The SEL-587 Current Differential Relay combines overcurrent and differential elements in an easy-to-apply power apparatus differential protection package. Relay security is achieved by an optimized set of user-selectable restraining and blocking elements. Dual-slope percentage, harmonic restraint and blocking, plus dc blocking are included. Zero-sequence currents are filtered out from the differential element for any combination of power and transformer CT connections. SELOGIC® control equations provide application flexibility when conditions warrant. ➤ Protection. Protect two-terminal transformers, generators, reactors, and other power apparatus using a combination of differential, instantaneous, definite-, and inverse-time overcurrent elements. Differential scheme security is achieved by the following: ➢ Dual-slope percentage restraint ➢ Second- and fourth-harmonic blocking or restraint plus dc blocking for magnetizing inrush ➢ Fifth-harmonic blocking for transformer overexcitation ➢ CT and transformer connection compensation ➤ Monitoring. Metering quantities are available for phase, ground, negative-sequence, differential, and harmonic currents. Post-fault analysis is simplified by information recorded in event reports having 15-cycle duration times. As many as 10 event reports are stored in nonvolatile memory. Self-test and alarm functions are standard. ➤ Relay and Logic Settings Software. ACSELERATOR QuickSet® SEL-5030 Software reduces engineering costs for relay settings and logic programming. The built-in HMI provides phasor diagrams that help support commissioning and troubleshooting.