A new time-frequency analysis based supervision method for the transformer restricted ground fault relay

摘要

The low-impedance restricted ground fault (RGF) relay is a protective scheme of power transformers but its operation degrades when current transformers (CTs) are saturated. In this study, for the first time, a new supervision method based on a time-frequency analysis tool is proposed to improve the immunity of this protection scheme against CT saturation. For this purpose, two distinguishing features are extracted using Stockwelltransform (S-transform) and then by determining proper threshold values, the relay operation is conditioned. A comprehensive study is conducted by simulation of a real power transformer in PSCAD/EMTDC environment. Moreover, the precise Jiles?Atherton model is employed to simulate the transient behavior of CTs during saturation conditions. The obtained results show that the immunity of the proposed RGF protection scheme is improved significantly by applying the proposed supervision method.