Basler Electric BE1-87G Generator Differential Relay

The Basler Electric BE1‑87G is a solid‑state high‑impedance differential relay specifically designed to protect synchronous generators against internal winding faults, including phase‑to‑phase, phase‑to‑ground, and turn‑to‑turn faults. It compares the currents entering and leaving the generator windings; any imbalance indicates an internal fault and triggers a high‑speed trip. The relay’s high‑impedance principle provides inherent stability for external faults and CT saturation conditions, ensuring reliable operation.

Operating Principle

The relay uses a voltage‑operated high‑impedance circuit. Current transformers (CTs) on each phase are connected in parallel with a stabilizing resistor. Under normal or through‑fault conditions, the CT secondary currents are balanced, resulting in negligible voltage across the relay. During an internal fault, the imbalance produces a voltage that exceeds the pickup threshold, causing the relay to operate. The pickup setting is adjustable via tap selection and a potentiometer.

Key Features

The BE1‑87G offers adjustable pickup settings (typically 0.1‑2.0 A secondary), a built‑in test circuit for functional verification, and a target indicator with manual reset. It includes two independent output contacts (Form C) for tripping and alarm. The relay features a wide operating temperature range and is immune to DC offset and harmonics.

Technical Specifications

Input CT secondary: 1 A or 5 A. Frequency: 50/60 Hz. Pickup range: 0.1‑2.0 A (adjustable). Operating time:<30 ms at 5x pickup. Output contacts: 2 SPDT, rated 5 A at 250 VAC. Power supply: 24‑250 VDC or 120‑240 VAC. Stabilizing resistor: built‑in or external (user‑selectable). Operating temperature: –30°C to +65°C. Enclosure: metal, panel‑mount.

Applications

This relay is used on generators of all sizes, from small industrial sets to large utility turbines. It provides primary protection for stator winding faults and is often coordinated with backup overcurrent or distance relays. The BE1‑87G can also be applied to protect transformers or reactors where differential protection is needed.

Installation and Commissioning

Mount the relay in a standard panel cutout. Connect the CT leads from the generator neutral and line sides, ensuring correct polarity and grounding. Commissioning involves setting the pickup tap, adjusting the stabilizing resistor, and performing secondary injection tests to verify trip levels and timing. The relay includes a test pushbutton for quick functional checks.

Reliability and Standards

Compliant with IEEE C37.91 and IEC 60255, the BE1‑87G is built with high‑quality solid‑state components and conformal‑coated boards for environmental resilience. It has a proven track record of reliability in critical applications. Periodic testing is recommended to maintain accuracy.

Conclusion

The Basler Electric BE1‑87G generator differential relay is a fast, secure, and stable protection solution for generator stator faults. Its high‑impedance design and adjustable settings make it a preferred choice for protection engineers worldwide.