A virtual instrument for the determination of the electric power quality

The number and power of loads that pollute, from an electric point of view, the electric network (non-linear, time-variant loads, ...) is constantly increasing. Their connection to the electric network causes a significant distortion in the line current and, when their overall power is no longer negligible with respect to the network power, also some distortion in the line voltage, thus deteriorating the electric supply quality. The availability of accurate instruments able to detect the presence of a polluting load and to quantify the resulting deterioration of the supply quality is hence an important and critical point for the correct operation of the electric power system. The paper proposes a method, based on the evaluation of the harmonic powers, to identify whether the source producing distortion in the line currents and voltages of a three-phase system is the presence of a polluting load after the metering section or is the distortion of the line voltages. Some parameters are also defined in order to quantify the effects of the polluting load on the power quality. A Virtual Instrument is also described, realized to implement the proposed method and to verify it experimentally. The instrument accuracy is discussed