Basler BE1-59N Ground Fault Overvoltage Relay

The Basler BE1-59N is a solid‑state overvoltage relay specifically designed to detect ground faults in high‑impedance grounded systems. It measures the voltage across a neutral grounding resistor or transformer, which rises during a ground fault, and trips when this voltage exceeds a preset threshold. This relay is essential for protection of generators, transformers, and motors against single‑phase‑to‑ground faults.

Operating Principle

The relay senses the neutral voltage (Vn) through a voltage transformer connected to the neutral point. Under normal conditions, Vn is near zero. When a ground fault occurs on one phase, the neutral voltage increases proportionally to the fault severity. The BE1-59N compares Vn to the pickup setting and operates with a time delay to coordinate with other protection devices.

Key Features

• Adjustable pickup voltage: 5–150 VAC (secondary).

• Adjustable time delay: 0.1–60 seconds.

• True RMS sensing for accurate measurement.

• High immunity to transients and harmonics.

• LED indicators for power, alarm, and trip.

• Output relay (SPDT) rated 5 A at 250 VAC.

• Drawout case for panel mounting.

Technical Specifications

The relay operates from an auxiliary supply of 24–250 VDC or 120/240 VAC. The voltage input range is 5–150 VAC at 50/60 Hz. The pickup accuracy is ±2 % of setting. The time delay accuracy is ±5 % or ±50 ms. The burden on the VT is less than 1 VA. The relay also includes a built‑in test point for calibration.

Setting and Calibration

The pickup voltage is set using a front‑panel potentiometer, calibrated in volts AC. The time delay is set with another potentiometer. The relay also features a hysteresis adjustment to prevent nuisance tripping. Calibration is performed by injecting a known AC voltage into the input and adjusting the pickup until the relay trips.

Installation and Wiring

Mount the relay in a standard panel. Connect the VT secondary leads to the input terminals. The auxiliary supply is connected to the power terminals. The output contact is wired to the trip circuit. Ensure proper grounding of the VT neutral.

Applications

Used for stator ground fault protection of generators connected through a high‑resistance grounding. Also applied in transformer neutral grounding and motor ground fault detection. The relay is suitable for both solidly grounded and impedance‑grounded systems.

Testing and Commissioning

Apply a variable AC voltage to the input and gradually increase it until the relay trips. Verify the trip time with a timer. Test the alarm output at a lower preset level.

Maintenance

Periodic inspection of connections and re‑testing of pickup settings is recommended. The solid‑state design ensures long‑term stability.

Advantages

Provides high sensitivity and fast response compared to electromechanical types. The true RMS measurement eliminates errors from harmonics.

Compliance

Meets IEC 60255 and IEEE C37.90 standards.

Conclusion

The Basler BE1-59N is a reliable and precise ground fault overvoltage relay, essential for protecting critical equipment against single‑phase faults.