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 in creasing 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.

I. Introduction

The wide spread of power electronic devices from household appliances to industrial applications is increasing the distortion on currents and voltages in the electric power systems to levels that are no longer negligible, and is responsible for decreasing the electric power quality. The need for measuring power quality is a straightforward consequence of the increasing presence of distortion and disturbance sources connected to the electric network, especially in a deregulated market, where electricity is more and more considered as an industrial product that has to conform to the quality control rules [1], [2].