A new technique for transformer protection based on transient detection

This paper proposes a new technique for transformer protection. The techniq ue is concerned with the detection of the fault generated high frequency cu rrent transients by means of a specially designed relay unit. The relay, tu ned to a band of high frequencies, is used to capture the transient current s from both sides of the transformer; the differential and average currents Between the two sides are then calculated, The spectral energies of these current signals are extracted to produce the operate and restraint signals; a comparison between the levels of the two signals determines whether the fault is internal or external to the protected zone. A new technique for in rush detection has also been proposed in this paper. The technique detects inrush current by using the high frequency components contained in its curr ent transient signal. The restraint signal is derived by computing the rati o of the spectral energy of the transient signal to the fundamental current . A comparison between the level of restraint signal and a pre-defined thre shold determines whether a magnetizing inrush is in process. Simulation stu dies with respect to different fault and inrush conditions have been conduc ted, and the results prove that the proposed technique is able to offer fas t responses in protection and accurately discriminate between inrush magnet izing current and internal faults.