The reverse power protector provides continuous surveillance for ac generators operating in parallel or for boosting mains supplies. On site adjustment of the trip point and time delay ensures accurate protection against ‘motoring’ in the event of engine failure and prevents tripping from surges during synchronizing.
Reverse power protectors provide continuous surveillance of ac generators against motoring. Reverse power relays are used to detect the failure of the prime mover (engine) when active energy (Watts) flows into the generator causing rotation – the set will operate like an electric motor which can cause significant mechanical damage. This relay offers an adjustable reverse power set point between 2% and 20% of nominal power and time delay adjustment range of 0 to 20 seconds.
As soon as the reverse power level increases above 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. These units are powered from the measuring supply.
The protector relay estimates the power level in the system by measuring current and power factor, but does not actually measure the system voltage. When the reverse power level exceeds the set point, the time delay is started. When the time has elapsed, the relay will energize and the red LED will illuminate to indicate the trip condition. The relay will automatically re-set once the power level falls below the set point minus the differential. The LED will extinguish and the relay de-energizes.
The time delay is not active when resetting. The reverse power level will trip as expected at the calibrated point for unity power factor. However, the system power factor does affect the trip point calibration. The relay becomes more sensitive at lagging power factors, as almost all systems exhibit inductance. At leading power factors, this relay is less sensitive.
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