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Understanding UPS Operation
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.
7-5
EATON Powerware
9390 UPS (100–160 kVA) Installation and Operation Manual S 164201554 Rev E powerware.com
®
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