Determination of the Symmetric Short-Circuit Currents of Synchronous Permanent Magnet Machines Using Magnetostatic Flux Maps

The three-phase symmetric short-circuit is a reference fault condition for the qualification of a newly designed permanent magnet (PM) synchronous machine against the risk of irreversible demagnetization. To date, the accurate determination of the peak transient short-circuit current condition requires coupled circuital and transient Finite Element Analysis (FEA) to take magnetic saturation properly into account, and several simulations to determine the worst case pre-fault conditions. This work presents a method for the fast evaluation of the transient short-circuit currents of a PM synchronous machine by manipulation of its flux linkage maps, using the maps obtained via magnetostatic FEA. Besides providing a fast and accessible means of estimate, the flux-map based method gives insights on the effect of the pre-fault conditions, showing that the higher the initial flux linkage, the worse, and that generator operation is more severe than motor operation. The hyper-worst-case short circuit concept is also defined, which is a magnetic property of the machine under test, and a procedure for its fast-FEA computation is given. The method is validated against the results of transient FEA obtained using a commercial software.