Basler Electric BE1‑851 – Advanced Overcurrent Protection System

The Basler Electric BE1‑851 is a versatile microprocessor‑based overcurrent protection relay designed for feeder, transformer, and motor protection in distribution and industrial power systems. This relay combines multiple protection elements, including instantaneous and time‑overcurrent, directional control, and ground fault detection, in a compact and configurable package suitable for modern switchgear and motor control centers.

Protection Elements and Functions

The BE1‑851 integrates the following protection functions:

• Three‑phase instantaneous overcurrent (50P) – for high‑speed fault clearing.

• Three‑phase time‑overcurrent (51P) – with selectable inverse‑time curves (IEC, IEEE, or custom).

• Ground overcurrent (50N/51N) – for earth fault protection.

• Negative sequence overcurrent (46) – for unbalanced load and phase loss protection.

• Directional control (67) – for coordinated fault detection on radial and looped networks.

• Thermal overload (49) – for motor and cable protection.

Each element is independently configurable with multiple setting groups for different operating modes.

Current Sensing and Accuracy

The relay accepts inputs from standard CTs with 1 A or 5 A secondary ratings, with a measurement accuracy of ±2% of setting for overcurrent and ±3% for time delay. The unit offers a wide frequency tolerance of 45‑65 Hz, suitable for various grid conditions. The ground fault input can be derived from a dedicated CT (zero‑sequence) or calculated from phase currents (residual method).

Directional Overcurrent Capability

The directional control function (67) uses phase‑voltage reference to determine fault direction, enabling selective tripping on radial feeders and loop networks. The directional element has a characteristic angle adjustable from -90° to +90°, with a minimum operating voltage of 5 V. This feature ensures coordination with upstream and downstream protection devices.

Motor Protection and Starting

For motor applications, the BE1‑851 includes stall protection, start inhibit, and lock‑out functions. It can be configured to allow a specified number of starts per hour, preventing thermal damage to the motor winding. The relay also monitors the motor starting current profile to detect abnormal conditions such as mechanical binding.

Setting and Configuration

Settings are entered via a front‑panel keypad and LCD display, or through the BESTCOMS software. Up to four setting groups are available, allowing the relay to adapt to different system configurations. All settings are password‑protected. The relay includes a built‑in test mode for commissioning and maintenance verification.

Outputs and Indications

The relay provides multiple output contacts (form‑C) for trip, alarm, and auxiliary functions. Front‑panel LEDs indicate power, pickup, and trip status for each phase and ground element. A large backlit LCD shows real‑time currents, setting group status, and event logs. The relay also includes an oscillography function that captures current and voltage waveforms before, during, and after fault events.

Communication and Integration

Standard RS‑485 port with Modbus RTU protocol is provided for SCADA integration. Optional Ethernet interfaces support Modbus TCP and DNP3. The relay includes an IRIG‑B input for time synchronization, enabling accurate fault location and event correlation across multiple devices.

Environmental and Mechanical

The BE1‑851 is housed in a robust metal case for panel or rack mounting, with dimensions optimized for standard relay panels. It operates from -40 °C to +85 °C and is rated IP40. The relay meets IEC 60255 and ANSI C37.90 standards and carries CE and UL certifications.

Typical Applications

This relay is commonly used for protection of distribution feeders, transformer secondary circuits, large motors, and capacitor banks. Its directional overcurrent capability makes it suitable for grid‑connected and co‑generation applications where fault current direction is critical.

Maintenance and Diagnostics

Continuous self‑diagnostics monitor internal circuitry, memory, and power supply. The relay logs events for post‑analysis. Periodic testing of pickup and timing accuracy is recommended, with test procedures provided in the instruction manual.

In summary, the Basler Electric BE1‑851 provides a comprehensive, flexible, and reliable overcurrent protection solution for a wide range of power system applications.