RadioBanter - View Single Post

Owen Duffy · June 8th 08, 01:14 AM posted to rec.radio.amateur.antenna

wrote in
:

On Jun 7, 12:43�am, Owen Duffy wrote:
wrote
innews:73353273-a079-499c-89df-c11975b37c78@z66g200
0hsc.googlegroups.com:

...

The maximum power theorem gives conditions where power in the load,
is equal to internal power in the generator. �Not always a good
ide
a. �A
50HZ generator capable of Megawatts of power would dissiapate 1/2
in the generator and 1/2 in our houses if they designed them to
conform to the MPT. �The 50HZ generators would melt. �Utilities
design their
Generators to have nearly 0.0 ohms internal impedance.

Actually, the AC power distribution system from alternator down has a
manged substantial equivalent source impedance.

The source impedance serves to limit fault currents, which reduces
the demands on protection devices.

Sure, the network is not operated under Jacobi MPT conditions, but
neither

does it have near zero source impedance.

Owen

Not really sure I agree. A multi-megawatt 60HZ generator by necessity
has near zero source impedance. The ones I am familar with require
forced air cooling on their output buses. If you are pumping out
Mega- watts, then any non -zero source impedance results in serious
heat. I^2R.
Gary N4AST

Gary, you use the terms impedance and resistant as if they were
equivalent.

Alternators have a designed value of leakage reactance, and they also
have resistance. The combination make the equivalent source impedance,
and it is sufficient to limit fault current to something typically in the
range of 20 to 50 times the rated output current.

Transmission lines and transformers in the transmission and distribution
networks are usually designed in the same way.

It is not zero, and it is not purely resistive. Most supply authorities
would not allow you to connect a capacitive load (a leading PF load), so
another concept, conjugate matching (in the Jacobit MPT sense) is also
not practiced.

Understanding the electricity network does not really give an insight
into a typical ham radio transmitter, they do not share the same design
objectives.

Owen