A contribution in partial discharge detection

The proposed system allows the measurement of: 1. Apparent charge by means of direct analog integration of the current induced by the PD event; 2. The corresponding value of the applied voltage "V" 3. The time instant in which the Partial Discharge occurs "t/sub PD/". This particular instrumentation, devoted to the measurement of partial discharges, is able to detect, measure and store in a large size memory the three measured data. It is possible to track the real time evolution of the partial discharges. In order to obtain a good evaluation of the discharge characteristics a high-sensitivity and high accuracy detector has been developed using a mixed analog and digital signal processing technique. The system uses a high Q-notch filter to stop industrial frequency and the first odd order harmonics. Integration of signal is then used to achieve apparent charge with lower spectrum distortion of the pulse than classical techniques. A block performs an analog to digital conversion of signals and stores them in memory for subsequent mathematical treatment. All the steps of measurement are supervised by microprocessor. This work presents an analysis which validates the previous results. In particular the practical difficulties to achieve an integration circuit for very sharp pulses in nanosecond range with very quick restoration for PD detection, minimizing errors and noise, are discussed.