Protection Scheme for Fast Detection and Interruption of High-Impedance Faults on Rate-Limited DC Distribution Networks

Abstract

This article presents a protection scheme for dc power distribution systems based on a unique rate-limited operating mode. The concept of this protection scheme is that extremely slow ramp-rate limits can be imposed on the dc network voltage and all currents drawn from the network through control of the power electronic interfaces. Meanwhile, all fast transients produced by loads and DGs can be absorbed by local energy storage-typically a battery-behind the interface converter. The removal of all transients from the distribution network enables a very effective method to differentiate the normal operation from fault conditions, including high-impedance faults, such as vegetation faults and human-body faults. In the proposed scheme, the ramp rates of the current and voltage on the network are sensed by each interfaced converter to check for compliance with the defined rate limits. It is unlikely that a given fault on the network will comply with the stringently slow rate limits, so this scheme allows the system to quickly detect the fault and deploy suitable protections. Experimental results show that the presented protection scheme is capable of detecting and interrupting a human-body-impedance fault quickly enough to prevent electrocution on a dc distribution cable operating at voltages of 1000 V and above, leading to unprecedented safety on a power distribution network of this voltage level.