| The power grid of ultra-high voltage(UHV) has a characteristic of transmitting power with a large capacity under a low loss in a long distance. Recently, with the construction and operation of UHV substation and transmission line, a nationwide modern power grid which is based on the1000kV grid has been formed gradually. However, the VFTO produced by the operation of disconnector in GIS of UHV threatens equipment insulation. Therefore, the development of sensors and on-line monitoring of the VFTO are of great importance and far-reaching significance. Previous studies showed that broadband window sensor with relatively wide frequency band keeps the measurement stability, yet this kind of sensor has shortcomings that the power supply of GIS needs interval cut off during its long time installment.In order to solve the problem mentioned above, this paper designed a dielectric window VFTO measurement system. By using the dielectric plate, the system can isolate the sensor from the gas in GIS. The paper analyzes the theoretical value of the sensor’s high and low cutoff frequency according to the circuit model in measurement system. There’s also a design of1kV square wave generator to calibrate the new dielectric window sensor of VFTO and having the calibration test of sensor in conventional TEM wave cavity at the same time.We carried out low-frequency response tests in laboratory, while high voltage square-wave and long wave tail response test in the TEM cavity. According to the test result, we choose the PETE as the material of dielectric plate. The experimental results prove that the high cut-off frequency of the system is above175MHz, while the low cut-off frequency stays below10Hz. In addition, the results of both the air&water pressure test and the252kV GIS overvoltage measurement test for hundred times have confirmed the good stability and reliability of this system. |
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