Danfoss VLT AutomationDrive FC 300 Series - Use of EMC-Correct Cables; Earthing of Screened Control Cables

Transmitter
96 97 9998
91 92 93 95
50
12
L1 L2
L1
PEL3
W PEVU
F1
L2
L3
N
PE
130BA175.12
18
53
37
55
54
M
3
5 kΩ
Illustration 7.63 Electrical Connection Diagram
7.8.2
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
T
). The screen of a cable is normally designed
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 manufac-
turers 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 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
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
175ZA166.13
0,01 0,1 1 10 100 MHz
10
10
10
1
10
10
10
10
10
a
b
c
d
e
f
g
The lower the Z the better the cable screening performance
Transfer impedance, Z
t
mOhm/m
Illustration 7.64 Transfer Impedance
7.8.3
Earthing of Screened Control Cables
Correct screening
The preferred method in most cases is to secure control
and cables with screening clamps provided at both ends
to ensure best possible high frequency cable contact.
If the earth potential between the frequency converter and
the PLC is different, electric noise may occur that will
disturb the entire system. Solve this problem by fitting an
equalizing cable next to the control cable. Minimum cable
cross section: 16 mm
2
.
Electrical Installation
VLT
®
AutomationDrive FC 300 Design Guide, 0.25-75 kW
146 MG33BE02 - VLT
®
is a registered Danfoss trademark
77
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