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 uses the principle of differential current measurement to provide fast, sensitive 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, for through-fault stability)

• 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

• Dimensions: 200 x 150 x 80 mm

• Certifications: CE, UL, RoHS

Functional Capabilities

• Percentage Differential Protection: Provides reliable protection for internal transformer faults by comparing the currents entering and leaving the transformer, with percentage restraint to prevent tripping for external faults.

• Harmonic Restraint: Blocks tripping during transformer energization (second harmonic) and overexcitation (fifth harmonic), preventing nuisance trips.

• Fast Operation: Trip times of less than one cycle ensure rapid clearing of internal faults, minimizing transformer damage.

• Adjustable Settings: Pickup, slope, and harmonic restraint levels can be field-adjusted to match the specific transformer characteristics.

• Target Indicators: Seal-in target flags for trip indication to assist in post-fault analysis.

Typical Applications

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

• Generator transformers: Differential protection for unit-connected generators.

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

• Distribution transformers: Backup or primary protection for critical distribution transformers.

Installation and Configuration

Mount the BE1-87T on a panel using the provided brackets. Connect the CT inputs from both sides of the transformer, ensuring correct polarity for differential current calculation. Connect the power supply and output contacts. Configuration is performed using the front-panel potentiometers and DIP switches: set the differential pickup, slope, harmonic restraint levels, and trip time delay. The relay includes test points for measuring currents and verifying operation.

Compliance

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

Conclusion

The Basler BE1-87T provides reliable, high-speed differential protection for power transformers, ensuring rapid clearing of internal faults and preventing costly transformer failures. Its proven solid-state design and adjustable settings make it a trusted solution for transformer protection.