Parker Hannifin S.p.A. - S.B.C. Division HPD N User’s Manual
10
3.2. Interference suppression hints
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. It is therefore prudent to calculate the presence of an amount
of spurious energy that depends on the size of the system (drives, motor lines, motor).
Spurious energy generates EM radiation that can interfere with the operation of nearby
systems. Existing standards do not set down limits for this type of radiation.
Preventive measures
Basic methods for preventing interference are: decoupling of drive from its surroundings,
high quality and properly sized conductors to neutralise voltages (earthing), and adequate
shielding. Shields, filters and drives must have a large contact area to achieve the maximum
possible decoupling and hence optimal noise suppression. Attention must be paid, however, to
the entire installation, as this is one of the most important precautions in assuring efficient
noise suppression.
High frequency interference takes the form of radiation, especially from the motor lines.
This effect can be reduced with the use of 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; the motor feeding output can be
protected with output filters that minimise interference levels (generally torroidal ferrite core
coils bearing several windings of all three motor wires).
3.3. Mains filter installation instructions
To guarantee electromagnetic compatibility in compliance with the relevant standards the
maximum priority must be awarded to EMC requirements when designing the control cubicle.
To obtain the best results from filters follow the instructions in this section carefully, because
even a complex and expensive filter is ineffective unless it is installed
taking EMC aspects into consideration.
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