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Understanding U PS Operation
3-3
EATON Powerware
®
9315 UPS (200–300 kVA) Operatio n Manual S 164201036 Rev F powerware.com
3.2 Bypass Mode
The UPS automatically switches to Bypass mode if it detects an overload, load fault, or
internalfailure.ThebypasssourcesuppliesthecommercialACpowertotheloaddirectly.
CAUTION
The critical load is not protected while the UPS is in Bypass mode.
Figure 3-2 shows the path of electrical power through the UPS system when the UPS is
operating in Bypass mode.
Bypass
Input
Rectifier
Input
Output
Path of electrical power
Battery
Rectifier Inverter
Bypass
K4
Transformer
K3
(Open)
CB1
Figure 3-2. Path of Current Through the UPS in Bypass Mode
You can transfer the UPS 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. 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 10-minute period). The fourth transfer will lock
the critical load on the bypass source and requires operator intervention to transfer.
Bypass mode is a n ormal operating mode, and 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.