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Digsilent PowerFactory, ETAP and EMTP.

Kiribanda, 643А is not charging current, it's current which flow through neutral of ZNyn1 transformer. If you look at parameters you will see that this TR provide Io current 1000A during EF. 33 kV side works with low resistance neutral. 1) Is the 33kV system a real "DELTA" system? Yes. 2)...

Kiribanda, yes, you completely right, it's delta connection, but if you be more attentive, you will see transformer ZNyn1 at 33 kV side.

Kiribanda, look at 36 kV side, there is EF condition.

I was wrong about overvoltage at LV side of transformer ZNyn1. I built simple model of your SLD and got these results: Nothing happens with phase voltage at LV side. Can you please provide more details about what happens at LV side during EF condition (records)?

Actually, this is not typical solution for supply auxiliary. You will have overvolatge all time during EF condition because of transformer ZNyn1.

Hi! I have one question. We have ungrounded 10 kV network. Transfromer 10/0.4 kV YYn0 connected to this network. 0.4 kV side of TR is solid grounded. Question: If I perform loop test at 0.4 kV side, I will see real earth fault current? For example I check it by Megger LTW425.

You have to limit short current to 31.5 kA for existing substation. How is old SS and new SS connect? Install series reactors at interconnection lines will help to limit SC for old SS.

In this case, sym9910_1 has less rotor angel therefore out of step condition didn't happen. I think this generator works with close critical rotor angel and even short disturbance lead to out of step. Try to reduce active power for this generator and look at result.

Misunderstood you. Try to reduce time to 20-30 ms. Initial rotor angle for sym9910_1 is close to critical, so in this case it will be difficult to keep stability under SC.

1 sec is too long for such rotor angle.

Yes, it's unstable. You have out of step condition for sym9910_1. Try to reduce clearing time of protection.

Cross tie feeder is normally closed, isn't?

7anoter4, thanks for good explanation!

Additional question: There will be contribution current from LCI converter (load-commutated inverter 24 MW) which feed synchronous motor?

Dear Che, thanks!

Additional info: I calculate SC at 110 kV bus, many LV motors 0.4 kv connected to transformers of 10/0.4 kV, then transformers 35/10 kV and then 110/35 transformers. Group of LV motors 0.4 kV => transformers 10/0.4 kV => transformers 35/10 kV => transformer 110/35 kV.

Hi! When we perform SC calculation, should taking into account motor contribution current from LV motors (0.4 kV or less) or only from MV motors? In which standard I can find information about this? Thanks in advance.

Do you use motor acceleration or transient stability case? Check again motor paraments like CKT model, characteristic model, load model, inertia.

Typically for 10 kV generator side we use follow protection: 50,51,59,27,32,40,46,81H/L,50N,69R,51V,87G. For 10 kV incomer side: 67, 67N (direction in generator)