A Computational Approach for Optimizing Coil Current Settings in Resonance Grounded Systems with Distributed Coils for Mitigation of Temporary Overvoltages

The operation of resonant grounded power systems can be challenging due to high temporary overvoltages (TOVs) during asymmetrical faults (broken conductor, ground fault, hanging breaker pole). In the case of a broken conductor, the resulting overvoltages are strongly dependent on the fault location, placement and setting of the Petersen coils (P-coils), system topology and power flow. This work presents a systematic approach for adjusting the coil current settings such that the maximum overvoltage is minimized, considering a large number of possible fault locations. The approach is based on a frequency domain network model that is established from the network data. A 1-ph network model is generated which provides the load flow solution, from which a 3-ph model is initialized. The regulating (“auto”) coil is tuned until the desired compensation level is reached, and a screening process is started where the fault is applied systematically at different locations in the system. The screening is combined with optimization of the coil current settings to minimize the maximum overvoltage. Acceptable CPU times are achieved, thanks to systematic use of the matrix inversion lemma. A speed gain by two orders of magnitude over matrix inversion is reported for a 59-bus system with 14 P-coils.