Chapter 3 Electrical Wiring｜VP3000
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3-9 Electromagnetic Interference Prevention
When using an AC motor drive to drive the equipment, the harmonic noise will be generated on the
power input and output sides of the drive and generates EMC interference on the power supply network
and the electrical equipment around the AC motor drive. The AC motor drive is usually installed in an
industrial environment with high electromagnetic interference. Under these circumstances, the drive may
not only be a noise generator, but more possibly a noise receiver.
Delta drives have been optimized for EMC during design and comply with the EMC power system
product standard EN61800-3. Correctly install the drive can reduce the EMC interference. To ensure a
long-term normal operation of the power system, the drive must be correct wiring and grounding.
The prevention methods are as follows.
3-9-1 Grounding
The grounding can be set with different forms of grounding terminals as grounding electrodes
according to different equipment. Use a grounding wire on the electrical equipment that needs to be
grounded to guide the leakage current to the ground. According to Ohm's law, there may be different
potential difference between these electrodes and the earth due to different grounding resistance
values.
The main purpose of EMC is to prevent noise, and the main consideration of this kind of signal
grounding is frequency. When the frequency is lower than 10 kHz, single-point grounding is sufficient;
but if the frequency is higher than 10 kHz, multi-point grounding is more effective.
⚫ Single-point ground: Gather the signal grounding points of all IT equipments and connect them to
one point. In terms of the grounding, it can be connected to the earth or to the grounding
reference. You can also consider connecting the ground to a safety ground point that has been
connected to the earth.
⚫ Multi-point ground: Gather the signal grounding points of all IT equipments and ground them
independently.
When the DC passes through a conductor, it passes through the entire conductor. If the AC passes
through a conductor, and the current moves increasingly close to the surface of the conductor as the
frequency increases, this is so-called the Skin effect. In this case, the effective cross-sectional area of
the conductor will be smaller, and the resistance value will increase. In conclusion, in order to reduce
the influence of the skin effect, you should enlarge the effective cross-sectional area of grounding to
increase the current flow at high frequencies. For the above circumstances, you may consider
changing the grounding wire from a single wire to a braided conductor or a strip conductor.
3-9-2 Shield
What is a shield?
Electrostatic Shielding: In order to avoid the influence of the external electric filed on the equipment,
or to avoid the influence of the internal electric filed of the electrical equipment on other equipments,
use a conductor to cover the external electrical filed, so that the internal circuit and the external
equipment are not affected, that is called the electrostatic shielding.
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