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picotube
Joined: 24 Sep 2004
Posts: 86
Helped: 4
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 21 Oct 2004 18:58 Does even harmonic have some special characteristics? |
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I attended a class on power harmonic couple of years ago. The presenter shared one of his experience, which I think it's interesting, that he gained during his visit to a Canadian university (if my memory is not corrupted yet  ). In the university, a guy (probably a professor) showed him some interesting phenomenon regarding the measurement of even and odd harmonic current using a current clamp (hall effect type, non-custom-made, i.e. available in the market). When the current clamp was placed around a conductor/wire that carried EVEN harmonic current ONLY, he could not 'remove' the clamp from the wire because the jaws of the clamp could not be opened. He told us that it's like a strong 'magnetic force' that hold the jaws together. This 'strange' phenomenon did not happen when the current clamp was installed around a wire that carried ODD harmonic current.
Has anyone ever heard about this before? If YES, would you please share your experience or provide links to those sites?
Thank you very much.
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golfbumb
Joined: 29 Sep 2004
Posts: 40
Helped: 5
Location: California
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| 21 Oct 2004 23:21 Re: Does even harmonic have some special characteristics? |
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Odd harmonics superimposed on a fundamental wave create resulting waveforms that are symmetrical about zero, i.e., have no net DC offset. Examples of this are the square wave (which is the sum of all odd harmonics) and the triangle wave. The average AC current over time is therefore zero. Ampere's law states that the magnetic field around the wire is a function of the current flowing through it. The net magnetic field is zero since the magnetic field is reversing with the current, as the wave reverses polarity. This net magnetic field keeps zero net force on the ferromagnetic pickups of the "amp clamp."
Even harmonics superimposed on a fundamental wave create non-symmetrical waveforms. The sawtooth wave, for example, is the sum of all harmonic waves, both odd and even. The resulting waveform has an offset off of the zero line. This offset causes a continuous net current to exist and, therefore, a net magnetic field to exist. This net magnetic field, in turn, circulates through the ferromagnetic clamps of the "amp clamp" in your picture and keep them held tight.
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djalli
Joined: 10 Nov 2001
Posts: 887
Helped: 15
Location: 1600 Pennsylvania Avenue, Washington DC 20500
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| 22 Oct 2004 6:15 Does even harmonic have some special characteristics? |
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golfbumb above mentioned square wave sum of all odd harmonics. It is not only for sqare wave but for all waves composed by these harmonics to have stange phenomena like in case of sqare wave you have Gibbs Ears. It happens mathematically and so in reality.
So expect strange phenomena.
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