Eaton 9395 UPS User Manual

UNDERSTANDING UPS OPERATION
Eaton 9395 UPS (450–825 kVA) Installation and Operation Manual S 164201725 Rev 4 www.eaton.com/powerquality
6-5
When a UPM is placed into VMMS mode, the UPM will stop gating the inverter and
rectifier and keep the output contactor closed in order to maintain voltage match and
phase lock to the critical bus. In this mode the UPS actively monitors the critical bus,
keeping the UPM input contactors closed in order to keep the DC link primed (through
the rectifier diodes) and also to allow the UPM to immediately return to active mode
in the event of a disturbance or load step on the critical bus.
VMMS limits the maximum power available from a UPM when in VMMS mode. The
default setting is 80% of the UPM full power rating. If the limit is exceeded, additional
UPMs take on the increased load. The VMMS redundancy setting sets the number of
redundant UPMs that the customer requires. Both the VMMS UPM load limit and
UPM redundancy are customer configurable.
In High Alert mode, the UPS defaults to double conversion mode and all UPMs go
active for one hour (customer configurable). At the completion of the hour, the UPS
defaults back to VMMS mode. If the High Alert command is received during the one
hour, the one hour timer will be restarted.
6.2.5 Bypass Mode
NOTE Bypass mode is not available on a UPS configured as an IOM.
The UPS automatically switches to Bypass mode if it detects an overload, load fault,
or internal failure. The UPS can also be transferred from Online mode to Bypass mode
manually. The bypass source supplies the commercial AC power to the load directly.
Figure 6‐3 shows the path of electrical power through the UPS system when
operating in Bypass mode.
In Bypass mode, the output of the system is provided with three-phase AC power
directly from the system input. While in this mode, the output of the system is not
protected from voltage or frequency fluctuations or power outages from the source.
Some power line filtering and spike protection is provided to the load but no active
power conditioning or battery support is available to the output of the system in the
Bypass mode of operation.
The internal bypass is comprised of either of a solid-state, silicon-controlled rectifier
(SCR) momentary static switch and motorized wraparound bypass breaker CB4 or a
SCR continuous static switch, and a backfeed protection contactor K5. The static
switch is used instantaneously anytime the inverter is unable to support the applied
load. CB4 is also wired in parallel with the momentary static switch. Both the
momentary and continuous static switches are wired in series with the backfeed
protection contactor, and together they are wired in parallel with the rectifier and
inverter.
C A U T I O N
The critical load is not protected from voltage or frequency fluctuations or power outages while the UPS is in
Bypass mode.
The static switch, being an electronically-controlled device, can be turned on
immediately to pick up the load from the inverter while inverter output contactor K3
opens to isolate the inverter. Bypass breaker CB4 also closes and the static switch
stops conducting with a momentary static switch. The backfeed protection contactor
is normally closed, ready to support the static switch unless the bypass input source
becomes unavailable.

Eaton 9395 UPS Specifications

General

Brand	Eaton
Model	9395 UPS
Category	UPS
Language	English