Fault Current Improved Grey Slope Relational Analysis Based Unit Protection Scheme for DC Distribution Lines

Multi-terminal flexible DC distribution line faults develop rapidly, and power electronic equipment has a poor ability to withstand overcurrent. To solve the aforementioned problem, a DC line unit protection scheme based on improved Grey Slope Relational Analysis (GSRA) of fault currents is proposed to address the issue of achieving a balance between the reliability and speed of relay protection for DC distribution lines. This scheme uses the fault current measured at both ends of the line under various operating conditions, and calculates the correlation between the current at both ends of the positive and negative lines using the slope distance and polarity of the current increments. Based on this, GSRA is used to analyze the correlation of fault signals so that line faults can be eliminated quickly. This protection scheme allows the selectivity of traditional unit protection to be improved. Simulations using PSCAD/EMTDC have shown that this method can achieve fault discrimination and fault pole selection by simultaneously measuring the current at both ends of the line. This fast protection action is not affected by the line distribution capacitance and converter blocking, strong resistance to transition resistance and noise interference, and reliable identification under heavy loads and high-resistance ground faults.