Research On UHF Detection For Partial Discharge In GIS

There are three key technologies in the on-line detection of the partial discharges in Gas Insulated Substations (GIS), the classification of partial discharge (PD), the location of PD source and the estimate of PD quantities.In ths dissertation, one kind of portable ultra-high frequency (UHF) sensor is developed, and it consists of UHF antenna, UHF amplifier and high-pass filter, the whole measure bandwidth range is 500~5000MHz. To improve the sensibility and security of the sensor, a new filled dielectric UHF sensor is developed, and chooses the CT chamber and hand hole as the best installation point. The CT chamber is of semi-closed constructure, if the sensor installed there, the insulation and sealed ability is not invariable, furthermore, the EM noise is very low, as installation of intenal sensor. In the hand hole, the high dielectric constant medium is filled in front of antenna to enhence the EM energy coupling capability. The best parameter is that depth is 2cm, and the dielectric constant is 5.The PD detector allows extracting meaningful data from UHF signal of PD, such as the amplitude and pulse phase, that can be reduce the sample rate of measurement equipment. The data from the detector can be used to statistics during some power frequencies for monitoring the PD in GISThe difference in arrival times of UHF signals at two sensors can be measured to assist with locating faults in GIS. The test results in the laboratory indicate that the fault location precision depends on the digital rate of the oscilloscope. In on-site test, if the sample rate is low, it is could not have enough sample plots to recover the real pulse wavefronts, which is difficult to identify the arrival times at the two sensors by the first peak of UHF waveform. A new algorithm has been described, which applies cubic spline interpolation to increase points between two real sample points, and improve the location precision of time flight method.In this dissertation, author used multi-sensor to locate the PD souce's direction in GIS, which distuibuted around the spacer vertical cross. The signal will be maximium when the sensor is vertical to the PD source.In this dissertation, GIS cavity configuration is utilized and transmission of PD electromagnetic wave in wave-guide is simulated by FDTD method. Therefore, factors influencing UHF signals are analyzed, including PD current amplitude and pulse width of PD source. The results showed that the UHF signals have no directe relation to the PD of souce. When the pulse width is constant, the square root of UHF signal energy is direct retio to the amplitude of the real pulse. Supposed that the maximium width of the pulse in GIS is 2.4ns, the original max PD quantities is composed by the maximium width and amplitude of the pulse, According to relationship between UHF signals energy and PD pulse, the original max PD quantities can be estimated, which contributes to marking GIS partial discharge.