A method and related digital instrument for the measurement of the electric power quality

The ever increasing number and power of polluting loads (nonlinear, time-variant loads) connected to the electric power network causes a significant distortion in the line current and, as their overall power is no longer negligible with respect to the network power, also some distortion in the line voltage. This causes a deterioration of the electric power quality that may disturb the other connected loads. The availability of an instrument able to quantify the deterioration of the power quality due to the harmonic distortion, to assess whether or not this deterioration is caused by a polluting load connected after the metering section and to quantify the effects of such a load on the power quality therefore represents an important point for the correct operation of the electric power system. This paper proposes a measurement method, based on the evaluation of the harmonic powers, for the identification of the source producing pollution in a three-phase power system. Some parameters are also defined in order to quantify the electric power quality and the deteriorating effects of a polluting load. A digital instrument is also described, realized by means of virtual instrument techniques to implement the proposed method and to verify it experimentally. The measurement accuracy is discussed