Cable manufacturers rarely state the transfer impedance (Z
T
), but it is often possible to estimate transfer impedance (Z
T
) by
assessing the physical design of the cable, such as:
•
The conductibility of the shield material.
•
The contact resistance between the individual shield conductors.
•
The shield coverage, that is the physical area of the cable covered by the shield - often stated as a percentage
value.
•
Shield type, that is braided or twisted pattern.
175ZA166.13
0,01
0,1
1
10
100 MHz
10ˉ2
10ˉ3
10ˉ1
1
101
102
104
103
105
a
b
c
d
e
f
g
The lo
w
er the Z the bett
er the cable scr
eening per
for
manc
e
Transfer impedance, Z
t
mOhm/m
a
Aluminum-clad with copper wire.
b
Twisted copper wire or armored steel wire cable.
c
Single-layer braided copper wire with varying percentage shield coverage (this type of cable is the typical Danfoss
reference cable).
d
Double-layer braided copper wire.
e
Twin layer of braided copper wire with a magnetic, shielded/armored intermediate layer.
f
Cable that runs in copper tube or steel tube.
g
Lead cable with 1.1 mm (0.04 in) wall thickness.
Illustration 9.8 Cable Shielding Performance
EMC and Harmonics
Design Guide
MG37N102
Danfoss A/S © 6/2016 All rights reserved.
99
9
9
Summary of Contents for VLT 380-500 V
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