The electrical network is planned to stay in the most reliable operation conditions, without any violated operation constraints. Many optimization and simulation models are used to define the safe operation region. The Optimal Power Flow (OPF) is a useful tool for the search of the best safe operation point. However, the computational complexity associated to its non-linear constraints implies in a heavy computation time and makes it difficult to be used whenever a fast response is required, as in on-line oporation or even most operation planning problems. On the other hand, the Linearized Optimal Power Flow (LOPF), due to its simplicity, is a very fast tool. However, it does not consider reactive (voltage) constraints, and is not able to detect any violation. This work presents a model to incorporate voltage constraints in the Linearized Power Flow.