Danfoss VLT 5000 Series, Инструкция по эксплуатации, Страница: 187 / 240

Electrical installation, selection 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 im-
pedance (Z
T
). The screen of a cable is normally de-
signed to reduce the transfer of electric noise;
however, a screen with a lower transfer impedance
(Z
T
) value is more effective than a screen with a higher
transfer impedance (Z
T
).
Transfer impedance (Z
T
) is rarely stated by cable man-
ufacturers, but it is often possible to estimate transfer
impedance (Z
T
) by assessing the physical design of
the cable.
Transfer impedance (Z
T
) can be assessed on the basis
of the following factors:
- The conductibility of the screen material.
- The contact resistance between the individ-
ual 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 percent-
age 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.
VLT
®
5000 Series
184 MG.51.C5.22 - VLT
p
is a registered Danfoss trademark.