Calculation result from ETAP, LL & LLG fault is higer 3phase fault

[PAP]

I've run ETAP program for isolated power system. The system consists of 3x6.5MW turbogenerator (10A NGR) supply 6.6kV motors and 2x 6.6/.4kV 3MVA DYN11 transformer (solid earth).
The calculation result surprise me and I would ask why this happen?
In which case that LL and LLG can go over 3 phase fault?
(I may go wrong with parameters of component.)

Thanks for help.

 

[ScottyUK]

This is typical behaviour close to the generators because the zero sequence impedance of the synchronous machines is low.

 

[vandal06]

Scotty, wouldn't the 10A NGRs negate the low Z0 of the turbo-gens contributing to a SLG fault?

 

[waross]

When looking at a line to line fault the addition of 10 Amps to ground has negligible effect.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[vandal06]

My mistake, I thought the original poster was also asking about SLG faults.

 

[healyx]

I wouldn't have thought a L-L fault could exceed a L-L-L fault. Neither have any zero sequence influence. As scotty said, the low zero sequence close to a generator can definitely result in L-L-G and L-G faults higher than L-L-L.

 

[healyx]

Correction to my post above. L-L can exceed L-L-L, but that is related to negative sequence impedance being lower than positive sequence impedance, which of course can occur with a generator.