抄録
We proposed a new insulation diagnosis system which can detect partial discharge (PD) signals in power equipments in service rapidly and accurately.
The system is consist of a conventional wide range current probe for measurement of PD current on the grounding conductor, a high speed A/D converter and a computer system for application of digital signal processing techniques. The partial discharge signal is detected as a bast signal from these current signals on the grounding conductor by FFT and bandpass filtering. The beat signal is processed by the Hilbert transform for providing the envelope which includes amplitude, phase angle and frequency informations.
The envelope can be calculated as the magnitude |F(t)| by the detected current signal which can be viewed as the real component of a complex trace.
The degree of insulation degradation is judged by two methods. One is the method which evaluates the energy of PD from the value of envelope area and the other is the method which evaluates the repetition rate of the PD phenomena from the number of envelopes over the threshold relating to the insulating performance.
