Short Circuit Current Single Phase Transformer Primary

[MrJLH]

Looking for some help on determining a L-L short circuit on the primary side for a single phase transformer on a three 480V phase bus. Feeder is less than 10 feet. Is a short on one of the legs of the transformers to ground near the same current as a the short circuit current from the three phase bus to ground? I understand the secondary side well enough, but having trouble with a single phase transformer on the primary side.

Thanks

 

[iceworm]

Looking for some help on determining a L-L short circuit on the primary side for a single phase transformer on a three 480V phase bus. Feeder is less than 10 feet. Is a short on one of the legs of the transformers to ground near the same current as a the short circuit current from the three phase bus to ground? I understand the secondary side well enough, but having trouble with a single phase transformer on the primary side.

Thanks

I'm lost. If the short is on the primary side on the transformer - what does the transformer have to do with it? The transformer is not going to limit the fault current.

You have the available short circuit at the 480V Bus, and the impedance of the feeder to the transformer - nothing else in the circuit.

Curiosity question: Is it the Line-to-Line or Line-to-Ground fault currents? Not really part of your question - just curious.

ice

 

[templdl]

I'm lost. If the short is on the primary side on the transformer - what does the transformer have to do with it? The transformer is not going to limit the fault current.

You have the available short circuit at the 480V Bus, and the impedance of the feeder to the transformer - nothing else in the circuit.

Curiosity question: Is it the Line-to-Line or Line-to-Ground fault currents? Not really part of your question - just curious.

ice

In trying to read between the line I am to understand that you are looking for the available fault current at the primary terminals of the subject transformer. If so it would be dependent upon the kva of the transformer which feeds this tansformer, the size of which is unknown and any impedance of the bus/ conductor between the transformers.

 

[kwired]

The current at the point you are describing is limited by what is upstream and about the only downstream impact would be if there were any motor contribution.

 

[Phil Corso]

MrJLH,

Are you asking for:

a) the magnitude of a line-to-line fault on secondary-winding terminals of a 3-phase transformer-bank,

b) comprised of three, single-phase, 2-winding transformers, in which,

c) the HV-side winding voltage is unknown, but the secondary winding is 480 Volts?

Regards, Phil Corso