Effect of Gassing Material on Partial Discharge Characteristics in MCCB

Partial discharge (PD) already occurs at operating voltages in the low-voltage circuit breaker due to the miniaturization accompanied by increased power density and raised operational voltage. The paper evaluates the PD behavior in a molded case circuit breaker (MCCB) to consider the insulation degradation caused by gassing materials. In order to localize sources of field enhancement and partial discharge, intensified charge coupled device (ICCD) and infrared thermal imager are used to accurately determine the position. Furthermore, field strength of the whole conductor path in MCCB is numerically calculated with taking the action mechanism of metal particles and carbon layer into consideration to verify the correlation of the test results. It demonstrates that partial discharge occurs at the corner of iron splitters and the operating mechanism, which may be helpful for the design optimization of the MCCB.