Liebert Hipulse E - Chapter 4 - 1+N System

Installation Manual Liebert Hipulse E Chapter 4 - ‘1+N’ System
Single or '1+N' UPS System
(07/04) Page 4-1
4 Chapter 4 - 1+N System
4.1 General
The 1+N system has two or more (up to a maximum of six) modules of the same size (kVA). The load is equally
divided between the units that form the system. The system can be of two types:
• Parallel power
All the UPS's are able to provide the full power requested for the load.
• Parallel redundant
The system comprises a higher number of UPS's able to provide the full power required for the load.
For more detailed information on the operating principle of 1 + N parallel systems, see Chapter 7.
The 1+N system is used to:
• Increase the reliability of the system in order to ensure a good supply to the critical load connected.
• Increase the power availability (system expansion) in the event an unforeseen power demand occurs. This
guarantees a greater flexibility in relation to the critical load connected.
• Increase serviceability and allow the execution of maintenance operations and reparations without affecting the
ordinary operating conditions of the system (depending on the redundancy level).
The system can comprise of up to 6 UPS modules of the same power rating connected in parallel without the need for a
centralized mains static bypass.
The following components are installed inside each UPS unit in the 1+N parallel system:
The parallel logic board, the parallel connector board and the corresponding flat connection cables.
From a ‘power’ viewpoint each module is internally identical to the ‘single module’ configuration. A 1+N parallel
system requires inverter and bypass supplies, inter-module control signals to manage current sharing, synchronizing
and bypass switching between the modules. In figure 4-1 this is shown as the ‘inter-module control bus’, which is
facilitated through the use of multi-way ribbon cables connected between the units of the system.
The number and length of these flat cables is determined by the positioning of the equipment in the system, so this
supply is determined when the order is placed.
If the load is transferred onto a static bypass line, in a configuration in which three or more units are connected in
parallel, there may be a problem dividing up currents on the power circuit. Each case is different, and depends on the
length of the cables used, for example the resistance upstream and downstream of the static bypass line.
The differences between the impedances could result in undesirable division of currents over one or more UPS units.
This problem may be solved by including an optional inductance on the static bypass line of each UPS unit.
Note: For each additional UPS unit, the operator control panel must be programmed with the correct size and the
configuration of the static switch must be identified as ‘internal’.
1 + N Configuration (>2 UPS's) or two UPS's with parallel power connection
IMPORTANT
(*) With configurations consisting of two UPS's with parallel power or 1+N systems integrated with more than two
UPS's, where the load level is above the rated power of the single UPS, it is necessary to install an adequate
external maintenance bypass. It is also necessary to adopt all the measures required to prevent the internal manual
bypass switch of the UPS (Q3) from being used. This can be done by removing the handle of the switch and by
placing a warning label for the maintenance personnel.
For information on the external maintenance bypass, see paragraph 4.4.