Measurement of negative sequence voltage argument in multi-phase rectification method

Powerful single-phase electrical energy consumers distort the voltages of three-phase networks. The use of adjustable symmetric devices assumes measuring the asymmetry of voltages. Since the asymmetry of voltages in three-phase networks is limited by the level of 2%, an accurate measurement of its parameters, and especially the argument of negative sequence voltage, is complex. A brief analysis of the known methods for measuring the parameters of asymmetry of a three-phase voltage system is given. The multi-phase rectification method has the highest accu-racy. In this method the investigated three-phase system of voltages is converted into a multi-phase voltage system that feeds the multi-phase rectifier and the output voltage of this rectifier is analyzed. The constant component of the output voltage of the rectifier gives information as to the direct sequence voltage. The second harmonic of the output voltage of the rectifier gives information as to the negative sequence voltage. It is shown that the negative sequence voltage argument can be measured as a phase shift between the second harmonic voltage of the rectified line voltage and the second harmonic voltage of the output signal of the multi-phase rectifier fed from the voltage system that is being studied. But the accuracy of such measurement is low. It is shown that the introduction of a correcting signal significantly improves the accuracy of the measurements. The correcting signal is formed from the measurement results of the asymmetry voltages factor and the phase shift between the second harmonics. Introduction of the correction will reduce the absolute maximum methodical measurement error, by a factor of 20 for 10% asymmetry of voltages