A negative phase sequence relay (or phase unbalance) is essentially provided for the protection of generators and motors against unbalanced loading that may arise due to phase-to-phase faults. Essentially such a relay has a filter circuit which is responsive only to the negative. Protective Relays - Technical Seminar Nov 2016 - Copyright: IEEE 2 Abstract: Protective relays and devices have been developed over 100 years ago to provide “lastline”of defense for the electrical systems. This method, first introduced by Charles Fortescue, simplifies complex scenarios, enabling easier fault. Negative sequence overvoltage protection is used for protection of service main, motor circuits, sensitive loads for conditions such as reverse phase rotation (reverse phase sequence), unbalanced phase voltage and unbalanced phase angle. While this is bad, It's not a. In the design of electrical power systems, the ANSI Standard Device Numbers denote what features a protective device supports (such as a relay or circuit breaker).
[PDF Version]