The 250 series combined voltage and frequency protectors provide continuous surveillance of the monitored circuit. When the voltage or
frequency moves outside the set point limit the respective relay will operate giving an alarm, control or tripping signal. An illuminated LED
indicates when the relay is energised. This protector can be used to protect against over and under-speed and over and under-voltage.
Operation
Combined voltage and frequency protectors provide the most popular relay functions in one convenient package. The products offer user adjustable trip point (set point) for
voltage and frequency, plus adjustable time delay settings. The set point adjustment
range is 25%, operating between 75% and 100% of the nominal supply for undervoltage
and between 100% and 125% for over voltage. The frequency set point
adjustment range is centred around the nominal 50Hz, 60Hz or 400Hz system
frequency. The time delay setting adjustment range is typically 0 to 10 seconds,
although longer delays are available.
As soon as the monitored signal moves outside of the set point limit, the time delay is
activated, after which a trip will occur. The time delay prevents the relay from tripping
for a predetermined period to prevent nuisance tripping. The products also feature an
internal differential (hysteresis) setting of 1% to reduce nuisance tripping if the
measured signal is noisy or unstable. The product is available for single-phase systems
only and draws its operating power from the measuring input.
Over-Voltage and Frequency
When the monitored value exceeds the set point and the time delay has elapsed,
the relay will energise and the red LED will illuminate to indicate the trip condition.
Under-Voltage and Frequency
The relay will de-energise after the time delay has elapsed and the red LED will
extinguish to indicate the trip condition.
Options
250 series protector relays offer various customised options to suit individual
requirements.
- Adjustment ranges – different adjustment ranges are possible for the set point and
time delay controls.
- Differential – internally fixed value between 1% and 15%.
- Relay operation – standard models are fail safe, but the relays can be customised
to energise or de-energise on trip.
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