AFR 131 is an active load to protect metering VT against ferro-resonance in MV power distribution systems

AFR 131 smart load is an instrument designed to monitor and protect three voltage transformers (VT) in open delta connection against the potentially harmful effects of ferro-resonance in a high voltage distribution network. Ferro-resonance occurs between the inductance of the transformer and the capacitance of the MV lines or switching equipments. Ferro-resonance can be initialized by switching, disconnection, ground connections or by other transient events. During the ferro-resonance a significant over-voltage and concurrent current peaks can occur due to the saturation of the magnetic circuit of the VT. This often leads to a fatal destruction of the VT.

AFR 131 acts as a protection of the VT against the unwanted effects of such events. AFR is only selectively activated during the occurrence of ferro resonance and stays inactive during the normal operation.

AFR 131 is intended for connection into open delta of auxiliary secondary windings of three VTs. AFR 111 is intended for stand-alone operated VTs, i. e. for single phase measuring, V connection measuring or for one pole power feeders.