Basler Electric BE1-81 Underfrequency Protective Relay

Basler Electric BE1-81 Digital Underfrequency Relay is a single‑phase, solid‑state protective relay that monitors the frequency of the applied AC voltage and actuates external control circuits or alarms when the frequency falls below a user‑set threshold for a programmable time. It supports 40–70 Hz sensing with 50 Hz and 60 Hz style versions and offers either definite‑time or inverse‑time delay characteristics; the trip frequency is set with three front‑panel thumbwheels in the range of 0.05–5.00 Hz below the nominal system frequency. For the definite‑time option, delay is adjustable from 01 to 99 cycles, with the actual trip time equal to the delay plus one cycle. The relay is mounted in a drawout cradle inside a standard semi‑flush housing, with PC boards accessible for maintenance and testing via an extender card (Basler part number 9 1655 00 100); a front‑panel target can be electrically reset to indicate a fault event.