Figure 40. Path Of Current Through The Ups In Normal Mode - Eaton 93PM Installation And Operation Manual

Understanding UPS Operation
5 5 . . 2 2 . . 3 3 N N o o r r m m a a l l M M o o d d e e
During Normal mode, power for the system is derived from a utility input source through the rectifier
switchgear. Three-phase AC input power is converted to DC using IGBT devices to produce a regulated DC
voltage to the inverter. When the battery switchgear is closed the battery is charged directly from the regulated
rectifier output through a buck or boost DC converter, depending on the system voltage and the size of the
battery string attached to the unit.
Figure 40 shows the path of electrical power through the UPS system when the UPS is operating in Normal
mode.
The battery converter derives its input from the regulated DC output of the rectifier and provides a bucked
regulated DC voltage charge current to the battery. The battery is always connected to the UPS and ready to
support the inverter should the utility input become unavailable.
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 inverter switchgear.
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 and is configured for capacity, it switches automatically to Bypass mode
and remains in that mode until the failure is corrected and the UPS is back in service.

Figure 40. Path of Current Through the UPS in Normal Mode

Bypass Input
Rectifier Input
90 Eaton 93PM UPS (400V/480V Four-Wire – 100 kW Frame) Installation and Operation Manual 164000566—Rev 04
Bypass Switchgear
Rectifier
Rectifier
Switchgear
Switchgear
Closed
Open
Static
Switch
Inverter
Battery Converter
Battery
Switchgear
Battery
Output
Inverter
Switchgear
Main Power Flow
Trickle Current
Energized
De-Energized