Harmonics

They exist!

Can I assume you mean on an AC mains supply? Or do you mean a guitar string!

Any load which takes current pulses in sync' with the mains frequency will alter the shape of the wave form. Fourier analysis basically says any waveform can be expressed as the sum of harmonics....so there you have it.

The original 'pure' mains has it's fundamental frequency, all the other harmonics just happen to have amplitude=0 !

Distort the waveform and the other harmonics suddenly show up with !

Now...the guitar string...press lightly at some point on the string.....

Harmonics usually arise in a 3 phase 4 wire unbalanced system. When the three phase load is unbalanced and the neutral carries the portion of the unblanced current both in magnitude and phase angle.

When the current in the neutral is out of phase with the voiltage due to reactive loads the haramics can occur. One of the main causes in basic installations was excessive magnetic dischagre lighting loads where the PF was partially corrected within the fittings.

Harmonics are nothing but distortion in sinusoidal wave form which is generated from 03 phase system where you have a conversion of 3 phase ac converted to dc voltage or from dc to ac in which a thyristor is used and is due to firing of thyristors . generally harmonics are from 01 - 7 in this 3 rd and 5 th harmonics are not safe as the amplitude of these harmonics are high . To nullify this we have to use harmonic filters Of suitable design .

Harmonics are generated from power thyristors which is more then 500 kw and suppose you connect your load through Disel generator suply your alternator winding may get effected.To reduse the harmonic effect we have to use harmonic filters

Why third or fifth harmonics are mostly preferred for further studies?

In simple terms Harmonics are different wave forms generated in addition to the desired weave forms ,when electronic Inverters ,Frequency converters etc are used as generators .you can get a better idea with the following link.

http://www.copper.org/applications/electrical/pq/issues.html

Distortion in sine or cosine wave is harmonics. This often come from saturation of transformer core by over drawing of power, using load which does not consume power uniformly throughout the AC cycle and even some time pumps back stored power from sources like inductor. Harmonics also come from resonant frequencies of the load. In Inverters and UPS when you have square wave output means it has all frequencies above switching frequencies embedded in the harmonics. If you are good at Calculus then look at Fourier Transforms and De Moivre's theorem etc.

http://en.wikipedia.org/wiki/De_Moivre's_formula

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

Thank you for providing a brief but informative answer, clarifying the topic very well.

In our word harmonics is information or knowledge about the world. Each interaction to any object puts its signature on the incident energy that interacts with it and then we know about it from the harmonics or changes in its original rhythm. Think of Doppler effect which is direct measurement of velocity of another object using the harmonics or frequency shift in the main incident frequency.

Harmonics are disturbances represented by vibrations shown some time in electrical signal form. However, harmonics are possible in many forms including mechanical vibrations of sound, in visible and invisible light as Raman Effect and so on.

In nonlinear systems, one frequency gets converted into all multiple frequencies of multiple higher frequencies f, 2f, 3f, 4f etc and these are all harmonics which may be used or may be cause of problems. Your vehicle on road generates a lot of sound that you can hear are harmonics from such a slow motion generated by mechanical stimulation of natural frequencies of the objects. Heat energy is molecular vibrations and is see as Planks Black Body Radiation Spectrum. Our brain learns, stores and recalls information using natural frequencies and harmonics.

There is one simple word that I know is that harmonics is knowledge for all intelligent systems.

Other sources of harmonics on power sine wave might be flourescent lighting which draws current at the peak of the waveform, and triac controlled light dimmers which chop the waveform to reduce power.

Yes, these loads do not draw power uniformly. CFL usually draws power uniformly as these devices have internal high voltage DC power supply from which they derive power for their high frequency oscillator. Hence, CFL are not a bad load. However SCRs are worst kind of loads as power is switched in a part of the cycle. Zero-cross triac relays are somewhat better as they switch when power crosses zero volts and hence cause minimum harmonics of about 10% to 20% of the peak voltage and for a very short time.

On the effects of harmonics, I wish to share information with CR4 forum, [gathered from the website <www.aimeurope.com>], as quoted below:

"The main effects of voltage and current harmonics within the power system are:-

• Amplification of harmonic levels resulting from series and parallel resonance;
• Reduction of efficiency of power generation, transmission, and utilization;
• Aging of the installation of electrical plant components and as a consequence the shortening of their useful life;
• Plant mal-operation;
• Malfunctioning and failure of electronic equipment;
• Overheating and failure of electric motors;
• Overloading, overheating and failure of power factor correction capacitors. Resonance due to interaction of capacitors with harmonics;
• Overloading and overheating of distribution transformers and neutral conductors;
• Excessive measurement errors in metering equipment;
• Spurious operation of fuses, circuit-breakers and other protective equipment;
• Voltage glitches in computers systems resulting in lost data. Excessive flicker on VDU's;
• Electromagnetic interference with TV, radio, communication & telephone systems;
• Damage and disruption to standby generators and associated AVR control equipment;
• Interference with ripple control systems."