Answer
![Berwin](https://data3.answerbase.com/answerbase/2948/Images/Avatars/avatar_01.jpg)
Oct 03, 2020 - 02:16 AM
For the terminal fault of the generator the short circuit current keeps changing with respective time.
Since synchronous machine has variable reactance, calculation at any instant requires a formula
involving time as one of the variables. Usually for the sake of simplicity, the reactance is considered
fixed over the time interval for which the fault current is calculated .
Please refer the below formula
![](https://data3.answerbase.com/answerbase/2948/UserFiles/Answers202010/questionImage2403679-03090902.jpg)
Here reactance, voltage is in p.u and t in seconds
In this case if you need to calculate the final steady state short curcuit currrent, You can use Isc=E/Xd and multiply with your acutal rated current to get the actual short circuit current.
Since synchronous machine has variable reactance, calculation at any instant requires a formula
involving time as one of the variables. Usually for the sake of simplicity, the reactance is considered
fixed over the time interval for which the fault current is calculated .
Please refer the below formula
![](https://data3.answerbase.com/answerbase/2948/UserFiles/Answers202010/questionImage2403679-03090902.jpg)
Here reactance, voltage is in p.u and t in seconds
In this case if you need to calculate the final steady state short curcuit currrent, You can use Isc=E/Xd and multiply with your acutal rated current to get the actual short circuit current.
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