Fan Application With Resonance Vibrations; Energy-Saving Examples; Why Use A Frequency Converter For Controlling Fans And Pumps; The Clear Advantage - Energy Savings - Danfoss VLT DriveMotor FCP 106 Design Manual

Application Examples
nameplate data in parameter 1-24 Motor Current
and parameter 1-37 d-axis Inductance (Ld).
•
For the best adjustment of the frequency
converter, carry out AMA on a cold motor.
Repeated AMA runs may lead to a heating of the
motor, which results in an increase of the stator
resistance, Rs. Normally, this increase is not
critical.
•
AMA can only be carried out if the rated motor
current is minimum 35% of the rated output
current of the frequency converter. AMA can be
carried out on up to 1 oversize motor.
•
It is possible to carry out a reduced AMA test
with a sine-wave filter installed. Avoid carrying
out a complete AMA with a sine-wave filter. If an
overall setting is required, remove the sine-wave
filter while running a total AMA. After completion
of the AMA, reinsert the sine-wave filter.
•
If motors are coupled in parallel, use only
reduced AMA if any.
•
The frequency converter does not produce motor
torque during an AMA. During an AMA, it is
imperative that the application does not force the
motor shaft to run. This situation is known to
occur with, for example, windmilling in ventilation
systems. The running motor shaft disturbs the
AMA function.
•
When running a PM motor (when
parameter 1-10 Motor Construction is set to [1] PM
non-salient SPM), only [1] Enable complete AMA
can be activated.
4.1.6 Fan Application with Resonance
Vibrations
In the following applications, resonant vibrations can arise,
which can result in damage to the fan:
•
Motor with fan mounted directly on the motor
shaft.
•
Running point in field weakening area.
•
Running point close to or above nominal point.
Overmodulation is a way to increase the motor voltage
delivered by the frequency converter for f
•
Advantages of overmodulation:
- Lower currents and higher efficiency are
achievable in the field weakening area.
- The frequency converter can give
nominal grid voltage at nominal grid
frequency.
MG03M202
Design Guide
•
Solutions to avoid fan damage:
•
•

4.2 Energy-saving Examples

4.2.1 Why Use a Frequency Converter for
A frequency converter takes advantage of the fact that
centrifugal fans and pumps follow the laws of propor-
tionality for such fans and pumps. For further information,
see chapter 4.2.3 Example of Energy Savings.

4.2.2 The Clear Advantage - Energy Savings

45–65 Hz.
mot
The clear advantage of using a frequency converter for
controlling the speed of fans or pumps lies in the
electricity savings.
When comparing with alternative control systems and
technologies, a frequency converter is the optimum energy
control system for controlling fan and pump systems.
Danfoss A/S © 06/2016 All rights reserved.
- When the mains voltage occasionally
drops below the correct motor voltage,
for example at 43 Hz, overmodulation
can compensate up to the required
motor voltage level.
Disadvantage of overmodulation: The non-
sinusoidal voltages increase the harmonics of the
voltages. This increase results in torque ripples,
which can damage the fan.
The best solution is to disable the overmodu-
lation, reducing vibrations to a minimum.
However, this solution can also cause derating of
the applied motor in the range 5–10%, due to
the missing voltage no longer applied by the
overmodulation.
An alternative solution for applications where it is
not possible to disable the overmodulation is to
skip a small frequency band of the output
frequencies. If the motor is designed to the limit
of the fan application, the voltage losses in the
frequency converter result in inadequate torque.
In these situations, the problem of vibration can
be reduced significantly by skipping a small
frequency band around the mechanical resonance
frequency, for example at the 6th harmonic.
Perform this skip by setting parameters
(parameter group 4-6* Speed Bypass) or by using
the semi-auto bypass set-up parameter 4-64 Semi-
Auto Bypass Set-up. However, there is no general
design rule for making an optimal skip of
frequency bands as this depends on the width of
the resonance peak. In most situations, it is
possible to hear the resonance.
Controlling Fans and Pumps?
4 4
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