UNDERSTANDING UPS OPERATION
7.1.2Bypass 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.
CB4
|
| (closed) |
|
| Bypass |
|
| Static Switch |
Bypass | FBP |
|
|
| |
Input | (closed) |
|
|
| |
| Rectifier | Inverter |
CB1 |
| DC |
| Link | |
Rectifier |
| |
|
| |
Input |
|
|
(open) | Input |
|
|
| |
| Transformer |
|
CB3
(open)
Output
Transformer
Output
CB2
(open)
Path of Electrical Power
Battery
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.
EATON Powerware® 9315 UPS |
