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 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