Modelling and Experimental Investigation on the Differential Protection of Transmission Line

Abstract

Due to the significant impact of the fault on power systems and the failure of protection devices, power system operators and researchers have given reliability a great deal of consideration. The modern IEC 61850 standard is used recently to improve communication systems in digital substations and allow signals to be shared between the devices. Differential protection is used to protect the transmission lines, cables, and transformers, as it detects the faults by comparison of the currents flowing into and out of the protected devices. In this research, MATLAB/Simulink has been utilized to simulate the differential protection by using two current transformers (CTs) and to analyze the current waveforms of CTs. A model of the transmission line has been implemented in Taylor’s University Lab to validate the simulation results and measure the differential current, which equals the current summation of two CTs. The outcomes of the research show that the phase shift in the secondary side of CTs between two terminal points is zero and the value of differential current is zero under normal operating situations. However, the differential current has increased in each of the following cases: one CT is connected to the system with the wrong polarity or under an internal fault.