Development and Experimental Research of Impedance Converter for VFTO Measurement

Very fast transient overvoltage (VFTO) is a special electromagnetic transient in gas-insulated switchgear (GIS). It is necessary to obtain the characteristics of VFTO to guide the insulation design of GIS and the electromagnetic protection of secondary equipment. In this work, we have designed and developed a differential impedance converter by using the compensation between poles and zeros in closed loop circuit and compared its measurement performance with a following type on a 220 kV test platform. The calibration and practical tests results showed that the low cut-off frequency of differential type has been greatly expanded, which can reach 0.1mHz, and the measurement accuracy of very fast transient signal has also been greatly improved than the following type. Thus, the differential impedance converter can fully meet the measurement needs of high-frequency transient voltage, power frequency voltage, and trapped charge voltage in the VFTO waveform. It can be recommended for VFTO test measurement in extra-high voltage (EHV)and ultra-high voltage (UHV) GIS substations and provide accurate data support for insulation design and energy saving of GIS equipment.