OPTI-UPS MD120L - Manual (Page 81)

24 Chapter 2 Operations
24
Fig 2-1 System principle framework
2.1.2 Bypass Module
The circuit blocks labeled “bypass module” in fig 2-1 contain electronically controlled switching
circuits that enable the critical load to be connected to either the inverter output or to a bypass power
source via the static bypass line. During normal system operation the load is connected to the inverter;
but in the event of a UPS overload or inverter failure, the load is automatically transferred to the static
bypass line.
To provide a clean (no-break) load transfer between the inverter output and static bypass line, the
inverter output and bypass supply must be fully synchronized during normal operating conditions. This is
achieved through the inverter control electronics, which makes the inverter frequency track that of the
static bypass supply, provided that the bypass remains within an acceptable frequency window.
A manually controlled maintenance bypass supply is incorporated into the UPS design. It enables
the critical load to be powered from the utility (bypass) supply while the UPS is shut down for routine
maintenance.
警告 危 险
Note
When the UPS is operating in bypass mode or on maintenance bypass, the connected equipment is
not protected from power failures or surges and sags.
2.2 Operation Mode
The MD UPS is an on-line, double-conversion, reverse-transfer UPS that permits operation in these
modes:
 Normal mode