A simplified unit for distance relaying

One method of providing an intermediate step between the performance, cost, and complexity of overcurrent and conventional 3-zone distance relays is described here. RELAY APPLICATION naturally varies widely with the practices of the various operating utilities. However, it seems to be a general trend that for low-voltage short lines, simple overcurrent relays are employed most commonly, while for longer moderate- to high-voltage lines a high-speed form of protection is used such as high-speed distance relaying. Modern high-speed 3-zone distance relaying is necessarily more complex and expensive than overcurrent relaying, and, while the fine performance of these relays might be considered desirable for intermediate-voltage lines, cost factors may swing the balance to straight overcurrent relaying. One method of providing an intermediate step between the performance, cost, and complexity of these two basic forms of relaying is described here. A previous article¹ has described another scheme for providing distance relays economical for use on subtransmission lines.