Powerware 9315 - Manual (Page 54)

UNDERSTANDING UPS OPERATION
EATON Powerware ® 9315 UPS (500–750 kVA) Installation and Operation Manual S 164201244 Rev E www.powerware.com 7-4
7.1.2 Bypass Mode
The UPS automatically switches to Bypass mode if it detects an overload, load fault,
or internal failure. The bypass source supplies the commercial AC power to the load
directly.
Figure 7‐3 shows the path of electrical power through the UPS system when the UPS
is operating in Bypass mode.
C A U T I O N
The critical load is not protected while the UPS is in Bypass mode.
FBP
Input
Transformer
Path of Electrical Power Battery
Inverter Rectifier
DC
Link
CB2
(open)
Output
Transformer
(open)
CB3
(open)
CB1
Rectifier
Input
Bypass
Input
(closed)
Output
Static Switch
(closed)
CB4
Bypass
Figure 7‐3. Path of Current Through the UPS in Bypass Mode
The UPS can be transfered from Normal mode to Bypass mode manually. However,
the UPS switches automatically to Bypass mode whenever the inverter can no longer
supply the critical load. Initially, the static switch fires and conducts power from
breaker FBP to the load. When breaker CB4 closes, the static switch stops
conducting and breaker FBP opens. If the UPS transfers to Bypass mode from Normal
mode due to any reason other than operator intervention, the UPS automatically
attempts to transfer back to Normal mode (up to three times within a ten minute
period). The fourth transfer locks the critical load to the bypass source and requires
operator intervention to transfer.
Bypass mode is a normal operating mode, not an alarm condition. However, if the
UPS is unable to return to Normal mode following an automatic transfer to Bypass
mode, an alarm condition is recorded.