5.2.6 EMI Propagation
Frequency converter generated EMI is both conducted to
the mains and radiated to nearby conductors. See
Illustration 5.2.
1AC line
2 Frequency converter
3Motor cable
4Motor
5 Stray capacitance
6 Signal wiring
7 Signal wiring
8 Signal wiring
9Ground
Illustration 5.2 Ground Currents
NOTICE
Stray capacitance between the motor conductors,
equipment ground, and other nearby conductors results
in induced high frequency currents.
High ground circuit impedance at high frequencies results
in an instant voltage at points reputed to be at ground
potential. This voltage can appear throughout a system as
a common mode signal that can interfere with control
signals.
Theoretically, these currents return to the DC-bus via the
ground circuit and a high frequency (HF) bypass network
within the frequency converter itself. However,
imperfections in the frequency converter grounding or the
equipment ground system can cause some of the currents
to travel out to the power network.
1AC line
2 Frequency converter
3Motor cable
4Motor
5 Stray capacitance
6AC line, to BMS
7 Signal wiring
Illustration 5.3 Signal Conductor Currents
NOTICE
Unprotected or poorly routed signal conductors located
close to or in parallel to motor and mains conductors are
susceptible to EMI.
Signal conductors are especially vulnerable when they run
in parallel to the power conductors for any distance. EMI
coupled into these conductors can aect either the
frequency converter or the interconnected control device.
See Illustration 5.3.
While these currents tend to travel back to the frequency
converter, imperfections in the system cause some current
to ow in undesirable paths. This ow exposes other
locations to the EMI.
NOTICE
High frequency currents can be coupled into the mains
supplying the frequency converter, when the mains
conductors are located close to the motor cables.
Frequency Converter and Mot... TR150 and TR170 Service Manual
BAS-SVM04B-EN 02/2017 All rights reserved. 43
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