Practical Considerations for High Impedance Restricted Earth Fault Relay Settings

Abstract

A strategy for practical specifications of restricted earth fault (REF) relay settings of power transformers based on the high impedance principle has been described in this work. The conventional REF relay settings rely on the principle that the REF current transformers on the phase and neutral sides of the main power transformer are having identical parameters and hence the normal settings for REF relays depend on this assumption. It is found that in the conventional literature for REF relay settings normally available there is no attempt has been made to assume unequal CT parameters on the phase and neutral ends of the power transformers. In this work, an attempt has been made to formulate generalized equations for REF relay spill currents based on unequal CT parameters and to derive practical REF relay settings therefrom.