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Series 7400 Single Phase 1+N UPS
The circuit block annotated ‘Static Switch’ in figure 2 contains an
electronically controlled switching circuit, which enables the critical
load to be connected either to the Inverter output or to a Bypass
power source via the ‘static bypass line’. Normally, the load is
connected to the inverter; but in the event of a UPS overload, or
inverter failure, it is automatically transferred to the static bypass
line due to static switch action. Note that the Bypass supply should
be in normal condition and enabled.
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 synchronised 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. The synchronising window is pre-selected to 2% of
nominal frequency, giving an acceptable frequency window of
±1Hz.
A warning message [INVERTER UNSYNCHRONIZED] is displayed
on the operator control panel when the inverter and bypass
supplies are not synchronized.
A second, manually controlled, ‘Maintenance bypass’ supply is also
incorporated into the UPS design. Its purpose it to enable the
critical load to be powered from the mains (bypass) supply while
the UPS is shut down for maintenance or troubleshooting.
Note:- The load is unprotected against mains power supply aberrations or
failure when it is connected to either the static bypass or maintenance bypass
supply.
Figure 2: Series 7400 UPS Isolator configurations
1.2.3 Bypass Supplies
RECTIFIER
STATIC
SWITCH
INVERTER
BATTERY
Bypass
Supply
Mains
Supply
UPS
Output
Supply
Battery
Breaker
Output
Isolator
Input
Isolator
Maintenance Bypass
Isolator
Maintenance Bypass Line
Static Bypass Line
Bypass Isolator
A. BLOCK SCHEMATIC FOR 230V OUTPUT 1PH. UPS SYSTEM
RECTIFIER
STATIC
SWITCH
INVERTER
BATTERY
Bypass
Supply
Mains
Supply
UPS
Output
Supply
Battery
Breaker
Battery
Breaker
Output
Isolator
Input
Isolator
Maintenance Bypass Line
Static Bypass Line
Maintenance Bypass
Isolator
Bypass
Isolator
B. BLOCK SCHEMATIC FOR 110V OUTPUT 1PH. UPS SYSTEM