The biggest example of the same is the Tacoma Bridge Collapse , in which the frequency of the air matched with the frequency of the bridge, leading to its collapse.
Have you ever noticed the walls and furniture of your home vibrating when you play music on a heavy beat? This is because the natural frequency of the furniture gets resonated with the frequency of the sound of the music, and, hence, causing them to vibrate. People who are not very good at singing sound much better while singing in the shower because the pure notes emitted are resonated in the shower cubicle. The bathroom is enclosed space and sometimes small; as you sing the sound waves hit the walls more frequently causing the wall to vibrate since the walls are parallel to each other.
The reflected sound hit each other, thereby causing the wall to vibrate at your natural frequency and the louder sound is transmitted. When we turn the knob of the radio to our favourite channel, we are changing the natural frequency of the receiver. The natural frequency of the receiver then matches the transmission frequency of the radio station. When two frequencies match, energy transfer occurs and we listen to the selected channel. The food is heated quickly in a microwave because of resonance.
The radiations emitted by a microwave oven have a certain wavelength and frequency. And like all other objects, molecules of water and fat also have a resonance frequency. At a certain frequency, the molecules absorb wavelengths and start vibrating, causing cooking and heating up of food. For motors, the higher frequency harmonic components place additional electrical stress on windings, increase rotor heating and reduce motor life.
Potentially the most detrimental effect of harmonics is that they could excite a system resonance that damages motors and pumps or even causes system failure. Harmonics can also cause faulty meter readings, motor bearing failure due to electrical currents , blown fusing on power-factor-corrected systems and telephone communication interference. Many of these problems may go undetected until the affected equipment fails. When a VFD or other non-linear device injects a harmonic current at the resonant frequency, the system becomes excited or unstable.
When I amps and Z impedance are simultaneously high, V voltage becomes exceptionally high. This causes excessive heating or possibly immediate dielectric failure in capacitors, transformers or other devices. Another issue is that most manufacturers of VFDs specify a maximum lead length between their equipment and the motor. This specification varies by manufacturer and drive but typically ranges from to ft to m.
Because this restriction can make application difficult, impractical or even impossible, many VFD users disregard it, leading to more motor failures and downtime. If the resonant frequency of the lead conductors falls within the frequency range of the VFD voltage waveform, the conductors themselves will go into resonance.
That will amplify the voltage components at or near the natural resonant frequency of the conductors, causing voltage spikes that can exceed 2. The obvious solution for preventing voltage spikes in VFD systems is to keep the lead length between the motor and drive within the drive manufacturer's specifications.
As mentioned earlier, VFDs also can be programmed to "skip" problem frequencies. Commonly available solutions for reducing harmonics include line reactors, isolation transformers, filters and higher-pulse VFDs e. Carefully consider all the strengths and weaknesses to determine which is best for a particular installation. The simplest and most common way to reduce harmonics is to add impedance to the system.
This solution offers the largest reduction in total harmonic distortion relative to cost. In fact, increasing impedance by just 3 percent will reduce current harmonics about 50 percent in a standard 6-pulse VFD.
This solution is often accomplished at the VFD by installing a DC choke or input line reactor, an isolation transformer or combination of these. Line reactors. Line reactors provide the impedance to reduce harmonic current but are smaller and usually cost less than isolation transformers. Also called inductors, they are available in standard impedance ranges of 1. Applying a line reactor at the drive terminals can help reduce the resonant frequency of the total circuit, but additional losses in the copper and core of the inductor increase overall circuit dampening.
While this reduces the peak of the overshoot voltage voltage spikes , it also increases its duration, which still results in additional stress on the motor windings.
Isolation transformers. If a loudspeaker system has a resonant frequency, it will reproduce sounds at the resonant frequency much more efficiently than those at other frequencies.
In most cases, loudspeakers are designed so that their unavoidable resonant frequency is far below or above the normal range of music the loudspeaker is intended to reproduce. Have you ever noticed that automobiles with powerful sound systems when heard from outside the vehicle seem to only make a dull thud instead of distinct bass notes? The occupant of the vehicle may be hearing distinct bass notes but what leaks out into the neighborhood is sound at the resonant frequency.
Loudspeakers utilize acoustic technology to provide reproduction of all frequencies at similar amplitude. The effects of resonance are at the base of the science of controlling and minimizing or maximizing sounds at particular frequencies.
This is why the swing has such a large swinging momentum. If you hit before or after the swing reaches its highest point, the force is transmitted less efficiently or even goes nowhere.
The body of an acoustic guitar, a swing, a glass or a bridge can vibrate at their respective resonant frequency. But this is not desired everywhere and can even cause great damage.
This is because systems can vibrate so violently that the construction cannot withstand the stress. This phenomenon can be observed when a person points his voice at a wine glass from a short distance.
If the pitch of the voice corresponds exactly to the natural frequency of the glass, it breaks after a relatively short time — the so-called resonance catastrophe occurs. If the vocal chords cause the air molecules to vibrate at a higher or lower frequency, the glass remains intact.
The natural frequency of the glass can be heard when you strike it with an object. One of the most famous resonance catastrophes occurred in the USA in , when the wind caused the Tacoma Narrows Bridge to vibrate so strongly that it collapsed.
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