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#214865 - 02/01/15 01:29 PM Inductive loads  
ANNEMARIE  Offline
Member
Joined: Oct 2012
Posts: 39
DORSET UK
Hi all I've seen it stated that an inductive load like a fluorescent lamp with conventions ballast will put some power back into the supply at or near the zero of the mains cycle. Is this in the form of a pulse that is there for a fraction of a second or is it actually usable by other loads on the same phase. And does it have an effect on the energy meter. Thanks in advance guys I'm having real trouble getting my head around this


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#214867 - 02/01/15 05:35 PM Re: Inductive loads [Re: ANNEMARIE]  
gfretwell  Offline


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Joined: Jul 2004
Posts: 9,099
Estero,Fl,usa
This is more just that the current and the voltage are not in phase so you can end up with undesirable current on the neutral. It is most pronounced in 3 phase. At the time when resistive loads are at the peak, the inductive load on another phase is piling on and be adding to the resistive load, burning up the neutral.

It you google up "triplen harmonics", there are plenty of articles about it.


Greg Fretwell

#214868 - 02/01/15 06:44 PM Re: Inductive loads [Re: gfretwell]  
ANNEMARIE  Offline
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Joined: Oct 2012
Posts: 39
DORSET UK
Thanks for that gfretwell I think I got it now its that inductive loads create harmonics and it's these that circulate round and make a nuicence of themselves


#214869 - 02/01/15 08:16 PM Re: Inductive loads [Re: ANNEMARIE]  
winston_1  Offline
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Joined: Jul 2008
Posts: 24
London, UK
Inductive loads don't create harmonics.


#214870 - 02/01/15 08:30 PM Re: Inductive loads [Re: ANNEMARIE]  
ANNEMARIE  Offline
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Joined: Oct 2012
Posts: 39
DORSET UK
It looked like that's what the article gfretwell pointed me too said I guess its a combination of fluorescent tube and choke makes all these extra frequency's multiples of 50 cycles otherwise how can you explains the answer to my original question thanks


#214872 - 02/01/15 08:52 PM Re: Inductive loads [Re: ANNEMARIE]  
gfretwell  Offline


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Joined: Jul 2004
Posts: 9,099
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All inductive loads are not created equal but when you are talking about electronic ballasts and PC power supplies (switchers) you are talking about harmonics.


Greg Fretwell

#214873 - 02/01/15 09:13 PM Re: Inductive loads [Re: ANNEMARIE]  
ANNEMARIE  Offline
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Joined: Oct 2012
Posts: 39
DORSET UK
Yes I think I got it now its all to do with non linear loads and the fact that current flow stops before the zero volts point this creates a little back EMF but of course it happens 100 times per second therefore there are 100 little pulses per second right?


#214875 - 02/02/15 01:18 AM Re: Inductive loads [Re: ANNEMARIE]  
gfretwell  Offline


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Joined: Jul 2004
Posts: 9,099
Estero,Fl,usa
It is not really back EMF, it is a harmonic. These switching power supplies run at very high frequencies and they generate harmonics. The 3d harmonic just ends up adding to the current on a given phase.


Greg Fretwell

#214876 - 02/02/15 02:03 AM Re: Inductive loads [Re: ANNEMARIE]  
Trumpy  Offline


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Joined: Jul 2002
Posts: 8,217
SI,New Zealand
AnnMarie,
If you're talking about a standard wire-wound ballast and switch type starter, then harmonics don't really come into the equation.
It's really only when you get into the phase-chopping aspects of electronic ballasts that harmonics become a thing.


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#214880 - 02/02/15 11:18 AM Re: Inductive loads [Re: ANNEMARIE]  
ANNEMARIE  Offline
Member
Joined: Oct 2012
Posts: 39
DORSET UK
I know that electronic PSU put all sorts of rubbish on their mains input your only got to go near one with a AM radio and you hear all sorts of squeeks and whistles and I appreciate they also create harmonics of the mains 50 or 60 cycle fundamental frequency. I think that inductive loads also put out a small pulse of energy as the waveform gets near zero this is not as you say a harmonic as such just a low level pulse I hope this isright. Sorry to labour the point im just trying to get it in my head


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