Fast fault current VIA statcom with electronic tap-changer

Reducing levels of fault current infeed as inverter-based resources (IBR) displace synchronous machines are a concern for system operators. The reduction undermines the ability of a conventional protection system to identify and locate faults in an effective manner. A possible route to avoid elevated ratings is to recognise that the increased current is generally needed at times of decreased voltage such that a tap-change transformer could be used to change how the voltage-current rating of an IBR is presented to the network. This paper proposes a thyristor-based electronic tap-changer (eTC) fitted to the coupling transformer of a STATCOM. The thyristors of the tap-changer can be commutated rapidly by using the STATCOM to drive phase currents to zero briefly. The case-study circuit demonstrates delivery of substantial fault current contribution (FCC) of up to 4 pu at the point of common coupling (PCC) in less than half a cycle (10 ms) after detection of three- and single-phase faults.