How to Calculate Voltage drop

[vitzwaters]

Help, I have 415V, 150A which i want to transmit with ABC 50mmsq ALI 3 Core(XLPE)+ Bare Support over 350 Metre. From specs, 3 Phase vdrop is 1.43mv/A/m

Hence Vd=150*350*1.43/1000 =75V Phase to Phase. Which is too much. Where am I making the mistake?

Vitzwaters

 

[ScottyUK]

Use a bigger cable or move the load closer to the source?


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If we learn from our mistakes I'm getting a great education!

 

[wareagle]

I used 1/0 copper which is 53 mm2 and has a resistance of 0.39 ohms per km.
150 amps x 0.39 x 350m/1000 = 20 volts L/N or 35 v L-L which is the same as my voltage drop program produced.
Perhaps this is incorrect "3 Phase vdrop is 1.43mv/A/m".

 

[trosepe]

If cable is AL:
1.73*.62*(350/1000)*150= 56V L-L

If cable is CU:
1.73*.43*(350/1000)*150= 39V L-L

 

[vitzwaters]

Thanx for your contributions
vitzwaters

 

[7anoter4]

I think you mean ABC [Aerial Bunched Cables] of 3*50+25 sqr.mm Aluminum conductor XLPE insulated. See:

http://www.capcabindia.com/aerial_bunched_cables2.html

If the conductor is aluminum stranded made then the D.C. resistance at 20oC is 0.641 ohm/km and at 90oC [XLPE maximum admissible temperature] for 350 m length will be about 0.2876 ohm. A.C. resistance factor is approx.1.There is also a reactance of 0.028 ohm.
Suppose pf=0.8 using the formula:
VD = Vs + IRcos(fi) + IXsin(fi) - sqrt(Vs^2 - (IXcos(fi)- IRsin(fi))^2)
where VS=415/sqrt(3)
we shall get VD=37.9 V [phase to neutral] or 66 V [phase to phase] =15.9% drop.
The voltage at the cable end will be then 415-66=349 V.
This is not so bad for a motor starting but it is bad for a steady state current.
If the rated motor voltage is 400 V than the actual drop is only 51/400=12.75%
If the rated motor voltage is 380 V than the drop is only 31/380=8.16%.
If you may increase the Vs voltage -closer to the source as Scotty suggested- the voltage at the end will be elevated and the actual drop will be less.
By the way, 149 A indicated in the table from the above link is admissible for 40oC ambient air but no exposure to the sunshine.
If the cable is exposed to sunshine the admissible may drop to 100A or less[depends on latitude and maximum ambient temperature]

 

[7anoter4]

Another remark : if pf[cosFi]=1 and frequency=60 Hz the drop will be 75 V indeed.