Demonstration of DC Fault Detection and Isolation on a Laboratory Scale HVDC System

This paper presents the implementation of a method for the detection and isolation of DC faults in HVDC systems, which has been developed and tested in a scaled laboratory environment to increase the Technology Readiness Level (TRL). In order to achieve this, the system's responses to pole-to-pole (P2P) and pole-to-earth (P2E) faults without any fault protection were analyzed in both the simulation and laboratory environments. This involved a point-to-point connection with a Modular Multilevel Converter (MMC), four DC cable models and a four-quadrant power amplifier. Based on the foregoing results, a number of parameters for fault detection were selected and parameterized. The algorithms for the protection system were than implemented, and four mechanical DC circuit breakers (DCCB) were added to the laboratory system. Subsequent tests of P2P and P2E faults with various short circuit resistances demonstrated the basic functionality and effectiveness of the system. The fault scenarios tested were quickly and reliably detected within a few microseconds. Afterwards the DC-line was isolated using the four DCCBs. Simulations were used to predict the scenarios and to analyze the system responses at different DCCB switching times, demonstrating the importance of synchronizing the different DCCBs during the isolation process.