Influence of core gap in design of current-limiting transformers

Core gaps are used in the magnetic shunt paths of current-limiting transformers to limit secondary current under short-circuit conditions. It is shown here that for short-circuit current limited to twice normal a current limiting transformer has only 55% of the rating of a noncurrent-limiting transformer of the same physical size. Part of the reduction in rating stems from the space required for magnetic shunts, part from the greater space needed for winding insulation, and part from the increased loss due to the gaps. Reliability of a previously tested gap-loss equation is established, and design examples are given for both stamped laminations and strip-wound cores.