New method to control Petersen coils by injection of two frequencies

In this paper we present a new method for the calculation of the zero-sequence network parameters and the control of Petersen coils in resonant grounded networks. The major problems for the correct calculation of the line-to-ground capacity respectively of the resonant-point are the missing or very low zero-sequence voltage and the non negligible crosstalk of the varying load currents to the zero-sequence-voltage. As a consequence the number of tuning operations and non correct tuning operations increases in today´s networks. The new method uses the injection of two currents with frequencies unequal to 50 Hz into the zero-sequence system for the calculation of the network parameters. Therefore it is possible to supervise complete symmetrical networks and to suppress the 50 Hz crosstalk of the load current. In consequence the number of coil movements and also the numbers of wrong tuning positions are drastically reduced.