An excited electromagnetic acoustic sound is a direct-to-hear sound produced by a vibrating material under the excitation of an electromagnetic force. Some examples of excited electromagnetic acoustic noise include the hum of a transformer, the whining of several rotating electric engines, or the buzzing of neon lights. High voltage transmission line flame is caused by corona release, not magnetic power.
This phenomenon is also called audible hearing noise, electromagnetic acoustic sound, or induced electromagnetic acoustic sound, or more rarely, electrical noise, "coil sound" or "coil winding", depending on the application. The term electromagnetic sound is generally avoided because the term is used in the field of electromagnetic compatibility, dealing with radio frequencies. The term electrical noise describes electrical noise occurring in electronic circuits, not sound. For subsequent use, the term electromagnetic vibration or magnetic vibration, which focuses on structural phenomena is less ambiguous.
Acoustic noise and vibration due to electromagnetic forces can be seen as the opposite of microphonics, which illustrates how mechanical vibrations or acoustic sounds can cause unwanted electrical interference.
Video Electromagnetically excited acoustic noise and vibration
General description
Electromagnetic forces can be defined as forces arising from the presence of an electromagnetic field (electric fields, magnetic fields only, or both).
Electromagnetic forces in the presence of magnetic fields include equivalent power due to maxwell voltage tensor, magnetostriction and Lorentz forces (also called Laplace strength). Maxwell's strength, also called the aversion style, is concentrated in the interface of high magnetic relicivity changes, for example between air and ferromagnetic materials in an electric machine; they are also responsible for the attraction or repulsion of two opposing magnets. The force of magnetostriction is concentrated in the ferromagnetic material itself. Lorentz or Laplace force acts on a conductor that falls in an external magnetic field.
Electromagnetic force is equivalent because of the electric field can involve electrostatic, electrostatic, and reverse piezoelectric effects.
This phenomenon has the potential to produce vibrations of the ferromagnetic, conductive, coil and permanent magnets of electrical, magnetic and electromechanical devices, producing audible sound if vibration frequencies lie between 20 Hz and 20 kHz, and if high sound levels are sufficient to hear (eg radiation surfaces large and large vibration levels). The level of vibration increases in the event of a mechanical resonance, when the electromagnetic force corresponds to the natural frequency of the structural mode of the active component (magnetic circuit, electromagnetic coil or electrical circuit) or of its enclosure.
The noise frequency depends on the nature of the electromagnetic force (quadratic or linear function of the electric field or magnetic field) and on the frequency content of the electromagnetic field (especially if DC components exist or not).
Maps Electromagnetically excited acoustic noise and vibration
Electromagnetic sound and vibration in electrical machine
Electromagnetic torque, which can be calculated as the average value of the Maxwell tensor voltage across the air gap, is one of the consequences of electromagnetic forces in an electric machine. As a static style, it does not create vibration or acoustic sound. But the torque ripple (also called the cogging torque for the permanent magnet synchronous machine in open circuit), representing the harmonic variation of electromagnetic torque, is a dynamic force that creates the torsional vibrations of both the rotor and the stator. The torsional deflection of a simple cylinder can not emit efficient acoustic noise, but with certain boundary conditions the stator can emit acoustic noise with torque wave propagation. Noise generated by the structure can also be generated by torque ripples when the vibration of the rotor shaft line propagates to the frame and shaft lines.
Some harmonic tangential magnetic forces can directly create magnetic vibrations and acoustic noise when applied to the stator's teeth: the tangential force creates the bending moment of the stator gear, producing the radial vibration of the yoke.
In addition to the harmonic force of the tangential force, Maxwell's pressure also includes the harmonic radial force which is responsible for the radial vibrations of the yoke, which in turn can emit acoustic noise.
Electromagnetic sounds and vibrations in passive components
Inductor
In inductors, also called reactors or chokes, magnetic energy is stored in the air gap of magnetic circuits, where large Maxwell forces apply. Generates noise and vibration depending on airgap material and magnetic circuit geometry.
Transformer
In transformers, magnetic sound and vibration are generated by several phenomena depending on the load case that includes the strength of Laplace on the winding, Maxwell's force in the laminate joint, and the magnetostriction inside the laminated core.
Capacitor
Capacitors are also subject to large electrostatic forces. When the capacitor voltage/current waveform is not constant and contains timing harmonics, some harmonic electrical forces emerge and an acoustic sound can be generated. The ferroelectric capacitor also exhibits a piezoelectric effect that can be an audible sound source. This phenomenon is known as the "singing capacitor" effect.
Resonance effect in electric machine
In an electrically rotating flux flux machine, the resonance due to electromagnetic force is special because it occurs in two conditions: there must be a match between the attractive Maxwell style and the stator or natural frequency of the rotor, and between the stator or rotor form of capital and of interest. Maxwell harmonic wave numbers (periodicity of forces along the airgap).
For example resonance with the form of stator ellipse capital may occur if the force of the wave number is 2. In resonance conditions, the maximum electromagnetic excitation along the airgap and the maximum modal shift is in phase.
Numerical simulation
Methodology
Vibration and vibration simulation of excited electromagnets is a multiphysical modeling process done in three steps:
- electromagnetic force calculation
- calculate the magnetic vibration generated
- the resulting magnetic noise calculation
This is generally regarded as a weakly coupled problem: the deformation of the structure under the electromagnetic force is assumed not to significantly alter the distribution of the electromagnetic field and the resulting electromagnetic voltage.
Applications to electrical machines
Assessment of magnetic noise that can be heard in an electric machine can be done using three methods:
- using special electromagnetic and vibro-acoustic simulation software (eg MANATEE)
- using electromagnetics (eg Flux, Jmag, Maxwell, Opera), structural (eg Ansys Mechanical, Nastran, Optistruct) and acoustics (eg Actran, LMS, Sysnoise) numerical software together with special coupling methods
- using a multipyysics numerical simulation software environment (eg Comsol Multiphysics, Ansys Workbench)
Examples of devices subject to electromagnetic noise and vibration
Static device
Static devices include systems and electrical components used in electrical power storage or power conversion such as
- inductor
- transformer
- power inverter
- capacitor
- resistors: braking resistors of electric trains, used to dispose of electrical power when catenary does not receive during braking, can create electromagnetic-vibrant acoustic sound
- coils: in magnetic resonance imaging, "coil noise" is part of the total system noise associated with the receiving coil, since the temperature is not zero.
Rotate device
Rotating devices include radial fluxes and axial rotary electric machines used for the conversion of electrical power to mechanics such as
- induction motor
- synchronous motor with permanent magnet or rotor with DC coil
- replace the reluctance motor
In such devices, the dynamic electromagnetic force comes from a variation of the magnetic field, which either comes from a stable AC coil or a rotating DC field source (permanent magnet or DC winding).
Source of magnetic noise and vibration on electric machine
The harmonic electromagnetic force responsible for magnetic noise and vibration in a healthy machine can originate
- Supply pulse-width modulation from machine
- slotting effect
- magnetic saturation
In a damaged engine, additional sound and vibration due to the electromagnetic force can originate
- eccentric static and dynamic mechanics
- uneven air gap
- demagnetization
- short circuit
- loss of magnetic slice
Pull Unbalanced Magnet (UMP) describes electromagnetic equality of mechanical rotating imbalance: if electromagnetic force is unbalanced, a non-zero net magnetic force appears on the stator and rotor. This force can generate the bending mode of the rotor and create additional vibration and noise.
Electromagnetic noise and vibration reduction
Noise and magnetic vibration reduction in electric machines
NVH mitigation techniques in an electric machine include
- reduces the magnitude of electromagnetic excitation, regardless of the structural response of the electric engine
- reduces the magnitude of the structural response, regardless of electromagnetic excitation
- reduces the resonance that occurs between electromagnetic excitation and structural mode
The techniques of electromagnetic noise and vibration mitigation in electric machines include:
- choose the right slot/pole combination and the winding design
- avoid the corresponding resonance between the stator and the electromagnetic excitation
- shrink the stator or rotor
- applies polar milling techniques/polar poles/
- implementing a harmonic current injection or spreading the spectrum PWM strategy
- using a notch/flux barrier on the stator or rotor
- increase attenuation
Reduction "coil noise"
Coil mitigation actions include:
- add some glue (eg glue layer is often added at the top of the television roll, for years, the glue decreases and the sound level increases)
- change the shape of the coil (eg change the shape of the coil to number eight rather than the traditional coil shape)
- isolate the coils from the rest of the device to minimize noise generated by the structure
- increase attenuation
Experimental illustration
Variable electromagnetic forces can be generated either by a DC magnetic field moving source (eg a permanent magnetic spin or a rotating coil supplied with DC current), or by a constant source of an AC magnetic field (eg a variable rated coil).
Forceful vibrations with permanent magnets spinning
This animation illustrates how the ferromagnetic sheet can change shape because of the magnetic field of the rotating magnet. This corresponds to one pair of synthetic permanent magnets with an ideal pole machine with a slotless stator.
Acoustic resonance by variable frequency coil
The resonant effect of magnetic vibration with structural mode can be illustrated using a tuning fork made of iron. A branch of the tuning fork is wrapped with a coil fed by a variable frequency power supply. A variable flux density circulates between two branches and several dynamic magnetic forces appearing between two branches at twice the supply frequency. When the attractive force frequency corresponds to the basic mode of the tuning fork approaching 400 Hz, a strong acoustic resonance occurs.
Sample audio file
Motor PMSM (traction application)
External links
- The resonant tuning fork video magnetically driven by the current variable frequency on YouTube
- Video magnetic tuning fork is fired up by fixed frequency flows on YouTube
- The ferromagnetic cylinder video transformed by a rotating magnet on YouTube
See also
- Magnetostriction
- Noise
- Main parent
References
Source of the article : Wikipedia
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