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#129463 - 03/28/05 11:35 AM Harmonics
Dnkldorf Offline
Member

Registered: 12/12/04
Posts: 1091
Loc: nowhere usa
(continued from General issues Thread)

From the site Joe provided under this thread, it provides alot of information for power quality in the future.
I noticed it suggests oversizing nuetrals and grounds, but I can't find any mention of the advantage/disadvantage of solid wire vs. stranded.

Either one of these better than the other for harmonics?

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#129464 - 03/28/05 06:32 PM Re: Harmonics
Scott35 Offline

Broom Pusher and
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Registered: 10/19/00
Posts: 2724
Loc: Anaheim, CA. USA
I wouldn't think Stranded vs. Solid would be a significate issue - but who knows!

Also, the reference to increased Common Grounded Conductor size makes sense, but increased size of the EGC regarding Harmonics doesn't make sense - it's not normally carrying Currents!
If it is, something is - a - wrong - a.

More later.

Scott35
_________________________
Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

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#129465 - 03/30/05 08:04 AM Re: Harmonics
Dnkldorf Offline
Member

Registered: 12/12/04
Posts: 1091
Loc: nowhere usa
Scott, or anyone.

If the 3rd harmonic is at 180hz.

F=1/T

Is this the rate the power supplies are turning on/off "switching", causing this to signal to back to the supply?

Is it true harmonics are negligable"spelling" on single phase "180" supplies vs 3 phase"120" "polyphase" supplies?

"180 degree phases" "120 degree phases"

[This message has been edited by Dnkldorf (edited 03-30-2005).]

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#129466 - 03/30/05 06:40 PM Re: Harmonics
Scott35 Offline

Broom Pusher and
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Registered: 10/19/00
Posts: 2724
Loc: Anaheim, CA. USA
Dnkldorf;

I'll try to address these questions with brief replies.

 Quote:

If the 3rd harmonic is at 180hz.
F=1/T
Is this the rate the power supplies are turning on/off "switching", causing this to signal to back to the supply?


This is more like the "First Odd Order Harmonic" in that Circuit on that System.
It is the beginning of the "Triple-N" scenarios found on the Common Grounded Conductor of a 4 Wire Wye Polyphase System.

A SMPS (Switch Mode Power Supply) "Switches" according to the desired output needed to drive the connected load(s).
It will switch on for a short period of time, then switch off (over and over) to create a certain output Power level (Voltage of "x" level, current of "x" amperes - combined to equal required power level).

Higher power level loads will switch on/off less rapidly than low power draws.

The resulting output looks more like a semi steady DC output, than a series of off and on pulses.
What gets reflected "outward" back into the AC power system, is mostly from the chopping of the Rectified AC input (what is seen at the output), along with the input Rectifier section.

Maybe someone could describe these effects, like as in Waveform Analysis per Fourier's Series and/or Fischer-Hinnen's method, without doing what I would do... make no sense what so ever!

 Quote:

Is it true harmonics are negligable"spelling" on single phase "180" supplies vs 3 phase"120" "polyphase" supplies?


Yes, the accumilative effects of "Triple-N" do not exist on 1Ø Systems - due to the fact there is only one Phase/Waveform dealt with.

Harmonics exist on 1Ø Systems too, they just don't have as extreme of issues - like the 3Ø 4 Wire Wye Systems do with the overloading of Commons (Grounded Conductors) in Balanced, fully-loaded 4 wire multiwire circuits.

[ Old-Rant = On ]
Of course, there is no "180° Phase Offset" in any 1Ø System - nor in any Polyphase (usable) System...
"180° Phase Offset" would result in a 2 Phase System with a Zero level output:
  • Zero Volts,
  • Zero Amperes,
  • Zero Wattage,
  • Zero Volt-Amperes,
  • Zero VARs.

...not a very useful System at all!
[ Old-Rant = Off ]

Scott35
_________________________
Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

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#129467 - 03/31/05 04:18 AM Re: Harmonics
Dnkldorf Offline
Member

Registered: 12/12/04
Posts: 1091
Loc: nowhere usa
Once again I thank you for the info.

If I sound like a knucklehead with these questions, just be firm and tell me to go away.
It has been many years, 20+ since basic electricity and circuit education, and the old saying "if you don't use it, you lose it", is hitting me.

I am going back to brush up on this stuff.

If you, or any one has some helpful links pertaining to the cause/effects of harmonics, and would like to share them with a "greeny", I'd appreciate it.

Dnk.......

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