AbstractOptimal power flow (OPF) with transient stability constraints is a nonlinear optimization problem in functional space that is not easy to deal with precisely even for small‐scale power systems. Instead of directly tackling this tricky problem, in this paper, OPF with transient stability constraints (OTS) is equivalently converted into an optimization problem in Euclidean space via a constraint transcription, which can be solved by any standard nonlinear programming techniques adopted by OPF. The transformed OTS problem has the same variables as those of OPF in form, and is tractable even for large‐scale power systems with a large number of transient stability constraints. © 2001 Scripta Technica, Electr Eng Jpn, 137(1): 17–27, 2001