The SEL-387E Current Differential and Voltage Relay provides protection to two- or three-winding power transformers. Voltage inputs for power metering, overexcitation protection, and over-/underfrequency load shedding provide versatile solutions for power apparatus protection. Automation features reduce total project construction and operation costs through elimination of traditional external control switches, meters, and indicating lamps.

Applications

Three-Winding Current Differential Protection—Protect two- to three-winding power transformers with programmable single- or dual-slope percentage restraint, supervised by a choice of second- and fourth-harmonic blocking or restraint elements, plus fifth-harmonic and dc blocking elements.

Overexcitation Protection—Detect overexcitation conditions to prevent overheating and damage in the protected apparatus with the volts-per-hertz elements. Choose definite-time elements, multiple curves, and custom programmable curves for alarm and tripping applications.

Overcurrent Protection—Each three-phase current input terminal has a total of 11 overcurrent elements, 9 of which are torque-controllable, providing comprehensive overcurrent protection on each winding input. For backup overcurrent protection in ring-bus or breaker-and-a-half configurations, two combined overcurrent elements operate on the sum of the currents from Windings 1 and 2. The combined currents from two separate breaker CTs emulate the current as if from a single bushing CT applied on the transformer.

Restricted Earth Fault (REF) Protection—The REF function compares the directions of neutral current and winding residual current for sensitive ground fault detection in grounded–wye or autotransformer–connected windings.