Harmonics In An Electrical Circuit

http://en.wikipedia.org/wiki/Harmonic

Dear SIr Nonlinear components draw current disproportionately with respect to the source voltage, causing non-sinusoidal current waveforms. Examples of nonlinear components include gas-discharge lamps, semiconductor power-control devices (diodes, transistors, SCRs, TRIACs), transformers (primary winding magnetization current is usually non-sinusoidal due to the B/H saturation curve of the core), and electric motors (again, when magnetic fields within the motor's core operate near saturation levels). Even incandescent lamps generate slightly nonsinusoidal currents, as the filament resistance changes throughout the cycle due to rapid fluctuations in temperature. Any distortion of an otherwise sine-wave shaped waveform constitutes the presence of harmonic frequencies. When the nonsinusoidal waveform in question is symmetrical above and below its average centerline, the harmonic frequencies will be odd integer multiples of the fundamental source frequency only, with no even integer multiples. Most nonlinear loads produce current waveforms like this, and so even-numbered harmonics (2nd, 4th, 6th, 8th, 10th, 12th, etc.) are absent or only minimally present in most AC power systems. The impacts are heating effect and distortion. regards SGR

Hello Guest : I have not had any cooperation from manufacturers of fluorescent ballasts and of desktop PCs,LCD monitors and laser printers . I know that they operate from line to neutral ( 120vac/60hz-N.A. and 240vac/50hz- elsewhere) and generate harmonic currents at their input, in the form of 3rd,5th,7th, etc. I just don't know the magnitude of each . Do you have any documentation or source for this kind of data? Thanks.

signal distort in circuit to produce some mulit-frequencies signal above it.

some times its useful and can be used by us, but most of time it neddnt and harmful

Harmonics generates mostly due to fast switching devices like drives and rectifier units and as mentioned in #2 comments. Harmonics are extremely dangerous for electronic circuitry/cards, can be analyzed with "harmonic analyzer", remedy is usage of power filters before devices like PLCs.

Harmonics not only produce from swithch device, but from most of nonlinean devices, almost all device are nonlinearn, striktly speak.

As I said before, its not terrible sometime. whereas it s very useful. if there is not it sexisting , we can do nothing. under help of it, we can get many goal and equipment.

but some times we have to overcome it.

Dear Sir,

I am completely agree with you, but we have a bad experience over it.

There were frequent problem of electronics cards getting faulty like PLC I/Os,CPUs, firing or gating cards etc., after close monitoring found Harmonic presence in the power CKT. What we had done was just we put Siemens power filters in control power and additionally we installed a delay timer for spike prevention i.e for powering on control power after 20 seconds of main power ON(11Kv). After again monitoring found 90% of harmonics were eliminated and since then the frequency of fault is also cut down tremendously.

Regards,

Syed Zia uddin

oh, can I add one word here? hope dont mind.

every electronic engineers met such trouble in their works. but the proper items would be interference.they have many forms nd have many wide freqency spectrum,especially spike,not only harmonics.

hamonic harm behavier otfen in other eqiupments like reciever and sampler adopter etc.