Effects of geomagnetically induced currents on the transfer characteristics of current transformers

Summary With the arriving peak of the solar cycle, the effects of geomagnetically induced currents (GICs) on power systems attract more attention. The direct current magnetic bias caused by GIC has a more complex influence on the transient transfer characteristics of the current transformers (CTs) than that caused by high-voltage direct current due to its randomness and time variation. In this paper, a cosine function with lower frequency is simply adopted to simulate the time-variation feature of GIC. The mathematical analysis of CT transfer characteristics with the input of the GIC cosine model is presented based on electromagnetic equations and the excitation characteristics of the CT. Afterward, the physical model of the CT is built and tested under various input conditions. Furthermore, comparisons between the physical model and the simulation model are given to verify the reliability of the simulations. The simulation results show that the saturation level of the CT, such as partial transient saturation and deep saturation, is controlled by the magnitude and frequency of GIC and excitation characteristics of the CT. Moreover, CT saturation may affect the performance of the transformer differential protection, to which should be paid adequate attention. Copyright © 2016 John Wiley & Sons, Ltd.