Installation Consideration; General Aspects Of Emc - GE AF-650 GP Design And Installation Manual

Installation Consideration

7 Installation Consideration

7.1 General Aspects of EMC

7.1.1 General Aspects of EMC Emissions
Burst transient is conducted at frequences 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 inverter, motor cable, and the motor.
Capacitive currents in the motor cable coupled with a high dU/dt from the motor voltage generate leakage currents.
The use of a shielded motor cable increases the leakage current (see Illustration 7.1) because shielded cables have higher
capacitance to ground than unshielded cables. If the leakage current is not filtered, it causes greater interference on the
mains in the radio frequency range below approximately 5 MHz. Since the leakage current (I
through the shield (I ), there is only a small electro-magnetic field (I
3
The shield 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 and to the motor enclosure. This is best done by using
integrated shield clamps to avoid twisted shield ends (pigtails). These increase the shield impedance at higher frequencies,
which reduces the shield effect and increases the leakage current (I
If a shielded cable is used for networknetwork, relay, control cable, signal interface, and brake, the shield must be mounted
on the enclosure at both ends. In some situations, however, it is necessary to break the shield to avoid current loops.
1 Ground wire
2 Shield
3 AC mains supply
4 Frequency converter
5 Shielded motor cable
6 Motor
Illustration 7.1 EMC Emission
If the shield is to be placed on a mounting plate for the frequency converter, the mounting plate must be made of metal,
because the shield 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.
When unshielded cables are used, some emission requirements are not complied with, although the immunity requirements
are observed.
MG35M402
AF-650 GP™ Design and Installation Guide
) from the shielded motor cable.
4
).
4
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) is carried back to the unit
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