has gain self confidence in this high precision activity. ØIncreased motivation and positive attitude of team members. ØEffectiveness of team working is achieved.

CONCLUSION DURGAP UR ØAt present both the transformers are running successfully ØPre mature failure of very critical equipments has been avoided ØAbove all reliability of the system has improved which is of utmost importance for a captive power plant.

DURGAP UR MAJOR ROLE PLAYED SHRI. B. K. KONAR SUB ENGINEER SHRI. T. K. BARUI TECH.

DURGAP UR THANK YOU

DURGAP UR DGA LIMIT AS PER IEEE std C 57104 -2008 SR NO NAME OF THE GAS CHEMICAL SYMBOL PERMISSIBLE LEVEL(PPM V/V) 1 HYDROGEN H 2 100 2 METHANE CH 4 120 3 ACETYLENE C 2 H 2 1 4 ETHYLENE C 2 H 4 50 5 ETHANE C 2 H 6 65 6 CARBON MONOXIDE CO 350 7 CARBON DI-OXIDE CO 2 2500 TDCG=H 2+CH 4+C 2 H 6+C 2 H 2+CO AS PER IEEE std C 57 -104 -2008

DURGAP UR Evaluation of Transformer Condition Using Individual and TDCG Concentrations(AS PER IEEE std C 57 -104 -2008) STATUS H 2 (PPM) CH 4 (PPM) C 2 H 2 (PPM) C 2 H 4 (PPM) C 2 H 6 (PPM) CO 2 (PPM) TDCG REMARKS COND-1 100 120 1 50 65 350 2500 720 SAFE COND-2 101700 121400 2 -9 51100 66 -100 251570 25004000 7211920 CAUTION COND-3 7011800 4011000 10 -35 101200 101150 5711400 400110000 19214630 PLANNED OUTAGE COND-4 >1800 >1000 >35 >150 >1400 >100000 >4620 FORCED OUTAGE