TOSHIBA
22
Operating the UPS
Operation Modes
AC Input Mode (normal operation)
The following illustration shows circuit power flow when the UPS is operating normally in the ac
input mode. The UPS unit's rectifier, including a boost chopper circuit, converts ac input power to
dc power. The boost chopper circuit maintains a constant voltage, with current limiting, for
charging the batteries. It also supplies a dc voltage of the proper level to the inverter section. The
inverter section generates a high quality sinewave output voltage. The unit's batteries are always
maintained in a constantly charged state when the UPS is in the normal operation mode.
Power flow in AC input mode for the 2.4, 3.6, 6, and 8 kVA Models
Input
power
MCCB
Batteries
Inverter
Rectifier/
charger/
chopper
Line
filter
Surge
absorber
*Static
switch
Isolation
Transformer
(optional)
Output
power
Bypass
Power flow
* Switches are
solid state devices
Circuit-bypass Mode
If the UPS unit is severely overloaded or develops an internal fault, power flow is automatically
switched from the unit's main circuit to the bypass circuit. Power flow through the bypass
is shown in the following illustration. This change-over occurs automatically in less than
4 milliseconds in phase. The switching period is not long enough to cause interruptions to
occur in most loads. If the power flow is transferred to the bypass circuit because of an
overload and that overload condition ends within a specified period of time then the power
flow will be "re-transferred" to the AC input mode (normal operation) automatically.
If the power flow is transferred to the bypass circuit due to an external fault the UPS will
shut down power through the bypass to the load and indicate a system fault message.
If the power flow is transferred to the bypass circuit due to an internal fault the UPS will
continue to supply power to the load through the bypass and indicate a system
fault message
(see system fault message DC-OC on page 41).
If the power flow is
transferred to the bypass circuit due to an overload condition
(see system warning
message OL: REDUCE LOAD on page 36 and AUTO RETRANSFER on page 38)
, then the
power flow will automatically transfer from the UPS's bypass circuit back to the inverter
circuit after removing the overload if set to do so
(see auto-transfer setting on page 32).
Power flow
Power flow in circuit-bypass mode for 2.4, 3.6, 6, and 8 kVA Models
Rectifier/
charger/
chopper
Line
filter
Surge
absorber
MCCB
Input
power
Inverter
*Static
switch
Output
power
Batteries
* Switches are
solid state devices
Bypass
Line
filter
Line
filter
Isolation
Transformer
(optional)
Input
fuses
Output
fuses
Output
fuses
Input
fuses
_
+
_
+
