Low Frequency Currents Source Identification

Low frequency currents (LFC) in transformer neutral points can lead to disturbances in high voltage grids. Half-cycle saturation of transformers, caused by LFCs, results in increased audible sound, voltage distortions and led in the past even to blackouts. The main source of LFCs are changes in the Earth’s geomagnetic field, caused by solar storms. However, LFC measurements reveal additional man-made causes as well. In this paper, two known sources of LFCs are discussed briefly and a new source is introduced and documented by combining neutral point measurements and phasor measurements in the Austrian power grid.