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Short Circuit Calculations and Symmetrical Components - Part 1
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- เผยแพร่เมื่อ 20 ก.ค. 2015
- In this video, Jim Phillips diagrams and demonstrates the calculations by walking you through a few equations. To learn more check out Jim's Short Circuit Analysis CEU on demand class brainfiller.co... or his Electrical Power Systems Engineering livestream course brainfiller.co....
Per Unit System and Symmetrical Components are used for many short circuit calculations. Electric Utility Data is also often provided in terms of Per Unit and Symmetrical Components. In this video Jim explains how to use the positive, negative and zero sequence impedances in a per unit format to calculate the three phase and line-to-ground short circuit current.
Obviously there is more to the theory of symmetrical components then Jim shows here, but as far as the calculations, they are simple.
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How to calculate the short circuit current for Zigzag Transformer?
Nice video, very educational.....great presentation, and good graphics........Thx for taking the time to do this.
Glad you enjoyed it!
Hi, where can view the Part 2 ?
nice presentation
Thanks a lot
it is very useful tip! thank you a lot.
Where can find the Part 2?
how we can Z0 value?
Why are we not using phase angles? I have also worked high power RF transmission, 400Hz military, 25Hz legacy, and any actual symmetry is an assumed condition. When things do go to ground, take a look at plotted data from any metered parts of the system. I have seen conductors get into foliage, and slowly arc trickle leak down a tree, for instance, until the tree gets good and carbonized, and establishes a nice carbon arc track. After that you move onto an ionized air plasma arc running down the carbon arc track, of the tree. That is hardly a bolted short, and the over current protection may or may not open the circuit in a timely manner. Trying to foresee anything of that magnitude is akin to picking next week's lottery numbers. Thanks for the great primer on arc flash calcs. It seems like the NFPA has been influenced by engineers with an agenda, yet again. I have seen true bolted shorts, but they are rare, and 100% of those I have seen were the result of negligence and plain old stupidity. We had some 69KV lines with a lot of slack start flailing around, when someone switched on the power, while the medusa was still shorting all the phase conductors to earth. Ooops! One of the overhead pieces of ACSR wound up laying across an adjacent phase conductor. That, unlike the medusa clamped short, was not really true bolted short. Both lines were burned through, and wound up dancing around on the asphalt of a major street, and again, not a true bolted short. The OCP took almost 20 seconds to open the circuits. That 20 seconds seemed like an eternity.
The more robust solution would use phase angles but in this illustration, I was showing how determining the magnitude is relatively easy. When evaluating the interrupting rating of equipment, the magnitude is the more significant value.
There should be some kind of test to show and teach people in the trade how to calculate the SCCR for their application.
Agreed. The US National Electrical Code is requiring the calculated short circuit current to be listed on more equipment. But to actually determine that value takes a bit of calculation experience. Even if software is used, it can be a challenge.
@@Brainfiller I believe Bussman has an app(that I've tried to use), called FC2 calculator; something like that.
Nice sir
MVA base is 100 MVA I wont ask you..where are 100 culculate..?
yeah, but where to obtain that MVAbase?
It's around 2:40 into the video. Most use a 100 MVA base to be consistent with others but technically you can select what you want. Just be consistent. However, 100 MVA means your data is likely compatible with other's data.
Sorry, my bad. Didn't notice Z was in p.u., and thought if i take any mva i'll get different current every time. That was a bit confusing. But then I saw the p.u. and understood that Z will also be changed
In theory, you "randomly" select it however, the industry has mostly standardized on 100 MVA so each entity's data is referencing the same base for compatibility.
I wish you explain it as Fortescue did on 1918
Thanks for your comment. This was only meant to be a brief "how to" for short circuit calculations given Z1, Z1, Z0 from a source such as an electric utility. I go into details such as developing sequence diagrams on one of the live training programs that I conduct.
@@Brainfiller Where did he get the 3.12 the Z0