Asset Management - Replacement Criteria for Distribution Transformers


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This session is part of the Clean Energy Regulators Initiative Webinar Programme.

Theme 2 - Pressure Points

Module 3: Asset Management - Replacement criteria for distribution transformers

In today's power grids, transformers represent a significant capital investment and play a crucial role in the reliability of the grid and the availability of electric power. It is the task of the asset or plant manager to safeguard reliability and control risks at limited cost. The asset management instruments that may be used, in increasing order of effectiveness and cost, are monitoring, maintenance, refurbishment and replacement.

Asset management has moved from "doing the best we can" to "doing what is necessary to maintain the balance between performance, cost and risk, given the company business values". This paradigm shift has changed the way replacement decisions are being taken. On the basis of company business values, risks are being identified and assessed, from the combination of failure probability and impact. Decisions are based on the hazard risk score (urgency) and on the risk reduction capability of the mitigating measure (effectiveness), and are dependent on the company's risk appetite.

Whereas replacement alternatives are often attractive for high power transformers due to the relatively high cost of replacement, this situation is quite different for distribution transformers. Distribution transformers are often regarded as commodities. They are relatively inexpensive and can be delivered off stock. Therefore alternatives for replacement need to be low cost, and thereby effective, efficient and standardized. As a result such alternatives are at present often cost effective only on a fleet scale, and too expensive for individual transformers. This situation may change when alternative solutions such as monitoring devices will be integrated as a low cost commodity in new distribution transformers.

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Asset Management - Replacement Criteria for Distribution Transformers

  1. 1. ENERGY ECI webinar Replacement criteria for distribution transformers Dr Jos Wetzer 16-01-2014 1 DNV GL © 2013 NL-OPE-AM JW001 16-01-2014 SAFER, SMARTER, GREENER
  2. 2. CONTENTS  Introduction  Modern asset management  Transformer lifetime issues  Transformer risk management  Mitigation options  Decision making process  Decision making criteria  Conclusions 2 DNV GL © 2013 16-01-2014
  3. 3. INTRODUCTION  Recent Trends – Increased societal dependence on reliable energy supply – Upcoming replacement due to investments in 60s and 70s – New diagnostic- and monitoringtechnology – Introduction of risk based asset management concepts  Question Addressed How have recent trends influenced transformer asset management, and in particular transformer replacement decisions 3 DNV GL © 2013 16-01-2014
  4. 4. MODERN ASSET MANAGEMENT  Asset management has changed: – from "doing the best we can" – to "doing what is necessary to maintain the balance between performance, cost and risk, given company business values“ 4 DNV GL © 2013 16-01-2014
  5. 5. MODERN ASSET MANAGEMENT 5 DNV GL © 2013 16-01-2014
  6. 6. MODERN ASSET MANAGEMENT  Introduction of PAS55, based on risk management process: – definition of business values (reliability, safety, etc) – identification of hazards – analyse hazard probability, impact and risk – define degree of risk acceptance (appetite) – decision based on risk score (urgency) and on risk reduction effectiveness Business value: RELIABILITY Business value: ENVIRONMENT Business value: SAFETY 6 DNV GL © 2013 16-01-2014 • • • Explosion of transformer (part) Fire Toxic byproducts • • • Maintenance Monitoring Replacement Impact limitation  Example of hazard Preventive measures  Example distribution transformer • • • • Protection Firewalls Pressure relief Safety measures
  7. 7. LIFETIME ISSUE 1: DO TRANSFORMERS REACH THE END OF LIFE?  The most frequent causes of failure o Tap changer failure, bushing failure (tap changers and bushings can be replaced)  Only few failures are caused by external causes o Short circuit current, lightning strike, transient overvoltage  End of life is not based on age but on remaining life o Only insulation winding paper shows irreversible degradation o Remaining life from loading guide, furfural analysis or statistical analysis  The transformer end of life o Determined by paper insulation degradation o Depends on acceptable failure probability o Is hardly ever reached o Hardly ever reason for replacement  What are the main replacement criteria? 7 DNV GL © 2013 16-01-2014
  8. 8. LIFETIME ISSUE 2: WHAT ARE THE REASONS FOR REPLACEMENT?  Unacceptability of failure probability  Transformer losing functionality Inability of the grid to deliver sufficient power, or inability to comply with government or SHE regulations (acoustic emission, PCB presence in oil), due to – Increasing grid demands (power rating) – Changing environmental requirements  Transformer losing maintainability – Spare parts are no longer available – Insufficient knowledge, capacity or willingness to keep maintaining equipment. – Too much diversity for efficient maintenance  Transformer showing operational issues – Replacement by low-loss alternatives may outweigh losses 8 DNV GL © 2013 16-01-2014
  9. 9. (TRANSFORMER) RISK MANAGEMENT Acceptance Criteria Portfolio Management RISK ANALYSIS RISK TREATMENT • Hazard • Probability • Impact 9 RISK ASSESSMENT • • • • • Inventory / problem Scenario’s / likelihood Alternatives Constraints Objectives (cost, life expectancy) • Decision • Prioritization • Selection & postponement • Planning • Execution DNV GL © 2013 16-01-2014
  10. 10. RISK MITIGATION (IN GENERAL) 10 DNV GL © 2013 16-01-2014
  11. 11. MITIGATION OPTIONS (TRANSFORMERS)  Adjust functional characteristics – Increase power rating by enhanced cooling (insufficient power rating) – Apply acoustic insulation (acoustic emission) – Cleaning or containing the oil (PCB containment)  Intensify monitoring and maintenance Ensure performance; timely identify replacement need, by: – Higher frequency, additional maintenance activities – Apply transformer monitoring – Health Index tools 11 DNV GL © 2013 16-01-2014
  12. 12. MITIGATION OPTIONS (TRANSFORMERS)  Refurbishment and life time extension – Often transformers exceed design life (moderate loading, prevailing design margins) – Lifetime may be extended by replacing critical parts  O&M policy and practice – Load control (slow down degradation, buy time) – Intensification of maintenance, keeping a supply of spare parts, contracting alternative providers  Replacement – Distribution transformers: end of life (or: increasing failure probability) is seldom a replacement criterion on its own – Other criteria include: lack of spare parts or service, losses, or inability to meet (future) requirements – Recent criterion: instrument to spread costs and manpower needed for large scale replacement and delivery risks 12 DNV GL © 2013 16-01-2014
  13. 13. DECISION MAKING PROCESS (Suspected) end of life (Suspected) capacity bottleneck Quantification of problem Quantification of (future) limitations Failure probability and impact Congestion probability and impact Opportunities for improvement Opportunities for improvement Life time extension Option 1 Replacement Option 2 Costs & Benefits Uprating Costs & Benefits Decision making 13 DNV GL © 2013 16-01-2014 Replacement Reduce restraints Upgrading Costs & Benefits Reduce load Costs & Benefits Decision Making
  14. 14. DECISION MAKING PROCESS For a more detailed treatment of transformer replacement see e.g. APPLICATION NOTE TRANSFORMER REPLACEMENT DECISIONS ECI Publication No Cu0185, available from Bruno De Wachter, November 2013 14 DNV GL © 2013 16-01-2014
  15. 15. DECISION MAKING CRITERIA  The key criteria in this decision process are: – Failure probability and failure impact – Risk profile (urgency) and appetite (acceptability) – Effectiveness of different alternatives (prioritized action) – Cost & return on investment of the different alternatives.  Aging population: additional constraints to manage replacement wave: – Concentration of investments required – Concentration of manpower required – Production capacity of manufacturers 15 DNV GL © 2013 16-01-2014
  16. 16. CONCLUSIONS 1 DECISION PROCESS  Asset management decision taking is governed by company business values, risk evaluation (probability and impact), risk appetite and risk based urgency, and on the risk reduction capability of the mitigating measures. RISK BASED DECISION PROCESS 16 DNV GL © 2013 16-01-2014 RISK APPETITE
  17. 17. CONCLUSION 2 DECISION CRITERIA  Transformer age is not a replacement criterion  End of life is a replacement criterion, but is hardly ever reached – End of life is governed by loss of life / remaining life (load, temperature)  Common replacement criteria include – Transformer losing functionality – Transformer losing maintainability – Transformer showing operational issues  Replacement alternatives include – Adjusting functional characteristics – Intensifying monitoring and maintenance – Refurbishment and life time extension – Adjusting O&M policy and practice 17 DNV GL © 2013 16-01-2014
  18. 18. CONCLUSION 3 HIGH POWER & DISTRIBUTION TRANSFORMERS  Replacement alternatives are often attractive for high power transformers (high replacement cost).  Distribution transformers are often regarded as commodities, relatively inexpensive, deliverable off stock. (Identification of) alternatives for replacement need to be low cost, effective, efficient and standardized. 18 DNV GL © 2013 16-01-2014
  19. 19. CONCLUSION 4 DISTRIBUTION TRANSFORMER ALTERNATIVES  For distribution transformers, alternatives for one-to-one replacement are only worthwhile if: – Monitoring devices are integrated as low cost commodities – Replacement need is monitored, analysed and prioritized on a fleet scale, and supported by Health Indexing Tools 19 DNV GL © 2013 16-01-2014
  20. 20. Thank you for your attention! Replacement criteria for distribution transformers +31 26 356 6388 SAFER, SMARTER, GREENER 20 DNV GL © 2013 16-01-2014