OPERATION
Step User Action System Response
3 Open all DC breakers at the DC energy source
if configured to do so
Table 8.6: MV UPS Emergency Power Off steps
8.7. Hard fault
Hard faults are extremely rare situations where multiple failures occur at the same time, and the system
is not capable of holding the voltage any longer.
In the case of hard-parallel configuration, the remaining units will support the load (N+1 configuration,
for instance). If the load power exceeds the remaining units overload capability, the system will be
commuted to bypass mode.
8.7.1. During Power Conditioning mode
Step User Action System Response
1 System encounters a hard fault, which
prevents it from normal operation
2
MV UPS output voltage synchronizes with
utility voltage magnitude, frequency and
phase, while simultaneously commands S
abp
to close
1
3 When S
abp
is closed, S
in
and S
out
are
commanded to open
4 After S
in
and S
out
are opened, MV UPS stops
the PEBBs and reverts to bypass mode
Table 8.7: System reaction to fault while in PCM
1. Closing the bypass applies for single unit configuration where no unit redundancy is achieved
8.7.2. During Independent mode
Step User Action System Response
1
System encounters a hard fault, which
prevents it from normal operation
2
Commands to close S
abp
. If MV UPS is locked
with input voltage then simultaneously
synchronizes load voltage with mains voltage
frequency, phase and magnitude. Otherwise,
MV UPS waits in the previous state until S
abp
closes
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