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Series 7400 Single Phase 1+N UPS
1.1 Introduction
The Uninterruptible Power Supply system is connected between a
critical load, such as digital drives & automation, distributed digital
Process Control System, telecom equipment, programmable logic
controller, mission critical applications, computer, and its three
phase mains power supply. Being designed to furnish a well
regulated 1 PH output power supply under all rated load and input
supply conditions the system offers the users the following
advantages: -
Increased power quality :
The UPS has its own internal voltage and frequency regulator
circuits which ensure that its output is maintained within close
tolerances independent of voltage and frequency variations on the
mains power lines.
Increased noise rejection :
By rectifying the input AC power to DC power, and then converting
it back to AC, any electrical noise present on the input mains
supply line is effectively isolated from the UPS output, therefore the
critical load sees only clean power.
Power blackout protection:
If the mains power fails, the UPS continues to power the critical
load from its battery source, leaving the load immune from power
disturbances.
1.2 Design Concepts
The one-plus-one system comprises two standard 7400 series UPS
modules which are modified to allow their outputs to be connected
in parallel. These can then be used in a “redundant” or “non-
redundant” configuration as explained below.
In a non-redundant module configuration, the system is sized such
that both UPS modules are required to feed the potential load, and
if one of the two modules develops a fault, or is for some reason
shut down, the other module automatically shuts down also.
Note: In such an event the load is transferred to an unprocessed bypass supply -
as described later.
In a redundant module configuration the system is sized such that
the potential load can be provided by just one of the two modules.
Under normal circumstances both modules are operational and
share the load current equally; but if one module develops a fault,
or is shut down, the second module is able to take over the full load
demand and continue to provide it with processed, backed-up
power. The advantages of a redundant system over a non-
redundant system in terms of overall system reliability are self-
evident.
Changing a one-plus-one system’s configuration between
redundant and non-redundant is quite straightforward, being
carried out by configuration links on the circuit board, which
governs the modules’ parallel control operation.
1.2.1 Redundant vs
Non-Redundant
configuration
Chapter 1Chapter 1
General Description