Takao Tsurimoto

Correlation between two frequency components of various PD pulses in GIS

Detection of partial discharge (PD) signals is one of the most important methods for predictive maintenance of gas insulated switchgears (GIS). Because type of PD source, configuration of a GIS tank and frequency response of a sensor influence a PD spectrum, detected PD pulse has a specified frequency spectrum. Although frequency spectrum is one of valuable information for PD in a GIS, the spectrum measured with spectrum analyzer or FFT processing is generally a result of averaging of many signals so that statistical features of PD are lost. In addition, frequency spectrum is complex and special experience is needed to recognize it. Thus convenient method is required to discriminate various PD pulses. In this paper, we attempt to extract two frequency components from a PD pulse and to process them in order to categorize it easily. Correlation between pulse heights of two frequency components and pulse height distribution resolved with power voltage phase are shown as effective methods to distinguish the type and the location of PD sources.

Partial discharge monitoring system for cubicle type GIS

Partial discharge (PD) monitoring system for cubicle type gas-insulated switchgear (C-GIS) filled with compressed dry air as an insulation gas was developed. The shield electrodes embedded in the solid insulator of bushings are used as PD sensors. For verification of the sensitivity of the sensors and propagation characteristics of PD pulse, artificial defects such as fixed particle on high voltage conductor and defect on creepage surface of insulator in C-GIS were used. It is clarified that the sensors had good sensitivity to PD pulse propagating along high voltage conductor in the range from VHF to UHF and that the amplitude of the sensor output had good correlation with apparent charge, pC, detected by conventional PD detector. The PD monitoring system is connected with our condition based maintenance (CBM) controller, which also monitors the abnormality of circuit breaker, disconnecting switch, gas pressure and so on, as a total diagnosis tool for our C-GIS.

Characteristics of discharge generation across insulation barrier in the oil/Pressboard composite insulation system

This paper deals with the discharge characteristics in the oil/Pressboard composite insulation system under the application of a standard lightning impulse voltage. Discharge images were observed using a digital camera. We investigated the barrier effect on partial discharge inception voltage (PDIV) and breakdown voltage (BDV). Furthermore, we observed the discharge generation across the insulation barrier and also evaluated the voltage required for the phenomenon by the electric field analysis.

Influence of filler added into one side of insulation layers on electrical treeing characteristics

To understand the electrical treeing properties at the interface, the treeing breakdown test was performed. The effect of the filler added into one side of the insulation layers on the treeing breakdown was investigated. Time to breakdown of the epoxy/epoxy sample including the silica fillers at upper epoxy resin layer became shorter than that not-including the silica filler as the filler content increased. The addition of the filler increased the propagation speed with a few branches, accelerating tree propagation. As the filler content further increased, the time to breakdown epoxy/epoxy sample including the silica fillers at upper epoxy resin layer became longer than that not-including the silica. The increase in the effective length between electrodes, field relaxation of tree tip and dispersion of discharge energy were caused by the many branches due to high filler content. From these results, it was clarified that the filler on the insulation layer caused the change of the tree structure around the interface of the multilayer.