Measurement and analysis of the transient radiation electric field excited by the breaker when closing the unloaded transformer in GIS

In order to study the waveform characteristics of transient electromagnetic field excited by operation of switches in substations, this paper measured and analyzed the radiated electric field (E-field) during the very fast transient over-voltage (VFTO) progress in a 220kV gas insulated substation (GIS). The measured VFTO radiation E-field was excited by a three phase circuit breaker when closing the no-load transformer during the power-off maintenance of the GIS. First, an electro-optical E-field measurement system was developed and fabricated. This measurement system had many advantages, such as wide-band response, anti-interference and long transmission distance, compared with traditional E-field measurement method. Then three representative measuring points in the 220kV GIS are chosen and the corresponding VFTO radiation E-field is measured. The measuring result is analyzed both in time and frequency domain. The measuring result shows that radiated electromagnetic field can be generated when the breaker close the no-load transformer. The highest amplitude of the radiated E-field can be 7kV/m, the fastest rise time can be 5ns, and the slope of the E-field can reach 1.2(kV/m)/ns. This kind of transient E-field can threaten the normal operation of the electric devices around the GIS. So, it is important to study the waveform characteristics of the VFTO radiation E-field. It can be concluded that VFTO radiation E-field is a group of pulses with millisecond intervals. Each pulse oscillates and attenuates with the time and has many characteristic frequencies. Furthermore, each pulse can be divided into three periods in time domain according to the different attenuation rate of different characteristic frequencies.