Installation Consideration; General Aspects Of Emc - GE AF-600 FP Series Design And Installation Manual

Installation Consideration

7 Installation Consideration

7.1 General Aspects of EMC

7.1.1 General Aspects of EMC Emissions
Electrical interference is usually conducted at frequences in the range 150 kHz to 30 MHz. Airborne interference from the
drive system in the range 30 MHz to 1 GHz is generated from the inverter, motor cable, and the motor.
Capacitive currents in the motor cable coupled with a high dV/dt from the motor voltage generate leakage currents.
The use of a screened motor cable increases the leakage current (see illustration below) because screened cables have
higher capacitance to earth than unscreened cables. If the leakage current is not filtered, it will cause greater interference
on the mains in the radio frequency range below approximately 5 MHz. Since the leakage current (I
unit through the screen (I ), there will only be a small electro-magnetic field (I
3
The screen reduces the radiated interference but increases the low-frequency interference on the mains. The motor cable
screen must be connected to the frequency converter enclosure as well as to the motor enclosure. This is best done by
using integrated screen clamps so as to avoid twisted screen ends (pigtails). These increase the screen impedance at higher
frequencies, which reduces the screen effect and increases the leakage current (I
If a screened cable is used for networknetwork, relay, control cable, signal interface and brake, the screen must be mounted
on the enclosure at both ends. In some situations, however, it will be necessary to break the screen to avoid current loops.
Illustration 7.1 EMC Emission
1 Earth wire
2 Screen
3 AC mains supply
4 Frequency converter
5 Screened motor cable
6 Motor
Table 7.1 Legend to Illustration 7.1
If the screen is to be placed on a mounting plate for the frequency converter, the mounting plate must be made of metal,
because the screen currents have to be conveyed back to the unit. Moreover, ensure good electrical contact from the
mounting plate through the mounting screws to the frequency converter chassis.
TM
AF-600 FP Design and Installation Guide
DET-768b
) is carried back to the
1
) from the screened motor cable.
4
).
4
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