Protection of transformer due to external fault between two voltage levels using overvoltage protection and sequence component of currents

Abstract

The main role of the transformer protection is based on satisfying fast and reliable relay to isolate the power transformer from the grid with minimum damage. Also, to avoid the mal-operation of the protection system during different operating conditions. This paper presents a simple method to protect the power transformer due to the short circuit between two different voltage levels that may be produced when two overhead transmission circuits with different voltages intersect with each other. This leads to the failure of all equipment on the lower voltage especially the power transformer due to the resulting overvoltage. The proposed methodology depends on the combination between the sequence components of the currents from both sides of the transformer. Moreover, it uses the voltage measurements of the lower voltage side to detect the resulting overvoltage. The magnitude and phase angle of current measurements are computed using Fast Fourier Transform (FFT). The modelling and simulation of the fault between high-and medium-voltage are carried out using PSCAD/EMTDC program. The results reveal the accuracy, security and the applicability of the proposed methodology.