Mar 2013
Electricity Transmission
Fault Management of the Multi-terminal VSC HVDC using Delayed Auto-Re- Configuration (DARC) Schemes
Mar 2013
National Grid Electricity System Operator
National Grid TO Innovation Team
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Voltage Sourced Converter (VSC) High Voltage Direct Current (HVDC) technology becomes increasingly popular due to its capability of providing reactive power support and flexible bidirectional power flow control as well as black start. It is also well suited to multiterminal HVDC connections. However managing the faults, particularly those ones on the DC side remain as a major challenge for a real application of such a HVDC system. Under current situation where there are no commercially available DC Circuit Breakers (CB) in the market, one practical way to clear a DC fault is to use AC CBs to shut down the whole HVDC network which need to be quickly restored after the fault is cleared. The work proposed here is to examine the use of the Delayed Auto Re-Configuration (DARC) scheme to automatically manage such a situation.

The Delayed Auto-Reclosure (DAR) scheme has been widely used by the utilities to automatically restore circuits tripped by a fault. This is based on the statistics that over 80 percent of faults on the Over Head Lines (OHL) are transient ones. In most cases, after the first re-closure attempt, if the circuit is tripped again within a ‘re-claimed’ time, the fault is deemed to be persistent, and the DAR will be ‘locked out’. Such schemes are usually not used for the faults on cable, busbar or primary plant except for the Mesh Corner substations.

Although the DARC scheme for the HVDC system has many similarities to the traditional DAR scheme, its principle is fundamentally different. The aim of the proposed DARC here is to deal with a persistent fault on the DC network of the VSC HVDC system, and automatically restore the healthy part of the network back to service. A typical DARC sequence will include Trip, Time delay, Fault locating and isolation, DC circuit reconfiguration, and converter re-energisation, etc.

This project is to examine a Fault Management method for a Multi-terminal VSC HVDC using DARC Schemes. The project will concentrate on the following four areas:

  • A DARC scheme is going to be developed to deal with a persistent fault on the DC network of a multi-terminal VSC HVDC system, and automatically restore the healthy part of the network

  • The transient and dynamic behaviour of a VSC HVDC system after a DC fault, which will have significant impact on the design for each stage of the DARC consequence, will be investigated and establish achievable operation time for the re-configuration

  • Some practical experience drawn from the Operational Tripping Schemes (OTS) and DAR schemes within National Grid Transmission System will be used in the DARC simulation using a real time digital simulator (RTDS) at the University of Birmingham

  • The results will be presented in a International Council on Large Electric Systems (CIGRE) VSC HVDC conference while some general conclusions will be drawn for the application of DARC in VSC HVDC systems.