Basler Electric BE4‑27/59 Over/Under Voltage Relay

The Basler Electric BE4‑27/59 (also known as model 307‑2552) is a solid‑state relay that combines both undervoltage (ANSI 27) and overvoltage (ANSI 59) protection in a single compact unit. It continuously monitors single‑phase or three‑phase AC voltages and trips when the voltage falls below the undervoltage pickup or exceeds the overvoltage pickup for the respective time delays. This relay is ideal for protecting generators, transformers, and distribution feeders from voltage anomalies that can cause equipment damage or system instability.

Operating Principle

The relay has independent undervoltage and overvoltage elements. Each element has its own adjustable pickup setting and time delay. The undervoltage pickup is typically set from 1 to 120 VAC, and the overvoltage pickup from 1 to 300 VAC. Time delays are adjustable from 0.1 to 10 seconds. A built‑in filter reduces harmonics and transients to prevent nuisance tripping. The relay includes a target indicator for trip identification.

Key Features

Front‑panel potentiometers allow independent adjustment of undervoltage pickup, overvoltage pickup, and each time delay. LED indicators show voltage status and trip conditions. A test pushbutton enables functional verification. Output contacts: 2 Form C (SPDT) – one for undervoltage trip, one for overvoltage trip – each rated 5 A at 250 VAC. The relay is housed in a rugged metal enclosure suitable for panel mounting.

Technical Specifications

Input voltage: 1‑300 VAC, 50/60 Hz. Pickup accuracy: ±2% of setting. Time delay accuracy: ±3% or 50 ms. Output contacts: 2 SPDT, 5 A at 250 VAC. Power supply: 24‑250 VDC or 120‑240 VAC. Burden:<5 VA. Operating temperature: –20°C to +65°C. Meets ANSI/IEEE C37.90 surge withstand.

Applications

The BE4‑27/59 is used on generator sets, automatic transfer switches, and motor control centers. It provides comprehensive voltage protection by tripping for both undervoltage (brownouts, load shedding) and overvoltage (regulator failure, load rejection). It can be coordinated with other relays for selective protection.

Installation and Commissioning

Mount the relay in a standard panel cutout. Connect voltage sensing leads and control power. Commissioning involves setting each pickup and time delay, then testing with a variable AC source to verify trip accuracy. The relay includes built‑in test jacks for signal injection.

Reliability and Quality

Basler Electric’s BE4‑27/59 is built with solid‑state technology and conformal coating for environmental resilience. It is factory calibrated and requires minimal maintenance. The relay has a long service life and proven performance in critical applications.

Conclusion

The Basler Electric BE4‑27/59 over/under voltage relay (307‑2552) is a precise, reliable, and space‑saving solution for combined undervoltage and overvoltage protection. Its adjustable settings and robust construction make it an essential component in modern power system protection schemes.