×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

How to Calculate Voltage drop

How to Calculate Voltage drop

How to Calculate Voltage drop

(OP)
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

RE: How to Calculate Voltage drop

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

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

RE: How to Calculate Voltage drop

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".

 

RE: How to Calculate Voltage drop

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

 

RE: How to Calculate Voltage drop

(OP)
Thanx for your contributions
vitzwaters

RE: How to Calculate Voltage drop

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]
 

RE: How to Calculate Voltage drop

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

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources