adccommunitymod (AutomationDirect) asked a question.

WYE Power calc

Created Date: November 25,2014

Created By: dieseltwitch

**** This post has been imported from our legacy forum. Information in this post may be outdated and links contained in the post may no longer work.****

Trying to figure out how to calculate load on a 208/120 V Generator. Heres my example L1-L2 = 50A L2-L3 = 50A L3-L1 = 25A L1-N = 25A L2-N = 25A L3-N = 25A Given these loads here is what i get L1 = 90A L2 = 112A L3 = 90A Im also lost as to how to calculate total kVa? a calculator i downloaded (but can't see the code of) says for the above loads I have a total 35 kVA but by my math I have a total load of 291Amps and using (V*A*Sqrt(3))/1000 I get 105kVA.... so who's wrong? I feel like i have missed something and have way to much power spec'd?


  • adccommunitymod (AutomationDirect)

    Created Date: November 25,2014

    Created by: Tinker

    If one calculates all the powers individually and adds them it does come out to 35kW.

    (50+50+25) * 208 = 26kW

    (25+25+25) * 120 = 9kW

    Your "(V*A*Sqrt(3))/1000 " only works for a balanced circuit where A is the current in one leg, one doesn't add all three legs (your 291, though it looks like you did some rounding or have a typo 'cause 90+90+112 = 292)). Actually, if you average your three legs: (90+90+112) / 3 = 97-1/3

    then plug that into your equation: 208 * 97-1/3 * sqrt(3)/1000 = 35.07kW or "close enough for government work "

    I'm not sure I actually know how to directly calculate the power for three unbalanced line currents, and considering how close averaging worked out I'm not too motivated to get the textbooks out.

    Expand Post
  • adccommunitymod (AutomationDirect)

    Created Date: November 25,2014

    Created by: dieseltwitch

    thank you!

  • adccommunitymod (AutomationDirect)

    Created Date: November 25,2014

    Created by: dieseltwitch

    Trying to figure out how to calculate load on a 208/120 V Generator.

    Heres my example

    L1-L2 = 50A

    L2-L3 = 50A

    L3-L1 = 25A

    L1-N = 25A

    L2-N = 25A

    L3-N = 25A

    Given these loads here is what i get

    L1 = 90A

    L2 = 112A

    L3 = 90A

    Im also lost as to how to calculate total kVa? a calculator i downloaded (but can't see the code of) says for the above loads I have a total 35 kVA but by my math I have a total load of 291Amps and using (V*A*Sqrt(3))/1000 I get 105kVA.... so who's wrong? I feel like i have missed something and have way to much power spec'd?

    Expand Post