Self-adaptive differential relaying for power transformers using FPGA

The differential relay is able to meet its ultimate goal reliably, if it has the characteristics of a simple differential relay during the internal fault condition and percentage differential relay characteristics during external fault. It has been the focus of study to incorporate both these characteristics in a single relay and hence to improve the sensitivity and security of the relay. However, it is difficult to achieve a high degree of security and sensitivity at the same time by conventional percentage restraint differential criteria based on a fixed predetermined characteristic curve. Therefore a novel adaptive protection criterion is proposed in this study, which can self-regulate the parameters of percentage differential characteristic on the basis of operating conditions of power transformers. The simulation results shows that the proposed scheme provides a high operating sensitivity on internal faults, while retaining higher security on all external faults.