Coordination is a different concern.
Our Max KVA for a fuse has been based upon the assumption that a distributed set of transformers has the same inrush current as one equivalent big transformer. Intuitively, this does not seem to be true. The concern is that if the fuse is not sized for...
True, we would not typically fuse the 4/0. For the 480 kVA we would use #2 aluminum. Our guidelines call for an 80K fuse. It seems to some that this may be extremely conservative for the example I posed.
We are thinking we could put a relay on a section that is likely to operate soon and take...
I work for municipal that distributes electrical power. Voltage is 12,470 phase-to-phase. Understanding/calculating transformer inrush for a single transformer is pretty straightforward -- 12X rated load for 0.1 second.
We have fused sections of distribution where the connected transformer...
Thanks everyone. This has been a great forum for finding information I have been trying to get for some time.
It was too practical to find the answers using the Internet search method.
Cuky2000: Your data and graphs are very interesting. Thanks
Our transformer sizing guides will allow as many as 10 small residences on a 50kva and as many as 7 larger residences on a 50kva. We can put 10 large homes on a 100kva [at 2% Z, 240-volts, the short circuit at the trasformer is 21,000...
The 1.5 times is a good rule of thumb. I modify the R and X and perform the calculation but how to modify the R and the X is also a rule of thumb. True, the 1/2 winding short circuit drops off rapidly with the impedance of the secondary. Usually at 15 to 20 feet the full winding short circuit...
All of the comments I have been seeing are very good. True, the short circuit for a 50kva, 2% transformer is 10,400 amps. However, we are finding anymore due to increases in AC useage that a 50kva is just not big enough. 2% Z is typical for a padmount but we have legacy overhead...
We are an electric distribution entity where in some instances the fault current could exceed 10,000 amps and could be as high as 30,000 amps. Some utilities state that they make sure there is enough service lead to drop the short circuit to a safe level (not always practical). I have found...
A practical question:
What is the most common short circuit rating of 120/240 volt service panels for 100 amp, 150 amp and 200 amp services? What should be done if the available short circuit exceeds this rating?
