Powerware 9390 UPS 100160 kVA - Manual (Page 56)

UNDERSTANDING UPS OPERATION
EATON Powerware ® 9390 UPS (20–80 kVA) Installation and Operation Manual S 164201603 Rev 2 www.powerware.com 7-4
The neutral from the system input is connected to the neutral regulator in the DC
capacitors. The output neutral of the system is connected with the required neutral
supplied at the utility bypass input and should never be bonded to ground at the
module's output.
The inverter produces a three-phase AC output to a customer's load without the use
of a transformer. The inverter derives regulated DC from the rectifier and uses IGBT
devices and pulse-width modulation (PWM) to produce a regulated and filtered AC
output. The AC output of the inverter is delivered to the system output through the
output contactor K3.
If the utility AC power is interrupted or is out of specification, the UPS automatically
switches to Battery mode to support the critical load without interruption. When utility
power returns, the UPS returns to Normal mode.
If the UPS becomes overloaded or unavailable, the UPS switches to Bypass mode.
The UPS automatically returns to Normal mode when the overload condition is
cleared and system operation is restored within specified limits.
If the UPS suffers an internal failure, it switches automatically to Bypass mode and
remains in that mode until the failure is corrected and the UPS is back in service.
7.1.3 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.
Static
Switch
K5
Rectifier Inverter
K1 K3
Battery
Converter
Battery
Battery
Breaker
Main Power Flow
Trickle Current
Energized
De-Energized
Closed
Open
Breakers Contactors
Figure 7‐3. Path of Current Through the UPS in Bypass Mode – RT