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Condition-based maintenance (CBM)
On MV power networks
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Focus maintenance costs and investments on the parts of the underground cable network that really need it! Determine a strategy, select the cables to be diagnosed and then take action! This is the systematic, logical approach to CBM developed by KEMA.
This will result in reduced operational costs, reduced claims because of fewer outages and investments in those parts of the network that really need to be refurbished. The savings realized exceed the costs!
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Strategy for CBM on Power Cables
The starting point is determining a strategy. It is important to identify goals and then focus efforts accordingly. Typical goals include eliminating problem circuits, determining the risk of failure and reducing claims.
Based on the strategy adopted, rules are developed for selecting network components for diagnosis.
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Selection rules
The history, operational and laying conditions, together with the importance of the cable circuit in the network, provide clues to the asset manager that are helpful in deciding whether or not to perform diagnostic testing.
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Diagnostic testing
The type of cable and the nature of failures experienced in the past will determine the most effective diagnostic method in each case. In about 90% of the cases, partial discharge diagnostics (PDD) is the best method to apply since weak spots generating partial discharges will be detected. Based on the results of the partial discharge diagnostic testing, a recommendation for action will be prepared for each circuit. Typical recommendations include:- Immediate repair
- Repair within 1 year
- Repeat measurement after 1 year
- No action needed
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Selection of additional circuits for diagnosis
The recommended actions prepared on the basis of the results of the partial discharge tests can be extended to other circuits having similar constructions and performance records. In addition, decisions can then be made regarding the selection of additional circuits in the network requiring condition assessment. The results of these additional assessments can then be extended to circuits and network components having similar constructions and performance records. Using this approach, the results of a limited number of tests can be extended to a large section of the entire network.
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Maintenance and investment strategy
Knowing the actual condition of circuits diagnosed and the assumed condition of similar parts/components in the network, informed decisions can be made regarding maintenance, repair and future investments. This proactive strategy should result in fewer outages, increased network reliability and reduced costs.
"An ounce of prevention is worth a pound of cure."
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Experiences
Asset managers at electric utilities who have applied the CBM
methods to power cables have reported very positive results. The
savings realized have exceeded the costs of the CBM diagnostic
tests.
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Benefits
Diagnostic testing provides a reliable assessment of the present condition of the underground MV cable network components. Your benefits are:- Replacement decisions can be based on the actual (not the assumed) condition of the network components
- Reliability of the network will be enhanced
- Unscheduled outages will be decreased
- Operating costs will be reduced
- Liability claims will be reduced
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KEMA services
KEMA can support you in - Selecting a maintenance strategy
- Finding the background of degradation
- Selection of effective diagnostic methods (method, third parties that can do these measurements, price)
- Performing diagnostic measurements such as:
o Partial discharge diagnostics on all types of MV cable circuits
o Water tree diagnostics on MV polymeric circuits
o PD diagnostics on MV and HV cable accessories
o Outer sheath and voltage withstand testing of cable insulation
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