Abstract
The non-directional overcurrent protection (International Electrotechnical Commission standard IEC 617 or American National Standards Institute ANSI/Institute of Electrical and Electronic Engineers IEEE C37.2 standard device number 51) is one protection type/relay function that has stood the test of time. The latest generation of relays has brought about enhanced capabilities. The most popular overcurrent protection, which is the Inverse Definite Minimum Time (IDMT) function, has proven to provide coordination of electrical nodes with ease. This is one of the oldest but extremely reliable relay characteristic. A number of new protection functions and enhancements to existing functions are commensurate to the advanced technical capabilities of the newer generation protective devices. The new development techniques include “acceleration”, which is a technique of sending the circuit breaker status of the near end of a line or feeder to the far end to influence the relay decision at the far end. Impedance protection, unit line protection, etc. have come with many advanced characteristics and properties. The enhancements to protection devices bear special features but cannot substitute inverse time overcurrent protection, which, up to now, is a reliable backup in feeder protection schemes in South Africa. The superior feature is the capability to achieve coordination between a series of protective devices. This is achievable without excessive damage to the electrical components of the circuit. ..
M.Eng. (Electrical Engineering)