The stability characteristics of a typical high voltage transmission circuit have been considered together with the requirements for short-circuit protection, as a basis for the selection and application of relay protective devices. In this paper, the performance of the 132 kv New York Edison-Niagara Hudson interconnection under fault and swing conditions is analyzed, the characteristics of various protective devices are discussed, and the performance of the selected equipment under both calculated and actual operating conditions is given. A protective scheme involving carrier current control is shown to be highly satisfactory.