OPERATION
8.5. Resynchronize mode
While the MV UPS(s) is (are) disconnected from the input and supplying the load, it monitors the input
voltage for the return of the grid supply or a backup generator.
When the voltage reappears at the input, the MV UPS system waits for 1-2 seconds to make sure that the
supply is stable and reliable enough for reconnection. Then the resynchronization to the input voltage
starts automatically, as shown in the below steps.
Step User Action System Response
1 No user action required; the system will
operate fully autonomously during this event
2 Utility voltage has recovered within nominal
range
3 The MV UPS block resynchronizes the load
voltage to the mains voltage magnitude,
frequency and phase
4
When the Output voltage, frequency and
phase angle aligns with Utility voltage then
MV UPS closes S
in
of all blocks simultaneously
5 The MV UPS system is now in Power
Conditioning Mode
Table 8.5: MV UPS resynchronize mode and transfer to PCM
8.6. System EPO (Emergency Power OFF)
Emergency Power Off (EPO) is a self-powered 24Vdc digital input on the MV UPS that inhibits the MV
UPS operation in case of emergency power shut down. This input is linked out by default from the
factory using a terminal jumper. If the EPO input is deployed, then the jumper shall be removed, and this
input shall be connected to a normally closed volt-free dry contact from the site EPO switch. Every MV
UPS block has its individual EPO input. For a hard-parallel configuration, EPO input on every individual
MV UPS block shall be connected to separate volt-free dry contacts from the site EPO switch.
The system will follow the below steps to shut down and eventually will fall into bypass and isolated
state.
Step User Action System Response
1 Press “EPO”
2
If the MV UPS unit is running, it will command
the S
abp
breaker to close and S
in
and S
out
circuit
breakers to open. If the unit is in bypass
mode, the MV UPS confirms that S
abp
is closed
and S
in
and S
out
are opened
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