Rockwell Automation System Design for the Control of Electrical Noise - Manual (Page 61)

Publication GMC-RM001A-EN-P — July 2001
Power Distribution 7-3
Transformers
An isolation transformer is frequently assumed to give good noise
isolation. In fact, this only applies if the transformer is equipped with
one or more electrostatic (ES) shields, as shown in the figure below.
Figure 7.3
Electrostatically shielded transformer
This technique is very effective, though generally EMC filters are
required to meet European regulation standards. Observe the
following guidelines when installing transformers.
• Install the transformer to the same panel as the rest of your system
(or HF bond from panel-to-panel).
• Treat wiring between transformer and drive as very-dirty (provide
shielding as required).
• Bond shield, if used, with braid directly to the panel. The
transformer mounting bolts are useful for this purpose.
• Segregate input and output wiring as far as possible.
Primary Secondary
Ground Plane
Frame bonded to
ground plane
Shield(s) bonded to
ground plane
IMPORTANT
The effectiveness of the transformer depends solely
on the HF bond between shields and drive chassis.