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Distribution

Distribution

Distribution

(OP)
If I have a transmission line with a 8% reactance on a 200MW base connects two substation. And At the 1st substation the voltage 1.03pu at 5 deg and the 2nd voltage is .98pu at -2.5 deg. How will I find the power in MW and the volt-amperes reactive flowing out of the first substation? Now I ‘m able to find the MW power base on the given (base) on the Power in 200 MW but how can I find the MVAR if it base MVAR is not given? I'm trying to prepare for the PE exam and this is the type of question they will ask any help with this would be greatly appreciated. If you can picture two substation 1st at a V = 1.03pu @ 5 deg in between a Z= j0.08 pu and the 2nd substation with a V=.98pu@ -2.5 deg. The answer given to me in this example say you take the Q pu multiplied by the Q base which is said to be 200MVAR but it wasn’t given in the question.

RE: Distribution


SUGGESTION:

Review the Symmetrical component chapter of you power system book and try a solution of this problem and let us know what you think.

As a reminder, part of your training responsibility is to learn understanding the specific issue, analyzing problems and built confidence before asking questions.

RE: Distribution

The base is MVA, not Watts or Vars. Think of a vector in the P-Q frame. It's length represents volt amps. If it is drawn at 0 degrees it is power, with respect to the reference. If it is drawn at 90 degrees it is VArs. Wouldn't you want to have the same base for both? Otherwise the length of the constant MVA vector would change based on phase angle.

Try drawing your voltage and current vectors at both ends of the T-line for your analysis. Draw the vectors representing the line IR and IX drops and the solution should make a little more sense. Vreceiving should = Vsending - Vdrops.

RE: Distribution

(OP)
Thank you Rcwilson and Cuky2000 I had to go two chapter ahead to the symmetrical component section which then referred me back 4 chapter back from the distribution section to complex power I see where S can have the same overall magnitude based on Q and P associated power angle. What I’m trying to say is the reactive power can be determine for the actual 200 MW just by taking into account the Vpu and the Ipu complex gives the P and Q at their associated power factor angle values.
Rcwilson you seem to explain it quick. The explanation the way my PE book has it bases it on P and Q vector relation with real and imaginary power . I think I understand just not quite sure on how to explain it but I do see now where the 200MVAR came from now

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