Fairford Electronics QFE Series, Manual

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QFE
page 4-7
EMC
FD841505_F
4.7.4 Emissions - Radio Frequency (RF)
Radio frequency emissions are propagated in two ways:
Conduction along the leads supplying the soft-starter.
Radiation from the operating equipment.
They also have two sources:
Source 1: The high frequency currents associated with the control electronics (this includes
the microprocessor)
Source 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 QFE soft-starters show levels
lower than the allowed limits. Further, enclosures (or cubicles) of metallic construction provide
additional shielding for QFE 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.
4.7.5 Emissions - Conducted
Conducted emissions are able to travel great distances and may cause interference to any
neighbouring consumers connected to the common low-voltage supply network.
Allowable levels for conducted emissions generated by semiconductor motor controllers
and starters are influenced by the nature of the low-voltage power distribution network. The
determining factor is whether the source of power is,
either(a)
A private supply with a single consumer whose Point of Common Coupling (PCC)
is at a high or medium voltage transformer.
or,
(b) A public low-voltage network with more than one consumer, where the individual
PCC is made directly to the network itself.
The first type of supply is identified as "Industrial" and requires the use of soft-starters compliant
with EN 60947-4-2 Table 14: 'Equipment Class A Emission Levels'.
The second type of supply is identified as "Residential" and requires the use of Equipment
Class B Apparatus. QFE soft-starters are able to comply with either classification provided the
appropriate action is taken. (Section 4.7.7 describes the strategies for attaining and maintaining
compliance.)
4.7.6 Important Systems Information:
The specification limits for both equipment classes assume systems are earthed at the
star-point of the supply transformer through low impedance connections.
Certain industries, particularly continuous process industries, employ distribution systems
that operate either with an earth through a high impedance or without an earth at all. These
systems may cause severe problems of operator safety when fitted with capacitive high
frequency filters -such systems are not considered in this document.
In the case of an isolated or high impedance earthed system, seek advice from your supplier
before fitting a capacitive high frequency filter to a QFE soft-starter. It is essential that the
specifying authority, user or installer has a clear knowledge of the type of network to which the
product is to be fitted before making decisions as to which EMC strategy to adopt.
As supplied, all QFE products comply with the conducted emissions requirements for Equipment
class A soft starters as defined by EN 60947-4-2:1996 Table 14. However, the length and type of
cable connecting the motor to the starter module materially affects the level of emissions
generated, and can amplify them greatly. The standard also allows different levels of emissions
depending on motor rated current, which also affects the need to fit filters. The EN 60947-4-
2:1996 standard only requires consideration of steady-state conditions for EMC purposes and