DC Component in SC

[cruzy]

Do you think we will need to include the DC component in any fault calculations? I don't exactly have the grasp on this concept as it is, but a couple of my books discuss it. I think that you use include it for subtransient calculations only, which the exam could very well have, but I haven't seen any implementation of this in any of the NCEES samples. One of my books included it in their solution, but that was the first time I saw that.

Should I even bother learning this, or is the DC component not going to be involved in our calculations for test purposes?

 

[HornTootinEE]

I haven't seen it yet in my studying.

 

[cableguy]

Hopefully I'm not too far off my base here, but my emphasis for study topics has gone "can this problem be solved in 3-4 normally written lines?"

If you can solve a DC component short circuit problem in a few steps, then I'd say it's fair game. If you have to do some crazy mathematical acrobatics, then no, I seriously doubt it'll appear. That said, nothing I've gone over has had it.

Closest I've gotten is a diode problem with a rectified sine wave and DC offset. Going RMS with that requires square root of an integral function, and it was rather ugly.

 

[cruzy]

In my book, they just multiplied the fault contribution current (one from the generator, one from the infinite bus) each by sqrt 2 to get the dc contribution and then the total Isc = sqrt (fault current^2 + dc contribution^2). So no complicated math, but I still don't get it.