Harmonics in power systems

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vinod

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Can anybody explain to me about Harmonics in electrical power system? How we can define Harmonics? how it will inpact on power system? How can we reduce the Harmonics? What is 1st Harmonics, 2nd Harmonics,Hrd harmonics, etc..? If there is any informative web site, Kindly give to me the address.
 
Perform a search on this Forum. You will get lots of topics covering this issue. Or, google the topic.

This forum is more designed to handle specific questions on speciifc installations or situations. Your questions are so broad that simple responses wouldn't be suffiicent for your total understanding of the subject matter.
 
There is a lot of information out there, but most of it comes from sources with a vested economic interest in solving the "harmonic" problem. This is not to say that there are not problems cause by harmonics, but in the experience of most of us the problem in no where near as widespread as many documents suggest.
Don
 
Don brings up a good point. While the internet has provided the world an incredible amount of information it is also full of tons of mis-information.

Try to stay away from websites that are trying to sell a product while educating you (convince) on why that product is so important.
 
I posted the following information on this Forum before, and I kept the Word file. So it will take me no effort to post it again.
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First of all, you should keep in the back of your mind that harmonics are pure fiction. They do not exist. They are a mathematical model of a real situation, but they are not real in themselves. The "real situation" that they are modeling is a voltage or current curve that does not look like a pure and simple sine wave.

What do I mean by "pure and simple sine wave"? I mean that every peak is constant in height, every valley is constant in depth, the time intervals between peaks and valleys are the same for every cycle, and the curve is smooth. But for some loads, the ones we call "non-linear," the voltage and/or current waves look jagged or clipped or otherwise just plain weird. From the start of one cycle to the start of the next, there is not one smooth positive half and one smooth negative half. Rather, there are lots of miniature peaks and valleys along the way to what should be a single positive peak, and lots more along the way to what should be a single negative peak.

Some brilliant mathematician long ago figured out that any weird wave form can be imitated, as closely to the original as you like, by adding together the following, pure and simple, sine waves:
  • One sine wave based on 60 hertz,

  • [*]Plus another sine wave based on 2 times 60 hertz,
    [*]Plus another sine wave based on 3 times 60 hertz,
    [*]Plus another sine wave based on 4 times 60 hertz,
    [*]Plus another sine wave based on 5 times 60 hertz,
    [*]Plus another sine wave based on 6 times 60 hertz,
    [*]Plus as many others as you need to make your imitation waveform look like the original.

What you do to determine the amount of harmonics is to calculate how much of the 120 hertz, and how much of the 180 hertz, and how much of the 240 hertz, and how much of the others, you need to put together, to get a close enough approximation of the original signal. Therefore, "harmonics" is simply a mathematician's tool for approximating a weird looking waveform through the addition of a bunch of "more normal looking" sine waves.

The "first harmonic," or "fundamental frequency," is 60 hertz.
The "second harmonic" is 120 hertz, or 2 times 60.
The "third harmonic" is 180 hertz, or 3 times 60.
The "fourth harmonic" is 240 hertz, or 4 times 60.
etc.
 
charlie said:
First of all, you should keep in the back of your mind that harmonics are pure fiction. They do not exist. They are a mathematical model of a real situation, but they are not real in themselves. The "real situation" that they are modeling is a voltage or current curve that does not look like a pure and simple sine wave.
Click to expand...
Charlie
you need to explain you self on this. If they don't exist, then why do I get
a reading with my harmonic clip on showing values of 1st, 3rd, 5th etc?


Vinod
read this article http://www.dranetz-bmi.com/pdf/harmonicsall.pdf.
 
Charlie BRILLIAN....SERIOUSLY BRILLANT

What do I mean by "pure and simple sine wave"? I mean that every peak is constant in height, every valley is constant in depth, the time intervals between peaks and valleys are the same for every cycle, and the curve is smooth. But for some loads, the ones we call "non-linear," the voltage and/or current waves look jagged or clipped or otherwise just plain weird. From the start of one cycle to the start of the next, there is not one smooth positive half and one smooth negative half. Rather, there are lots of miniature peaks and valleys along the way to what should be a single positive peak, and lots more along the way to what should be a single negative peak.
Click to expand...

Very to the point, I expend myself with twice the verbage and get no where close to this.
 
Vinod,
Harmonics,at least 3rd order harmonics (the ones that add up and burn neutrals) are caused by electronics. When we use ac to power electronic ballasts, freq drives contols, printers and computers etc. etc. the load device actually needs DC, so these items change our AC to a useful DC. when this happens the AC sine wave is not used completely. The remains are a distorted sine wave that must come back on the neutral. "Triplen" (third order harmonics) are additive so, while the branch wire of each circuits may be okay, when the circuits come together at the neutral and the harmonics add up it is to much for a standard neutral to carry and over time they over heat and potentially burn up. We try to compensate with a super neutral
I hope this simple explanation is useful
Tom
 
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bob said:
Charlie, you need to explain you self on this. If they don't exist, then why do I get a reading with my harmonic clip on showing values of 1st, 3rd, 5th etc?
Click to expand...
You get a reading because your test equipment is able to extract the numbers I spoke of earlier. It is designed to perform the mathematical manipulations, and to present the results in terms of the content of each harmonic.

The only things about harmonics that are ?real,? or that represent ?truth,? are the facts that voltage and current vary from moment to moment, that they repeat the same pattern from cycle to cycle, and that the pattern is not that of a pure and simple sine wave. To decompose that strange pattern into a sum of sine waves is a mathematical manipulation that gives us nothing more than a mathematical model of a real situation.
 
bob said:
Charlie
you need to explain you self on this. If they don't exist, then why do I get
a reading with my harmonic clip on showing values of 1st, 3rd, 5th etc?
Click to expand...

I will try making the point in a slightly different way:

Harmonics are not some _separate_ physical thing running in the wire; rather you have _one_ thing: a voltage (or current) which changes in time. If you were to graph this voltage (or current) versus time, you would see the 'wiggle' of a waveform. In the ideal case for power distribution, this waveform is a pure sinusoid. However in the real world this waveform probably has a more complex shape.

Harmonic analysis can be used to describe this complex shape. In much the same way that moving 14 miles North-East can be described in terms of moving 10 miles North and 10 miles East, any waveform can be described as the sum of a number of sinusoids. You have only a _single_ waveform with a complicated shape, but you are describing it as the sum of several separate waveforms; just like taking a _single_ trip North-East but describing it as several trips in your 'basis' directions.

To the extent that you have _one_ waveform but are describing it as a sum of many, the basis waveforms are simply mathematical fiction.

However harmonics are very real in the following fashion: in the case of electrical power distribution, it is a very good approximation that the way a system responds to a complex waveform can be described by figuring out how it will respond to the basis sinusoids, and then adding up the responses.

So, for example, in the real world you have a voltage waveform that could be described as the sum of fundamental plus third harmonic. You figure out how the system draws current to 'pure' fundamental voltage, and how the system draws current to 'pure' third harmonic voltage, and add these two responses up, and you have a very good approximation to the net current drawn by the system. Still only one system, and one complicated voltage waveform, and one complicated current waveform. But you figured it out by thinking of the basis sinusoids.

To the extent that this approximation holds, you can actually think of the basis sinusoids as separate physical things in the wire.

You can measure the voltage waveform, and calculate the amplitude of the basis sinusoids that make up the real waveform. You can design systems to explicitly respond to one component but not others. Various components can cause problems on electrical systems. The mathematical 'fiction' of harmonic decomposition can be expressed in physical form, and thus take on physical meaning.

But you still only have one complex voltage or current waveform that is being 'broken down' in to the harmonics.

-Jon
 
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