Online Partial Discharge Monitoring to Predict Arc Faults in Medium Voltage Bus Ducts

Medium Voltage (MV) bus ducts use a nonuniform insulation system that relies on air and solid materials to achieve the required dielectric strength. The insulation defects commonly generate Partial Discharges (PDs) under nominal operating voltages, which eventually result in bus duct insulation deterioration and catastrophic failures due to arc faults. In this paper, online PD measurements conducted for 13.8kV bus ducts installed at an offshore substation are discussed. The PD measurements were performed using a portable monitor with an ultrasonic contact sensor. The measurement analysis was performed using established criteria based on best in-class industry practices and hands-on experience gained during several tests to assess the condition of HV equipment insulation systems. The measurement analysis concluded the presence of unacceptable PDs as per the industry practice acceptable limits. The bus ducts’ insulation faults were detected and accurately localized after analyzing several PD test results from different measurement points based on the amplitude comparison method. Further investigation revealed, the immediate cause of the PD was surface or tracking discharges due to moisture and dust accumulation in the air gap around the cushion insulating material placed between the bus ducts and the insulator supports. The deteriorated bus duct cushion material was replaced with new one. The PD measurements were repeated, and found at an acceptable level, confirming the integrity of the bus ducts’ fixed sections. In conclusion, the predictive maintenance of the bus ducts can be achieved on the basis of online PD monitoring, which is an effective, nondestructive, and noninvasive diagnostic tool to help detect and localize insulation defects. Thus prompt fixes can be planned accordingly to reduce equipment damage, flashovers, and personnel injuries, while enhancing the safety and reliability of the power systems in the future smart grid environment.