A comprehensive method of determining the performance of distance relays

DURING the past few years rapid progress has been made in the development of distance relay protective schemes, and there are now available a number of various types of distance measuring and directional elements which may be utilized in various combinations to afford the protection desired. In determining the performance of these elements under various fault conditions it would be of great benefit to be able to express the performance of each type of element under a given fault condition in terms of a simple quantity such as the effective line impedance between the relay and the point of fault. Unfortunately it will be found that the performance of certain elements, notably those connected to the unfaulted phases will be affected by changes in system setup and in system capacity. Lewis and Tippet have provided an excellent theoretical treatment of this problem¹ which Calabrese has supplemented by a study of the effect of wye-delta and delta-wye transformers interposed between the relay and the fault.²