Devin Van Zandt

GE Power Systems Energy Consulting

Schenectady, N.Y.

There have been widespread reports of flashovers during operation of distribution cable elbows (separable connectors) and insulated bushing caps. These failures have occurred primarily during routine switching when very small load currents, or just cable charging current, are interrupted. The numerous flashovers during insulated cap removal have been particularly perplexing because virtually no current is interrupted.

These flashovers are of particular concern due to the proximity of operating personnel to the faults. Customer interruptions, material replacement costs and lost crew time are additional negative consequences.

There is consensus within the industry that a partial vacuum phenomenon is a significant cause for the flashovers. Removal of an elbow or cap expands the sealed air volume inside the elbow, creating a partial vacuum that reduces the dielectric strength of the air. In response, major manufacturers have introduced redesigned components that seek to mitigate the partial vacuum condition.

The Distribution Systems Testing, Application, and Research (DSTAR) group- a consortium of utilities supporting distribution systems research, testing, and software tool development-began an extensive series of investigations and tests in 1995 to determine the causes of these flashovers. During the investigation, flashovers occurred for which the partial vacuum theory may not provide a satisfactory explanation. Some flashovers were experienced after the elbow cuff was clear of the bushing when partial vacuum along the elbow/bushing interface should have been equalized.

Because there remains a degree of uncertainty about root causes for elbow flashover problems, there is a need to gather more information on component performance.

DSTAR has launched a two-year project to collect and evaluate reports of separable connector field failures. A web-based survey form, located on the DSTAR web site, www.dstar.org, allows utilities across North America to contribute information related to separable connector field failures. The survey has been developed based upon the inputs of industry experts and the DSTAR-sponsored testing results. Data to be collected will include loading conditions, hardware involved, voltage level, switching configuration and environmental conditions.

The submitted data will be periodically analyzed and reports will be generated that summarize the industry experience and show any correlations. DSTAR may also use the information to plan future laboratory or field testing work.

Wide participation in the survey is of vital importance to the success of this project. DSTAR invites and encourages all utilities having data on elbow flashovers to participate in this survey by inputting information to the web site survey (follow the link to "Elbow Flashover Reporting").

Any questions regarding the survey should be directed to Devin Van Zandt, GE Power Systems Energy Consulting, telephone 518-385-9066, or e-mail devin.vanzandt@ps.ge.com.