Eaton 9390 - Page 53

Eaton® 9390 (100–160 kVA) UPS Installation and Operation Manual 164201604—Rev F 38
77..11..22 NNoorrmmaall MMooddee –– RRTT
Figure 10 shows the path of electrical power through the UPS system when the UPS is operating in Normal
mode.
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Static
Switch
K5
retrevnIreifitceR
K1 K3
Battery
Converter
Battery
Battery
Breaker
Main Power Flow
Trickle Current
Energized
De-Energized
Closed
Open
Breakers Contactors
Static
Switch
K5
retrevnIreifitceR
K1 K3
Battery
Converter
Battery
Battery
Breaker
Main Power Flow
Trickle Current
Energized
De-Energized
Closed
Open
Breakers Contactors
During normal UPS operation, power for the system is derived from a utility input source through the rectifier
input contactor K1. The front panel displays “Normal,” indicating the incoming power is within voltage and
frequency acceptance windows. Three-phase AC input power is converted to DC using IGBT devices to
produce a regulated DC voltage to the inverter. The battery is charged directly from the regulated rectifier
output through a buck or boost DC converter, depending on whether the system is 208V, 380V, 400V, 415V or
480V and the size of the battery string attached to the unit.
The battery converter derives its input from the regulated DC output of the rectifier and provides either a
boosted or bucked regulated DC voltage charge current to the battery. The UPS monitors the battery charge
condition and reports the status on the control panel. The battery is always connected to the UPS and ready to
support the inverter should the utility input become unavailable.
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.
Understanding UPS Operation
For Internal Use Only