Electromagnetic Spectrum Caused by Partial Discharge in Air in High Voltage Substations

Abstract

We have been investigating characteristics of electromagnetic spectrum for partial discharge (PD) diagnosis systems for SF₆ gas insulated switchgears (GIS). We measured noise spectrum in air at three different types of high voltage substations; 550kV open-air insulation substation, 550kV open-air GIS substation and 275kV underground GIS substation. A biconical antenna acting in a frequency range from 30 to 300 MHz was placed at a few meter away from GIS or gas circuit breaker (GCB) in the substations. From the experimental result, we obtained the average gain Ga of electromagnetic spectrum at each frequency in the substations. Next, we discussed the relationship between Ga and atmospheric conditions using an empirical formula of PD inception electric field Ec. As a result, we found the inverse proportionality of Ga against Ec which was determined by the temperature, pressure and radius of high voltage overhead conductors. We also investigated the relationship between PD pulse and the emitted electromagnetic spectrum from fundamental experiment for a needle-plane electrode configuration. Finally, we introduced “equivalent charge: qe” for substations, and concluded that the charge magnitudes of the 550kV open-air insulation substation were about 7 times larger than those in the open-air GIS substation.