10.14 Electromagnetic Compatibility (EMC) Overview
Electrical devices both generate interference and are affected by interference from other generated sources. The electro-
magnetic compatibility (EMC) of these effects depends on the power and the harmonic characteristics of the devices.
Uncontrolled interaction between electrical devices in a system can degrade compatibility and impair reliable operation.
Interference takes the form of the following:
•
Electrostatic discharges
•
Rapid voltage fluctuations
•
High-frequency interference
Electrical interference is most commonly found at frequencies in the range 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.
Capacitive currents in the motor cable, coupled with a high dU/dt from the motor voltage, generate leakage currents. See
. Shielded motor cables have higher capacitance between the phase wires and the shield, and again
between the shield and ground. This added cable capacitance, along with other parasitic capacitance and motor inductance,
changes the electromagnetic emission signature produced by the unit. The change in electromagnetic emission signature
occurs mainly in emissions less than 5 MHz. Most of the leakage current (I1) is carried back to the unit through the PE (I3),
leaving only a small electromagnetic field (I4) from the shielded motor cable. The shield reduces the radiated interference
but increases the low-frequency interference on the mains.
1
2
z
z
z
L1
L2
L3
PE
U
V
W
C
S
I
2
I
1
I
3
I
4
C
S
C
S
C
S
C
S
I
4
C
S
z
PE
3
4
5
6
175ZA062.12
1
Ground wire
Cs
Possible shunt parasitic capacitance paths (varies with different
installations)
2
Shield
I
1
Common-mode leakage current
3
AC mains supply
I
2
Shielded motor cable
4
Drive
I
3
Safety ground (4
th
conductor in motor cables)
5
Shielded motor cable
I
4
Unintended common-mode current
6
Motor
–
–
Illustration 10.25 Electric Model Showing Possible Leakage Currents
Electrical Installation Con...
VLT® AutomationDrive FC 302
166
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