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Topic Title: capacitors melted
Topic Summary: any ideas????
Created On: 11 December 2012 06:53 PM
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 11 December 2012 06:53 PM
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aargeitakis

Posts: 141
Joined: 14 July 2005

Hi


I tested some offices yesterday and today. Electricians installed new ring ccts and replaced the ccu last week.
They used to be 2 houses so now they got suspended ceilings with 1200mm x 600mm and 600mm x 600mm fluorescent fittings.
Yesterday I was there and within 30min from switching the lights on, burning smell and smoke came out from one of the fittings. I switched the power off and found that the capacitor from a 1200mm x 600mm melted. That fitting disconnected straight away.
This morning I went back and the same scenario. In the other side of the building another capacitor melted and smoke was everywhere.
They fed from different ccts. The building is empty for a month now and it was very cold inside, about 0 degrees C. The fittings are about 5 years old but in good condition. The electricians used the lights for 3 days, last week without any problems. I check the voltage and it was 241V.
Test results were normal. Capacitors are 16microfarad.

Any suggestion for the reason caused capacitors to melt.
My supervisor believe is a coincidence but I am not agree with him.

Thanks

Paul.
 11 December 2012 07:16 PM
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jamieblatant

Posts: 513
Joined: 11 January 2006

A NETURAL I suspect

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 11 December 2012 07:28 PM
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TeesdaleSpark

Posts: 661
Joined: 12 November 2004

As already suggested check for a loose neutral or maybe condensation.
 11 December 2012 08:33 PM
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aargeitakis

Posts: 141
Joined: 14 July 2005

thanks
for your replies,

there is not condesation.
the lighting ccts are exsisting, so the electricians just move them from the old ccu to new ccu. The capacitors were on different ccts and different mcbs. I ll check the neutrals.

Regards

Paul
 11 December 2012 09:07 PM
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leckie

Posts: 1864
Joined: 21 November 2008

I've never heard of a loose neutral causing a pf capacitor in a fluorescent fitting to burn out and I'm ancient and have connected thousands. I must have made lots of loose neutral but have never once seen a overheated capacitor in one of my installed fittings. Perhaps I've been lucky!
 11 December 2012 09:42 PM
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AdrianWint

Posts: 262
Joined: 25 May 2006

Is this office full of PCs?

I suspect triplen harmonics causing sympathetic 3rd harmonic voltages on a high impedance supply. When 3rd order voltages meet the pfc caps they cause currents to flow in them which are much greater than they would be with just the 50Hz fundamental, hence the caps cook.

Adrian
 11 December 2012 10:04 PM
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leckie

Posts: 1864
Joined: 21 November 2008

That's interesting. So why aren't there more lights frying in office blocks?
 11 December 2012 10:14 PM
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daveparry1

Posts: 6210
Joined: 04 July 2007

I'm still trying to think why a loose neutral would fry a capacitor! If there was a loose connection on the capacitor itself that would be a different matter, quite understandable then,

Dave.
 11 December 2012 10:37 PM
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Ricicle

Posts: 841
Joined: 23 October 2006

I had a spate of pf capacitors burn and smoke in fluorescent fittings recently. One lot was in Tam**** fittings, the other in Crom****. All were fitted at about the same time and all started failing around the same time.
Unless there is severe or regular over voltage I put it down to age.

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 11 December 2012 11:13 PM
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jcm256

Posts: 1867
Joined: 01 April 2006

In the past Investigated a couple of fluorescents caught fire, the cause was lost neutral and whole place was supplied with three phase only. Nearly equal balance saved the day but not the fittings.
Below is only to stimulate your thoughts, rule out unbalanced mains voltages.


http://www.wseas.us/e-library/...u/ACACOS/ACACOS78.pdf

Or use this method:

http://support.fluke.com/find-...18873_6251_eng_b_w.pdf
 12 December 2012 12:02 AM
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aargeitakis

Posts: 141
Joined: 14 July 2005

Hi Adrian,
there are no PC's at the moment, as I said earlier it is empty.
 12 December 2012 12:07 AM
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aargeitakis

Posts: 141
Joined: 14 July 2005

Hi Adrian,

There are not PC's, as i said earlier it is empty.
 12 December 2012 09:51 AM
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AJJewsbury

Posts: 11462
Joined: 13 August 2003

Cheap fittings/bad batch of capacitors? I'd report it to the manufacturer, you might not be the only one.
- Andy.
 12 December 2012 02:02 PM
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Delbot321

Posts: 77
Joined: 06 November 2012

I'd go with either a bad batch of capacitors although unlikely given they've all gone so close together or a neutral problem.

My money is on a neutral problem. Its not a neutral problem within the installation - it will be a joint that has developed a high resistance out on the network. The network being 3 phase - what happens when you loose the neutral with an unbalanced load (which the network is) the voltage goes off all over the place and you can end up with 400v accross the line and neutral.

You may have tested and got 214v but that is a sign that there is a problem already - should be very near 240 - as far as I know they haven't started changeing distribution voltage of regional electricity companies down to 230v yet although we use the 230v as nominal for design purposses. If you can measure it on a gegular basis or use a voltage monitor to do so then you will find its going up and down particularly as the distribuiton network loads change. This can often happen when off peak heating is on as it changes the balance completely.

If you can find evidence of these voltage changes then you'll need to report it to the supply authority as they will need to find the offending joint and repair - also you can claim for damage to equipment caused by their network problem.

Hope this helps.
 12 December 2012 02:24 PM
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AJJewsbury

Posts: 11462
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You may have tested and got 214v but that is a sign that there is a problem already

Didn't the OP say 241V?
- Andy.
 12 December 2012 04:00 PM
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Delbot321

Posts: 77
Joined: 06 November 2012

Your right he did - my mistake - not likely to be neutral then
 12 December 2012 07:02 PM
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colinhaggett

Posts: 364
Joined: 08 July 2004

Is it possible to damage a capacitor doing a insulation test? maybe using to higher test voltage.
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