Rockwell Automation 1398-DDM-xxx USE MNL/ULTRA 200 DIG.SERVO.DR - Manual (Page 283)

Publication 1398-5.0 – October 1998
Electromagnetic Compatibility Guidelines for Machine Design E-3
One method to improve the EMC characteristics of a drive is to use an
isolation AC power transformer to feed the amplifier its input power.
This minimizes inrush currents on power-up and provides electrical
isolation. In addition, it provides common mode filtering, although the
effect is limited in frequency by the interwinding capacitance. Use of
a Faraday shield between the windings can increase the common
mode rejection bandwidth, (shield terminated to ground) or provide
differential mode shielding (shield terminated to the winding).
One alternative to AC line filters to reduce the conducted EMI
emitting from the drive. This allows nearby equipment to operate
undisturbed. In most cases an AC line filter will not be required unless
other sensitive circuits are powered off the same AC branch circuit.
The basic operating principle is to minimize the high frequency power
transfer through the filter. An effective filter achieves this by using
capacitors and inductors to mismatch the source impedance (AC line)
and the load impedance (drive) at high frequencies.
AC Line Filter Selection
Selection of the proper filter is only the first step in reducing
conducted emissions. Correct filter installation is crucial to achieving
both EMI attenuation and to ensure safety. All of the following
guidelines should be met for effective filter use.
1. The filter should be mounted to a grounded conductive surface.
2. The filter must be mounted close to the drive input terminals. If
the distance exceeds 1 foot, then a strap should be used to connect
the drive and filter, rather than a wire.
3. The wires connecting the AC source to the filter should be
shielded from, or at least separated from the wires (or strap) con-
necting the drive to the filter. If the connections are not segregated
from each other, then the EMI on the drive side of the filter can
couple over to the source side of the filter, thereby reducing, or
eliminating the filter effectiveness. The coupling mechanism can
be radiation, or stray capacitance between the wires. The best
method of achieving this is to mount the filter where the AC
power enters the enclosure. “AC Line Filter Installation” shows a
good installation and a poor installation.
When multiple power cables enter an enclosure, an unfiltered line can
contaminate a filtered line external to the enclosure. Therefore, all
lines must be filtered to be effective. The situation is similar to a leaky
boat. All the holes must be plugged to prevent sinking.