Induction Voltage

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bmadhu_srao Commentator Join Date: Nov 2007 Posts: 86	Induction Voltage 04/23/2009 11:12 AM
	Hi guys, We have laid a 16core, 8sqmm armoured power cable between panel and a centrifuge. Cable distance between them is about 100mt. We have only used 8 cores out of them. Now when panel is powered, we are seeing a voltage of 150volts in the spare unused core. Some suggested that it could be due to inductance. We checked cable insulation and continuity every looks fine. What could be the reason, because we cannot let the machine running with it armoured and Spare cable having voltage in it
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jack of all trades Guru Join Date: Sep 2006 Location: Auckland, New Zealand Posts: 8777 Good Answers: 376	#1 Re: Induction Voltage 04/23/2009 3:35 PM
	Short answer is your likely getting magnetically induced voltages on the unused cores. Grounding the unused cores at one end (which you should have done in this application environment) should fix your problem. __________________ jack of all trades
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sb Guru Join Date: Mar 2007 Posts: 2550 Good Answers: 103	#2 Re: Induction Voltage 04/23/2009 10:23 PM
	It is induced voltage all right- created due to mutual inductance between cables. But makes me wonder . In balanced 3 phase lines this should have been cancelled off. 150V is a bit much, as you are obviously not using high voltage. Why 8 cores being used? __________________ Fantastic ideas for a Fantastic World, I make the illogical logical.They put me in cars,they put me in yer tv.They put me in stereos and those little radios you stick in your ears.They even put me in watches, they have teeny gremlins for your watches
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Chankley Power-User Join Date: Sep 2007 Location: South coast of England Posts: 411 Good Answers: 36	#3 In reply to #2 Re: Induction Voltage 04/24/2009 4:56 AM
	The unused core will not couple equally to all the cores used for the 3 phase supply due to the different spacing between cores. It is highly unlikely that there will be complete cancellation. The unused core will become a current transformer which will generate a high voltage into a high impedance load.
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sb Guru Join Date: Mar 2007 Posts: 2550 Good Answers: 103	#4 In reply to #3 Re: Induction Voltage 04/24/2009 7:02 AM
	The difference in flux linkage will be minimal. And it will be more like voltage Transformer (1:1) ratio than CT. Also on this logic, if the armour is not earthed/ gets its earh disconnected, we should get a high voltage ? Anyway 150V unbalance seems to be a bit high. Some thing seems to be not Ok. Is the load balanced ? __________________ Fantastic ideas for a Fantastic World, I make the illogical logical.They put me in cars,they put me in yer tv.They put me in stereos and those little radios you stick in your ears.They even put me in watches, they have teeny gremlins for your watches
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Anonymous Poster	#5 Re: Induction Voltage 04/24/2009 10:21 AM
	Why not just parallel up your unused conductors. At least it will reduce the resistance and you won't have them just floating. I would also suggest that you get the armor to a good ground.
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Andy Germany Guru Join Date: Sep 2006 Location: Near Frankfurt am Main, Germany. 50.390866N, 8.884827E Posts: 17996 Good Answers: 200	#6 In reply to #5 Re: Induction Voltage 04/24/2009 10:27 AM
	GA as yours was the best answer I read. They should have laid two seperate cables, the problem would have been much reduced, if not completely fixed!! __________________ "What others say about you reveals more about them, than it does you." Anon.
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dhayanandhan Guru Join Date: May 2008 Location: CHENNAI, TAMIL NADU, INDIA. Posts: 1851 Good Answers: 65	#7 Re: Induction Voltage 07/05/2009 4:19 AM
	Mr.bmadhu WHAT WAS THE NEED TO USE 16 CORE CABLE WHEN 8 CORE ALONE IS USED.? You have mentioned only the distance between the machine and board. what was the cable length used.? If it is more than the required if it is coiled to adjust the length, then the induction and hence the problem starts. Sorry for the delay in interacting. DHAYANANDHAN.S
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bmadhu_srao Commentator Join Date: Nov 2007 Posts: 86	#8 In reply to #7 Re: Induction Voltage 07/05/2009 11:20 AM
	Hello every one, This all started, because we had no proper drawing at the time of cabling and it was urgent.We had to lay it based on other centrifuge drawing. Later only 8 cores were used. Since this one was a old one with not many interlocks.It connects two panels through a cable tray and no cable is looped in between. and to my surprise it has glands on both ends both of them are earthed, still we have voltage on unused cores
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