ABB HiPerGuard MV UPS User Manual page 22

3.2.2. Independent mode
If the utility power is no longer available or in a prolonged sag event, the HiPerGuard MV UPS opens the
input circuit breaker and transfers the load to the energy storage, operating now in Independent mode.
The energy storage allows ride-through time for either the utility power to be restored or for the time
necessary for an alternative energy source to be activated, such as a generator, for example.
Figure 3.3: HiPerGuard MV UPS Independent mode
3.2.3. Transition from Power Conditioning to Independent mode
The HiPerGuard MV UPS System Controller (SC) manages the input circuit breaker, based on the input
voltage and current measurements shown in Figure 3.4.
– If the voltage at the input side is between 110% and 90% of the nominal value, it is conditioned to 1
p.u. at the load side (Power Conditioning Mode).
– If the voltage is between 90 and 85% of the nominal value, the HiPerGuard MV UPS will monitor and
will be ready to transition to the Independent mode. The expected threshold for the transfer depends
on the sag depth and remaining voltage.
– If the voltage is between 85% and 50%, the MV UPS will open the input circuit breaker. The time delay
to command the breaker to open will be between approximately 1 and 10 seconds, depending on the
input voltage level.
– If the voltage is below 50%, the MV UPS will command the input circuit breaker to open in
milliseconds.
– In case of an outage or prolonged sag event, the MV UPS opens the input circuit breaker and goes
into the Independent mode.
The Input breaker opening time is design to minimize input breaker operation while maximizing voltage
conditioning and securing the load.
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