The three components of relay protection are

Relay protection consists of three main parts: the sensing element, the relay operating element, and the tripping circuit, which together detect faults and isolate faulty sections.1. Sensing ElementThe sensing element detects abnormal electrical quantities such as current, voltage, frequency, or impedance in the power system. This is typically achieved using instrument transformers like current transformers (CTs) and voltage transformers (PTs), which step down high voltages and currents to measurable levels for the relay. The sensing element continuously monitors the system and provides input signals to the relay logic when a fault occurs .2. Relay Operating ElementThe relay operating element is the decision-making part of the protective relay. It evaluates the signals from the sensing element against preset thresholds or logic conditions. If the measured quantity exceeds the relay's set point, the operating element activates. This can be an electromechanical mechanism, a static electronic circuit, or a numerical microprocessor-based system. Its function is to determine whether a fault exists and to initiate a trip signal .3. Tripping CircuitThe tripping circuit is the output section that executes the protective action. Once the relay operating element detects a fault, it closes its contacts to energize the circuit breaker trip coil, causing the breaker to open and isolate the faulty section. The tripping circuit may be powered by AC or DC sources and ensures that the faulted equipment is disconnected quickly to prevent damage and maintain system stability .SummaryTogether, these three parts form the decision chain of relay protection: the sensing element detects abnormal conditions, the relay operating element decides if a trip is necessary, and the tripping circuit executes the isolation. Proper coordination among these parts is essential for reliable protection of electrical equipment and the overall power system .