Danfoss VLT Midi Drive FC 280 Design Guide

2.6 EMC Emission and Immunity
2.6.1 General Aspects of EMC Emission
Burst transient is conducted at frequencies in the range 150 kHz to 30 MHz. Airborne interference from the frequency
converter system in the range 30 MHz to 1 GHz is generated from the frequency converter, motor cable, and motor.
Capacitive currents in the motor cable coupled with a high dU/dt from the motor voltage generate leakage currents.
Using a shielded motor cable increases the leakage current (see Illustration 2.26) because shielded cables have higher
capacitance to ground than unshielded cables. If the leakage current is not ltered, it causes greater interference on the
mains in the radio frequency range below approximately 5 MHz. Since the leakage current (I
1
) is carried back to the unit
through the shield (I
3
), there is only a small electro-magnetic eld (I
4
) from the shielded motor cable.
The shield reduces the radiated interference but increases the low-frequency interference on the mains. Connect the motor
cable shield to the frequency converter enclosure and the motor enclosure. This is best done by using integrated shield
clamps to avoid twisted shield ends (pigtails). The shield clamps increase the shield impedance at higher frequencies, which
reduces the shield
eect and increases the leakage current (I
4
).
Mount the shield on the enclosure at both ends if a shielded cable is used for the following purposes:
•
Fieldbus.
•
Network.
•
Relay.
•
Control cable.
•
Signal interface.
•
Brake.
In some situations, however, it is necessary to break the shield to avoid current loops.
1
2
z
z
z
L1
L2
L3
PE
U
V
W
C
S
I
2
I
1
I
3
I
4
C
S
C
S
C
S
C
S
I
4
C
S
z
PE
3
4
5
6
175ZA062.12
1 Ground cable
2 Shield
3 AC mains supply
4 Frequency converter
5 Shielded motor cable
6 Motor
Illustration 2.26 EMC Emission
If placing the shield on a mounting plate for the frequency converter, use a metal mounting plate to convey the shield
currents back to the unit. Ensure good electrical contact from the mounting plate through the mounting screws to the
frequency converter chassis.
Product Overview
VLT
®
Midi Drive FC 280
36 Danfoss A/S © 03/2016 All rights reserved. MG07B102
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Danfoss VLT Midi Drive FC 280 Specifications

General

Brand	Danfoss
Model	VLT Midi Drive FC 280
Category	DC Drives
Language	English