In calculations,it is assumed there is no load current before the fault.Because load current is too small compared to fault current. So that's why IA=0. But I'm saying what if Ia is not equal to zero. As I said before it must flow as ground current in a grounded system.
As far as I know no ground current flows during line to line faults. But when there is a load current on healthy phase,it must flow as ground current according to the formula.Let’s Say there is b-c fault. I0= 1/3(Ia+Ib-Ic). In this case 3I0 equals to Ia which is the load current before fault...
Let me make this clear.So impedance of a transformer is constant if we ignore temperature.In this case when I change the power from 100MVA to 110MVA, the fault current must increase according to the formula since other values are constant.ISC(kA)= ( MVA/[1.73xkVRMS)x(%Ztransformer + %Zsource)].
ONAF POWER rating of the transformer is 100 MVA.But it still can be operated up to 11O MVA for a a short time in case the second transformer is out of service.I want to know the maximum short circuit current the transformer is able to deliver.
I want to calculate the max short circuit current of a power transformer.But I'm confused about something.The rating power on the nameplate is 100 MVA but the transformer can be operated up to 110 MVA for short periods.In this case,what power should I choose to calculate the max. short circuit...
Thank you very much for answering my questions in your busy time :) So in this case looks like I can ignore high voltage side impedance since it's effect is too low for a low voltage side fault due to division by square of transformer winding ratio.Can I only use grounding transformer x/r ratio...
Thanks for the answer.I noticed you divide the R value by 3 since what you found is the total resistance of 3 phases.But you don't divide the X value ? Why is that ? The other thing is that you calculate the high voltage side x and r values.But I want to calculate the secondary side fault x/r...
Hello;
We have a 125 MVA YNd11 380/33 kV transformer on the field.Low voltage side is connected to ground through a zig zag grounding transformer without a resistor.I want to calculate the x/r ratio of a L-G fault in order to find the decaying time of DC component.As far as I know there is no...
