Design Guide | VLT® AutomationDrive FC 360
13 Common ground busbar. Follow local and national
requirements for cabinet grounding.
14 Brake resistor
15 Metal box 16 Connection to motor
17 Motor 18 EMC cable gland
7.14 Harmonics
7.14.1 Harmonics Overview
Non-linear loads such as those found with drives do not draw current uniformly from the power line. This non-sinusoidal current has
components which are multiples of the basic current frequency. These components are referred to as harmonics. It is important to
control the total harmonic distortion on the mains supply. Although the harmonic currents do not directly affect electrical energy
consumption, they generate heat in wiring and transformers that can affect other devices on the same power line.
7.14.2 Harmonic Analysis
Since harmonics increase heat losses, it is important to design systems with harmonics in mind to prevent overloading the transformer,
inductors, and wiring. When necessary, perform an analysis of the system harmonics to determine equipment effects.
A non-sinusoidal current is transformed with a Fourier series analysis into sine-wave currents at different frequencies, that is, different
harmonic currents I
N
with 50 Hz or 60 Hz as the basic frequency.
Table 22: Harmonics-related Abbreviations
Abbreviation Description
f
1
Basic frequency (50 Hz or 60 Hz).
I
1
Current at the basic frequency.
U
1
Voltage at the basic frequency.
I
n
Current at the n
th
harmonic frequency.
U
n
Voltage at the n
th
harmonic frequency.
n Harmonic order.
Table 23: Basic Currents and Harmonic Currents
Basic current (I
1
) Harmonic current (I
n
)
Current I
1
I
5
I
7
I
11
Frequency 50 Hz 250 Hz 350 Hz 550 Hz
Table 24: Harmonic Currents vs. RMS Input Current
Current Harmonic current
I
RMS
I
1
I
5
I
7
I
11-49
Input current 1.0 0.9 0.5 0.2 <0.1
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