Partial Discharge Monitoring to Predict Failures in 230 kV GIS Substation using UHF and Ultrasonic Sensors

Partial Discharge (PD) monitoring in Gas Insulated Switchgear (GIS) is one of the leading diagnostic techniques that helps to predict potential failures. Approximately 90% of insulation breakdowns can be attributed to PD activities, which when detected, can help avoid unplanned power interruptions. A recent failure of a voltage transformer (VT) in a GIS substation triggered a recommendation to conduct PD measurements to evaluate the VTs’ insulation healthiness. The incident occurred due to a flashover inside the VT compartment, with noticeable flashover traces on the insulation spacer and around the High Voltage (HV) coil of the VT. This paper presents the outcome of the conducted PD measurements on 186 VTs, installed in four GIS substations, using Ultra High Frequency (UHF) and Ultrasonic Contact (UC) sensors; followed by the measurement outcome, PD data analysis, and corrective actions. In addition to the PD measurements, visual inspection was conducted on the manual Integrated Isolating Device (IID) locking condition, which is used to isolate the VT from other GIS High Voltage systems. Noting that GISs under consideration were not installed with internal PD sensors, hence, external UHF barrier and UC sensors were used to conduct online PD measurements on the subject VTs. The paper further presents the impact of the corrective action that was implemented on the VTs that showed high PD measurements in the vicinity of the IID, which indicate that the IIDs were not in the desired position. The major recommendations issued from analyzing the measurements were, locking the VT IIDs in the end position and including PD measurements in the Preventive Maintenance program. In conclusion, the predictive maintenance of the GIS equipment 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.