SEL-387

Current Differential and Overcurrent Relay

The SEL-387 is a versatile current differential and overcurrent relay designed to protect various power apparatus, including transformers, buses, generators, and reactors. It is capable of protecting power transformers with two to four windings (or terminals). By integrating the primary differential protection and backup overcurrent protection into a single device, it provides an economical and highly reliable protection solution.

Key Features

Multi-Winding Differential Protection (87)

Supports up to four terminals and offers a choice of single- or dual-slope percentage restrained differential characteristics to ensure stability and prevent misoperation during through-fault conditions.
Harmonic Control

Provides 2nd, 4th, and 5th harmonic restraint or blocking to maintain security during transformer inrush or overexcitation conditions, supplemented by DC element detection.
Restricted Earth Fault (REF) Protection

Includes REF protection to sensitively detect ground faults in wye-connected transformers.
Comprehensive Overcurrent Protection (50, 51)

Performs multi-layered backup protection including phase, negative-sequence, and residual overcurrent elements.
Phase Angle and Magnitude Compensation

Automatically compensates for phase shifts caused by transformer connection types and differences in CT ratios through internal relay settings, eliminating the need for external correction CTs.
Optional Thermal Modeling (49)

Offers an optional thermal model based on the IEEE C57.91 standard to prevent thermal damage caused by overloads in mineral-oil-immersed transformers.

Powerful Monitoring Capabilities

Disturbance Analysis: Enables precise root-cause analysis of system faults through high-resolution oscillographic event reports and Sequential Events Recorder (SER).
Asset Management: Standard features include breaker contact wear monitoring (Breaker Monitor) and station battery voltage monitoring to support efficient maintenance.
SELogic Control Equations

Provides the flexibility for users to write their own control equations to customize complex logic or automation sequences.
Flexible Communication Configuration

Equipped with a total of four independent communication ports (three EIA-232 serial ports and one EIA-485 serial port), allowing simultaneous connection to multiple supervisory systems.
User-Friendly Interface

The front-panel display and programmable text points allow for immediate on-site status monitoring and control.
Robust Design and Environmental Compliance

Supports a wide operating temperature range from -40°C to +85°C, with optional conformal coating available to protect circuit boards from corrosive environments.

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