Methodic of calculation of the non-sinusoidal voltage index within electrical networks with high-voltage frequency convertors

The paper gives the procedure for calculation of the voltage non-sinusoidality ratio of the electric mains supplying electric drives with high voltage frequency convertors. It includes the calculation charts which help to predict its value for the cases with six- or similar twelve-phase rectifiers and various relations of inductive impedance of the matching transformer (input reactor) and similar one of the electric supply system. The paper determines the ratio of short circuit power and variable frequency drive power providing specified values of the non-sinusoidality ratio for convertors with various rectification circuits. It considers activities providing electromagnetic compatibility of the power frequency convertors with the electric supply main. They include changes within the electric supply system structure, improvement of the frequency converter circuits and application of devices for changing the unified power quality index. It proves that it is more reasonable to raise the rectifier pulse number and apply the rectifier with pulse width modulation.