Harmonic Problem Single Phase

pc --300w, tv set ---300w?

What type of pc and tv are you using? too much power!

THD --1.99 and 1.67? >1?

wht are they? they must be useless machine. are you sure you are not making a mistake at the figures?

that THD more than 1 is that I used % of fundamental, rather than % of RMS.

thats kinda quite confusing.

I was wrong on the PC and TV. PC only 120W. typo error. sorry! heh

We have here a problem with schoolwork. Maybee we can make an exception with thesis.But, you have to do a lot of footwork with data, we do not understand. So, go back, review, and present again. For example, PC THD 199% is flat, I mean flat impossible. You cannot have more distortion in an amplifier than the fundamental. So, please go back, review, represent. Then we can talk sense.

You have to make sure you understand what the thd is?

I don't think you know what it is now.

for example, in a TV set, there are several parts which can have thd concept.

1, power, 2, audio, 3 video. so you have to make clear to us at first.

ask your teach for more details.

today pc use generally 200 --240w. a little box use 300w. but TVs from 60w -- 90w

GO BACK TO SCHOOL

thanks for your replies anyway

for someone with big heart (and maybe big head) helping the others should be something like langlay in the park. easy. and they do that (helping the others) anytime and anywhere. because they like to help people.

but thats not something everybody likes to do and i dont know why. and thats a fact.

for that THD thing, it is current harmonic I meant, and, I have already stated that, I measured with the % to the RMS. meaning, the harmonic readings ratio-ed to the RMS value. if you set your Flukemeter to the % to the fundamental, or %f, then you'll get those big, over 100% value. by the way, I am using one Flukemeter for the measurement because somebody think I am just playing around and not knowing what I am doing. goggle Fluke if you wanted to know more about the meter I am using or just wanted to make sure I dont BS everyone.

that PC on 120W? if anybody bother to try, then find one measurement unit, true rms or whatever you like, clamp the PC cable connected to any 13Amp socket, then you will read that the wattage says 0.12KW, which mean 120W. and that you also can see that harmonic reading on the measuring instrument.

and ahhh.. i just did what one of you told me - read and review things up. I'll answer this one myself.

Lets say, there are 3 PCs connected to 3 difference 13Amp sockets. each of them has its own harmonic (current) with maybe the same magnitude of harmonic. but then, you CANNOT simply add them together. if u insist to know the current harmonic magnitude of the three, connect them to one parallel connector which you can buy at shops. Then, the total THD/ harmonic of the drawn current of the three PCs can be measured.

It is not so hard to help people. certainly if someone dont bother to help me, surely I'll work out the other ways to find the answers.

Good job everyone. keep it up.

drMpower,

I am glad you clarified the way the thd was being calculated for your meter. I have seen thd's much higher than what you stated on variable frequency drive inputs, when measured or calculated as you stated: ∑(% harmonics)/(% base). The method cnpower was thinking of was: ∑(% harmonics)/(∑(% harmonics)+(% base)).

The problem you have in trying to add the thd's when you have more than one load is that some of the individual harmonics orders, one load may be 180° out of phase with another load, while for other orders, one load may be in phase with another load. Therefore the sum will include additive and subtractive components. I hope that this made sense! (I expect the ones which will be 180° out of phase are the even orders of harmonics, so the sum will include only the imbalance of the even orders and the total of the odd orders.)

However, when you add a load with very little thd to one with a large thd, then you can calculate the thd for the sum, because there will not be any significant amount of subtractive orders of harmonics.

I would think that to do a mathematical calculation of the thd on a complex load you would need to have the actual %thd for each order of harmonics. I don't know if your meter can give you this type of information.

Good question!--JMM

Dont vexed any more. I enjoy answer a good question. I know this company for its famous test instuement, but I hvnt ever use any one of them.

I wish I could keep up with fashion, new concept, new idea, but I hve to list the difine of thd as I know, and most of old textbook said so.

thd, generally speaking, give out in the form of power, means useful pwer ratio to general power, it can be behaviored by current as weell as voltage.

one of form is as follow,

THD = SQRT(v2²+v3²+v...)/v1 as well as current instead of.

From this form I think we are in the same way. and from this form, we can get thd more than 1, the signal quality is very worst for audio equipment. and this might take place at some rectifier beginning output terminal.

a moment...

i believe ur test is right,120w,but we define a machine power is according to its max possible. we talk it later, lets back to the subject.

i seem to knwo a little about ur problem.

u must test input terminal current of a set. so that you got so large thd. this is first we met. we ofter deal with amplifier which thd is less than 0.3% or more litle.

at the line of rectifier, the current is very distortion, so that we often use pfc to corrent it. we can talk it later.

its very difficult for calculation in formula of math, its not simple algebraic sum and not simple geometry average, it depends on many factors, for example load features etc. you can try test in practice.

If you are student, you can practse as an exercise. list load sum and split sum current and compare with individual value.

I hvnt ever do such work before.

Switching power supplies can generate extremely high harmonic currents. I have find an interesting article in the EDN a couple of years ago. I have put it onto my server so you can download it from the following link:http://extpic.samunet.hu/Pfc.pdf

For those, who cling to THD (total harmonic distortion) over 100%:

IF what you guys say is really true, then I can take such an (amplifier, whatever), rectify its, say 200% THD, feed that power back to the amplifier, get twice the THD power, rectify, feed back..... Guys, that is the very DEFINITION OF ENERGY FROM NOTHING. Or a perpetuum mobile. Good try, but no taker, even from that angle.

What really is going on, is the use of average voltage / peak voltage and average power / peak power recalculation within the measuring device. To do that, certain assumptions are made that are definitely NOT VALID under just any conditions. The peak ratio to average is one of them.

If you really want to know, what is going on, use an oscilloscope, do the (approximate) integration by hand, and you will find, that:

THERE IS NO THD OVER 100%, but definitely there are misleading measurements.

Leveles,

Go back to my post #7, to see two different ways to calculate THD. If you calculate it as a percent of the total signal, there can never be THD over 100%, but if you calculate it as a percent of the base frequency in the signal, then it can (and often does) easily exceed 100%.

Regarding your "DEFINITION OF ENERGY FROM NOTHING", nope. Each theoretical pass degrades the base frequency into harmonics even more, so the percent of base frequency decreases. There is nothing which indicates that the total output has a greater power or energy content than the input; just that it is increasingly distorted.

--JMM

JMuller

You were (and still are) absolutely right. The whole thrust of my note to the original posting was, that his results energyvise were nonsense, and why the way the measurements are made and converted, matter very much. Handheld devices convert peak to average in one of the possible (assumed) ways, and the user frequently does not know or understand, which and why. Going with a scope, getting the current and voltage recordings, doing the whole thing of getting power out of it by hand gets you the real understanding, of what is going on.

And a perpetuum mobile - I am sorry to say - is still impossible. We all could use one, after all.

Going back to our student: pushing a button and taking a reading does not qualify somebody to wear the title ENGINEER at all. Exploring, and finally understanding a thorny problem does that very well, and will stay with him all his life.