Figure 6.3 Commutating Load Circuit - Fujitsu M10 Series Installation Planning Manual

(1) UPS load specifications
Some server systems adopt condenser-input type rectifier circuit (commutating load)
as shown in
Rectifier of this type turns the current waveform of a server system into a distorted
waveform containing harmonics. The amplified crest (peak value) of distorted
waveform containing harmonics is about 2.8 times to the effective value.(It means
that if effective value is 10 A, the peak value is 28 A.) If the UPS is so designed that
output voltage is regulated by resistor, driving at 50% or less of the UPS's deliverable
output voltage is needed. Make sure that the rectifier has a mechanism that lowers the
distortion (peak value is about 2.8 times) current passing the rectifier to 10%
(distortion factor) at peak wave (crest factor). Also check this point for loads of
transformers and motors (linear amplifier).
As the conclusion, the recommendable UPS rectifier load specification is:
 Linear load or Peak-to-valley ratio (at peak) must not exceed 2.8
(2) Prediction of rush current and load variation of the equipment
Turning on the power to connected devices generates rush current. For example, a
component operating at a steady-state current of 3 A may generate a current of
0-P
30 A when it is turned on. Even when connected devices generate rush current, the
UPS output voltage fluctuation must stay within ±15%. Special attention must be
paid to cases where multiple devices are connected, since the rush current generated
by each connected device at its power-on time may cause a UPS voltage drop, and
other components in operation may stop operating. Therefore, the rush current and
load variability of the components must be reviewed together with the overcurrent
detection specifications of the UPS.
C120-H007-08EN
Figure 6.3.

Figure 6.3 Commutating load circuit

6.3 UPS Requirements
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