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#129616 - 06/15/05 03:24 PM Harmonics Again
Dnkldorf Offline
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Registered: 12/12/04
Posts: 1064
Loc: nowhere usa
I am reading where Harmonic currents get trapped in the Delta windings in a D-Y transformer, they circulate and heat them dry transformers up.

Question, Do they ever make it back to the POCO transformers, or do they stay circulating in the SDS transformer?


Dnk.....
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#129617 - 06/18/05 09:29 PM Re: Harmonics Again
renosteinke Offline
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Registered: 01/22/05
Posts: 5316
Loc: Blue Collar Country
I think we have to be careful, as all the various 'models' we use have their limitations.

I would say that, first of all, nothing gets "trapped." Converted to heat or motion, perhaps...but it simply can't just sit there accumulating.

Secondly, we are dealing with AC. While all electricity is invisible- we have to use our imaginations to try to understand it- AC has a few quirks that DC lacks. These quirks exist because AC is always in a state of change- even when nothing is happening. Induction, reactance, impedence, and even capacitance are strongly influenced by this constant flux.

The whole point of harmonics is the effect certain things have on the time something happens....delay some current a little, and it gets added to the current from another phase, thus overloading the neutral. I would say that, at the transformer, where the neutral originates, that all time-affected matters balance out- perhaps generating some heat in the process.

I expect that this "balancing" may not be perfect- that is, the current may not return to being exactly in sync with the voltage. This is 'power factor,' and is something that is sent on to the power company grid. Another facet of "power quality," this is addressed with capacitors.
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#129618 - 07/12/05 08:43 PM Re: Harmonics Again
sierra electrician Offline
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Registered: 02/12/05
Posts: 219
Loc: North Fork, CA USA
>Secondly, we are dealing with AC. While all electricity is invisible-

I've seen it John I swear to god.

Rob
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