Development of a digital acquisition system for partial discharges

A data acquisition system for partial discharges (PD) is being developed, which can simultaneously measure the phase ´φ´ and apparent charge magnitude ´q´ of PDs occurring on a given power line voltage and display the number ´n´ distribution of PDs n(q,φ) on a three dimensional plot. The two-channels (one for the PD signal and one for the reduced power line voltage) data acquisition can sample at a rate of 20MSamples/sec (MSa/sec) and store up to 8Mega bytes of data per channel, which represents 20 power line cycles (PLC) at 50Hz. This system has been tested using simulated PD pulses, of constant q and random φ and vice versa. The results show good agreement between the range of φ and q in the simulated input PDs and the resulting n(q,φ) plots. The analysis part of the system has been further tested using experimental PD data obtained from an RLC detection circuit and the corresponding PLC both taken at a sampling rate of 1.2MSa/sec. Good agreement is obtained between the apparent ranges of q and φ on the raw input data and the resulting n(q,φ) plot.