Installation Consideration; General Aspects Of Emc - GE AF-600 FP 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 frequencies
in the range of 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.
As shown in the figure below, capacitive currents in the
motor cable coupled with a high dV/dt from the motor
voltage generate leakage currents.
The use of a shielded motor cable increases the leakage
current (see figure below), because shielded cables have
higher capacitance to ground than non-shielded cables. If
the leakage current is not filtered, it will cause greater
interference on the line power in the radio frequency
range below approximately 5 MHz. Since the leakage
current (I ) is carried back to the unit through the shield (I
1
Figure 7.1
If the shield is to be placed on a mounting plate for the
adjustable frequency drive, 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 adjustable frequency driver
chassis.
AF-600 FP Design and Installation Guide
), there will in principle only be a small electro-magnetic
3
field (I ) from the shielded motor cable according to the
4
below figure.
The shield reduces the radiated interference but increases
the low-frequency interference on line power. The motor
cable shield must be connected to the adjustable
frequency drive enclosure as well as on the motor
enclosure. This is best done by using integrated shield
clamps so as 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 ).
4
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 will be necessary to break the shield
to avoid current loops.
When non-shielded cables are used, some emission
requirements are not complied with, although the
immunity requirements are observed.
In order to reduce the interference level from the entire
system (unit + installation), make motor and brake cables
as short as possible. Avoid placing cables with a sensitive
signal level alongside motor and brake cables. Radio
interference higher than 50 MHz (airborne) is especially
generated by the control electronics.
DET-768A
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