General Aspects Of Emc - Danfoss VLT HVAC Basic Drive FC 100 Series Design Manual

Introduction to VLT HVAC Ba...
2.6.8 Manual PI Adjustment
2 2 1. Start the motor.
2. Set 20-93 PI Proportional Gain to 0.3 and increase it until the feedback signal begins to oscillate. If necessary, start
and stop the frequency converter or make step changes in the set-point reference to attempt to cause oscillation.
Next reduce the PI Proportional Gain until the feedback signal stabilizes. Then reduce the proportional gain by
40-60%.
3. Set 20-94 PI Integral Time to 20 sec. and reduce it until the feedback signal begins to oscillate. If necessary, start
and stop the frequency converter or make step changes in the set-point reference to attempt to cause oscillation.
Next, increase the PI Integral Time until the feedback signal stabilizes. Then increase of the Integral Time by
15-50%.

2.7 General Aspects of EMC

2.7.1 General Aspects of EMC Emissions
Electrical interference is usually conducted at frequencies in the range 150kHz to 30MHz. Airborne interference from the
frequency converter system in the range 30MHz to 1GHz is generated from the inverter, motor cable, and the motor.
As shown in the illustration below, capacitive currents in the motor cable coupled with a high dU/dt from the motor
voltage generate leakage currents.
The use of a screened motor cable increases the leakage current (see illustration below) because screened cables have
higher capacitance to earth than unscreened cables. If the leakage current is not filtered, it will cause greater interference
on the mains in the radio frequency range below approximately 5MHz. Since the leakage current (I
unit through the screen (I
according to the below figure.
The screen reduces the radiated interference but increases the low-frequency interference on the mains. The motor cable
screen must be connected to the frequency converter enclosure as well as on the motor enclosure. This is best done by
using integrated screen clamps so as to avoid twisted screen ends (pigtails). These increase the screen impedance at higher
frequencies, which reduces the screen effect and increases the leakage current (I
If a screened cable is used for fieldbus, relay, control cable, signal interface and brake, the screen must be mounted on the
enclosure at both ends. In some situations, however, it will be necessary to break the screen to avoid current loops.
LINE
If the screen is to be placed on a mounting plate for the frequency converter, the mounting plate must be made of metal,
because the screen currents have to be conveyed back to the unit. Moreover, ensure good electrical contact from the
mounting plate through the mounting screws to the frequency converter chassis.
30
), there will in principle only be a small electro-magnetic field (I
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MG.18.C2.02 - VLT
VLT HVAC Basic Drive Design Guide
MOTOR CABLE SCREENED
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