Sequence Network / Fault Current Calculation

[jcbeck]

Hi Guys

Need some assistance to improve my knowledge and skills in understanding fault calculations. Go easy on me - I'm a mech eng who after 30 years since graduating has just started to study for an M.Sc. in Power Distribution Eng! I can't get my head around to calculate the equivalent parallel reactances in this diagram. I have inserted comments on the numbers I can't reconcile - trying again with diagram.
All assistance very gratefully received!



John

 

[mivey]

Hi Guys

Need some assistance to improve my knowledge and skills in understanding fault calculations. Go easy on me - I'm a mech eng who after 30 years since graduating has just started to study for an M.Sc. in Power Distribution Eng! I can't get my head around to calculate the equivalent parallel reactances in this diagram. I have inserted comments on the numbers I can't reconcile - trying again with diagram.
All assistance very gratefully received!

John

Sorry but I can't read your drawing. Need better resolution.

 

[jcbeck]

Hi Mivey

Agreed! Working on it!

Cheers

JB

 

[jcbeck]

Link to attachment

Link to attachment

You can find the attachment here: <a href=http://www.filedropper.com/workedexample51><img src=http://www.filedropper.com/download_button.png width=127 height=145 border=0/></a><br /><div style=font-size:9px;font-family:Arial, Helvetica, sans-serif;width:127px;font-color:#44a854;> <a href=http://www.filedropper.com >online backup storage</a></div>

 

[jcbeck]

Link to attachment

Link to attachment

Let's try again! Attachment can be found here: http://www.filedropper.com/workedexample51

 

[Smart $]

... I can't get my head around to calculate the equivalent parallel reactances in this diagram. ...

While they appear parallel, the solution uses a Y-"Delta" transform (or rather "Delta"-Y)...

Let us know if you need more assistance.

http://en.wikipedia.org/wiki/Y-Δ_transform

 

[Julius Right]

I think smart% is right.
If we?ll take the three-point configuration only and we?ll transform the Delta into Star we?ll get:
X1=X12*X31/(X12+X23+X31)
X1=0.6*0.25/(0.6+0.53+0.25)=0.1087
X2=X23*X12/(X12+X23+X31)
X2=0.53*0.6/(0.6+0.53+0.25)=0.2304
X3=X31*X23/(X12+X23+X31)
Z3=0.25*0.53/(0.6+0.53+0.25)=0.096
There are differences due calculation error [I guess].

 

[kingpb]

I very good document that may help you understand the basics of this is to find a copy of the "MVA Method" by Moon H. Yuen

if you have difficulty locating it, PM me.

 

[jcbeck]

Thanks and new circuit attached

Thanks and new circuit attached

Thanks to all for assistance - I also came to the conclusion that the j0.12 should have read j0.11! Working on a loop power network problem and having difficulty knowing how to incorporate the impedances on the loop with the load. I've a delta / wye transformation but cannot get the numbers to work out to the correct answer. Any assistance much appreciated - thanks!