Measurements of Breakdown Voltage Characteristics of Medium Voltage Vacuum Circuit Breaker After Current Interruption

We present a test circuit for measuring the breakdown voltage characteristics of a vacuum circuit breaker after current interruption process. The test circuit combines the high current part from the synthetic test circuit as per IEC Std. 62271-101 with the so-called Rabus high voltage part. The high current part reproduces the current phase before voltage build-up occurring after zero current crossing, then the Rabus high voltage part provides voltage breakdowns constituting breakdown voltage characteristics. The high current part can be adjusted to represent the actual current conditions which influences the physical conditions of the contact system upon which the interruption process is highly dependent. To illustrate the measuring system and the measuring procedure, the measurements of the breakdown voltages are reported for a commercial 12 kV/1250 A/31.5 kA vacuum circuit breaker. The breakdown voltages are measured primarily as a function of time and then converted via a contact travel curve into the vacuum interrupter contact gap function. This allows the results to be converted back and applied to a breaker with the same characteristics of the vacuum interrupter unit operating in similar current conditions, but with different mechanical characteristics of the breaker-specific actuator than the one used in testing.