Large-scale optimal power flow: effects of initialization, decoupling and discretization

Extensive numerical testing of a second-order OPF (optimal power flow) solution method was conducted using a 1500 bus network under various loading conditions. The results show that properly implemented second-order OPF solution methods are robust with respect to different starting points, the decoupled OPF solution is expected to be close to the full OPF solution, and the effects of discretization of load tap changing (LTC) transformer taps are very small and usually negligible. The test procedure required two optimizations. During the first optimization, the transformer taps were treated as continuous variables. Using the continuous solution, the LTC taps were moved to their closest allowable discrete values. During the second optimization the LTC transformer taps were held fixed at their discretized values. The second solution was compared to the first. A small difference between these two solutions indicates that the effects of the transformer tap discretization were minimal