In this paper, the effectiveness of restricted earth fault and bias differential protection against earth fault on of transformer winding is presented. Earth fault is one of the failures that occurs on a power transformer winding. Its magnitude depends on how the neutral is connected and the location of fault. For a transformer which is connected to Neutral Earth Resistance (NER), as the fault moves towards its neutral, the magnitude of fault current decreases and the detection of fault diminishes, thus limiting percentage of winding that can be protected. To overcome this problem, restricted earth fault is employed. This paper will show that based on its principles, restricted earth fault protection is more sensitive and provide better coverage for the star winding against earth fault especially resistance earthed.
