These input devices or instrument transformers provide insulation from the high-power system voltages and reduce the magnitudes to practical secondary levels for the relays. In circuit schematics and diagrams they are represented as shown in Figure 1. In electrical engineering, a protective relay is a relay device designed to trip a circuit breaker when a fault is detected. : 4 The first protective relays were electromagnetic devices, relying on coils operating on moving parts to provide detection of abnormal operating conditions such as. A protection relay is a crucial component of electrical systems that safeguard infrastructure, employees, and equipment from electric problems and malfunctions. It functions as a watchdog by constantly surveying multiple system components including voltage, current, frequency, and phase angle. It. A protection relay is a smart device that receives inputs like current, voltage, resistance, temperature, or even light, compares them to set points, and provides outputs such as visual feedback in the form of indicator lights and/or an alphanumeric display, communications, control warnings. An electrical device designed to detect some specified condition in a power system, and then command a circuit breaker either to trip or to close in order to protect the integrity of the power system, is called a protection, or protective, relay. The terminals of the relay mainly include; common, coil, NO (normally open) & NC (normally closed). Protection is the branch of electric power engineering concerned with the principles of design and operation of equipment (called 'relays' or 'protective relays') that detects abnormal power system conditions, and initiates corrective action as quickly as possible in order to return the power.