Use Of Emc-Correct Cables - Danfoss VLT FC51 Design Manual

How to Install

6.9 Use of EMC-Correct Cables

Danfoss recommends braided screened/armoured cables 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 designed
T
to reduce the transfer of electric noise; however, a screen
with a lower transfer impedance (Z
effective than a screen with a higher transfer impedance
(Z ).
T
Transfer impedance (Z ) is rarely stated by cable manufac-
T
turers but it is often possible to estimate transfer
impedance (Z ) by assessing the physical design of the
T
cable.
Transfer impedance (Z ) can be assessed on the basis of
T
the following factors:
•
The conductibility of the screen material.
•
The contact resistance between the individual
screen conductors.
•
The screen coverage, that is, the physical area of
the cable covered by the screen - often stated as
a percentage value.
•
Screen type, that is, braided or twisted pattern.
a. Aluminium-clad with copper wire.
b. Twisted copper wire or armoured steel wire cable.
c. Single-layer braided copper wire with varying
percentage screen coverage.
This is the typical Danfoss reference cable.
d. Double-layer braided copper wire.
e. Twin layer of braided copper wire with a
magnetic, screened/armoured intermediate layer.
f. Cable that runs in copper tube or steel tube.
g. Lead cable with 1.1 mm wall thickness.
®
VLT Micro Drive FC 51 Design Guide
) value is more
T
MG02K302 - Rev. 2013-12-03
Transfer impedance, Z
t
mOhm/m
10
10
10
10
10
1
10
10
10
0,01 0,1 1 10 100 MHz
Illustration 6.10 Transfer Impedance of Different Wires
a
b
c
d
e
6 6
f
g
49