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21st Nov 2019 Login  
How long Cable run?
by CL at 2008-09-29 13:58:56 (Forum::Public::Wind)
How long is the cable between the turbine and your inverter
Hi all,

I have a Proven 6Kw on a 15m Mast, the cable run from my Turbine to my inverter is about 160m, I'm starting to thing this might be a bit long and I might be losing some voltage, what length of cable runs do other members have and what is the recommended maximum?

Thanks

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CJL

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How long Cable run? CL - 2008-09-29 13:58:56
Re: How long Cable run? Stuart - 2008-09-29 15:53:31
Mine is 110m long!
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Stuart
Re: How long Cable run? Colin - 2008-09-29 18:03:13
160m is okay - I've seen installations in excess of 250m. Yes, you do lose a little. The cable that you want to be short is the one from the inverter to the grid connection - since you want a very low voltage drop on that section.
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Quisling
Re: How long Cable run? Simon Ridout - 2008-09-29 19:07:06
136 metres, no concerns
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Simonridout
Re: How long Cable run? Ted Marynicz - 2008-09-30 20:36:39
Mine is 450m and we used 16mm2 cable.

If you have used 10mm2 cable then the volt drop will be 4.0 mV/A/m. So at 20A over 160m you will be losing 12.8V.

With 16mm2 cable the volt drop is 2.5 mV/A/m giving you a volt drop of 8V at 20A over 160m.

The thicker the cable the lower the volt drop.

ted

Re: How long Cable run? CL - 2008-09-30 22:03:23
Thanks Guys

I must check what sort of cable was used, The run form the inverter to the Meter bos is about 12m so hopefully that should be OK?
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CJL

Re: How long Cable run? Stuart - 2008-10-01 09:40:57
I assume Proven specify the 16mm cable, so you should have that.
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Stuart
Re: How long Cable run? Bryan Rendall - 2008-10-26 18:19:17
Hi Ted,

Minor flaw in your calcs here... The voltage drop is considered across the 3 phase AC cable, unless you have the rectifier at the turbine, which although possible, would be very unusual.

Most installations are likely to use a 3 core armoured PVC insulated cable, i.e. table 4D4B from BS7671. From this, you have more or less got the right values for 10 and 16mm2 cable. But when calculating the current, you need to bear in mind a couple of things. Firstly, the AC voltage is lower than the DC voltage (quirk of AC to DC rectification), and secondly, the line current is spread over the 3 conductors (but not simply by dividing by 3 but the square root of 3!). So the line current in each of the 3 conductors isn't simply a division of power (6000W) by nominal DC volts (300) which is how I assume you have come to 20A?

Any length of cable is possible - Its just that the size of it has to be calculated to be sufficient to the current, the original voltage at the supply end, and the distance.


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Bryan Rendall

Re: How long Cable run? Ted Marynicz - 2008-10-27 11:17:27
Hi Bryan,

my figures were from Table 4E4B - for 3 core 3 phase ac armoured cable with XLPE insulation.

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ted

Re: How long Cable run? Tony Smith - 2008-10-27 12:56:45
"Firstly, the AC voltage is lower than the DC voltage (quirk of AC to DC rectification), and secondly, the line current is spread over the 3 conductors (but not simply by dividing by 3 but the square root of 3!). So the line current in each of the 3 conductors isn't simply a division of power (6000W) by nominal DC volts (300) which is how I assume you have come to 20A? "

Hi, once the current is known, lets say 14A in this case (6000W, 250V), how does the voltage drop work? For example supposing the table says you drop 8V, how do you work out the power lost? Do you lose that power from each conductor, giving a total loss of 14A x 8V x 3 phases = 336W.

Thanks, Tony S

Re: How long Cable run? haydn jones - 2008-11-13 20:34:02
Approx 650 metres
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hades
Re: How long Cable run? Bryan Rendall - 2009-10-24 10:56:28
about 110m of 35mm 3 core. Eoltec Scirocco on 15m tower
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Bryan Rendall
Re: How long Cable run? Peter - 2009-10-25 10:14:27
Not directly relevant to this thread, but included for general information.

Our 10kW Bergey Exel-S turbine is located 306m from the inverter & premises served. We have buried a 3 x core 35mm armoured cable (XLPE/PVC/SWA/PVC), being the nearest equivalent to the US specifications, which are attached.

The cable was purchased direct from Cleveland Cable in 2006 when copper prices were particularly steep. As a result, this was a major element of the total installed cost, at just over 2k.

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Peter

Attachments...
PDF file (3Mb limit) Bergey Excel 10kW wire sizing recommendations
Re: How long Cable run? Peter - 2009-10-25 10:20:40
Apologies - attachment to the previous post was made in an incorrect format - herewith again. N.B. the table shows US sizes.

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Peter

Attachments...
JPEG image (1Mb limit) Bergey Excel 10kW wire sizing recommendations
Re: How long Cable run? Bryan Rendall - 2009-10-25 16:28:19
Bergey tables say no more than 10% loss at rated power- 10%? Seems an awful waste of hard earned installed capacity going to heat up some ground!

We size for somewhere between 2 & 3% loss at rated power, which equates to about 1.something % of annual production.

Contractually, most windfarm electrical systems must have a 2% maximum loss between turbine and grid delivery point.

10% loss seems excessive, and would not comply with either BS7671 or MCS

From your data from 2007 on this site, you are netting about 13,000 kWh a year - If your cable loses 10% at peak power, lets guess 5% on average (depends on your wind distribution and voltage/power curve of the turbine), so over 20 years, the cable will lose around 700 kWh a year x 20 = 14,000 kWh - With a 23p/kWh feed in tarrif, and say 10p for the energy (average of import and export for easy counting), thats 4,620 lost in the cable. Makes it worthwhile to go up a size or 2, especially if you are using a turbine that is running at peak power a lot of the time!

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Bryan Rendall

Re: How long Cable run? Peter - 2009-10-25 18:35:32
Hi Brian,

Yes, that, together with the required length of over 300m, was the reason for putting in 35mm cable. I'm not sure what loss we are actually seeing, but I'm reasonably confident & hope it's nearer the figures you quote. You are correct regarding average production - today has been a very good day here!

Regards, Peter
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Peter

Re: How long Cable run? Peter - 2009-10-25 18:36:08
Hi Bryan,

Yes, that, together with the required length of over 300m, was the reason for putting in 35mm cable. I'm not sure what loss we are actually seeing, but I'm reasonably confident & hope it's nearer the figures you quote. You are correct regarding average production - today has been a very good day here!

Regards, Peter
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Peter

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