Bypass Supplies - Liebert 7200 Series User Manual

7200 Series UPS User Manual
Single Module and 1+1 Parallel System
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 the battery is fully discharged, whereupon the UPS
shuts down. The end of battery discharge is assumed when the battery voltage falls below a preset
value (i.e. 330V d.c. for a 400V 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'. Normally, the load is connected to the inverter via a contactor K1 (
Maintenance Bypass
power Switch Q3
Bypass
a.c.
Bypass power Switch Q2
Supply
Rectifier
input
a.c.
Rectifier
Supply
input
Switch Q1
controlled by the static switch circuits ); but in the event of a UPS overload, or inverter failure, it 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 the bypass supplies followed by the K1 contactor opening.
When switching from the bypass supplies back to the inverter the K1 contactor closes first followed by
the static switch turning off. 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.
An [INV: UNSYNCHRONIZED] warning message 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 is 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.
document in response to "powersure ups"
RECTIFIER INVERTER
Battery
Circuit
Breaker
BATTERY
Figure 1-B . UPS power switches configuration
STATIC
SWITCH
and K1
Output
Power
Switch Q4
Chapter 1 - General Description
Design Concept
UPS
a.c.
Output
Page 1-3
Issue 6
(03/98)