Partial discharge level is the key index for condition monitoring of GIS. At present, UHF monitoring method is widely used to monitor PD in the gas insulated switch.
So this paper summarizes several discharge characteristics of typical defects in GIS , in order to improve the sensitivity of partial discharge test, the reasonable layout of the PD UHF on-line detector sensor, and improve the detection efficiency.
When the high voltage rises to 20kV, the suspension metal body, which belongs to the position 1 of the discharge power source, produces a stable partial discharge. Discharge PD UHF signal from GIS exposed by the sensor measurement point P1, and record the original signal by oscilloscope and spectrum analysis, PD UHF signal and its spectrum is shown in figure 1.
Figure 1:Time domain signal and spectrum distribution characteristics of suspended metal discharge
It can be seen that the peak time peak value of partial discharge UHF signal in P1 is about 1400mV, and the duration is about 200ns. The partial discharge signal produced by suspended metal is widely distributed in frequency domain and almost covers 400MHz~2GHz, so it is easy to select the detection frequency band flexibly.
When the voltage rises to 35KV, the metal tip at the 1 position of the power source is corona, which excites the ultra high frequency signal. Recording the signals detected at P1 by oscilloscope, the time domain wave of PD and its spectrum distribution are shown in figure 2.
Figure 2: Time domain signal and spectral distribution characteristics of point exciting discharge
It is shown that the partial discharge extraordinary frequency signal produced by the metal tip is obviously smaller than that of the suspended metal body. The peak value of the time domain signal is about 20mV, the duration is less than 100ns, and it is obviously shorter than that of the suspended metal body. Spectrum analysis shows that the discharge spectrum of metal tip is distributed in 600MHz~1Ghz and 1.4GHz~1.7GHz.
