Relay Protection Methods and Setting Table

A Relay Protection Setting Change Table documents the key relay parameters—pickup current, plug setting multiplier (PSM), time multiplier (TMS), and operating times—to ensure proper coordination and selective tripping.Purpose of a Relay Setting Change TableA Relay Protection Setting Change Table is used to:Record the current settings of relays in a system.Provide a reference for adjustments during commissioning or system upgrades.Ensure selectivity, so only the faulted section trips while upstream and downstream relays coordinate properly.Facilitate troubleshooting and verification of relay performance.Key Parameters in the TablePickup Current (I_pickup): The minimum current at which the relay will detect a fault. Typically expressed as a multiple of the rated load current or CT secondary current .Plug Setting Multiplier (PSM): Indicates how many times the actual current exceeds the relay pickup. It is critical for IDMT (Inverse Definite Minimum Time) relays to determine operating time; higher PSM results in faster tripping .Time Multiplier Setting (TMS): Scales the base operating time from the relay's characteristic curve. Proper TMS selection ensures time grading between upstream and downstream relays, allowing backup protection without unnecessary tripping .Operating Time: The calculated or measured time for the relay to trip at a given fault current. It is derived from the PSM and TMS values and the relay's time-current characteristic curve .Relay Type and Curve: Specifies the relay model and the type of time-current characteristic (Standard Inverse, Very Inverse, Extremely Inverse, or Long Time Inverse) used for coordination .TAP or Scaling Factor: For transformer-connected relays, TAP scaling converts secondary currents to per-unit values, ensuring consistent operation across multiple windings .Example Structure of a Relay Setting Change TableRelay IDLocationI_pickup (A)PSMTMSOperating Time (s)Curve TypeNotesR1Feeder 12002.50.80.35Very InverseBackup for R2R2Feeder 21503.00.60.20Standard InversePrimary protectionR3Transformer1001.51.00.50Extremely InverseLV sideBest PracticesDocument all changes: Any adjustment to pickup, PSM, or TMS should be recorded in the table.Verify coordination: Ensure upstream relays have longer operating times than downstream relays for the same fault current.Re-evaluate during commissioning: Actual measured currents and system conditions may require updating the table .Include notes: Specify special conditions, such as zero-sequence compensation, hybrid circuits, or transformer winding scaling .This table serves as a central reference for engineers to maintain reliable, selective, and safe operation of the electrical protection system.