A calibration procedure for a digital instrument for electric power quality measurement

The measurement of power quality is becoming an impelling need in a deregulated electricity market where the sources producing distortion and disturbances are steadily increasing in number and power. The instruments for power quality measurement are based on complex digital processing of the input signals, whose waveforms are highly variable. The calibration of this kind of instruments is therefore an open topic, especially when the uncertainty propagation through the digital signal processing (DSP) algorithm is concerned. This paper proposes an innovative procedure, based on the Monte Carlo method. Starting from the determination of the probability density function of the uncertainty contribution of every device from the signal input stage to the analog-to-digital conversion stage, this procedure estimates the probability density function of the measurement results and the measurement standard uncertainty as the standard deviation associated with this function. The result of the experimental work done on a prototype of a power quality measurement instrument is reported.