R.G.A. Zoetmulder, S. Meijer and J.J. Smit Conditional Based Maintenance with On-line Partial Discharge Measurements of HV and MV Switchgear Systems R.G.A. Zoetmulder, S. Meijer and J.J. Smit Presented by J.J. Smit Good morning ladies and gentlemen. I would like to present a part of the work was has been done by one of my phd. students on condition based maintenance at High Voltage and Medium Voltage switchgear. Question number 8

Introduction and Goal Insulation test: 1: Detection 2: Defect identification 3: Defect localization 4: Risk assessment Goal: To apply the UHF measuring technique used for High Voltage Switchgear (HV GIS) also for : Although the installations have shown to be very reliable, inside a GIS failures can still occur. Presently maintenance at high voltage switchgear is performed depending on the condition of the insulating materials. Insulation tests as a tool of the Condition Based processes consists of 4 steps: - Detection, -Defect identification, -Defect localization,- Risk assessment . Because UHF measurement techniques became a more established PD technique for High Voltage GIS. It also became very interesting to look if based on this measuring system also measurements could be performed at other electrical switching equipment. So the goal of this research was: To apply the UHF measuring technique, normally used for High Voltage Switchgear (HV GIS), also on - medium voltage Gas Insulated - medium voltage Air Insulated and - medium voltage Oil Insulated Systems Medium Voltage Gas Insulated Systems (MV-GIS) Medium Voltage Air Insulated Systems (MV-AIS) Medium Voltage Oil Insulated Systems (MV-OIS)

The measuring system * Hard-ware Components: 1 a: Internal UHF coupler Broadband detection > UHF (till several GHz) With this method noises can be suppressed by measuring at a frequency band with a low noise-level Components: 1 a: Internal UHF coupler 1 b: external UHF coupler 2 : Pre-amplifier 3 : Spectrum analyzer 4 : Computer The hardware part of the partial discharge measurement system, what is used in Delft, is based on the UHF method.   The UHF measurement system consists mainly of 4 items: 1- UHF couplers ; internal UHF couplers and external UHF couplers can be used. 2- Pre-amplifier; directly connected to the coupler. 3- A spectrum analyzer; And 4- The computer; to post process the measured data. Modern GIS often are provided with internal UHF couplers. But for on-line measurements at older GIS the external UHF coupler are frequently used for PD measurements.

10 kV Air Insulated Switchgear system-1 - Vacuum Circuit-Breaker - Measuring locations are small inspection windows - UHF signals can propagate through these inspection windows and can than be detected Front-side Back-side Advanced stadium (More affected) Begin stadium (less affected) One of the installations to check if the UHF measurement system could also be used at medium voltage switchgear systems, was this 10 kV air insulated system. The AIS has at the front-side three inspection windows, see figure A. The UHF signals can propagate through the inspection windows and can be detected by the external UHF coupler fixed to one of these windows. This switchgear system has vacuum cylinders, but the connections from or to the circuit-breaker are air insulated as can be seen in figure b. It was not the first time insulation problems occurred in this installation. At an earlier moment, at the same location, also deterioration in a more advanced state of the insulating rubber was present. It was only at an other connector. Tracking due to surface discharges could clearly be seen. To plan future maintenance actions, it was decided to perform periodic PD measurements. During one of these inspections PD activity was observed. The measurement results will be presented on the next slide. After analysis of the PD measurements a visual inspection was performed and slight tracking was observed. Surface discharge at one of the phase connectors of the circuit-breaker

10 kV Air Insulated Switchgear system-2 At one of the bay’s a PD measurement was performed. A frequency spectrum was taken. The dashed line is the back ground noise signal. The pink solid line is the signal spectrum. Peaks can be clearly seen at the indicated frequencies. These peaks in the frequency spectrum might be due partial discharge and have therefore to be further analyzed. At 786 MHz a phase resolved PD pattern was made. The outcome of the database-reference was a surface PD and confirmed the visual inspection, shown in the previous slide.   It needed further investigation to understand the origin of the defect. This can be read in paper 1-15.

UHF PD measurements can contribute to CBM procedures. Conclusions Measurements with the external UHF coupler are applicable to medium voltage switchgear installations, e.g. air insulated switchgear, as well as to HV switchgear systems. Using advanced PD analysis techniques distinction can be made between the different patterns detected by the external UHF coupler. UHF PD measurements can contribute to CBM procedures. From this part of research the following conclusions could be drawn: 1-Measurements with the external UHF coupler are applicable to medium voltage switchgear installations, e.g. air insulated switchgear, as well as to HV switchgear systems. 2- Using advanced PD analysis techniques distinction can be made between the different patterns detected by the external UHF coupler. 3- UHF PD measurements can contribute to CBM procedures. 4- With UHF PD measurements one can also determine the position of system design errors, which then can be corrected. Hereby I would like to end the presentation With UHF PD measurements one can also determine the position of system design errors, which then can be corrected.