Bypass Supplies; Ups Power Switch Configuration - Liebert 7400 Series User Manual

7400 Series UPS User Manual
Single Module and One plus One Systems
1.2.2

Bypass supplies

1.2.3 UPS Power Switch
Configuration
6310018a.02.doc
immediately begin to recharge. Modern generators can be started and
brought on-line very quickly and where such a facility is incorporated
into the UPS installation it results in short battery discharge periods and
correspondingly rapid recharge times.
The circuit block annotated 'Static Switch' in figure 1-3 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 the static switch
action.
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.
An [
INVERTER UNSYNCHRONIZED
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
Note:- The load is unprotected against mains power supply aberrations or
failure when it is connected to either the static bypass or maintenance
The power switch locations in the various 7400 models are shown in
Figure 1-4.Figure 1-3 illustrates the 7400 series UPS module power
switches in what is known as a "Split Bypass" configuration. This is the
standard configuration for all models in the 7400 range.
In the "Split Bypass" configuration the static bypass line is switched by a
separate isolator to a dedicated 'bypass' power source which also feeds
the maintenance bypass line.
With the exception of the maintenance bypass isolator, all the isolators
shown must be closed during normal UPS operation.
Although it cannot be classified as a 'power switch', the reset switch may
be used as part of the UPS operating procedure. Fitted to the UPS Logic
Board, the reset switch is used by the operator to re-transfer the load to
the inverter following a detected overload or over temperature fault.
Chapter 1 - General Description
] warning message is displayed on the
or troubleshooting.
bypass supply.
Design Concept
1-5
Issue 2
(02/98)