Protective Grounding Line Method HVDC Systems

High Voltage Direct Current (HVDC) plays a significant role in the long-distance high-capacity transmission. The ground electrode line (also known as ground electrode lead wire) is an essential important part for HVDC system. Voltage level in DC ground electrode line is low, and the ground electrode line is located in mountainous area, with frequent thunderstorms, which lead the ground electrode line become more easy to get fault. Fault in the ground electrode line will affect the double poles of DC, moreover, and even cause double poles become shutting. When the ground electrode line is shorted to ground. Timely and accurately Judge the fault type, and then start the appropriate protection or control measures, such as start fault restart, which can not only reduce the probability of ground electrode line transient faults leading to DC outage, maintain the system’s power delivery, but also effectively ensure the DC system run steadily.This paper built a DC system simulation model consisting grounding line after analyzing the particularity of the grounding line and made a detailed analysis of the characteristics of voltage and current of the ground electrode. A time domain protection method based on transient components of the grounding line is researched proposed by analyzing protection approaches existed and the fault character of the leading line. This method not only can distinguish the proximal metal grounded fault and the single ground line disconnection fault, but also can identify most normal grounded fault. By studying the feasibility of the distance protection applied in grounding lines, theory and simulation results show that applying distance protection in grounding lines is feasible. And proposed differential current mutation and high frequency energy mutation based starting criterion of identifying HIF grounded fault is feasible verified by simulations. The paper also makes a research on the travelling wave protection applied in grounding line. High performance has simulated by PSCAD software that the method can start-up protection in ultra high-speed and is free from the influence of fault resistance and the balance of power between different electrodes.