The recent awareness about fossil fuels and the environment has arisen more sustainable alternatives regarding means of transport. The first alternative of green transport has been hybrid vehicles. This kind of vehicles reduces significantly the CO2 emission but not totally. Nowadays, the current trend is the utilization of a unique motor for vehicle. i.e. an electrical motor. It seems that the electric vehicles (EV) will become the cars of the future. Moreover, one kind of such vehicles, the plug-in electric vehicles (PHEV), will not only charge their batteries, but PHEV will also be able to inject power to the network when required. This fact suggests that EV penetration will affect current power system performance. Then, it is necessary to study some scenarios of penetration of such vehicles into the electrical network in order to maintain security and quality of power supply.