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Chapter 4: Electromagnetic Compatibility
4.7 – Basic EMC Considerations
4.7.1 – Immunity
The product standard for immunity requirements is EN 60947-4-2:1996. All SR44 Soft Starter
products meet, or exceed the industrial level immunity requirements laid down in this standard.
4.7.2 – Emissions
Emissions are classified as low frequency (below 9kHz), known as harmonics, and high or radio
frequency (above 9kHz). Both radio-frequency emissions and low-frequency harmonics are
generated by the action of the SR44 Soft-Starter.
4.7.3 – Emissions - Harmonics
During normal operation, soft starters turn their semiconductor switches on and off in order to vary
the voltage at the motor terminals, and this introduces supply discontinuities and generates
harmonics. However, the mode of pulsing used by SR44 Soft Starters minimizes these harmonic
effects, since SR44 power circuits are configured as a fully-controlled regulators (W3C).
Only non-triplen (integer multiples of the third harmonic), odd harmonic frequencies are created,
starting with and diminishing rapidly from the fifth harmonic, and virtually disappearing by the
nineteenth harmonic.
4.7.4 – Emissions - Radio Frequency (RF)
Radio frequency emissions are propagated in two ways:
1) Conduction along the leads supplying the soft starter.
2) Radiation from the operating equipment.
They also have two sources:
1) The high-frequency currents associated with the control electronics (this includes the
microprocessor)
2) The action of the semiconductor devices forming the power switching elements located in the
controller main circuits.
The radiation measurements made from operating versions of SR44 Soft Starters show levels lower
than the allowed limits. Further, enclosures (or cubicles) of metallic construction provide
additional shielding for SR44 Soft Starters mounted within them. The only radiated interference
effect that might arise from a soft starter would be if mobile telephones, walkie-talkies, etc. were to
be used in very close proximity to a unit which was operating with the enclosure door open. For
this reason, any enclosure must display a label that brings the possibility of electromagnetic
interference to the attention of the operator under these circumstances.
The generic limits for harmonics for soft starters which operate with a power level > 1kW are under
consideration.
Until these limits have been defined,
harmonic filters are not required for any SR44 Soft Starter .
SR44 Series Soft Starter User Manual
1st Ed, Rev B 07/31/2019
4–4