Flux-based turn-to-turn fault protection for power transformers

Since the internal turn-to-turn faults (TTFs), as a common cause of the transformer failures, result in minor changes on terminal currents/voltages, they maybe undetected by the conventional protective relays. In this study, a simple, sensitive and robust linkage flux-based technique is proposed to protect the power transformers against TTFs. In this approach, some separated multi-turn windings as search coils (SCs) have to be wrapped around the transformer core legs to sense the related passing flux. Since passing equal flux through a transformer core leg in normal condition induces equal voltages in the related SCs, variation of the induced voltages indicates the fault occurrence in that phase. Against the traditional differential protection schemes, current transformer error and saturation, tap changer operation, energising inrush current, over-fluxing etc. cannot impact the proposed technique performance. Therefore, it can be introduced as a comprehensive protection technique for power transformers.To confirm the proposed technique performance, it is tested on a real 50 kVA, 20 kV/400 V three-phase distribution transformer, in various conditions, too.