PRESENTATION ON PREVENTIVE & PREDICTIVE MAINTENANCE....A CASE STUDY

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

2. DURGAPUR SYNOPSIS 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

3. DURGAPUR 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 is more process industry than a generator- performance evaluation on no of tripping with PLF or PAF. At NSPCL Durgapur stresses more upon predictive and preventive maintenance instead of breakdown maintenance approach.

4. PLANT OVERVIEW DURGAPUR 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 11.5kV/33kV. At NSPCL Durgapur, Electrical Maintenance Department stresses more upon pro-active and preventive maintenance instead of breakdown maintenance. • 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 11.5kV/33kV

5. DURGAPUR 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.

6. DURGAPUR BHEL GT-2 RATING-75 MVA KV-11.5/33 HV AMPS-1312 LV AMPS-3765 OCTC: NO. OF TAPS-5

7. DURGAPUR NETRA DIAGNOSIS DGA ANALYSIS TABLE-1: DGA ANALYSIS OF GT-2 PRIOR TO SHUTDOWN

8. DURGAPUR DGA ANALYSIS 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.

9. DURGAPUR DECISION MAKING Valuable inputs received from NTPC-OS. GT replacement was a probable option. Accordingly shutdown planned after discussion. It was also decided to check for any defects in the transformer through testing after shut-down during the replacement process. Measurement of winding resistance. Through checking if any abnormality found.

10. DURGAPUR INHOUSE REPAIRING, RECTIFICATION & IMPROVEMENT TEST RESULTS WINDING RESISTANCE OF HV SIDE 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.

11. DURGAPUR OVERVIEW: OCTC OF BHEL GT FIXED CONTACTS MOVING CONTACT

12. DURGAPUR INTERNAL INSPECTION 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

13. DURGAPUR REPAIRING UNDER PROCESS The entire job has been executed departmentally.

14. DURGAPUR After contact replacement winding resistance measurement was done and following results were obtained TEST RESULTS WINDING RESISTANCE OF HV SIDE AFTER RECTIFICATION The results were found satisfactory and charging clearance has been given after oil filling & filtration of oil

15. DURGAPUR DGA RESULT AFTER RECTIFICATION 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.

16. DURGAPUR COST ANALYSIS FOR GENERATOR TRANSFORMER-2 REPLACEMENT In event of replacement of transformer time required will be approx 4 days Generation loss of four days will be Rs:92,16,000/-(approx considering fixed cost as Rs1.60/kwh)…A Due 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. Hence generation loss of 50 Hrs will be Rs:46,08,000/-(approx considering fixed cost as Rs1.60/kwh)---B Hence total minimum savings :(A-B)=Rs46,08,000/-

17. DURGAPUR 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.

18. DURGAPUR ABB GT-1 RATING-75 MVA KV-11.5/33 HV AMPS-1312 LV AMPS-3765 OCTC: NO. OF TAPS-5

19. DURGAPUR NETRA DIAGNOSIS DGA ANALYSIS 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.

20. DURGAPUR 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 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.

21. OVERVIEW:OCTC OF ABB GT DURGAPUR TAP CONTACTS PHASE SIDE FIXED CONTACTS NEUTRAL SIDE

22. DURGAPUR IDENTIFICATION OF PROBLEMS 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.

23. DURGAPUR IDENTIFICATION OF PROBLEMS 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 B-phase side Pyrolytic Carbon Growth

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

25. DURGAPUR TEST RESULTS WINDING RESISTANCE OF HV SIDE AFTER RECTIFICATION The results were found satisfactory and charging clearance has been given after oil filling & filtration of oil.

26. DURGAPUR DGA RESULT AFTER RECTIFICATION 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

27. DURGAPUR COST ANALYSIS FOR GENERATOR TRANSFORMER-1 In event of replacement of transformer time required will be approx 4 days Generation loss of four days will be Rs.92,16,000/-(approx considering fixed cost as Rs1.60/kwh) Cost of Replacement Rs.10,00,000/- Cost of Repairing Rs.30,00,000/- Hence total savings =Rs.1,32,16,000/-

28. DURGAPUR TANGIBLE BENEFITS Predictive 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 Unwanted long forced outage Equipment breakdown Maximize equipment life Increased safety Lower overall maintenance cost to a huge extent.

29. DURGAPUR INTANGIBLE BENEFITS Our team has gain self confidence in this high precision activity. Increased motivation and positive attitude of team members. Effectiveness of team working is achieved.

30. DURGAPUR CONCLUSION At present both the transformers are running successfully Pre mature failure of very critical equipments has been avoided Above all reliability of the system has improved which is of utmost importance for a captive power plant.

31. DURGAPUR MAJOR ROLE PLAYED

32. DURGAPUR THANK YOU

33. DURGAPUR DGA LIMIT AS PER IEEE std C57-104-2008 TDCG=H2+CH4+C2H4+C2H6+C2H2+CO AS PER IEEE std C57-104-2008

34. DURGAPUR Evaluation of Transformer Condition Using Individual and TDCG Concentrations(AS PER IEEE std C57-104-2008)