Through-Fault Current Calculator
- I = Inherent secondary-fault current, amperes
- P = Transformer self-cooled three-phase base rating, kVA
- E = System phase-to-phase voltage, kV
- %Z = Percent transformer primary-to-secondary impedance, referred
A protective device is appropriate for the application if its secondary-fault interrupting rating is equal to or greater than the value for “I” calculated above.
The inherent secondary-fault current for a 20/40/50-MVA, 115-kV, 8%-impedance transformer would be:
I = [(57.8) (20 000 kVA)] / [(8) (115 kV)] = 1257 A
Conditions of Use
S&C does not accept responsibility for, nor warrant the proper application of non-S&C protective devices. Moreover, S&C is not responsible for any errors, mistakes, or miscalculations that may occur through use of the Through-Fault Current Calculator application. Results should be reviewed and approved by a consultant or end user who is familiar with the principles of determining the secondary-fault interrupting rating required for the substation transformer protective devices, to properly protect a particular size and impedance of a transformer.
This calculator is the property of S&C Electric Company, Chicago, IL and may not be sold nor be used such as to produce a commercial, marketable product. To use the calculator above, the Adobe Flash® Player plug-in is required.