Basler Electric BE1‑87G – Variable Percentage Differential Relay

The Basler Electric BE1‑87G is a high‑speed variable percentage differential relay designed for the protection of generators, transformers, and large motors. This solid‑state relay employs the percentage differential principle with harmonic restraint to provide secure and reliable protection against internal faults while maintaining stability during external faults and inrush conditions.

Differential Protection Principle

The BE1‑87G compares the currents entering and leaving the protected zone. Under normal conditions, the differential current is near zero. For internal faults, the differential current rises significantly, triggering a trip. The percentage differential characteristic provides a slope that ensures stability for through‑faults with CT errors while allowing sensitive detection of low‑level internal faults.

Harmonic Restraint

Second‑harmonic restraint prevents misoperation during transformer energization or generator startup, when inrush currents can produce differential current. The harmonic restraint threshold is adjustable from 15% to 30%.

Current Inputs and Matching

Accepts up to six current inputs (three primary, three secondary) with 1 A or 5 A CT ratings. Adjustable CT ratio matching and phase shift compensation are built in.

Setting and Configuration

Settings are entered via front‑panel keypad and LCD, or through communication software.

Typical Applications

Protection of generators, transformers, and large motors in utility and industrial systems.

Overall, the Basler Electric BE1‑87G provides reliable differential protection for critical power system assets.