Cable Voltage Drop Calculation

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Salunkhem Associate Join Date: Feb 2011 Location: Pune, Maharashtra, India Posts: 32 Good Answers: 2	Cable Voltage Drop Calculation 06/15/2011 11:19 AM
	As experts and designers knows that, in cable voltage drop calculation we consider only real part of complete equation i.e. ( I.R.cos (fi) +I.X.sin (fi) ). we are assuming imaginary part of this equation as negligible hence not to consider. Pl. note due to addition of this imaginary part cable size for standard run lengths say 250 mtr. increases. In my openion, in comparison with conventional formula and it's application as standard practice in industry, this new complete equation un-necessarily increases cable size in turn cable cost...moreover wastage of national resources, probably. Whether, it is feasible and techno- commercially right practice to consider complete equation with its imaginary part also? When to use and when not to use this imaginary part? __________________ Engineering is an APPLICATION..
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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	#1 Re: Cable Voltage Drop Calculation 06/15/2011 11:23 AM
	British Standard 7671. __________________ "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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Tornado Guru Join Date: May 2009 Location: Richland, WA, USA Posts: 21017 Good Answers: 795	#2 Re: Cable Voltage Drop Calculation 06/15/2011 10:56 PM
	The angle in question is usually denoted by the Greek letter phi (φ). Depending on your browser, the composing window for CR4 posts includes a special symbol menu, shown by Ω in the tool bar. Selecting this menu allows you to insert such symbols as ©, ≥, ÷, √, →, ¿, and other useful items. Similarly, the x₂ and x² features allow you to insert subscripts (e.g., H₂O), and superscripts (e.g., πr²). __________________ In vino veritas; in cervisia carmen; in aqua E. coli.
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Salunkhem Associate Join Date: Feb 2011 Location: Pune, Maharashtra, India Posts: 32 Good Answers: 2	#3 In reply to #2 Re: Cable Voltage Drop Calculation 06/15/2011 11:13 PM
	My friend! Thanks for your reply but unfortunately this is not answer to my main question. Requested to involve if someone knows correct answer. Pl. note I stated this discussion only for knowledegous elect. Engineers for their expert sharings and not for MS world format editors or English teachers who will just increase their number of posts in forum!! __________________ Engineering is an APPLICATION..
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Tornado Guru Join Date: May 2009 Location: Richland, WA, USA Posts: 21017 Good Answers: 795	#4 In reply to #3 Re: Cable Voltage Drop Calculation 06/15/2011 11:50 PM
	Welcome aboard. Surely you will enjoy yourself here. __________________ In vino veritas; in cervisia carmen; in aqua E. coli.
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North of 60 Guru Join Date: Mar 2007 Location: Iqaluit, NU. Canada Posts: 1854 Good Answers: 140	#5 In reply to #4 Re: Cable Voltage Drop Calculation 06/16/2011 12:04 AM
	Geese Tornado... I guess you were told. Some people's kids! __________________ Joe Contractor to Electrical Inspector, "What do you mean you are going to make me follow the code?".
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Tornado Guru Join Date: May 2009 Location: Richland, WA, USA Posts: 21017 Good Answers: 795	#6 In reply to #5 Re: Cable Voltage Drop Calculation 06/16/2011 12:48 AM
	Somehow I thought the OP's formula was supposed to have an imaginary part. Too bad I am not a "knowledegous" EE, but as a mere "English teacher" I hazard this guess: IR cosφ + iIX sinφ. I haven't yet seen a Code that uses this formula for computing voltage drop, however. __________________ In vino veritas; in cervisia carmen; in aqua E. coli.
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nikolay Power-User Join Date: Dec 2007 Location: Brasov, Romania Posts: 255 Good Answers: 7	#7 Re: Cable Voltage Drop Calculation 06/16/2011 2:16 AM
	As long as the comsumer gets the voltage within the 10% range you can calculate the voltage drop as you wish. Try both ways and see which one gets the lowest value. Use that one for dimensioning the cable. __________________ The time is ......now
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TonyS Guru Join Date: Aug 2010 Location: Resting under the Major Oak Posts: 4347 Good Answers: 181	#8 Re: Cable Voltage Drop Calculation 06/16/2011 4:28 AM
	Salunkhem, if you can't take the banter that goes on between engineers I would suggest you close the door behind you when you leave. __________________ The reports of my death are greatly exaggerated.
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Anonymous Poster #1	#9 Re: Cable Voltage Drop Calculation 06/16/2011 8:43 AM
	I am not a cable designer, only humble EE. But I don't think the formulae that you gave is correct. V = IRCosφ + IX Sinφ The voltage drop is V = IZ = (ICosφ₁+jISinφ₁) (R+jX) (Though Finally if you simplify it to the modulus (non phasor values) and it may simplify to something like V = IZ(Cos(φ₁+φ₂) + jSin(φ₁+φ₂)) = \|IZ\| This is what must be taken for the drop calculation. As far as I know the cable ratings and calculations are dependent on load current (and thus it does take care of the powerfactor of I) and then there are some standard multipliers (must be for the cable reactance). But again it is IMHO since I do not indulge in cables.
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msamad Guru Join Date: Feb 2009 Location: Houston, USA Posts: 946 Good Answers: 244	#10 Re: Cable Voltage Drop Calculation 07/14/2011 9:32 PM
	This thread (especially the comment #12 and #14) may be related to the discussion: http://cr4.globalspec.com/thread/65251/Voltage-Drop-Calculation-for-Single-Phase - MS __________________ "All my technical advices in this forum must be consulted with and approved by a local registered professional engineer before implementation" - Mohammed Samad (Linkedin Profile: http://www.linkedin.com/in/msamad)
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Anonymous Poster (1); msamad (1); nikolay (1); North of 60 (1); PWSlack (1); Salunkhem (1); TonyS (1); Tornado (3)

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