Use Of Emc-Correct Cables - Danfoss VLT 8000 AQUA series Operating Instructions Manual

Use of emc-correct cables

Braided screened/armoured cables are recommended
to optimise EMC immunity of the control cables and
the EMC emission from the motor cables.
The ability of a cable to reduce the in- and outgoing
radiation of electric noise depends on the transfer
impedance (Z ). The screen of a cable is normally
T
designed to reduce the transfer of electric noise;
however, a screen with a lower transfer impedance
(Z ) value is more effective than a screen with a
T
higher transfer impedance (Z
Transfer impedance (Z ) is rarely stated by
T
cable manufacturers, but it is often possible to
estimate transfer impedance (Z
the physical design of the cable.
MG.83.A2.02 - VLT is a registered Danfoss trademark
).
T
) by assessing
T
®
VLT 8000 AQUA
Transfer impedance (Z ) can be assessed on the
T
basis of the following factors:
- The conductibility of the screen material.
- The contact resistance between the individual
screen conductors.
- The screen coverage, i.e. the physical area
of the cable covered by the screen - often
stated as a percentage value.
- Screen type, i.e. braided or twisted pattern.
Aluminium-clad with copper wire.
Twisted copper wire or armoured steel wire cable.
Single-layer braided copper wire with varying percentage screen
coverage.
This is the typical Danfoss reference cable.
Double-layer braided copper wire.
Twin layer of braided copper wire with a magnetic,
screened/armoured intermediate layer.
Cable that runs in copper tube or steel tube.
Lead cable with 1.1 mm wall thickness.
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