Basler BEI‑51 Overcurrent Relay

The Basler BEI‑51 is an electromechanical overcurrent relay widely used for protection of feeders, motors, and transformers. Its NSN identifier 5945‑01‑293‑2363 confirms its military and industrial acceptance. The relay responds to phase and ground fault currents with adjustable pickup and time‑delay settings, ensuring selective coordination with downstream devices.

Key Features

The BEI‑51 features a high‑torque induction disc mechanism that provides a definite‑time or inverse‑time characteristic. It includes a target reset button, a current indicator, and multiple tap connections for current transformer ratios. The relay is housed in a durable draw‑out case for easy maintenance.

Technical Specifications

CT secondary: 5 A. Pickup range: 1‑10 A (adjustable). Time dial: 0‑10. Time delay range: 0.1‑2.0 seconds at 10x pickup. Operating temperature: ‑10°C to +50°C. Contact rating: 5 A at 250 VAC. Dimensions: 200 x 150 x 100 mm. Weight: 3.0 kg.

Operating Principles

The current from CTs energizes the relay coil, producing torque on the induction disc. The disc rotates against a spring; when the torque exceeds the spring tension, the disc closes the contact. The time dial adjusts the contact gap, controlling the tripping time. The inverse characteristic ensures faster clearing of severe faults.

Applications

The BEI‑51 is used in utility distribution, industrial power systems, and military installations. It is suitable for overcurrent protection in radial and loop networks, and as backup protection for transmission lines.

Installation and Configuration

Install the relay into a standard panel cutout. Connect CT leads and auxiliary power. Select the desired tap and time dial settings using the front‑panel knobs. Perform a secondary injection test to confirm operation at the set points.

Maintenance and Reliability

Regular maintenance includes cleaning the contacts, checking the disc rotation, and verifying the time‑current characteristic. The BEI‑51 is built to withstand harsh environments and has a long operational history.

Conclusion

The Basler BEI‑51 Overcurrent Relay offers a proven, robust solution for overcurrent protection, backed by a national stock number and extensive field use.