Basler BE1-87T Solid-State Transformer Differential Relay

The Basler BE1-87T is a solid‑state differential relay specifically designed for protection of power transformers against internal faults such as turn‑to‑turn faults, winding short circuits, and core faults. This relay provides high‑speed, reliable protection while maintaining stability for external faults and transformer magnetizing inrush currents. The BE1-87T is a field‑proven, reliable solution for utility and industrial transformer protection.

The relay features solid‑state technology with high‑speed response and excellent thermal stability. It includes adjustable percentage slope settings and harmonic restraint to prevent maloperation during inrush and overexcitation conditions. The BE1-87T is housed in a rugged, compact enclosure suitable for panel mounting in substations and industrial control rooms.

Technical Specifications

• Model: BE1-87T

• Protection type: Differential (percentage restraint)

• Current sensing: 1/5 A CT inputs (primary and secondary side)

• Differential pickup: 0.1‑2.0 A (adjustable)

• Slope setting: 0‑40% (adjustable)

• Harmonic restraint: Second harmonic (15‑30%) and fifth harmonic (optional)

• Response time: < 20 ms (typical)

• Output contacts: 2 form C (trip and alarm)

• Power supply: 24‑240 V AC/DC (universal)

• LED indicators: Power, differential pickup, trip

• Operating temperature: -40°C to +70°C

• Certifications: CE, UL, RoHS

Functional Features

• Percentage differential protection: Provides sensitive fault detection while maintaining stability for external faults.

• Harmonic restraint: Blocks tripping during transformer inrush and overexcitation.

• Fast operation: Trip times less than one cycle.

• Adjustable settings: Pickup, slope, and harmonic restraint can be field‑adjusted.

• Target indicators: Seal‑in flags for trip indication.

Typical Applications

• Power transformers: Protection of two‑winding and three‑winding transformers.

• Generator step‑up transformers: Protection for unit‑connected generators.

• Industrial transformers: Protection for large furnace and rectifier transformers.

Installation and Configuration

Mount the relay on a panel. Connect the CT inputs from both sides of the transformer, the power supply, and the output contacts. Configure the pickup, slope, and harmonic restraint settings using the front‑panel controls. The relay includes test points for verification and a test mode for commissioning.

Compliance

Complies with IEEE C37.91, IEC 60255, CE and UL approved, RoHS compliant.

Conclusion

The Basler BE1-87T provides reliable, high‑speed differential protection for power transformers, ensuring rapid fault clearing and minimizing damage to critical equipment.