After several incidence of voltage collapse in electric power systems around the world, the voltage security has become a matter of utmost importance. The phenomenon of voltage stability is due to the operation of the system with high loading and is manifested by the existence of a maximum power transfer over the network and efforts to control voltage having the opposite effect than usual. With increased integration of distributed generation, usually connected to the existing distribution network at lower voltages, the possibility of occurrence of the phenomenon should be investigated. It is demonstrated the possibility of occurrence in buses of synchronous generators or synchronous condensers, where the maximum generated power could be limited and the voltage control could have the opposite effect. It presented the tools used in assessing the conditions of voltage stability composite indexes with physical and mathematical meaning. I was established a procedure for performing simulations on IEEE 34 bus and 70 bus test systems. It analyzed the impact of the generator under the conditions of voltage stability, voltage profile in the steady state and the power losses. It was concluded that, in tests, the injection of active power from the generator was limited by voltage out of range allowed and not by voltage stability problems.