Estimation of the primary and secondary leakage inductances for a Y-Δtransformer

A current differential relay with harmonic based blocking methods for transformers may maloperate for cases with very low harmonic contents in the operating current and its operation is delayed for the internal faults due to the harmonics. Thus, transformer model based protection techniques have been reported that rely on the electro-magnetic equations of a transformer. These methods require the separate values of the winding resistances and the leakage inductances. The former can be obtained experimentally whilst the latter cannot be obtained experimentally. This paper describes an estimation technique of the separate primary and secondary leakage inductances of a Y-Δ transformer. The method uses the line currents of the delta winding, which is available. The proposed technique can obtain the leakage inductances very accurately. The final paper will include the estimation results during the transient states such as magnetic inrush and over-excitation.