Extended second central moment approach to detect turn‐to‐turn faults in power transformers

Abstract

This study describes an extended approach to the differential protection of power transformers to identify turn-to-turn faults based on the second central moment (SCM). The proposal uses the differential currents as the input signals to the algorithm. Differential currents are filtered and normalised to allow the proposed algorithm to be independent of the transformer parameters (power, reactance, connection etc.). Then, the SCM magnitude of the differential currents is computed and compared with an established threshold to detect the internal faults. If the SCM magnitude exceeds the limit, an internal fault is detected. Otherwise, the event is determined as a transient event or steady state. The proposed algorithm was implemented in MATLAB and was tested on a three-phase system using a Real-Time Digital Simulator. For laboratory experiments, a real 55-kVA transformer setup was used to validate the effectiveness of the algorithm. The algorithm successfully identified turn-to-turn faults from steady state, as well as during transformer energisations, in over 1000 cases.