Danfoss VLT FC Series Service Guide

7.3.5 Preventive Measures
EMI-related problems are more eectively alleviated during
the design and installation phases rather than during
service.
Grounding
The drive and motor must be solidly grounded to the
equipment enclosure. A good high-frequency connection is
necessary to allow the high-frequency currents to return
back to the drive rather than to travel through the power
network. The ground connection is ineective if it has high
impedance to high-frequency currents. Therefore it must
be as short and direct as practical. Flat-braided cable has
lower high-frequency impedance than round cable. Simply
mounting the drive or motor onto a painted surface does
not create an eective ground connection. In addition,
running a separate ground conductor directly between the
drive and the running motor is recommended.
Cable routing
Avoid routing the following in parallel:
•
Motor wiring
•
Mains wiring
•
Signal wiring
If parallel routing is unavoidable, try to maintain a
separation of 200 mm (6–8 in) between the cables, or
separate them with a grounded conductive partition. Avoid
routing cables through free air.
Signal cable selection
Single conductor 600 V rated wires provide the least
protection from EMI. Twisted-pair cables and shielded
twisted-pair cables are available that are designed to
minimize the eects of EMI. While unshielded twisted-pair
cables are often adequate, shielded twisted-pair cables
provide another degree of protection. Terminate the signal
cable shield in a manner that is appropriate for the
connected equipment. Avoid terminating the shield
through a pigtail connection as this method increases the
high-frequency impedance and reduces the eectiveness
of the shield. Refer to chapter 4.9 Shielded Cable Grounding.
A simple alternative is to twist the existing single
conductors to provide a balanced capacitive and inductive
coupling. This method cancels dierential mode
interference. While not as eective as true twisted-pair
cable, it can be implemented in the eld using the
available materials.
Motor cable selection
The management of the motor conductors has the
greatest inuence on the EMI characteristics of the system.
These conductors must receive the highest attention
whenever EMI is a problem. Single conductor wires provide
the least protection from EMI emissions. Often, if these
conductors are routed separately from the signal and
mains wiring, then no further consideration is needed. If
the conductors are routed close to other susceptible
conductors, or if the system is suspected to cause EMI
problems, consider alternate motor wiring methods.
Installing shielded power cable is the most eective
methods to alleviate EMI problems. The shield forces the
noise current to ow directly back to the drive. This
prevents it from owing back into the power network or
other undesirable high-frequency paths. Unlike most signal
wiring, the shielding on the motor cable must be
terminated at both ends.
If a shielded motor cable is not available, then 3-phase
conductors plus ground in a conduit provides some
protection. This technique is not as eective as shielded
cable due to the unavoidable contact of the conduit with
various points within the equipment.
Serial communications cable selection
There are various serial communication interfaces and
protocols in the market. Each interface/protocol
recommends 1 or more specic types of cables. Refer to
the manufacturer documentation when selecting these
cables. Similar recommendations apply to serial communi-
cation cables as to other signal cables. Using twisted-pair
cables and routing them away from power conductors is
encouraged. While shielded cable provides extra EMI
protection, the shield capacitance can reduce the
maximum allowable cable length at high data rates.
Drive and Motor Application... Service Guide
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Danfoss VLT FC Series Specifications

General

Brand	Danfoss
Model	VLT FC Series
Category	DC Drives
Language	English