Relay protection action value

Relay protection action values are determined using parameters like pickup current, plug setting multiplier (PSM), time setting multiplier (TSM), and other relay-specific settings to ensure accurate and selective tripping of power system faults.Key Relay Settings1. Pickup Current (Current Setting): The pickup current is the minimum current at which the relay begins to operate. For overcurrent relays, it typically ranges from 50% to 200% of the rated current in steps of 25%, while for earth fault relays it ranges from 10% to 70% in steps of 10% . The pickup current ensures the relay does not trip under normal load conditions. 2. Plug Setting Multiplier (PSM): PSM represents the ratio of the actual fault current in the relay to its pickup current. It is a critical factor in determining the operating time of inverse definite minimum time (IDMT) relays. A higher PSM results in faster tripping . PSM is calculated based on the relay secondary current and the relay pickup setting. 3. Time Setting Multiplier (TSM): TSM scales the base operating time derived from the relay's characteristic curve. It allows coordination between upstream and downstream relays, ensuring selective tripping. Lower TSM values result in faster operation, while higher values provide backup protection . 4. Earth Leakage (EL) and Overload (OL) Settings:EL (Earth Fault Pickup): Determines the current threshold for earth fault detection.OL (Thermal Overload): Protects equipment from prolonged overcurrent conditions by tripping when thermal limits are exceeded . 5. Multiplying Factor (MF): MF, also called the metering or scaling factor, adjusts the relay input to match the actual system current, ensuring accurate operation .Distance Protection SettingsFor distance or impedance relays, action values are set based on line impedance and fault characteristics:Zone 1 Reach: Typically 80–90% of the line impedance for phase faults.Quadrilateral or Mho Characteristics: Mho characteristics are preferred for EHV systems due to high-speed operation, while quadrilateral characteristics are used for phase-to-ground faults.Zero Sequence Compensation: Applied to account for line impedance variations or hybrid circuits .Calculation and CoordinationRelay action values are calculated to ensure:Selectivity: Only the relay closest to the fault operates first.Speed: Fast tripping for severe faults.Reliability: Avoids nuisance tripping under normal conditions. Advanced methods, including simulation of extreme operating conditions, are used to optimize relay settings in modern power systems, especially with variable operating conditions due to renewables and power electronics .SummaryRelay protection action values are a combination of pickup current, PSM, TSM, EL, OL, and MF, along with distance relay parameters for line protection. Proper calculation and coordination of these values ensure fast, selective, and reliable fault isolation, maintaining system stability and equipment safety.