In a large interconnected power system, having large sizes of alternators and higher capacity transmission lines, the protective relays and circuit breakers should operate as fast as possible to improve the transient stability of the system. The transients consist of a large number of harmonic currents and voltages with the addition of doing. component, Both Fundamental component of current and voltage are with inherent large time delays required. For protective relaying purpose applications. Earlier, analog filters were used. The digital filters extract the fundamental components from the transient in about half a cycle.
The reasons for using digital protection relaying schemes in place of analog protection offers many advantages over analog protection. As minicomputers, microprocessors, microcontroller is developing the protective relaying schemes have been developed on these devices. These devices offer low burden, filter in operation, low maintenance, are not affected by external causes such as mechanical shocks and vibrations.
Digital protection Advantages
(a) Functional flexibility: A variety of protection functions such as distance relay characteristics (mho, ohm, quadrilateral, parabolic, etc.) can be obtained with a slight change in hardware and software.
(b) Low cost: The cost of equipment in digital protection is low.
(c) Self-checking functions: By using proper software, the hardware faults can be easily diagnosed.
(d) Easy communication: Using microprocessor-based relay, easy interface with digital communication equipment is possible.
(e) System integration and digital environment: The system of the digital relay can be easily integrated with other devices.
(f) Longer life: The performance of digital protection equipment does not change because of aging of components.