ABB HiPerGuard MV UPS User Manual page 23

P RO DU C T D ES C R IP T I ON
The input breaker management graph is split into two regions. The first part, a slow filter curve down to
50% input voltage, is designed for thermal management of the MV UPS and protection coordination.
It allows the MV UPS to keep the input circuit breaker closed for typically 1 second at 50%.
The second part, a fast filter for input values below 50% and down towards 0% remaining voltage,
responds quickly so as to prevent unnecessary tripping due to sub-cyclic events and transients.
Figure 3.4: Three phase under/over voltage input breaker management graph
3.2.4. Transition from Independent to Power Conditioning mode
As soon as the input voltage returns to the nominal level, the MV UPS starts the transition from the
Independent to the Power Conditioning mode. A "trust period" of 2 seconds before the transition
assures that the input voltage is stable, avoiding unnecessary breakers operations.
During this process, the MV UPS will synchronize the output voltage to the input voltage. While the MV
UPS is in "synchronizing state", if a power quality event reoccurs, the MV UPS will return to the
Independent mode.
When the MV UPS output voltage is phase-locked with the input voltage, the MV UPS commands the
input circuit breaker to close. After closing the input circuit breaker, the MV UPS transfers the load to the
utility while it controls the voltage phase across the reactor to make sure the voltage is being
conditioned to the nominal level at the load side.
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