The protection of the electrical system is a branch of electrical power engineering that deals with the protection of electrical systems from faults through the insulation of parts damaged from the rest of the electrical network. The purpose of a protection scheme is to keep the power supply system stable, isolating only those components that are in fault, while leaving as much of the network as possible still in operation. Therefore, protection schemes should be applied with a very pragmatic and pessimistic approach to compensation system failures. Devices used to protect faulty power systems are called protection devices.
Coordination of the protection device is the process of determining the "best fit" moment of the current interruption when abnormal electrical conditions occur. The goal is to minimize an interruption to the greatest extent possible. Historically, the coordination of protective devices was performed on translucent log-log paper. Modern methods usually include detailed computer analysis and reports.
Coordination of protection is also handled by dividing the energy system into protection zones. If a failure occurs in a particular zone, the necessary actions will be performed to isolate that zone from the entire system. The definitions of zones are generators, buses, transformers, transmission and distribution lines and motors. In addition, zones have the following characteristics: zones overlap, overlap regions indicate circuit breakers, and all circuit breakers in a given zone with a fault will be opened to isolate the fault. Overlapping regions are created by two sets of instrument transformers and relays for each circuit breaker. They are designed for redundancy to eliminate unprotected areas; however, the overlapped regions are designed to remain as small as possible, so that when a fault occurs in an overlap zone and the two zones encompassing the fault are isolated, the power system sector that is lost from Service is still small despite two areas being isolated.