List of Relay Protection Products

Protective relays are essential devices in power systems, with commonly used types including overcurrent, differential, distance, earth fault, voltage, and frequency relays.Types of Protective Relays by FunctionOvercurrent Relay (OCR): Operates when current exceeds a preset limit to protect equipment from overloads or short circuits . Variants include instantaneous, definite time, and inverse time relays.Differential Relay: Compares currents at two points and operates when there is a difference, commonly used for transformers, generators, and busbars .Distance Relay (Impedance Relay): Trips based on the impedance of a transmission line, widely used in line protection .Earth Fault Relay (Ground Fault Relay): Detects leakage currents to the ground, protecting against insulation failures .Over/Under Voltage Relay: Protects equipment from abnormal voltage conditions, ensuring stability in power systems .Frequency Relay: Trips when system frequency deviates from normal limits, safeguarding generators and sensitive loads .Directional Relay: Operates based on the direction of current flow, often used in complex network protection .Lockout Relay (86): Provides a lockout function for critical equipment like transformers to prevent repeated operation after a fault .Pilot Wire Relays: Used for long transmission lines, employing wire, carrier-current, or microwave channels to detect internal faults .Common ANSI/IEEE Standard Device Numbers50/51: Instantaneous/Time Overcurrent Relay50N: Instantaneous Ground Fault Relay51N: Time Ground Fault Relay87: Differential Relay21: Distance Relay59: Overvoltage Relay27: Undervoltage Relay81: Frequency Relay86T: Transformer Lockout Relay SummaryProtective relays are classified by function, operating principle, and mechanism (electromechanical, static, or numerical). Modern numerical relays combine multiple functions, offer fast response, self-diagnostics, and event recording, making them suitable for complex power systems . These devices ensure equipment safety, system reliability, and continuity of electrical supply.