Abstract
DC bias may affect the transferring characteristics of the current transformer, threatening the operation of relay protection. Compared with the high voltage direct current (HVDC) transmission in the unipolar-earth loop operation mode and geomagnetically induced current (GIC), the amplitude of the stray current is smaller, and the randomness and fluctuation are larger and accompanied by sudden changes. The amplitude-frequency characteristics of stray currents are studied. According to the equivalent circuit of current transformer considering eddy current loss, the mechanism of partial transient saturation and mathematical model of time-to-saturation due to stray current are discussed. Then simulation models are developed. Simulations are conducted to analyze current transformer transient saturation and partial transient saturation, the results of which demonstrate that the stray current is composed of a variety of low-amplitude low-frequency components, which amplitude, frequency and duration are the influencing factors that affect the CT transient transfer characteristics. The reason of the partial transient saturation is the stabilization of excitation impedance.
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