Basler Electric BE1-87G Solid State Generator Differential Relay

The Basler Electric BE1‑87G is a solid‑state differential relay specifically designed for the protection of synchronous generators. It compares the currents entering and leaving the generator windings; any difference indicates an internal fault (phase‑to‑phase, phase‑to‑ground, or turn‑to‑turn). The relay operates with high speed, typically within one cycle, to minimize damage and ensure rapid fault clearance. The high‑impedance design provides excellent stability for external faults and CT saturation conditions.

Differential Principle

The BE1‑87G uses a high‑impedance voltage‑operated principle. Current transformers on each phase are connected in parallel, and a stabilizing resistor is used to set the voltage level required for tripping. Under normal or external fault conditions, the CT currents balance, and the relay sees only a small spill current. During an internal fault, the currents are unbalanced, producing a voltage across the relay that exceeds the pickup setting, causing a trip.

Adjustable Settings

The relay provides a tap setting for the pickup current (typically 0.1‑2.0 A) and an adjustable time delay (optional). A front‑panel potentiometer allows fine‑tuning of the stabilizing resistor to match CT characteristics. The relay includes a built‑in test circuit for verifying operation without injecting fault currents.

Technical Specifications

Input current: 1 A or 5 A secondary. Frequency: 50/60 Hz. Pickup range: 0.1‑2.0 A (adjustable). Operating time:<30 ms at 5x pickup. Output contacts: 2 Form C, rated 5 A at 250 VAC. Power supply: 24‑250 VDC or 120‑240 VAC. Operating temperature: –30°C to +65°C. The relay is housed in a rugged metal enclosure.

Applications

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

Installation and Commissioning

Install the relay in the generator protection panel. Connect the CT leads from the generator neutral and line sides. Ensure proper polarity and grounding. Commissioning involves setting the pickup value and testing the relay with a secondary injection test set to verify trip levels and timing. The relay includes a target reset button for post‑trip indication.

Reliability and Standards

The BE1‑87G complies with IEEE C37.91 and IEC 60255 for protective relays. Its solid‑state design offers high reliability and immunity to environmental stress. Periodic testing is recommended to ensure CT and relay performance remain within tolerance.

Conclusion

The Basler Electric BE1‑87G solid‑state generator differential relay is a fast, dependable, and stable protection solution for critical generator assets. Its high‑impedance design, adjustable settings, and robust construction make it a preferred choice for generator protection engineers worldwide.