Short Circuit Calculations and Symmetrical Components – Part 1

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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[eracismm]

Nice video, very presentation, and good for taking the time to do this.

[Satchmoeddie]

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.

[vishvakarthick]

How to calculate the short circuit current for Zigzag Transformer?

[이진규-fi]

it is very useful tip! thank you a lot.

[MR-nlxr]

There should be some kind of test to show and teach people in the trade how to calculate the SCCR for their application.

[nutregina]

yeah, but where to obtain that MVAbase?

[niksontalan]

MVA base is 100 MVA I wont ask you..where are 100 culculate..?

[AZZEDDINE]

I wish you explain it as Fortescue did on 1918