asset management - replacement criteria for distribution transformers
TRANSCRIPT
DNV GL © 2013 16-01-2014 SAFER, SMARTER, GREENER DNV GL © 2013 NL-OPE-AM JW001
16-01-2014
Dr Jos Wetzer
ENERGY
ECI webinar
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Replacement criteria for distribution transformers
DNV GL © 2013 16-01-2014
CONTENTS
Introduction
Modern asset
management
Transformer
lifetime issues
Transformer risk
management
Mitigation options
Decision making
process
Decision making
criteria
Conclusions
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DNV GL © 2013 16-01-2014
INTRODUCTION
Recent Trends
– Increased societal dependence on
reliable energy supply
– Upcoming replacement due to
investments in 60s and 70s
– New diagnostic- and monitoring-
technology
– Introduction of risk based asset
management concepts
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Question Addressed
How have recent trends influenced transformer asset management,
and in particular transformer replacement decisions
DNV GL © 2013 16-01-2014
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“
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MODERN ASSET MANAGEMENT
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Business value: RELIABILITY
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
Example distribution transformer
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Business value: SAFETY
Example of hazard
• Explosion of transformer (part) • Fire • Toxic byproducts
Preventive measures
• Maintenance • Monitoring • Replacement
Impact limitation
• Protection • Firewalls • Pressure relief • Safety measures
Business value: ENVIRONMENT
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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?
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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
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(TRANSFORMER) RISK MANAGEMENT
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RISK ANALYSIS
• Hazard
• Probability
• Impact
RISK ASSESSMENT
• Inventory / problem
• Scenario’s / likelihood
• Alternatives
• Constraints
• Objectives
(cost, life expectancy)
• Decision
RISK TREATMENT
• Prioritization
• Selection &
postponement
• Planning
• Execution
Acceptance
Criteria
Portfolio
Management
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RISK MITIGATION (IN GENERAL)
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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)
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Intensify monitoring and maintenance
Ensure performance; timely identify replacement
need, by:
– Higher frequency, additional maintenance
activities
– Apply transformer monitoring
– Health Index tools
DNV GL © 2013 16-01-2014
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
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DECISION MAKING PROCESS
(Suspected) end of life (Suspected) capacity bottleneck
Failure probability and impact
Quantification of problem
Failure probability and impact
Opportunities for improvement
Replacement Life time extension
Opportunities for improvement
Replacement Life time extension
Option 1 Option 2Option 1 Option 2
Costs & Benefits Costs & BenefitsCosts & Costs &
Decision makingDecision making
Costs & Benefits
Decision Making
Replacement
Costs & Benefits
Reduce restraints
Uprating Upgrading Reduce load
Opportunities for improvement
Quantification of (future) limitations
Congestion probability and impact
Quantification of (future) limitations
Congestion probability and impact
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DECISION MAKING PROCESS
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For a more detailed treatment of transformer replacement see e.g.
APPLICATION NOTE TRANSFORMER REPLACEMENT DECISIONS ECI Publication No Cu0185, available from www.leonardo-energy.org Bruno De Wachter, November 2013
DNV GL © 2013 16-01-2014
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
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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 RISK APPETITE
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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
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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.
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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
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