Finding The Optimal Tap Positions Of Cascade-Connected On-Load Tap-Changer-Equipped Transformers

The paper proposes an algorithm for simultaneous finding optimal tap positions of cascaded on-load tap-changer (OLTC)-equipped transformers, operating on the primary and secondary level (110 kV/20 kV and 20 kV/0.4 kV substations). The algorithm developed to solve a constrained optimization problem uses differential evolution (DE) as an optimization tool. Its objective function minimizes the network power losses in a time-discrete operation and its penalization functions ensure that operational constraints (voltage profiles and line currents) are kept within the imposed limits. The algorithm operation is tested on a real power distribution network model consisting of three 20 kV feeders and two 0.4 kV networks supplied by a 110/20 kV substation and containing three OLTC-equipped transformers (one 110 kV/20 kV and two 20 kV/0.4 kV) for which the optimal tap positions are determined simultaneously. The impact of load modeling on the algorithm behavior is investigated.