Powerware 5075 kVA - Manual (Page 47)

39 Powerware BPIII Harsh Environment UPS 50--75 kVA Installation and Operatio n
164201261 Rev. F 111503
Understanding UPS Operation
Your UPS functions automatically to supply AC electrical power to your
critical load. The UPS always operates in one of four modes:
• In Normal mode, the critical load is supplied by the inverter, which derives its
power from rectified utility AC power. In this mode, the rectifier also provides
charging current for the battery.
• In Battery mode, the battery cabinet provides DC power, which maintains
inverter operation. The battery supports the critical load.
• In Bypass mode, the critical load is directly supported by the utility through an
isolation transformer.
• In Maintenance Bypass mode, the critical load is directly supported by the utility
through a Maintenance Bypass circuit breaker..
The UPS continually monitors itself and the incoming utility power, and
automatically switches between Normal, Battery, and Bypass modes as required,
with no operator intervention. The Maintenance Bypass mode is a manual
operation needing operator intervention. The sophisticated detection and
switching logic inside the UPS ensures that operating mode changes are automatic
and transparent to the critical load. The UPS switches automatic operating modes
in response to these system events:
• A command is an intervention that is externally initiated by an operator or by
some site action. A command causes the UPS to switch operating modes; it
usually does not require any further action by you.
• A notice is a minor system event that may or may not require your attention.
• An alarm is a system event that requires immediate operator intervention.
System events, alarm horns, and indicator lights are described in Chapter 12 ---
Responding to System Events.