Parker Hannifin S.p.A. - Divisione S.B.C. LVD User’s Manual
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2.2 Tips for interference suppression
Because of the high speed voltage wavefronts in PWM, high levels of stray current may
sometimes flow through capacitive couplings and earth systems.
Stray currents of this type can affect other functional units.
Therefore, in relation to the geometrical dimensions of the system (drive, motor cables, motor),
it is advisable to calculate a certain amount of spurious energy.
Spurious energy generates EM radiation that can interfere with the operation of nearby systems
Existing standards do not impose limits for this type of radiation.
Preventive measures:
Basic methods of preventing spurious emissions are: decoupling of the drive from its
surroundings, a properly executed conductor system to neutralise voltages (earthing) and
adequate shielding.
Screens, filters and drives must have a large contact area to achieve the maximum possible
decoupling and hence optimum noise suppression; attention must be paid, however, to the entire
installation as this is one of the most important precautions for obtaining efficient noise
suppression.
High frequency interference takes the form of radiation, especially from motor lines. This
effect can be reduced with appropriate shielding.
Another essential counter-measure for noise suppression is the use of filters.
The use of filters is aimed at reducing conducted interference on wiring and the return of
conducted interference to source (Drive) through routes offering the lowest impedance.
This method provides effective protection for other systems connected to the same electrical
line, also protecting the drive from interference originating from other systems.
When installing filters consider the mains input and motor feeding output.
There are various ways of connecting the power supply to the LVD drive; by using a
transformer with an electrostatic screen between primary and secondary windings it is possible
to dispense with the installation of EMC filters; on the contrary, EMC filters are required if you
use an autotransformer, a transformer without an electrostatic screen or a direct mains
connection.