Electrical

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kuppahalli Active Contributor Join Date: Mar 2011 Posts: 22	Electrical 04/09/2015 2:06 AM
	Hi, I have major Induction voltage issues in AHU stater boxes.Let me explain the problem, We have supplied the AHU boxes with star/delta starter & VFD arrangement.we had given the BMS connectivity like potential free contacts feed back had been wired up to outgoing termianals.The problem is if run the starter we found some induced voltage around 70V in the potentital free contacts terminals. we have seperated the BMS wires from the power ckt.hhen also there is around 30-40v olts found in the potential free contacts this induced voltage will damage the BMS control cards at the fields.Kindly help us to comeout from this induced volage in the system regards murali
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rogerggbr Commentator Join Date: Feb 2010 Location: West Yorkshire, UK Posts: 96 Good Answers: 11	#1 Re: electrical 04/09/2015 4:08 AM
	Sounds like you need to be looking at increasing the segregation, screening, changing some of the wiring to screened/twisted, all of the above etc. Have you also considered that you may be seeing the voltage due to very high input impedance on your meter and once earthed the actual energy induced will not be harmful to the BMS? Try decking the wire with a 10K resistor and measuring again for instance. __________________ rogerggbr
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SimpleMind Guru Join Date: Sep 2009 Posts: 1056 Good Answers: 88	#2 Re: Electrical 04/09/2015 5:39 AM
	The most likely source of that induced voltages is the VFD hard switching, VFD's are notorious for that, but this can be controlled using a suitable AC reactor on VFD output. Now I'm still surprised on the voltage level. Are you measuring this voltage relative to ground? This "voltage" is relevant only if the controller side is correctly connected AND grounded, ie NOT floating, else it mostly depends on your instrumentation impedance as rogerggbr said above. S.M. __________________ Life is complex. It has a real part and an imaginary part.
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PWSlack Guru Join Date: Jan 2007 Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on. Posts: 32175 Good Answers: 839	#3 Re: Electrical 04/09/2015 7:54 AM
	If the connection of a 15W tungsten light bulb between the <...potential free contacts...> and the earth/ground connection causes the bulb to light up, then there is a serious fault that warrants de-energising the equipment on safety grounds, followed by repair or replacement as applicable. __________________ "Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
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Yahlasit Guru Join Date: Dec 2008 Location: Cd. Juarez, Chihuahua, Mexico. Posts: 1023 Good Answers: 69	#4 Re: Electrical 04/10/2015 4:30 PM
	Read The Furnished Manuals ! and make sure your circuit is at least as accomplished as the basic application shown in the connection diagrams, installation chapter. Like every body here, I'd start for the type of signal/control cables, power wiring, how to segregate them, ground practices (ground loop avoidance etc.); and finally, to make sure you're not "measuring a ghost" either deck the unused contacts with a 10K resistor as quite correctly sugested by rogerggbr, or put your meter in low impedance mode (LoZ in Fluke). Good luck __________________ No hay conocimiento ni herramienta que sustituya al sentido comun.
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