Johnson Controls VSD II Series Installation Manual page 15

Voltage Balance
Because of the uneven loading on the conductor, and with
the direct connection of greater power ratings, deviations
from the ideal voltage form and asymmetrical voltages can
be caused in three-phase AC power networks. These
asymmetric divergences in the input voltage can lead to
different loading of the diodes in input rectifiers with
three-phase supplied frequency inverters, and as a result,
an advance failure of this diode.
In the project planning for the connection of three-phase
supplied frequency inverters (HMX32, HMX34), consider
only AC power networks that handle permitted asymmetric
divergences in the input voltage +3%.
If this condition is not fulfilled, or symmetry at the connection
location is not known, the use of an assigned main choke is
recommended.
Total Harmonic Distortion (THD)
The THD (Total Harmonic Distortion) is a measurement for
the occurring harmonic distortion of the sinusoidal oscillation
(input power side) input variables with the frequency
inverter. It is given in percent of the total value.
2 2
2
U + U + U
2 3 4
K =
---------------------------------------------------------------------------------------------------------- -
2 2 2
U + U + U +
1 2 3
U 1 = fundamental component
THD k = 0.1 K = 10% ~ –20 dB (THD suppression)
2
2 2
U 2 + 3 U + U 4
THD = --------------------------------------------------------------------------------------------------- -
U 1
With VSD Series II frequency inverters, the permitted value
for the total harmonic distortion THD is >120%.
2
+ ... + U
n
• 100%
2 2
U + ... + U
4 n
2
...
+ + U n
Idle Power Compensation Devices
Compensation on the power supply side is not required for
VSD Series II frequency inverters. From the AC power supply
network, they take on very little reactive power of the
fundamental harmonics (cos
In the AC power networks with non-choked idle current
compensation devices, current deviations can enable parallel
resonance and undefinable circumstances.
In the project planning for the connection of frequency
inverters to AC power networks with undefined
circumstances, consider using main chokes.
VSD Series II LIT-12011772—October 2012 www.johnsoncontrols.com
Engineering
~ 0.98).
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