The ac voltage protectors provide continuous surveillance of the
monitored circuit. When the measured voltage moves outside the
set point limit, the relay will operate after the selected time delay, giving
an alarm or initiation signal. Relays normally energise on overvolts and
de-energise on undervolts. An illuminated LED indicates when the relay
is energised.
Operation
AC voltage protectors offer user adjustable trip point (set point) and time delay settings.
The set point adjustment range is 25%, operating between 75% and 100% of the
nominal supply for under-voltage units and between 100% and 125% for the overvoltage
units. 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 units draw their
operating power from the measuring inputs, although a separate auxiliary supply input
option is available on some models. Single-phase and three-phase products are
available. Three-phase products monitor the voltage level for each phase and are not
phase sequence sensitive.
Over-Current Models
When the monitored voltage exceeds the set point, the time delay is started. When the
time has elapsed, the relay will energise and the red LED will illuminate to indicate the
trip condition. The relay will automatically reset once the monitored voltage falls below
the set point minus the differential. When reset, the LED will extinguish and the relay
de-energises. The time delay is not active when resetting.
Under-Voltage Models
When the monitored voltage falls below the set point, the time delay is started. When
the time has elapsed, the relay will de-energise and the red LED will extinguish to
indicate the trip condition. The relay will automatically reset once the monitored voltage
rises above the set point plus the differential. When reset, the LED will illuminate and
the relay energises. The time delay is not active when resetting.
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 differential controls.
- Separate auxiliary supply – sometimes required to maintain a time delay.
- 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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