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.

4.2.2 Bypass mode

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 4-3 shows the path of electrical power through the UPS system when operating in Bypass mode.

CAUTION

The critical load is not protected while the UPS is in Bypass mode.Figure 4-3. Path of current through the UPS in bypass mode

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UPS 450 - 550 kVA (2x225 - 2x275 kVA)

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Revision B

User’s and Installation Guide