Roger Sparks wrote:
On Tue, 15 Jan 2008 14:18:15 -0800
Roy Lewallen wrote:

Roger Sparks wrote:
I can see why you find "no power" at the zero voltage point, but does that imply that there is no energy flow and no power from every perspective? As I write, I am struggling how to clearly differentiate between "power" as "work done" and energy as "capacity to do work", and what "network" are we defining.
Power at a particular point on the line is the rate of energy flow past
that point. It does no imply that any work is done anywhere, since any
energy flowing past the point can be stored. That is, in fact, exactly
what happens with the open circuited line in my analyses and illustrated
with TLVis1. You can see from the TLVis1 demo 4 that power is present at
all times and places along the line except a few select points. No work
is being done; energy is simply moving back and forth along the line and
between the E and H fields.

Are you objecting to my link between power and work?

I have to correct my statement.

The strict definition of work is the same as energy. So moving energy is
technically doing work, even if no energy is being dissipated or being
put to any useful purpose. What I meant but failed to say accurately is
that no net work is being done. All energy being moved is being moved
back. None is being converted to heat (dissipated), mechanical energy,
or other useful work.

Consider a resonant circuit or, for that matter, an open or short
circuited transmission line. Energy is moved back and forth each cycle,
resulting in non-zero power, but without any *net* work being done.

It's possible that by "power" you mean "average power", which is not the
same as (instantaneous) power. (This is exactly the mistake I made,
using "work" to mean "net work".) The average power (and net work done)
is non-zero whenever the amount of energy moved in one direction during
one half the cycle isn't equal to the amount moved the other way during
the other half of the cycle.

I can understand how we might think of a moving voltage wave (on a transmision line) somewhat like a battery that moves along a straight line. With that view, there would be no power acting on the line, no work, and there would be no evidence of current.

Sorry, that doesn't make sense to me. A traveling voltage wave on a
transmission line is always accompanied by a current wave, and the ratio
of voltage to current is equal to the line's Z0 at every point and every
time.

If a capacitor discharges, work is done on the circuit receiving the discharge.

That's true. No net work is necessarily done -- if it's discharged into
an inductor, the energy is simply stored in the inductor, and returned
later by the inductor doing an equal amount of work on the capacitor.

It takes work to charge a capacitor.

Yes, in the strict instantaneous sense.

Are you thinking that on a continuous capacitor like a transmission line the energy just "slides" along (like a train on tracks) without change of energy, like a battery moving along?

A transmission line has both distributed capacitance and inductance.
Energy moves between the two. The little program TLVis1 I created and
posted a link to shows this graphically in demo 4, with the energy
stored in the capacitance being in one color and the energy stored in
the inductance another color. You can clearly see how the energy moves
back and forth between the two each cycle.

In my view, logic demands a smooth flow of power and energy from source to load.

Your logic is flawed. A load which contains both resistance and
reactance has energy flow in one direction during half the cycle and
energy flowing the other direction during the other half. Because of the
resistance, the two aren't equal; the difference is the energy being
dissipated each cycle. If the load is an open or short circuit, no
energy flows to the load at all. If the load is purely reactive, it
stores the energy for half the cycle and returns it during the other half.

We should be able to account for both energy and power for every instant of time, over every inch of distance. I thought you were doing that in TLVis1 demo 4.

I am indeed. It shows exactly that. If you'll look carefully at the
graphs, you'll see that it demonstrates what I've said above.

. . .
I personally define power as a state/condition where "work 'is being' done", . Power must act over time and have a physical movement component. Voltage by itself does not fulfill this definition because no movement is observed. Current is movement, voltage is only an indication of where a concentration of charges is found.
Of course you're free to define anything in any way you choose. But
you've chosen a definition that's different from the one accepted in all
of electrical circuit analysis and all textbooks. So you can expect to
have a good deal of difficulty communicating with people who are
acquainted with the universally understood definition and assume that's
what you mean, rather than your own personal definition. To them, power
is the time rate of energy flow, dE/dt, period.

Are you again objecting to my link between power and work?

I apologize for my careless use of "work". Instantaneous power is the
rate of flow of energy, or work. Average power is the average rate of
flow of energy or work. If the average power is non-zero, net work is
being done, e.g., energy is being dissipated in a resistance or being
radiated. But instantaneous power can be non-zero without this occurring.

This definition sounds consistant with power flowing on the transmission line.

Which definition, yours or the one used by everyone else involved with
electrical circuits? I maintain that power doesn't "flow". Energy flows,
and power is the rate of that flow. The standard definition says nothing
about power "flowing", on a transmission line or anywhere else.

We seem to fulfill the power definition of energy flow on a transmission line but you make the statement "No work is being done".

Please correct that to be "no *net* work is being done. It was made to
refer to the open-circuited line in my example. The average power
everywhere is zero, as you can see from demo 4 - the power waveform
oscillates equal amounts on both sides of zero. No net energy is being
transferred or dissipated.

Would you object to my example of requiring work to charge a capacitor?

I stand corrected - work is required. But the work can be returned.

Roy Lewallen, W7EL