CI Volume 1 #13, MVA Method

[danadiva81]

Okay, so I'm trying out the MVA method for CI Volume 1, #13....For some reason I keep on getting 1543 A.

I downloaded the "Short Circuit ABC" pdf from earlier posts on the forum, so I'm trying to follow along.

There's two "components" we are dealing with.....the transformer and the transmission line. Right?

For the transformer, I take 9/.084 = 107.14. And for the 40KV line, I take (40)^2/.032 = 50000.

The transformer and transmission line are in series, but I do "parallel math"........

(107.14 * 50000) / (107.14+50000) = 106.91

Then I take (106.91 * 1000)/( sqrt 3 * 40) = 1543A

I should be getting 1120A????

Thanks in advance. Trying to nail this down b/c I hate the per unit way with a passion......

 

[Ship Wreck PE]

I don't think that this problem is a good candidate for the MVA method because part of the problem is in PU. NCEES problems 513, 530, & 540 can be worked with the MVA method.

 

[iahim]

Okay, so I'm trying out the MVA method for CI Volume 1, #13....For some reason I keep on getting 1543 A.

I downloaded the "Short Circuit ABC" pdf from earlier posts on the forum, so I'm trying to follow along.

There's two "components" we are dealing with.....the transformer and the transmission line. Right?

For the transformer, I take 9/.084 = 107.14. And for the 40KV line, I take (40)^2/.032 = 50000.

The transformer and transmission line are in series, but I do "parallel math"........

(107.14 * 50000) / (107.14+50000) = 106.91

Then I take (106.91 * 1000)/( sqrt 3 * 40) = 1543A

I should be getting 1120A????

Thanks in advance. Trying to nail this down b/c I hate the per unit way with a passion......

You need to convert the feeder impedance from pu to ohms to use the MVA method. Zbase = 177.78 ohms , so Zline = 5.69 ohms. Replace your 0.032 with this value, and you should get 1120A.

 

[danadiva81]

Ah okay!! Now I see. Thanks a million!

 

[nasir]

Wow....MVA method is the best, quickest and easiest....

I solved all NCEES problems 530, 513, 540 and 132 Using MVA method....I am glad I understood this 4 days before Friday.......

4 days counting....

Good luck everyone....

 

[iwire]

Ok...I understand how you get 3 phase fault but I am still little confused about finding line to ground fault or line to line fault using MVA method? Any idea?

 

[daw4888]

http://www.jmpangseah.com/wp-content/uploads/2003/01/chapter-5.pdf

It explains some about other fault types.