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Hipulse - Single Phase ‘1+N’ UPS System 130 kVA - 110V
2
During normal operation both the rectifier and inverter sections are active and provide
regulated load power whilst simultaneously float charging the battery. In the event of
a mains power failure, the rectifier becomes inoperative and the inverter is powered
solely from the battery. Critical load power is maintained under these conditions until
battery is fully discharged, where upon the UPS shuts down. The end of battery
discharge is assumed when the battery voltage falls below a preset value (i.e. 330 /
340V d.c. for a 400 V a.c. system).
The period for which the load can be maintained following a mains power failure is
known as the ‘System’s Autonomy Time’ and is dependent upon both the battery A/Hr
capacity and the applied percentage load.
1.2.2 Bypass Supplies
The circuit block annotated ‘Static Switch’ in figure 1-2 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’. During
normal system operation the load is connected to the inverter and the ‘inverter -side’
of the Static Switch is closed; but in the event of a UPS overload, or inverter failure, it
is automatically transferred to the static bypass supply 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 the bypass supplies. 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. The synchronizing
window is pre-selected to 2% of nominal frequency, giving an acceptable frequency
window ±1 Hz.
A manually controlled, ‘Maintenance Bypass’ supply is also incorporated into the UPS
design. Its purpose is to enable the critical load to be powered from the mains
(bypass) supply while the UPS is shut down for routine maintenance.
Note: The load equipment is not protected from normal supply aberrations when operating on Bypass
side or in the maintenance bypass mode
Fig 1-2 : UPS Power switches configuration
RECTIFIER
STATIC
SWITCH
INVERTER
Bypass
Supply
Mains
Supply
UPS
Output
Supply
Battery
Isolator
Output
Isolator
Input
Isolator
Maintenance Bypass
Isolator
Maintenance Bypass Line
Static Bypass Line
Bypass Isolator
STATIC
SWITCH
BATTERY