Test environment for HVDC circuit breakers

High-voltage DC circuit breakers (DCCB) are considered to be a key element of a future meshed HVDC grid but are fundamentally different from the well-known AC circuit breaker. Due to the absence of natural current zeros in DC grids, the DCCB must artificially create a current zero as well as dissipate the magnetic energy stored in the DC grid. The DCCB is a system itself, in which the current is sequentially passed through various parallel paths with separate functions. Modules are connected in series to achieve the desired voltage rating.

ifferent DCCB technologies that differ in speed of operation, functionality, and cost, have been proposed. The state of development ranges from low-power desktop experiments, to full-scale production prototypes. Testing at pre-defined phases throughout a DCCB’s development cycle is a key to validate its functionality, ratings, and endurance prior to installation in the field. Final testing preferably takes place in independent test labs to avoid any doubts about the validity of the tests, or in the manufacturer’s facilities under witness of an independent inspector.

The type and sequence of tests, the applied test stresses and pass criteria are important parameters which are chosen carefully to strike a balance between sufficient performances whilst avoiding ‘gold plating’. For most AC and HVDC equipment, test requirements, procedures and criteria are accurately described in internationally accepted standards.

Test circuits are traditionally designed to synthesize the required test voltages and currents as accurately and economically as possible. At lower power ratings, equipment can often be tested ‘directly’, i.e. the same circuit provides both voltage and current stresses simultaneously. At high power ratings, synthetic test circuits in which voltage and current stresses are separated in time and supplied by separate sources are used to avoid large energy stresses.

For DCCBs, currently no standardisation exists. Furthermore, the conventional test circuits used for testing current interruption capability of AC circuit breakers cannot simply be utilized for testing DCCBs due to the large energy stress requirement. Both issues need to be resolved to increase the Technology Readiness Level of DCCB technology.

Work package 5 developed a comprehensive list of test requirements, i.e. aspects of DCCBs that should be verified. The test requirements consider the modular construction of DCCBs. Test procedures for verifying DC current interruption using a test circuit based on reduced-frequency AC short-circuit generators have been proposed. AC short-circuit generators are traditionally used to test AC circuit breakers and readily exist at many independent laboratories globally, avoiding the need for expensive new test circuits. The first experiments have already shown that reduced-frequency AC short-circuit generators can synthesize suitable voltage, current and energy stresses. In August 2017, the first full-power test at DNV GL’s KEMA Laboratories with a DCCB supplied by Mitsubishi Electric is planned, to verify the correct interaction between the DCCB and the test circuit. The test requirements, procedures and test circuits have been reported in deliverables 5.4, 5.5 and 5.6 respectively.

Download Deliverable 5.4: Documents on test requirements (PDF 1.1 MB)

Download Deliverable 5.5: Documents on test procedures (PDF 567 KB)