Calculation of Short Circuit Currents in HVDC Systems

This paper discusses the effect of short circuits on the DC side of HVDC systems. Special attention is given to the control system and its influence on the magnitude of the short circuit current. Determination of the fault is done in two ways: by means of simulation (here PSCAD(R) is used) and by applying the IEC 61660 standard. This standard deals with short circuit currents in DC auxiliary installations in power plants and substations. Analysis covers both classic, network-driven (thyristor-based) HVDC as well as self-driven voltage source converter HVDC (IGBT-based). The underlying differences of these two HVDC concepts result in completely different short circuit currents in the case of a fault on the DC side. The simulated short circuit currents are compared to the values obtained by IEC 61660, in order to check whether this standard can be also used for HVDC systems. Some principle differences between auxiliary DC systems and HVDC transmission systems are discussed on this basis. The paper concludes with general comments on the transient and steady-state current characteristics for a short circuit on the DC side of HVDC systems. Understanding of such fault current characteristics and the influence of the control system on them are important prerequisites on the way to multi-terminal HVDC systems.