Technical Maintenance of Pole Mounted Circuit Breaker (PMCB) on the Tanjung Tembaga Feeder at PT PLN (Persero) ULP Probolinggo Distribution Network

The reliability of electrical distribution systems is critically dependent on the performance of protection devices such as the Pole Mounted Circuit Breaker (PMCB). This study focuses on the maintenance and performance evaluation of the PMCB installed on the Tanjung Tembaga feeder operated by PT PLN (Persero) ULP Probolinggo. The evaluation process involved a series of tests, including trip current and response time measurements, alongside supporting measurements on the Vacuum Circuit Breaker (VCB). The test results revealed that while trip current values slightly exceeded the standard of 15 A, they remained within acceptable technical limits. However, two out of three tests recorded trip times of 2 seconds, far above the standard maximum of 50 milliseconds, indicating a significant delay in fault response. In contrast, the VCB demonstrated optimal performance, with a contact resistance of 95 µΩ, an operational voltage of 110 VDC, and an insulation resistance of 1100 MΩ. These findings suggest that although the PMCB remains functionally capable of interrupting current, improvements are needed in its tripping mechanism to enhance response time. This study emphasizes the importance of routine testing and calibration to ensure the reliability and safety of medium-voltage distribution systems.