Understanding UPS Operation
7.2.3 Bypass Mode – RT
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 operating in Bypass mode.
C A U T I O N
The critical load is not protected while the UPS is in Bypass mode.
Rectifier
K1
Battery
Converter
Breakers Contactors | |
Closed | Battery |
| Breaker |
Open
Battery
Inverter
K3
Main Power Flow
Trickle Current
Energized
De-Energized
Figure 7-3. Path of Current Through the UPS in Bypass Mode – RT
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 a solid-state, silicon-controlled rectifier (SCR) static switch (SSW) and a backfeed protection contactor K5. The static switch is rated as a continuous-duty device that is used anytime the inverter is unable to support the applied load. The static switch is wired in series with the backfeed protection contactor, and together they are wired in parallel with the rectifier and inverter. The static switch, being an electronically-controlled device, can be turned on immediately to pick up the load from the inverter while the inverter output contactor K3 opens to isolates the inverter. The backfeed protection contactor is normally always closed, ready to support the static switch unless the bypass input source becomes unavailable.
7-6 | EATON Powerware® 9390 UPS (100–160 kVA) Installation and Operation Manual S 164201604 Rev B powerware.com |
