In this paper the problem of reactive power dispatching in electrical power systems is studied. The problem is treated through optimal power flows (OPF) using an objective function that minimizes real power losses in transmission lines. A computer program that solves OPF was written in Matlab/Octave using the Newton-Raphson method (NR) and quadratic penalties. The employed algorithm is described, and is similar to one used in an ordinary power flow program (PF), therefore being an educational example on how the basic PF analysis is extended to include optimization. Simulations were run using small case studies found in the literature and the results show good agreement compared to those of a commercial simulator.