A virtual instrument for the determination of the electric powerquality

摘要

The number and power of loads that pollute, from an electric pointof view, the electric network (non-linear, time-variant loads, ...) isconstantly increasing. Their connection to the electric network causes asignificant distortion in the line current and, when their overall poweris no longer negligible with respect to the network power, also somedistortion in the line voltage, thus deteriorating the electric supplyquality. The availability of accurate instruments able to detect thepresence of a polluting load and to quantify the resulting deteriorationof the supply quality is hence an important and critical point for thecorrect operation of the electric power system. The paper proposes amethod, based on the evaluation of the harmonic powers, to identifywhether the source producing distortion in the line currents andvoltages of a three-phase system is the presence of a polluting loadafter the metering section or is the distortion of the line voltages.Some parameters are also defined in order to quantify the effects of thepolluting load on the power quality. A Virtual Instrument is alsodescribed, realized to implement the proposed method and to verify itexperimentally. The instrument accuracy is discussed