Application of saturated core fault current limiters to interconnected distribution networks

There is an increasing need for electricity utilities to limit fault levels in critical locations in power systems so that existing switchgear can continue to function as expected. This is particularly true in electrical distribution systems, where the increased penetration of renewable and decentralised generation is forcing the network to be highly interconnected in order to allow for higher integration capacity and reliable operation. Consequently, the short-circuit currents in distribution systems have increased significantly. In this background, application of fault current limiting devices is one of the solutions that is being considered by the Distribution Network Service Providers (DNSPs). A saturated core Fault Current Limiter (FCL) is one such device that can be used in existing and future electrical distribution systems to reduce the fault currents to a manageable level. This paper presents the potential performance of a saturated core FCL, in an interconnected 11kV test system, utilising a new comprehensive time-domain model to represent the FCL. PSCAD/EMTDC studies and numerical fault analysis are carried out to simulate the efficacy of an FCL when placed on a bus-tie of a looped circuit. The effect of the bus-tie FCL impedance on the network impedance and the subsequent fault current contributions is investigated. It is demonstrated that in a circuit with complex interconnections, suppression of fault currents need multiple FCLs in critical feeders.