Development of Recommendations for Changing Power Quality Standards Taking Into Account the Experience of Operating Frequency Converters with Active Rectifiers

To date, due to the appearance of high-power semiconductor converters using the principles of pulse-width modulation at production sites, the question arises about the relevance of the existing international standards regulating the electrical energy quality in the networks of industrial enterprises. In particular, frequency converters with active rectifiers as part of the main electric drives of rolling mills are widely spread. The operation experience of such electric drives has shown a high probability of voltage distortion of supply network of average voltage 6–35 kV over the permissible level by harmonics of high order, with numbers higher than 40–50. These voltage distortions arise due to high order current harmonics, generated by frequency converters with active rectifiers, on high impedance sections of the network frequency response, when even a small in amplitude high frequency current flows. The presence of high impedance sections in the frequency response of the 6–35 kV network is explained by the parallel resonance between the network transformer inductance and the equivalent capacitance of the cable lines leaving the substation. Modern power quality standards applied in the CIS, EU, and North America regulate the content of harmonics up to 40–50, which makes it difficult to assess the impact of high-power semiconductor converters on the voltage quality in the supply network. Therefore, the urgent task is to develop recommendations for changing the existing power quality standards, taking into account the experience of practical operation of frequency converters with high-power active rectifiers.