Basler BE1‑87T Solid State Protective Relay

The Basler BE1‑87T is a solid‑state protective relay designed for differential protection of transformers, generators, and large motors. It provides high‑speed fault detection by comparing the currents entering and leaving the protected zone. This relay is essential for preventing damage from internal faults, ensuring the reliability of critical power system assets.

Key Features

The BE1‑87T features adjustable pickup settings, harmonic restraint to prevent maloperation during transformer inrush, and a high‑speed output for tripping breakers. It includes a target indicator for fault identification and test points for calibration. The relay is housed in a rugged draw‑out case for easy maintenance and retrofitting.

Technical Specifications

CT secondary rating: 5 A or 1 A. Pickup current range: 0.1 to 2.0 times rated. Operating time: less than 25 milliseconds at 2 times pickup. Harmonic restraint: adjustable second‑harmonic blocking from 15% to 40%. Output contacts: 2 form‑C rated at 5 A at 250 VAC. Operating temperature: -20°C to +55°C. The relay operates from 120 or 240 VAC/DC auxiliary supply.

Operating Principles

The relay continuously monitors the current on both sides of the protected transformer. Under normal conditions, the currents are balanced, and the differential current is near zero. When an internal fault occurs, the differential current exceeds the pickup threshold, and the relay initiates a trip after a short delay. The harmonic restraint circuit prevents tripping during inrush by blocking on second‑harmonic content.

Applications

This relay is used in utility substations, industrial power systems, and generator step‑up transformers. It is suitable for two‑winding and three‑winding transformers, as well as for busbar differential protection.

Installation and Configuration

Mount the relay in a standard panel cutout. Connect the CT leads and auxiliary power. Adjust the pickup and restraint settings using the front‑panel knobs. Perform a secondary injection test to verify the operating characteristics and trip timing.

Maintenance and Reliability

The solid‑state design ensures long‑term reliability. Periodic testing with injection equipment is recommended to confirm calibration. Routine visual inspection of connections and cleaning are sufficient.

Conclusion

The Basler BE1‑87T solid state protective relay offers dependable differential protection with advanced restraint features, making it a trusted choice for safeguarding power transformers.