Design of test-circuits for HVDC circuit breakers

DC circuit breakers are essential components in the protection of multi-terminal and meshed DC grids. So far, no practical application of HVDC circuit breakers is known and intense research is being carried out regarding various concepts, practical realization and ultimately testing of such devices. In the present contribution, several breaker concepts, based on the hybrid method of DC fault current interruption, described in (patent-) literature, are modelled in order to investigate their interaction with a DC grid. For this purpose, the CIGRE B4 test-system, a combination of DC and AC grids, consisting of multiple in-feeds and having lines and cables, is modelled. The impact of a fault on the breaker is considered. Since industrial concepts of hybrid HVDC breakers are modelled including their key elements, the electrical stresses on various parts of the breakers are analyzed in detail. These stresses are used as a guide to design high-power test circuits that can be used to test DC switchgear under realistic conditions. Two classes of DC test circuits are considered and investigated based on high-power test circuits, supplied by AC generators: · One class can produce pseudo-DC currents of short duration that can be adequate to test DC equipment (including switchgear) under normal and fault conditions. Three basic circuits will be demonstrated and compared. · Another class is a set of basic test-circuits having capability of creating similar stresses on HVDC circuit breakers as in service. Four basic circuits are investigated and compared to an ideal DC circuit: discharge of a charged high-current reactor, discharge of a charged high-voltage capacitor bank and high-power high-voltage AC circuits of 16.7 and 50 Hz. Comparison of each of these circuits shows that low frequency AC circuits are possible candidates to represent the interaction of HVDC circuit breaker with a DC circuit adequately; regarding fault current rise, interruption performance, counter voltage creation and energy management.