PPI Practice exam problem #10

[Stephen2awesome]

Problem asks the required capacitance to correct the power factor. 60Hz, 3-ph, 208V load of 200+150j. I got C = 9.2uF but the answer is 1/3 that. The answer uses the 208^2 divided by 50 (QVars/3) to find Xc then ultimately C. My question is why did the solution use the 3-phase voltage with the single phase portion of the load?

 

[Stephen2awesome]

I don''t agree as of now since Line-Line voltage needs to be used with 3-ph load and Line-Neutral voltage needs to be used with 1-ph load. Please correct me if i'm wrong. 

 

[Omer]

Problem asks the required capacitance to correct the power factor. 60Hz, 3-ph, 208V load of 200+150j. I got C = 9.2uF but the answer is 1/3 that. The answer uses the 208^2 divided by 50 (QVars/3) to find Xc then ultimately C. My question is why did the solution use the 3-phase voltage with the single phase portion of the load?

see the below post for the same problem.

I think they got it wrong for this one.

 

[Stephen2awesome]

see the below post for the same problem.

I think they got it wrong for this one.

I've talked to my GT professor that is doing the PE review course and he said the problem is worded poorly. They mean the same load is across the A phase and the C phase. so Phase-Neutral and Phase C-Neutral. Simpler knowing that and the reason why they did that.

I'm not too sure about the one problem asking for the Vars to correct the PF to 1 and they used 50Vars in their calcs instead of 150Vars.