Principal Research Results

Study of Decision Support Programs for Maintenance Strategyof Electric Power Equipment (Ⅱ)
BackgroundIn sections responsible for the maintenance of electric power equipments, there is a need to rationalize inspection, maintenance and renewal strategies of service-aged equipments in order to cut maintenance costs and form a rational renewal plan for themany equipments that were installed in the high-growth period. One solution is to incorporate economic evaluation, which has notbeen systematically made up to now. From this viewpoint, there is a great deal of interest in the asset management technique and its
concrete introduction, and convenient decision support programs are being developed in CRIEPI.

Objectives
This study aims to develop support programs for overhaul planning and renewal strategy compilation based on the proposed
method ＊ 1, which evaluates according to average maintenance cost.

Principal Results
1. Support program for overhaul planningThis supports overhaul planning of equipments whose annual maintenance cost increases with operating time (e. g. transformer) (Fig. 1). Its features are as follows:(1) Relationship between annual maintenance cost and age is specified by three parameters, (i) constant base cost, (ii) starting age ofcost increase, (iii) cost increase rate (linear increase is assumed), in order to be applicable to the characteristics of various equipments.
(2) As overhaul condition, periodic/same scale and non-periodic/different scale are selectable.
2. Support program for renewal strategy compilation
By classifying and accumulating maintenance expenses along operation time, average maintenance cost during the life canbe evaluated. This program supports selection of renewal timing (economic life) of GCB (Gas-insulated Circuit Breaker) by evaluating average maintenance cost and operation period (Fig. 2). Its features are as follows:(1) The maintenance expenses are classified into (i) expense increasing with operation time (e. g. painting of tank surface), (ii)
expense needed periodically (e. g. periodic inspection), (iii) expense needed non-periodically (e. g. legal inspection and exchangeof control units) and (iv) accidental expense (e. g. failure cost). By accumulating these expenses, the life cycle cost is calculated,and relationship between average maintenance cost and operation time is derived. Appropriate renewal timing can be estimatedfrom this characteristic.
(2) Annual necessary maintenance cost is illustrated during operation time. It supports budget planning.

Future Developments
Evaluation programs including economic indicator for maintenance strategy of various equipments according to theircharacteristics will be developed, and a synthetic support tool (programs) for maintenance strategy with condition evaluation bydiagnosis will be investigated.
Main Researcher: Tsuguhiro Takahashi, Ph. D.,
Senior Research Scientist, Electric Power Apparatus Insulation Sector, Electric Power Engineering Research Laboratory
Reference
T. Takahashi, et al, 2008, “Study of decision support programs for maintenance strategy of electric power equipment Part II - Decision
support tools for maintenance strategy by evaluating average repairing cost” CRIEPI Report H07013 (in Japanese)＊1：T. Takahashi, et al, 2007, “Study of decision support programs for maintenance strategy of electric power equipment - Proposal of diagnostic
database application and repairing cost evaluation method,” CRIEPI Report H06014 (in Japanese)74

4. Power Delivery

Fig.1 Display of support program for overhaul planning(Costs are standardized according to cost of equipment)
By inputting characteristics of annual maintenance cost, failure probability and so on, low cost condition of overhaul strategy(timing and expense) can be examined with average maintenance cost during the assumed (expected) operation period.

Fig.2 Display of support program for renewal strategy
By inputting necessary costs (annual repair cost, failure cost, periodic and non-periodic expense) over time, relationship between
average cost and operating years is calculated. The number of years where the mean required cost is a minimum is suggested as
the time for renewal (economic life).

754