A novel transient-voltage based fault protection method for VSC-MTDC systems

Voltage source converters (VSCs) are highly vulnerable to DC fault current. Fast and reliable fault location and protection methods are necessities in VSC-based multiterminal DC (VSC-MTDC) systems for its safe and reliable operation. In this paper, a selective transient-voltage based fault protection method is proposed. The protection method first uses fast overcurrent criterion as the starting element. Then based on the boundary characteristic of the supplemental inductors, the transient-voltage difference between the internal fault and the external fault is used to locate the fault line. And the extraction of the transient-voltage is achieved by wavelet transform. The proposed method is based on local information, it can identify the fault line quickly without communication between protection units at different locations. The methods has no auxiliary directional criterion and additional fault pole selection criterion. Besides, this method can be realized with very low sample rates, and it is rather strong against various fault resistances. Corresponding simulations were carried out, verifying its feasibility and validity.