A current sensor for insulator corona discharge measurement

The results from reference [1] indicated that it could be a way to detect faulty insulators by measuring corona pulse current from the insulator string. This paper presents a pulse current sensor, with high sensitivity (mu A) and wide frequency band (7kHz-25MHz), developed for detecting pulse currents form insulator corona discharges on line. Through spectrum analysis of corona pulse currents produced by 110kV-suspension insulator string, we found that the frequency band and 3-dB cutoff frequency of the corona pulse currents are respectively 17MHz and 2. 5MHz. Based on the spectrum analysis, we developed a special designed Rogowski coil to detect corona currents on transmission line, which has a core made of super microcrystal material. We tested the core material and found that it is of high Ct value (magnetic permeability, >10000) and wide frequency characteristics (2kHz-25MHz). In order to make the best design, the influence of coil turns and integrating resistance on the frequency band and sensitivity of the sensor was investigated, it was found from the test that the sensitivity of the sensor changes with integrating resistance. The larger the integrating resistance is, the higher the sensitivity of the sensor is, and the narrower the Frequency band of the sensor will be. The central frequency of the band changes with coil turns. The more the coil turns are, the lower the central frequency will be, the lower the sensitivity of the sensor will be. Considering the sensitivity and on-site interference, the integrating resistance and coil turns are chosen as 100 Ohm and 25MHz. The designed sensor was used to measure the corona pulse current produced by an insulator string by coupling from a ground wire of a tower in our laboratory. It is shown from the on-site that the sensor is very suitable to detecting corona pulse currents from insulator string in service.