Field experiences using Radio Frequency Scanning (RFS) to detect partial discharge in bus duct and metal clad switchgear of electrical generating and transmission substations

It is well known that Partial Discharge (PD) is the latest stage of almost all failure modes in electrical insulation. Early detection of this phenomenon can avoid catastrophic failures of electrical equipments installed on transmission, distribution and generating stations. In this paper, two practical experiences using Radio Frequency Scanning (RFS) to detect partial discharge in electrical equipments are described. PD occurrence in two of three phases of a 13.8 kV air isolated bus duct was detected using RFS combined with single phase energizing of each phase of the bus at different voltages. In this case, RFS technique was used after suspicions of PD activity in a 115 kV GSU power transformer and a 160 MVA generator was detected using acoustic emission (AE) and EMI tests with Radio Frequency Current Transformers. Finally, the source of PD was detected in the 13.8 kV bus duct connecting generator with power transformer. The second case describes the use of RFS to detect PD and corona activity inside a 34.5 kV metal clad switchgear located on a 500 kV substation and close to an energized overhead line. Although the electrical interference in the area was the main concern to get a reliable measurement, digital filtering and wide band scanning of the RFS technique showed high efficacy to discriminate PD activity inside the switchgear. Additional infrared scanning was done with the purpose of locating the points where corona and PD occurred. Final RFS results confirmed the abnormal condition of a circuit breaker in the switchgear.