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 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.
VLT
®
5000 Design Guide
MG.52.B2.02 - VLT
®
is a registered Danfoss trademark
79
Electrical installation
