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Reducing Partial Vacuum Induced Flashovers in 25 kV Class Loadbreak Separable Connectors

By Randy Hurst

The 25 kV Class 200 Ampere loadbreak separable insulated connector system didn't always have today's reputation for safety and reliability. As 25 kV Class loadbreak connectors increased in popularity in the 1980's and 1990's, utilities reported unacceptably high numbers of flashovers during energized switching operations. These line-to-ground faults were more likely to occur in colder weather, at higher altitudes, with lower load currents, and with stuck interfaces. The partial vacuum induced flashovers were not seen in 15 kV Class connectors or 35 kV Class large interface connectors because the lengths of these interfaces, relative to their voltage ratings, are sufficient to prevent dielectric breakdown under normal service conditions even in the presence of severe partial vacuum. However, because the 25 kV interface is the same length as the 15 kV interface – and the rated line-to-ground voltage is almost twice as high – the voltage stress along the interface is almost double that of the 15 kV Class interface. This higher voltage stress makes it vulnerable to partial vacuum induced flashovers. In hindsight, the 25 kV Class 200 Ampere loadbreak bushing was designed too short for exceptional dielectric robustness.

Read full article in the Overhead and Underground T&D Special Edition 2021

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