Question for short-circuit study experts

[JPGQC]

Hi guys!

Here is a question for short-circuit study experts.

A small plant is fed by a 750 kVA, Yg-Yg transformer. The utility wont give X/R ratios.

IEEE std C37-010 gives a typical ratio of around 7 for that transformer.

Given that X1/R1 ratio, is there a way to estimate the X0/R0 ratio?

 

[davidbeach]

Figure that X0 is about 85% of X1 and R0=R1.

 

[JPGQC]

First, thank you for your quick reply.

Someone here told me the exact same thing but he wasnt able to tell me where it was from.

Is it form any standard?

Thanks again

 

[davidbeach]

General empirical data. Conrad St. Pierre's Short-Circuit book is a good source for such things.

 

[ThePunisher]

Check J & P Transformer Handbook and ABB Red Book.

 

[prc]

Hope you were referring to transformer X0/R0 ratio.For smaller 3 phase units, 85 % of positive impedance is right as David pointed out. But if the unit is formed from single phase units or the transformer is a 5 limbed core unit( which will be the case with large 3 phase units say above 150 MVA)X0 will be same as X1.