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 '/spl phi/' and apparent charge magnitude 'q' of PDs occurring on a given power line voltage and display the number 'n' distribution of PDs n(q,/spl phi/) 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 /spl phi/ and vice versa. The results show good agreement between the range of /spl phi/ and q in the simulated input PDs and the resulting n(q,/spl phi/) 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 /spl phi/ on the raw input data and the resulting n(q,/spl phi/) plot.