Fairford Electronics QFE Series, Руководство пользователя

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EMC
QFE
page 4-6
FD841505_F
4.5 EMC - Basic Criteria
The electromagnetic compatibility of a product is defined by two criteria:
1
Immunity to electromagnetic disturbances generated externally to the product
2 The type and amount of conducted and radiated electromagnetic emissions emanating
from the product.
Ascertaining the nature of the power supply is of primary consideration when deciding on
appropriate EMC requirements. The requirements for equipment installed in heavy industrial
environments (fed from their own isolated low voltage power supply) differ from those installed
in residential, commercial, light industry and health-care applications (directly connected to
a public low-voltage network).
Generally, industrial installations require higher immunity levels and permit higher levels of
conducted and radiated emissions than those for non-industrial installations. On the other
hand, lower levels of emissions output, and lower immunity levels, are specified for installations
connected directly to the public low-voltage network.
4.6 Purchasing Implications of Meeting an EMC Standard
Before purchasing components for the installation, the specifier must evaluate the expected
source of power for the Soft Starter and understand exactly the implications for meeting
EMC requirements. It is likely that failure to do so will result in the purchase and installation
of inappropriate equipment. Close consultation with your supplier will avoid these unnecessary
problems, particularly when you do not understand, or are unclear about any part of the
guidelines given later in this section.
If you have any doubt, please ask.
IMPORTANT:
The information and guidance given in section 4.7 forms part of the statutory requirements of
the European Union Directive 89/336/EEC on EMC.
4.7 Basic EMC Considerations
4.7.1 Immunity
The product standard for immunity requirements is EN 60947-4-2:1996. All QFE 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 QFE soft-starter.
4.7.3 Emissions - Harmonics
Harmonics arise from the intentional delay relative to the voltage wave zero, in the turn-on of
the semiconductor switches in order to vary the voltage at the motor terminals. This introduces
supply discontinuities and so generates harmonics. However, the configuration of the QFE soft-
starter power circuits as a fully-controlled regulator (W3C), and the mode of pulsing used results
in minimised harmonic effects. This means that 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.
Note The generic limits for harmonics for soft-starters which operate with a power
level greater than 1kW are under consideration. Until these have been defined, harmonic
filters are not required for any QFE soft-starter.