Chapter 4 Operations 39
LIEBERT APM UPS Module And Parallel System 30kVA~150kVA User Manual
5.2.2 Parallel Requirements Of UPS Rack Systems
A group of paralleled UPS Rack Systems behave as if it were one large UPS with the advantage of presenting higher
reliability and/or higher total output power.
The following requirements apply:
1.
All UPS Rack Systems must be connected to the same bypass source (i.e: must be in phase and have the same
neutral reference)
2.
The bypass and the main input sources of each UPD rack unit must be referenced to the same neutral potential.
3.
Any RCD (Residual Current detecting device), if installed, must be of an appropriate setting and located upstream
of the common neutral bonding point. Alternatively, the device must monitor the protective earth currents of the
system. Refer to the
High Leakage Current Warning
in the first part of this manual.
4.
The outputs of all UPS Rack Systems must be connected to a common output bus.
5.
The maximum recommended unbalance between the numbers of power modules in different racks is 3/5.
In order to comply to the above points even in a faulty condition, the following upgrade sequence is proposed.
30kW
60kW
90kW
120kW
150kW
180kW
240kW
270kW
300kW
330kW
360kW
390kW
420kW
450kW
480kW
Redundant
Required
Fig.
5-2 Recommended upgrade sequence
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