Calibration of VFTO bushing sensor based on convolution model

Disconnector switching operations in large gas insulated switchgear (GIS) systems may cause very fast transients overvoltages (VFTO), which produce dielectric stress to transformer connecting with the disconnector. A VFTO bushing sensor is developed to measure the VFTO at the transformer entrance. Since the high frequency ratio of the bushing sensor is not constant, calibration before the field measurement is needed. Based on the convolution model and step response, a new calibration method is used to identify the frequency response of the bushing sensor. Calibration of an 110 kV rated bushing sensor is carried on in our laboratory to investigate the effectiveness of this method, and the calibrated results agree well with the amplitude-response gained by frequency sweep test, which demonstrates the calibrating method can be applied in VFTO bushing sensor calibration. Calibration of an UHV rated bushing sensor is processed in a factory and the frequency response of the sensor is given at the end of the paper.