#### Peter John

##### Member

- Location
- Kirkland, WA

- Occupation
- 01 Commercial Electrician

Any help would be appreciated, thank you!

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- Thread starter Peter John
- Start date

- Location
- Kirkland, WA

- Occupation
- 01 Commercial Electrician

Any help would be appreciated, thank you!

- Location
- Wisconsin

- Occupation
- Retired Electrical Engineer - Power Systems

What software are you using? Most packages will accept X/R and %Z. I can't remember the last time I entered actual X and R values.

Any help would be appreciated, thank you!

- Location
- Kirkland, WA

- Occupation
- 01 Commercial Electrician

Thanks

- Location
- Wisconsin

- Occupation
- Retired Electrical Engineer - Power Systems

Have you searched the internet? For example:

Thanks

The X/R ratio can affect how two impedances are added together. The X/R defines the impedance angle and should be considered for short circuit calculations

brainfiller.com

X = Sin θ * Z

R = Cos θ * Z or X / (X/R)

Transformer R and X

%Z = 5.75 and X/R = 7

Inverse Tangent 7.00 = 81.8699°

X = Sin 81.8699* 5.75 % = 0.9899 * 5.75 % = 5.6919%

R = Cos 81.8699* 5.75 % = 0.1414 * 5.75 % = 0.8131%

The X/R ratio can affect how two impedances are added together. The X/R defines the impedance angle and should be considered for short circuit calculations

brainfiller.com

- Location
- Cherry Valley NY, Seattle, WA

What exactly are you trying to do? If you are given the fault current of 26,900, what more do you need? I have the old mike holt fault current calculator (I think its no longer on his "free stuff" page and hard to find) and it doesnt ask for XR but it gives 29,847 using 90% PF. Whether its 26,900 or 29,847 does that really make any difference?

Any help would be appreciated, thank you!

- Location
- Rutland, VT, USA

- Occupation
- Electrical Engineer, PE

Not sure what fault current calculations you need but seems like the first equipment downstream from the transformer would need to be sized greater than 27kA and then I would suspect the next level down you could go with 22kA rated equipment but your modeling will tell you for sure.