Ground Fault Directional Protection Method for HVDC Multiterminal Networks

The use of multiterminal HVdc networks is increasingly relevant in electrical power systems for transporting high powers over long distance. HVdc networks are not free from ground faults that represent the main cause of failures in electrical power systems. Their quick detection and actuation in an accurate and selective way are essential to avoid possible outages. For this reason, in this article, a new protection method that develops a directional evaluation of the ground current is presented. It is based on the measurement of the currents that circulate through the grounded shields at the endings of the HVdc cables, then only low voltage devices are required. Afterward, an analysis of the current polarity is performed. If the current in the shield circulates from the shield to ground, the fault takes place in the protected line and it should be disconnected as soon as possible. On the other hand, if the current goes from ground to the shield, there is a ground fault but not in the protected line. The proposed method has been validated by computer simulations and laboratory tests achieving satisfactory results.