Digital measurement equipment for steady-state PQ measurements

The monitoring of steady-state electrical quantities is a topic of wide interest for the evaluation of power quality. The voltage total harmonic distortion (VTHD%) and rms voltage (Vrms) are adopted as most significative quantities for the evaluation of steady-state voltage features. The simultaneous occurrence of transient events as dips and swells can involve the incorrect measurement of these indexes. To avoid the effect of a same event to the measure of different power indexes, the actual international trend is to adopt the flagging technique. In this paper a digital measurement equipment for the evaluation of steady-state voltage quantities is proposed. An algorithm for the measurement of Vrms and VTHD%, based on the sliding window technique, has been developed. The comparison with the traditional technique has been performed both by means of simulation and experimental tests. The proposed approach gives results according to the standards, allows for a better resolution and can be adopted for data flagging.