1. Maintenance strategies
ELEC-E Condition Monitoring of Electrical Equipment L
Eero Pehkonen

2. 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)

3. 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

4. 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

5. 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

6. 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)

7. 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.

8. Maintenance measures Strategy Measures Inspection Servicing Repairment
Renewal
Corrective -
In case of failure
Time based
Intervally
Condition based
Periodic inspections or continuous monitoring
According to condition
Reliability-centered
According to maintenance strategy on component base
Probabilistic
According to
condition, importance
and outage risk