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muratdeli

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Join Date: Apr 2011

Posts: 7

Single Core Parellel Conductor Current Balance

04/28/2011 10:11 AM

Hello,

at the below picture, you can see my installation. Now sysytem is starting to work. Beginning current is less than nominal current, you can see below table. Cable length, cable cross-section, cable manufacturer, cable termination system are the same. Cable laying on the cable tray. Cable cross-section is 120mmsquare

Do you have any idea why is the current different between cables and what can I do for balance the current?

Regards

Cable	Current	%
L1-1	6,7	11%
L1-2	7,7	12%
L1-3	5,2	8%
L1-4	4,5	7%
L1-5	4,4	7%
L1-6	3,3	5%
L1-7	2,8	4%
L1-8	3,7	6%
L1-9	4,2	7%
L1-10	9,7	15%
L1-11	6	10%
L1-12	4,7	7%
Total	62,9

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#1 "Re: Single core parellel conductor current balance" by rhkramer on 04/28/2011 10:24 AM (score 2)
#2 "Re: Single core parellel conductor current balance" by North of 60 on 04/28/2011 10:37 AM (score 7)
#5 "Re: Single core parellel conductor current balance" by msamad on 04/28/2011 7:13 PM (score 2)

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#3 "Re: Single core parellel conductor current balance" by rhkramer on 04/28/2011 12:50 PM (score 1)
#4 "Re: Single Core Parallel Conductor Current Balance" by jack of all trades on 04/28/2011 4:06 PM (score 1)

rhkramer Guru Join Date: Oct 2010 Posts: 1294 Good Answers: 35	#1 Re: Single core parellel conductor current balance 04/28/2011 10:24 AM
	Just to get my head on straight, I had to convert 120 mm square to AWG or similar--iiuc, thats close to 250 MCM. That's a lot of copper (or aluminum). Does each of those cables have 3 insulated cores of 120mm square conductor? I suspect that because of the arrangement of cables, each "core" sees a pretty significant difference in impedance. If the cables do each have 3 insulated cores, I'd seriously consider running one each of L1, L2, and L3 in each cable. Then I'd try to locate the N (neutral) cables more centered with the L1, L2, L3 cables located as symmetrically as possible around the neutral. (I'm not sure how important this is, or how much effect doing this would have.) If the cables do not have 3 insulated cores, I'd try to relocate each cable to make a more symmetric arrangement, with transitions at intervals along the cable tray where I switch a cable from one location to another--all of this aimed at trying to keep the impedance the same. How much current is in the N (neutral)?
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North of 60 Guru Join Date: Mar 2007 Location: Iqaluit, NU. Canada Posts: 1854 Good Answers: 140	#2 Re: Single core parellel conductor current balance 04/28/2011 10:37 AM
	You have setup the cables in just about the worst possible arrangement for inductive reactance to cause impedance differences in the cables to cause a imbalance of current flow. You need to think about rearranging the cables into... Bundles of 4 conductors, each bundle to consist of "1 L1 + 1 L2 + 1 L3 + 1 N". Each bundle should be separated by at least two cable diameters. You might want to take a look at the Appendix B notes to CEC rule 12-108 for more info. __________________ Joe Contractor to Electrical Inspector, "What do you mean you are going to make me follow the code?".
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rhkramer Guru Join Date: Oct 2010 Posts: 1294 Good Answers: 35	#3 In reply to #2 Re: Single core parellel conductor current balance 04/28/2011 12:50 PM
	Good answer (better than mine). After I read yours I went looking for the CEC on line. Didn't find it, but found this, which gets quite deep, but might be worth the OP's time to at least skim: A CABLE CONFIGURATION TECHNIQUE FOR THE BALANCE OF CURRENT DISTRIBUTION IN PARALLEL CABLES
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msamad Guru Join Date: Feb 2009 Location: Houston, USA Posts: 946 Good Answers: 244	#5 In reply to #3 Re: Single core parellel conductor current balance 04/28/2011 7:13 PM
	The answers from both "North of 60' and "rhkramer" are good. CEC (C22.1-09) Appendix B (notes to rule 12-108 and rule 4-008) clearly illustrates this topic with figures. While NEC simply applies the condition for single conductor installation in article 392.8(D) which is "Where single conductor cables comprising each phase, neutral, or grounded conductor of an alternating-current circuit are connected in parallel as permitted in 310.4, the conductors shall be installed in groups consisting of not more than one conductor per phase, neutral, or grounded conductor to prevent current imbalance in the paralleled conductors due to inductive reactance. …" This previous thread also may help: http://cr4.globalspec.com/thread/41241/Laying-of-Multiple-Cables-for-Each-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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jack of all trades Guru Join Date: Sep 2006 Location: Auckland, New Zealand Posts: 8777 Good Answers: 376	#4 Re: Single Core Parallel Conductor Current Balance 04/28/2011 4:06 PM
	Oh boy, as per comments in post #2 above you need to change your terrible cable configuration, quick! __________________ jack of all trades
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Tornado Guru Join Date: May 2009 Location: Richland, WA, USA Posts: 21017 Good Answers: 795	#6 Re: Single Core Parellel Conductor Current Balance 04/28/2011 9:36 PM
	I couldn't find L4, L5,..., L12 in the picture, which is a weird layout, anyway; as already noted. __________________ In vino veritas; in cervisia carmen; in aqua E. coli.
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rhkramer Guru Join Date: Oct 2010 Posts: 1294 Good Answers: 35	#7 In reply to #6 Re: Single Core Parellel Conductor Current Balance 04/28/2011 11:15 PM
	If you look at any one of the cables (in the picture) it looks like they are each a 3 conductor cable. There are 4 such cables for each phase (L1, L2, and L3) and the neutral. So that (I believe) is how he gets L1-1 thru L1-12, and likewise for the other phases. His table only shows the currents fro L1.
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North of 60 Guru Join Date: Mar 2007 Location: Iqaluit, NU. Canada Posts: 1854 Good Answers: 140	#8 In reply to #7 Re: Single Core Parellel Conductor Current Balance 04/28/2011 11:59 PM
	From his drawing, I understood that he had 12 single conductor 120 sq/mm conductors. __________________ Joe Contractor to Electrical Inspector, "What do you mean you are going to make me follow the code?".
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rhkramer Guru Join Date: Oct 2010 Posts: 1294 Good Answers: 35	#10 In reply to #8 Re: Single Core Parellel Conductor Current Balance 04/29/2011 7:02 AM
	Well, I guess he (the OP, muratdeli) needs to tell us. My clues were the table with L1-1 thru L1-12 and the three circles in an equilateral triangle spaced across the cable tray. If he does come back and respond, I'd like to also know what the units of current are--he has percents, and then currents that look like they are very low. I mean like 6,7; 7,7; 5,2, ...--are those 6.7, 7.7, 5.2, ... amps?
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North of 60 Guru Join Date: Mar 2007 Location: Iqaluit, NU. Canada Posts: 1854 Good Answers: 140	#11 In reply to #10 Re: Single Core Parellel Conductor Current Balance 04/29/2011 9:52 AM
	Agreed... I am pretty sure those are amps. In some languages, it is common to use a comma instead of a decimal to indicate a number like 6.5. He more then likely put a small load (was not the total in the 65 amp range) on the parallel sets to check the distribution of current. Good thing he did so, if he were to load this setup to its design loading, the inductive reactance and the current imballance would be far worse then what he presented to us in his only post (hey there OP... join the conversation or we will drop it). Given the imballance shown with only 60 some odd amps of loading... a failure in one or more of these conductors, once loaded at desing amperage, is a real possibility. Sounds to me like the engineer of record for this project needs his head shaken and his arse booted. It is clear, IMHO, that the EE on this job needed to have ensured that the installation contractor was aware of the need to arrange the cables in the tray properly. As well, given the load this setup was meant to carry, why was not bus duct specified? __________________ Joe Contractor to Electrical Inspector, "What do you mean you are going to make me follow the code?".
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rhkramer Guru Join Date: Oct 2010 Posts: 1294 Good Answers: 35	#12 In reply to #11 Re: Single Core Parellel Conductor Current Balance 04/29/2011 11:23 AM
	Good point--yes, that was probably a small test load.
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muratdeli Member Join Date: Apr 2011 Posts: 7	#15 In reply to #11 Re: Single Core Parellel Conductor Current Balance 04/30/2011 5:37 PM
	Dear North of 60, thank you for your all response. Sorry for my late answer I try to solve my problem. I'll add a new post and describe my new stiuation.
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muratdeli Member Join Date: Apr 2011 Posts: 7	#14 In reply to #10 Re: Single Core Parellel Conductor Current Balance 04/30/2011 5:30 PM
	Dear Rhkramer, thank you for your all response and sorry for my late answer as you see I have a big problem and try to solve. Yes 6,7 mean is 6.7 amps and total current is very low now.
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Shyam Guru Join Date: Aug 2006 Location: AM-51, Deen Dayal Nagar, Gwalior, Madhya Pradesh, MP 474001, India Posts: 3418 Good Answers: 32	#9 Re: Single Core Parallel Conductor Current Balance 04/29/2011 12:02 AM
	None of the cable pair used by you are identical. Looks like they are not of standard grade. __________________ Prof. (Dr.) Shyam, Managing Director for Sensors Technology Private Limited. Gwalior, MP474001, India.
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marcot Guru Join Date: Feb 2008 Location: Montreal, Canada. Posts: 1372 Good Answers: 80	#13 Re: Single Core Parellel Conductor Current Balance 04/30/2011 1:25 PM
	You are all assuming that the line voltages are equal and that the load is balanced. They are more likely the cause for the current imbalance. The OP should use a good meter to verify the line voltages and re-connect the load on different phasing to insure that the imbalance is really from the cable layout. __________________ Experienced is earned, common sense is taught, both are rare essentials of life.
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muratdeli

Member

Join Date: Apr 2011

Posts: 7

#16

Re: Single Core Parellel Conductor Current Balance

04/30/2011 7:05 PM

First thank you for all good comment and sorry for my late answer. I have three installed line. First at the upstream and it is 230 meter long. May be the best way is the bus duct application. But it is not very practical according to site conditions.

2. and 3. lines are between transformer and LV distrubition panel. They are 24 meter long.

2. and 3. lines conductor are the same. Single core 120 sq/mm copper.

You can see below picture and table how are the currents before and after your comments. All values are measured by 2 clamp meter and total measure period for 1 group 5-10 min.

As you see you are right 1 L1 + 1 L2 + 1 L3 + 1 N better then mine

I want to ask a new question. All currents are very small at now but later increase to nominal current. At now (small current) there are %5(for example) difference between two conductor when the currents increase what about the ratio?

Regards

		TR1
		Total Power(kW)	Length(m)	Cable/Ph	Nominal Current	Per Cable Current(A)	Cable Capacity(A)
		1440	24	8	2312,14	289,02	308

BEFORE						AFTER

Cable	Current(A) (measured)	Ratio to total current	At Nominal Current(A)			Cable	Current(A) (measured)	Ratio to total current	At Nominal Current(A)
L1-1	13	6%	137,88			L1-1	22,4	13%	304,66
L1-2	16	7%	169,70			L1-2	23,5	14%	319,62
L1-3	14	6%	148,49			L1-3	19,5	11%	265,22
L1-4	28	13%	296,97			L1-4	22,6	13%	307,38
L1-5	28	13%	296,97			L1-5	17,5	10%	238,01
L1-6	43	20%	456,06			L1-6	21	12%	285,62
L1-7	30	14%	318,18			L1-7	19,5	11%	265,22
L1-8	46	21%	487,88			L1-8	24	14%	326,42
Total	218		2312,14			Total	170		2312,14

						Cable	Current(A) (measured)	Ratio to total current	At Nominal Current(A)
						L2-1	19,5	13%	309,24
						L2-2	23,3	16%	369,50
						L2-3	17,7	12%	280,69
						L2-4	16,8	12%	266,42
						L2-5	18	12%	285,45
						L2-6	20	14%	317,17
						L2-7	15,3	10%	242,63
						L2-8	15,2	10%	241,05
						Total	145,8		2312,14

						Cable	Current(A) (measured)	Ratio to total current	At Nominal Current(A)
						L3-1	15	11%	260,18
						L3-2	17,3	13%	300,08
						L3-3	19,6	15%	339,97
						L3-4	16,5	12%	286,20
						L3-5	16,5	12%	286,20
						L3-6	16,1	12%	279,26
						L3-7	14,1	11%	244,57
						L3-8	18,2	14%	315,69
						Total	133,3		2312,14


		TR2
		Total Power(kW)	Length(m)	Cable/Ph	Nominal Current	Per Cable Current(A)	Cable Capacity(A)
		900	24	5	1445,09	289,02	308

BEFORE						AFTER

Cable	Current(A) (measured)	Ratio to total current	At Nominal Current(A)			Cable	Current(A) (measured)	Ratio to total current	At Nominal Current(A)
L1-1	18	15%	216,76			L1-1	35	25%	366,51
L1-2	18	15%	216,76			L1-2	26	19%	272,26
L1-3	36	30%	433,53			L1-3	27	20%	282,73
L1-4	24	20%	289,02			L1-4	23	17%	240,85
L1-5	24	20%	289,02			L1-5	27	20%	282,73
Total	120		1445,09			Total	138		1445,09

Cable	Current(A) (measured)	Ratio to total current	At Nominal Current(A)			Cable	Current(A) (measured)	Ratio to total current	At Nominal Current(A)
L2-1	19	15%	212,84			L1-1	30	19%	269,27
L2-2	25	19%	280,06			L1-2	32	20%	287,22
L2-3	32	25%	358,47			L1-3	30	19%	269,27
L2-4	21	16%	235,25			L1-4	34	21%	305,17
L2-5	32	25%	358,47			L1-5	35	22%	314,15
Total	129		1445,09			Total	161		1445,09

Cable	Current(A) (measured)	Ratio to total current	At Nominal Current(A)			Cable	Current(A) (measured)	Ratio to total current	At Nominal Current(A)
L3-1	18	21%	298,98			L1-1	31	20%	294,72
L3-2	24	28%	398,64			L1-2	30	20%	285,21
L3-3	13	15%	215,93			L1-3	30	20%	285,21
L3-4	16	18%	265,76			L1-4	26	17%	247,19
L3-5	16	18%	265,76			L1-5	35	23%	332,75
Total	87		1445,09			Total	152		1445,09

North of 60 Guru Join Date: Mar 2007 Location: Iqaluit, NU. Canada Posts: 1854 Good Answers: 140	#17 Re: Single Core Parellel Conductor Current Balance 05/01/2011 3:18 AM
	I think you are cutting it a little to close. The amount of inductive reactance will increase as the current increases. It is not a straight ratio from your test to what the cables will see when under full load. You may want to think about adding one more set of conductors to the parallel runs. I would. __________________ Joe Contractor to Electrical Inspector, "What do you mean you are going to make me follow the code?".
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Good Answers:

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#1 "Re: Single core parellel conductor current balance" by rhkramer on 04/28/2011 10:24 AM (score 2)
#2 "Re: Single core parellel conductor current balance" by North of 60 on 04/28/2011 10:37 AM (score 7)
#5 "Re: Single core parellel conductor current balance" by msamad on 04/28/2011 7:13 PM (score 2)

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#3 "Re: Single core parellel conductor current balance" by rhkramer on 04/28/2011 12:50 PM (score 1)
#4 "Re: Single Core Parallel Conductor Current Balance" by jack of all trades on 04/28/2011 4:06 PM (score 1)

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Users who posted comments:

jack of all trades (1); marcot (1); msamad (1); muratdeli (3); North of 60 (4); rhkramer (5); Shyam (1); Tornado (1)

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