Zero sequence component of SC current

[electpower]

Why is the zero sequence component of the grid very high (say 60kA) in comparison with the generator step up transformer( around 3kA) connected to it.Though both of them have the same voltage level.??
Is it because of the short circuit impedance, or is it because of some other factors??

 

[dpc]

The zero sequence impedance of a transformer is totally dependent on the transformer connection. It can be less than the positive sequence impedance, or it can be infinite, depending on how the winding is connected and grounded.

 

[rcw retired EE]

electpower- It sounds like you have a short circuit program telling you the contribution of a generator to a utility line fault through the GSU transformer is only 3 kA, but the system is delivering 60kA.

This is pretty typical. The contribution from the generator is limited by the generator impedance and the transformer impedance. The utility contribution is only limited by teh system impedance.

 

[alehman]

Both of the above are correct. You need to be careful that your short circuit software is correctly modeling the grounding and transformer connections. Your result is certainly believable if your GSU transf is grounded through a high impedance.