The Constant growth of the demand for electrical energy in Brazil is leading to an increased use of the country’s vast hydro potencial. The great size of the hydroelectric plants being planned for the near future, as well as their distance from the main load centers, will make it necessary to transmit vast amounts of power over long EHV lines. The electrical characteristics of some of these lines, specially those using series capacitores. Make it difficult, and in some cases impossible, to apply conventional protection schemes. This paper, using as an example a preliminary study of the above mentioned system, analyses specifically the problems related to the protection of series compensated transmission lines and describes two series computer programs suitable for circuit for short circuit studies and the evaluation of various protection schemes.