Study On Digital Percentage Differential And Ground Fault Relay For Power Transformer Based On Kalman Filter

With the development of electrical industry, more large power transformers will be widely used in power system. As the failure of them damages the power system normal operation seriously, the protection performance for the large power transformer must be improved.Differential relay is the key protection for power transformer. It is notable to improve the sensitivity and reliability of differential relay.The purpose of this paper is a discussion about how to design a sensitive protection device.The paper systematically discussed the developments and present situation of transformer protection. The paper has introduced and analyzed the principles of discriminating the magnetizing inrush and fault current, which had been developed in resent decades. A set of eleven-state Kalman filters is used to estimate the fundamental and up to fifth harmonic components of the transformer current signals. Here the calculation method for signals including aperiodic component based on the algorithms such as the Fourier algorithm and Kalman filter algorithm and so on are given. The paper presents the design and real-time implementation of a Kalman filter based digital percentage differential and ground fault protection scheme for three phase power transformers. The paper introduced the partly hardware used in the device.The paper also points out another question of surge inrush.