Test question: Harmonics

You also get harmonics from the generator itself. It's a function of the winding geometry and the field pole geometry.

Big John

Well, the iron in a generator is also "non-linear." And there would be "switching effects" when the magnetic field reverses.

I am sure that with over 100 years of experience, the designers have solved these problems but I would be amazed it an alternator that was "thrown together" would have a perfect sine wave output.

nonlinear load?

I'd say it is an unbalanced load..phase to phase...a lot of single phase and 110 on the same gen set...with one winding loaded more than the others... if you added in a non linear load, such as say single phase motors starting and stopping... that could worsen the problem. But if those were *3 phase motors and cycling the load would be non linear but still balanced ..... so there should be no harmonic issues in that case.

Phil Scott

nonlinear load?

there would be

designers have solved

was "thrown

The output should be to the norms regardless how the thing was thrown together since the winding confiration is not an option on assembly.. they are in pre fit locations... no getting around it.

Other harmonic issues related to the amount of metal in the stator etc are not assembly issues but part of the design, cheap or not cheaply built resulting in well knoefficiency curves These would not be variables.

And unbalanced load is a variable..and that will cause harmonics in the gen set beyond what it was designed with.

Phil Scott

The main answer would be the generator design- slots/pole, winding pitch, etc as well as non-linearity in the iron. In a balanced 3 phase machine there will be no triplen (3rd,9th, 15th .. ) harmonics but these can exist in the unbalanced case. Even harmonics will not be present due to half wave symmetry and design is such as to reduce or eliminate the 5th and 7th harmonics. If you touch the input of a scope while waving your other hand in the air (capacitive pickup) - you will see harmonics on the waveform- count them- 11th and 13th generally are the dominant ones. Generally, however, the generated harmonics are quite small and not a problem. Of course non-linear loads can generate harmonics but the question appears to be related to those in the generated waveform.

A well designed generator would not generate significant harmonics on its own (see Don Kelly's post). So if there are harmonics when a load is connected I would say that non-linear loads are responsible. Of course, if the harmonics are present with no load, then it's kind of hard to blame the load, isn't it?? :-)

But a simplistic generator can generate harmonics internally. Using less than an exact pole pitch can reduce some of the higher harmonics, but it sacrifices voltage output at the fundamental. A good machinery text can go into such decision trade-offs.

daestrom

But if those were *3 phase

Any non linear load (balanced or unbalanced) will couse harmonics. Inductive loads with feromagnetic core (non linear B-H characteristic) are always cousing harmonic distorsion, even if they are balanced (ex. transformer with open secondary wingding).