Question from HSC Online site on eddison/westinghouse. (1 Viewer)

[-X-]

But DC has the advantage of not causing losses through electromagnetic radiation or magnetic induction. With solid-state switching it is now relatively simple to change between DC and AC at high or low voltages. High voltage DC transmission is now practicable. Scientists are striving to develop super-conducting wires for power transmission. If they do, DC could become the preferred current for long distance transmission. There is already a 500 kV DC submarine transmission line carrying 2800 MW over 50 km between the two islands of Shikoku and Kansai in Japan.

What do they mean by "not causing losses through EM radiation"? And why would they want DC used for future when Superconducting wires are available? Is it because its more powerfull?


Thanks

 

[Dash]

About the EMR, I think its talking about when the brushes of the DC motor hit the edges of the commutator, sparks are given off and hence radiation. These sparks represent a loss of energy. But this does not occur in an AC motor since the brushes pass smoothly over the slip rings. (I'm not sure if the 100% correct, still have to revise my notes )

As you said, DC currents are more powerful than AC currents. So by using a DC current in superconducting wries, we will be able to transmit greater current with no resitance!! A nifty trick

 

[-X-]

Originally posted by Dash
About the EMR, I think its talking about when the brushes of the DC motor hit the edges of the commutator, sparks are given off and hence radiation. These sparks represent a loss of energy. But this does not occur in an AC motor since the brushes pass smoothly over the slip rings. (I'm not sure if the 100% correct, still have to revise my notes )

You sure u didn;t mix DC with AC there? Cause in my quote it says that DC doesnt loose energy due to EMR.

 

[Dash]

WTF?
Argh! I'm lost... wait, let me read up on this

 

[Affinity]

EMR... erh.. they're talking about the lines emitting radiowaves of 50 Hz..

forget it.. that very little compared to magnetic induction

 

[Skywalker]

Originally posted by -X-
And why would they want DC used for future when Superconducting wires are available? Is it because its more powerfull?

I think that you would use DC for transmission through superconducting wires. You get energy losses using an AC current in a superconducting wire hence you lose the advantage of using it the first place.

 

[fwong]

It is a consequence of EM Theory (way beyond high-school level)
that whenever charges are *accelerated* then EM waves will be given out. This is exactly how all transmitters work: mobile phones, radio or TV stations. In a high-frequency AC circuit, electrons oscillate to-and-fro, hence accelerate/decelerate. The same is true for low frequency AC of 50 or 60Hz, only that the EMR intensity is small because of its low frequency, unless current is large. And that is exactly the 'argument', debate, or 'concern' of EMR received if you live near power lines.

So back to the original question. If DC is transmitted, then there is no loss through EMR because if the current is steady, there is no acceleration of charges(electrons).

Hope it helps,
Frederick Wong