Motor Integration; Motor Selection Considerations; Sine-Wave And Du/Dt Filters; Proper Motor Grounding - Danfoss VLT Refrigeration Drive FC 103 Design Manual

System Integration
efficiency achieved with this form of energy conversion.
When a generator provides back-up power, the mains
impedance is usually higher than when power is taken
from the public grid. This causes the total harmonic
distortion to increase. With proper design, generators can
operate in a system containing devices that induce
harmonics.
When designing a system, consider the use of a stand-by
generator.
•
When the system is switched from mains
operation to generator, the harmonic load usually
increases.
•
Designers must calculate or measure the increase
in the harmonic load to ensure that the power
quality conforms to regulations to prevent
harmonic problems and equipment failure.
•
Avoid asymmetric loading of the generator since
it causes increased losses and may increase total
harmonic distortion.
•
A 5/6 stagger of the generator winding
attenuates the 5th and 7th harmonics, but it
allows the 3rd harmonic to increase. A 2/3
stagger reduces the 3rd harmonic.
•
When possible, the operator should disconnect
power factor correction equipment because it
causes resonance in the system.
•
Chokes or active absorption filters as well as
resistive loads operated in parallel can attenuate
harmonics.
•
Capacitive loads operated in parallel create extra
load due to unpredictable resonance effects.
A more precise analysis is possible using mains analysis
software, such as HCS. For analysing mains systems, go to
http://www.danfoss-hcs.com/Default.asp?LEVEL=START for
software download.
When operating with harmonic-inducing devices, the
maximum loads based on trouble-free facility operation are
shown in the harmonic limits table.
Harmonic limits
•
B2 and B6 rectifiers⇒maximum 20% of rated
generator load.
•
B6 rectifier with choke⇒maximum 20–35% of
rated generator load, depending on the
composition.
•
Controlled B6 rectifier⇒maximum 10% of rated
generator load.
MG16G202
Design Guide

3.5 Motor Integration

3.5.1 Motor Selection Considerations

The frequency converter can induce electrical stress on a
motor. Therefore, consider the following effects on the
motor when matching motor with frequency converter:
•
•
•

3.5.2 Sine-wave and dU/dt Filters

Output filters provide benefits to some motors to reduce
electrical stress and allow for longer cable length. Output
options include sine-wave filters (also called LC filters) and
dU/dt filters. The dU/dt filters reduce the sharp rise rate of
the pulse. Sine-wave filters smooth the voltage pulses to
convert them into a nearly sinusoidal output voltage. With
some frequency converters, sine-wave filters comply with
EN 61800-3 RFI category C2 for unshielded motor cables,
see chapter 3.8.3 Sine-wave Filters.
For more information on sine-wave and dU/dt filter
options, refer to chapter 6.2.6 Sine-wave Filters,
chapter 3.8.3 Sine-wave Filters and chapter 6.2.7 dU/dt Filters.
For more information on sine-wave and dU/dt filter
ordering numbers, refer to chapter 3.8.3 Sine-wave Filters,
and chapter 6.2.7 dU/dt Filters.

3.5.3 Proper Motor Grounding

Proper grounding of the motor is imperative for personal
safety and to meet EMC electrical requirements for low
voltage equipment. Proper grounding is necessary for the
effective use of shielding and filters. Design details must
be verified for proper EMC implementation.

3.5.4 Motor Cables

Motor cable recommendations and specifications are
provided in chapter 7.5 Cable Specifications.
All types of 3-phase asynchronous standard motors can be
used with a frequency converter unit. The factory setting is
for clockwise rotation with the frequency converter output
connected as follows.
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Insulation stress
Bearing stress
Thermal stress
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