2 Engineering
2.2 Electrical power network
DA1 Variable Frequency Drives 11/16 MN04020005Z-EN www.eaton.com 41
2.2.4 Total Harmonic Distortion (THD)
The THD value (THD = Total Harmonic Distortion) is defined in standard IEC/
EN 61800-3 as the ratio of the rms value of all harmonic components to the
rms value of the fundamental frequency.
2.2.5 Idle power compensation devices
Compensation on the power supply side is not required for the variable
frequency drives of the DA1 series. From the AC supply system they only
take on very little reactive power
of the fundamental
harmonics (cos
~
0.98).
￫
In order to reduce the THD value (up to 30 %), it is
recommended to use a DX-LN… mains choke
( Section 2.4, „Mains chokes“, page 47).
￫
FS5, FS6, and FS7 DA1 variable frequency drives feature chokes
in their DC link. Using mains chokes in order to reduce current
harmonics is not necessary in this case.
￫
Only for FS8 DA1 variable frequency drives:
DA1-34370FB-B20C, DA-34450FB-B20C
If it is not guaranteed that the system percentage impedance is
greater than or equal to 1 %, a mains choke must be connected.
Your u
K
value should fall between 1 and 4 %.
Examples:
DA1-34370FB-B20C
DX-LN3-370
DA1-34450FB-B20C DX-LN3-450
￫
In the AC supply systems with non-choked reactive current
compensation devices, current deviations can enable parallel
resonance and undefinable circumstances.
In the project planning for the connection of variable frequency
drives to AC supply systems with undefined circumstances,
consider using main chokes.
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