Earth Fault Measurement with the Frequency-Selective Earth Fault

Abstract

The safe operation of distribution networks, even in the case of earth faults, is related to the knowledge of the value of the earth fault current. In addition to the fundamental, which can be predicted with high accuracy, the harmonics must also be considered. At present these are still defy the prediction. In order to measure these without the known double earth fault risk, the frequency-selective ground fault method has been developed. As a result, the residual voltage remains low even during the measurement. However, the selected harmonic components of the residual earth fault current can flow almost unaffected. Based on the requirements, a reactance network is derived and its function is verified by tests in a 20 kV Grid. The contents of this essay, which deal with the theory of the proposed method, have already been published in [1] and [3]. Parts of the presented measurement results were also taken from [3].