What happens to current flow when an interrupting device is opened

[Jraef]

Physics should be a required course for electricians, you learn physics first, then electrical theory. Save the water pipe stuff for explaining stuff to your customers.

I use pool balls for explaining current "flow", I taught my son physics by dropping stuff off our deck and shooting pool. Now he is heaed off to get his engineering degree.

My dad taught me by dropping ME off the deck and shooting at me in the pool...

 

[rt66electric]

What???

What???

The speed of electrons in an energized conductor is very slow. You can walk faster than they move (if I remember my physics correctly). The electrical field in a conductor moves at the speed of light ( adjusted for permeablity factors of one thing or another.) .

There is no moving mass traveling at speeds where relativiistic mechanics or even Newtonian mechanics come into play. No like water in a hose.

I read many theories and explainations, but I have never heard of this one.
From what text book is this theory based? .. Electrical? practical? chemistry? electronics? physics? Popular science? Power-and-transmission?

 

[rattus]

I read many theories and explainations, but I have never heard of this one.
From what text book is this theory based? .. Electrical? practical? chemistry? electronics? physics? Popular science? Power-and-transmission?

["Electricity & Magnetism", F. W. Sears, Addison-Wesley, 1954]

This is a 2nd year college physics text, and the author states that the average velocity in a copper wire is something like 0.02 cm/sec. It helps to understand that the density of free electrons is copper is something like 8.5x10^28/cm^3.

 

[LarryFine]

I prefer the hose filled with marbles analogy. Pop a marble in one end, one instantly pops out of the other end.

The marble I pushed in doesn't itself move at the speed of light, but the effect of the push does.

 

[__dan]

There's a ton of stuff if you google "switching transients". There are pictures of blown up utility transformers.

When the circuit opens there is energy stored all over the system in equipment and devices that were powered, motors, transformers, capacitor filters. The switching transients, closing and opening, are a powerful noise in a short period of time. Any noisy signal can be resolved as a sum of sinewaves, and an arcing transient can contain every frequency well into rf and above. An event log would capture high frequency sinewaves, probably with components that are too fast for the recorder as the stored energy in each connected equipment releases that energy into the remaining system.

 

[Besoeker]

I prefer the hose filled with marbles analogy. Pop a marble in one end, one instantly pops out of the other end.

The marble I pushed in doesn't itself move at the speed of light, but the effect of the push does.

It's similar to the railway tunnel filled with carriages idea.

I understand the theory and can do the calculations but it still seems a bit counter-intuitive. And I can't think of a single occasion where I've used this in real life. Maybe in an exam paper so long ago that it was before the Dead Sea reported sick........

 

[glene77is]

It varies with current density but it is in the order of millimeters per minute rather than seconds.
But then bear in mind that AC reverses every half cycle (8.33 ms or 10 ms depending on your power frequency) so the actual distance travelled amounts to a very small "wiggle" back and forth.

Besoeker,
Thanks. I'll buy that.
The idea is the same, the concept is a stretch.
The energy transfer also has a torque component, not just straight.
( did Jraef mention that? )

 

[glene77is]

VAR flow: the frame is actually slightly twisted,
so some of the energy transfer is oblique
to the theoretical straight line up of balls . . .

Jraef,
You are right.
And this helps describe what happens when a fly hits a train head-on
Some would believe that the train stops for an instant :-?,
when in reality, the impact forces become almost entirely torque
on the part of the fly's mass. :grin:
I bet you can imagine this scenario