National Grid Electricity System Operator
National Grid TO Innovation Team
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Asset Management
£31,000.00
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.