General Description
2
1.1.1 Bypass Supplies
The circuit block labeled “Static Switch” and “Contactor” in Figure 1 contains an electronically con-
trolled switching circuit that enables 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 con-
nected to the inverter and the inverter contactor is closed; 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
static switch activates, connecting the load to bypass. To achieve this, the inverter output and bypass
supply must be fully synchronized during normal operating conditions. This is achieved through the
inverter control electronics, which make 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.
1.1.2 Operating Modes
The UPS is designed to operate as an on-line, double-conversion, reverse-transfer system in the fol-
lowing modes:
Normal Mode
Operating in normal mode, the NX rectifier derives power from a utility AC source and supplies regu-
lated DC power to the inverter, which regenerates precise AC power to supply the connected equip-
ment. The rectifier also uses the utility source power to charge the batteries.
Battery Mode
When utility AC power fails, the NX protects the critical load by instantaneously channeling battery
power to the inverter which continues supporting the critical load without interruption. When utility
power returns and is within acceptable limits, the NX automatically shifts back to Normal mode, with
the rectifier powering the critical load.
Bypass Mode
When the NX is in bypass mode, the load is directly supported by utility power and is without battery
backup protection.
The NX’s static transfer switch will shift the load from the inverter to bypass mode without an inter-
ruption in AC power if the inverter is synchronous with the bypass and any of the following occurs:
• inverter fails
• inverter overload capacity is exceeded
• inverter is manually turned off by user
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.
NOTE
If the inverter is asynchronous with the bypass, the static switch will transfer the load from the
inverter to the bypass WITH interruption in AC power to the critical load. This interruption
will be less than 15ms (in 50Hz), or less than 13.33ms (in 60Hz). This interruption time may be
altered by modifying the Output transfer interrupt time setting.
To Next Page
Loading...
Need help?
General
