Overview
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In recent years, the demand to reduce vibration and noise is growing while
the requirements for higher efficiency and smaller and lighter transformers
grow with environmental conservation trends. The primary cause of noise
for transformers is the electromagnetic vibrations and the resonance phenomena
at the eigenfrequency of the structure. A sound pressure analysis can be
performed with a coupled magnetic field and structural analysis that uses
the electromagnetic force as excitation force.
This example presents the use of a coupled magnetic field and structural
analysis to obtain the sound pressure distribution accounting for the electromagnetic
force of the core when the transformer is operating on a power supply frequency
of 6 kHz. |
Electromagnetic Force Distribution
The electromagnetic force distribution of the core when the transformer
is operating is indicated in Fig. 1.
There is a strong force acting in the Z-axis direction in the gap area,
as indicated in the figure. Furthermore, the frequency is 12 kHz, or two
times the power supply frequency, because the electromagnetic force is
only acting as attraction force. |
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Eigenmode
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The eigenmode of the transformer is indicated in Fig. 2.
The transformer is only minimally deformed in the Z-axis direction at the
low order eigenmodes relatively close to 12 kHz, which is the frequency
of the electromagnetic force. The mode causing deformation in the Z-axis
direction around the gap of the core is at 47 kHz and 66 kHz. |
Acceleration Distribution
The acceleration distribution at 12 kHz is indicated in Fig. 3.
The deformation mode is larger at 47 kHz and 66 kHz, as indicated by the
figure. This is because the electromagnetic force produced around the gap
of the core and the deformation mode at 47 kHz and 66 kHz are in the same
Z-axis direction. Furthermore, the sides of the core are also largely deformed
by the attractive force of the gap.
However, there is no resonant frequency produced because the frequency
of the electromagnetic force is sufficiently lower than the eigenfrequency. |
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Sound Pressure Level Distribution
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The sound pressure level distribution at 12 kHz is indicated in Fig. 4.
The electromagnetic force acting in the Z-axis direction and the sound
pressure in the X-axis direction causing the most deformation of the core
is large. The sound pressure level is not that large because the eigenfrequency
of the deformation mode causing the largest electromagnetic vibrations
and the 12 kHz frequency of the electromagnetic force are separated. |
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