Maintenance strategies
ELEC-E8401 - Condition Monitoring of
Electrical Equipment L
Eero Pehkonen
Maintenance
• Maintenance is the combination of all technical and
management actions intended to retain an item in, or
restore it to, a state in which it can perform as required.
(Source: IEC)
Why use maintenance strategies?
• Large amount of life-cycle cost are allocated to
maintenance activities
• Reliability has a significant economical role so condition
management is important
• Business area is more difficult because of regulations
and competition
• Extend lifetime of the system components or prolong the
period between repairs
Balance of maintenance
• Maintenance is one of the asset management
alternatives
• Aim is to achieve balance between costs and reliability
– Too little of maintenance can cause costly system failures
– Too much of maintenance is not cost-effective
• Component level or system level
Maintenance strategies
• CM - Corrective Maintenance
– Corrective maintenance actions in case of a fault in order to
return to normal condition
– Run to failure: inspections aren’t performed. Replacement is
done when component fails.
• TBM - Time Based Maintenance
– Age replacement
– Periodic inspections
– Sequential inspections
Maintenance strategies
• CBM - Condition Based Maintenance
– Continuous inspection
– Component is replaced when it doesn’t fill the requirements
• RCM - Reliability Centered Maintenance
– Systematic approach for identifying effective and efficient
preventative maintenance tasks for items in accordance with a
set of specific procedures and for establishing intervals between
maintenance tasks
– Selects the maintenance strategy to be used (CM, TBM, CBM)
Typically used strategies
• Scheduled Maintenance
– Big spread in reported maintenance intervals and durations (
generators, transformers, breakers)
– Preventive maintenance strategy
– Time intervals are based on probabilities
• Predictive (as needed) maintenance
– Use of periodic inspections (transformers) and continuous
monitoring (generators)
• Reliability-Centered Maintenance (RCM)
• Probabilistic Models
– Based on number estimations of system components
– Block diagrams, fault trees, Markov models, Monte Carlo
simulation etc.
Maintenance measures
Strategy
Measures
Inspection
Servicing
Repairment
Renewal
Corrective
-
-
In case of
failure
In case of
failure
Time based
Intervally
Intervally
In case of
failure
Intervally
Condition
based
Periodic
inspections or
continuous
monitoring
According to
condition
In case of
failure
According to
condition
Reliabilitycentered
According to maintenance strategy on component base
Probabilistic
Periodic
inspections or
continuous
monitoring
According to
condition,
importance
and outage risk
In case of
failure
According to
condition,
importance
and outage risk