SKM not displaying fault current on transformer secondary

[supermanengineer]

This job is so much pain in the butt.. I am calculating short circuit values in SKM using ANSI standard method of calculation. However, the short circuit current values are not displayed on the single line on the downstream of the transformer. Any suggestions!!! I think there would be an option to increase "Bus. level away to find source "

Thanks

 

[EddyWirbelstrom]

1. Go Run> Balanced System Studies > Select SC and ANSI
2. Click the Setup button to select all or selected buses, also check other settings
3. Click Ok > Run
4. With the single line( one-line ) diagram active go Run > Datablock format and select the datablock BUS Fault Currents (A_FAULT)

If a datablock with the calcualtd short-circuit curent does not appear on the single line diagram, select the bus, and from the One-Line pull down menu select Datablock > Visible

I recommend you make better datablocks than the ones which come with the software.

 

[supermanengineer]

Hi Eddy!!

Thanks for the reply!! I am using the the data blocks that are available from the SKM list. I am selecting "ANSI Asym 3P Mom", Datablock is visible because it is displaying 0 kA.

I think it not calculating the short circuit current values for the those buses when there exists two transformer between the bus and utility source.

 

[unclebob]

ANSI Asym 3P Mom is not good for low voltage. It's a medium voltage thing.
Try with ANSI 3P int, or something like that. I'm not at the office, so it's hard to tell you
the exact variable.

 

[EddyWirbelstrom]

I ran a project and noticed that ANSI Sym 3P Mom is only reported on HV buses.
I am not familiar with the ANSI Standard, in Australia we use the IEC60909-0 ( AS3851 ) method for short-circuit calculation which is different from the ANSI method.
The attached GE paper describes the application of the ANSI method where for voltages above 600V a short-circuit parameter called 'momentary rating' is used to calculate the rms value of the first cycle asymmetrical current wave. See pages 10-11 of attached GE paper.
Whichever Standard is used, the asymmetrical current ( based on system X/R ) must be considered for the initial short-circuit currents.

 

[supermanengineer]

Thank you for your precious advice!!

Yes, the bus which is connected to the secondary of the transformer is at LV 480V and ANSI Sym 3P Mom does not show value at LV.

ANSI 3P int works perfectly fine but it is not useful for my specific project as I need 1/2 cycle SC fault level at LV bus using ANSI standard method of calculation.