A New Inverse Time Overcurrent Relay with Adjustable Characteristics [includes discussion]

This paper describes a completely redesigned inverse time overcurrent induction-type relay. The principal goals sought in this new version of an old familiar relay were: (1) improved accuracy, (2) adjustability of the characteristic current-time curves, not only to meet the prescribed curve within close tolerances but also to provide as wide a spread as possible of other obtainable curve shapes, and (3) simplification and improvement of mechanical design, such as the elimination of gears, and a truly adjustable permanent magnet. This paper describes a relay in which these goals were met, see Figure 1.