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CIGRÉ Technical Brochure No. 509: Final Report of the 2004 – 2007 International Enquiry on Reliability of High Voltage Equipment, Part 1 - Summary and General Matters

In 2002 CIGRÉ established working group A3.06 “Reliability of High Voltage Equipment” which was instructed to organize and carry out a worldwide enquiry into the service experience of circuit breakers, disconnectors, earthing switches, instrument transformers and gas insulated switchgear (GIS). The time period covered by the survey is 2004 - 2007, and the enquiry comprises equipment rated for voltages greater than or equal to 60 kV. For circuit breakers: only single pressure SF6 technology is included ; therefore, in practice equipment installed before around 1970 has been excluded. For disconnectors, earthing switches and instrument transformers there are no limitations in age or technology. Both equipment installed in air insulated and gas insulated substations are covered. Information has been collected by asking utilities to complete and return questionnaires ; 90 utilities from 30 countries have contributed. The surveyed service experience includes 281 090 circuit breaker years, 935 204 disconnector and earthing switch years, 1 290 335 instrument transformer years, and 88 971 GIS circuit breaker bay years. Service experience is counted in three phase units multiplied by time, except for instrument transformers which are counted as single phase units multiplied by time. The number of failure cards received for all components types combined amounts to 15 834, of which 3 847 concerned major failures. This makes this survey by far the most comprehensive reliability survey for high voltage apparatus ever carried out. The overall major failure frequency for circuit breakers is found to be 0.30 major failures per 100 circuit breaker years of service (three phase units). This is significantly lower than in a previous survey, and the improvement is observed for all types of enclosures. The failure frequency is found to increase with increasing rated voltage. For the first time the dependency of the failure frequencies to the kind of service is investigated. It is found that for all ages and kinds of circuit breakers shunt reactor switching results in the highest failure frequencies. The operating mechanisms account for the majority of all failures, which was also observed in a previous survey. Concerning the influence of age, younger circuit breakers tend to show lower failure frequencies than older ones. Wear and aging are the most frequently reported causes for minor as well as for major failures. For disconnectors and earthing switches the overall major failure frequency is determined to 0.21 failures per 100 equipment years of service (three phase units). The failure frequencies are significantly higher for disconnectors and earthing switches installed in air insulated substations than in gas insulated substations. One interesting result of the analysis is the overall 3:1-ratio between failures caused by the operating mechanisms and failures caused by the primary components of the equipment. Instrument transformers show an overall failure frequency of about 0.05 major failures per 100 single phase instruments transformer years of service. The major failure frequency for gas insulated substation instrument transformers is less than for those installed in air insulated substations. Instrument transformers with voltages between 60 and 100 kV have a lower major failure frequency also. The overall major failure frequency for GIS bays is about 0.4 major failures per 100 GIS circuit breaker bay years of service. This is lower than in the previous survey, and the difference is greater for indoor GIS. A GIS circuit breaker bay includes one circuit breaker and all associated disconnectors, instrument transformers, interconnecting busducts and/or parts of busbars and associated terminals. The major failure frequency for voltages up to 300 kV is found to be almost independent on voltage rating and lower than for GIS operating at higher voltages. Plots of failure frequency vs. GIS manufacturing year exhibit the bath tube curve shape. In general, individual equipment installed in GIS appears to have lower failure frequencies than equipment in air insulated substations. The evaluation of GIS maintenance and diagnostic practices shows that there is room for future improvement in efforts for preventing major failures and for initiating major maintenance at the right time. These efforts are mainly concerned with on-site GIS high voltage dielectric testing after erection and extension, and with diagnostic measurements and monitoring methods and their interpretation.

high voltage equipment; reliability; maintenance; enquiry; circuit breakers; disconnectors; earthing switches; instrument transformers; gas insulated switchgear; major failures; minor failures; major failure frequencies; failure characteristics

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