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Science Forum Index » Physics Forum » Why Is DC Power Transmission 10X More Efficient Than AC?
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| Paul E. Schoen |
 Posted: Wed Apr 23, 2008 3:11 pm |
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"Bret Cahill" <BretCahill@aol.com> wrote in message
news:155f31ec-16a8-4bf3-a872-36772b553f99@i76g2000hsf.googlegroups.com...
Quote: you came up
with.
Never end sentences with prepositions.
But it sounds funny to say, "up with which you came."
Paul |
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| Phil Allison |
| Posted: Wed Apr 23, 2008 6:32 pm |
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"Benj"
( snip nauseating verbal diarrhoea)
** Fuck OFF - you asinine, illiterate cretin !!!
..... Phil |
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| Phil Allison |
| Posted: Wed Apr 23, 2008 6:34 pm |
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"Bret Cahill = TROLL "
Quote: Never end sentences with prepositions.
** So it is a rote thinker -
as well as a complete fuckwit.
...... Phil |
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| Benj |
| Posted: Wed Apr 23, 2008 8:21 pm |
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On Apr 23, 7:32 pm, "Phil Allison" <philalli...@tpg.com.au> wrote:
Quote: "Benj"
( snip nauseating verbal diarrhoea)
** Fuck OFF - you asinine, illiterate cretin !!!
.... Phil
GREAT NEWS PHIL!!!!
Google Groups now can be rigged with a killfile!
Bye Bye, fuckwit! |
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| Phil Allison |
| Posted: Wed Apr 23, 2008 8:30 pm |
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"Puppet_Sock"
The situation where DC transmission is better is where the
transmission line is long compared to a 1/4 wavelength of
the AC transmission frequency. The typical transmission is
60 cps. So 3E8 m/s divided by 60/s, then divided by 4, is
1,250 km. So when you get transmission distances in
that range, radiative loss starts to be significant, and it
gets tough to match the impedance of the line to the load.
Basically what you get is a very large dipole antenna.
Anyway, long distance transmission is sometimes done
on DC lines to reduce radiative loss.
** I think this is entirely false.
There is no comparison with a 60 Hz dipole antenna.
AC power transmission is done with 3-phases ( spaced by exactly 120
degrees ) running a few metres apart, all in exact parallel across the
country - so the net 60Hz eclectic field at a distance always cancels to
ZERO !!.
Ergo, there simply is no "radiation loss" .
The real losses encountered are due to resistive heating, voltage drop and
phase angle changes on very long lines.
http://en.wikipedia.org/wiki/Electric_power_transmission#Limitations
...... Phil |
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| Y.Porat |
| Posted: Wed Apr 23, 2008 8:37 pm |
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On Apr 23, 1:17 am, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
Quote: On Tue, 22 Apr 2008 12:13:06 -0700 (PDT), Bret Cahill
BretCah...@aol.com> wrote:
Is there some low frequency radiation or hysterisis loss or what?
Bret Cahill
If you mean long-distance transmission lines, DC can be run at higher
average voltages (less corona losses, relatively) and has no skin loss
or inductive coupling to the world. I don't know about 10:1.
DC systems do need inverters and rectifiers on the ends, which have
losses.
John
----------------
i dont know what you mean by inverters
AFAIK
DC cannot be transform to very high volages-
OTHOA
AC can be transformed to huge voltages by trasformers
yet transformers can work only on AC
and hight voltage AC is much more efficient than
any low voltage current
do i remember correctly ??
ATB
Y.Porat
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| Benj |
| Posted: Wed Apr 23, 2008 8:44 pm |
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On Apr 23, 8:02 pm, tadchem <tadc...@comcast.net> wrote:
Quote: Isn't it great when a so-called "scientist" can simply quote
mathematical equations as if they were making sense
...and they do make sense, especially when you consider that these
equations are definitions and not open to debate.
Since when are equations in science and engineering "not open to
debate"? It is only in MATHEMATICS that they are unquestioned
(assuming they were done "correctly" which means according to the
arbitrary rules the original mathematician who defined the given
system invented.) In science and engineering (contrary to popular
belief) mathematical models are determined to be "correct" by their
agreement with reality. mathematical definitions play NO role!
Quote: and pretend to win
arguments by doing so?
I pretend nothing. Why do you pretend to understand when your
argument violates simple arithmetic?
Because simple arithmetic leads to an absurd answer and therefore
simply does not apply!
Quote: 2 x 92% is 184%, and 184% efficiency is impossible as efficiency is
defined.
Correct. Absurd answer so the calculation is simply untenable and
thrown out without regrets.
Quote: Can you show me *HOW* 2 x 92% = 96%? I don't think so.
By looking at the data. It's clear that if one system has half as
much loss as another the one with the greater loss is twice as
inefficient. Hence it logically follows from the data that one is
twice as efficient as the other. If you want to play English word
games have at it, but language doesn't have to make sense either,
ESPECIALLY "muttish" English! If you wish to make up equations that
have no basis in reality and then claim that somehow it shows you are
"correct" because the laws of arithmetic are being followed, you can
say that, but you make no sense in a practical world. Say, how is
life up there in the Ivory Tower?
So the REAL question is what is going on in the system? Trying to
press mathematical dogma or the rules of English grammar upon any
situation in no way impresses the power transmission systems. They
don't listen to either mathematics OR English. If what is going on is
understood and described, that is sufficient for those people who deal
with these things. Goofy arguments by you don't make you look any
smarter.
If you want to look smart then tell us what the best efficiency of
AC<>DC HV converters are these days... (only values under 100% will be
considered valid) |
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| Guest |
| Posted: Thu Apr 24, 2008 12:20 am |
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On Wed, 23 Apr 2008 13:06:05 -0700 (PDT), Bret Cahill
<BretCahill@aol.com> wrote:
Quote: you came up
with.
Never end sentences with prepositions.
Why?
jack |
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| Phil Allison |
| Posted: Thu Apr 24, 2008 12:49 am |
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<spamfree@spam.heaven>
Bret Cahill = TROLL
Quote: you came up with.
Never end sentences with prepositions.
Why?
** Cos it is a preposterous thing to do.....
...... Phil |
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| Bret Cahill |
| Posted: Thu Apr 24, 2008 2:18 am |
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Quote: Are modern "scientists" really this dense? �Ten times efficient isn't
920%! �What you must have just graduated from a "modern" high school?
Dig. �If standard transmission is 92% efficient, then that means there
is 8% of the energy lost. TWICE as efficient would only have 4% of the
energy lost or would be 96%.
Your terminology seems pointlessly confusing. �Presumably you think
a 100% efficient system is 20 times as efficient as another 100%
system.
The simple answer is that if something is 92% efficient, you can't
make it 10 times more efficient.
Supposing you wanted a catchy title to your thread?
Bret Cahill |
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| Guest |
| Posted: Thu Apr 24, 2008 6:49 am |
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On Thu, 24 Apr 2008 15:49:20 +1000, "Phil Allison"
<philallison@tpg.com.au> wrote:
Quote:
spamfree@spam.heaven
Bret Cahill = TROLL
you came up with.
Never end sentences with prepositions.
Why?
** Cos it is a preposterous thing to do.....
Sez who?
jack |
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| tadchem |
| Posted: Thu Apr 24, 2008 2:03 pm |
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On Apr 24, 2:44 am, Benj <bjac...@iwaynet.net> wrote:
Quote: On Apr 23, 8:02 pm, tadchem <tadc...@comcast.net> wrote:
Isn't it great when a so-called "scientist" can simply quote
mathematical equations as if they were making sense
...and they do make sense, especially when you consider that these
equations are definitions and not open to debate.
Since when are equations in science and engineering "not open to
debate"?
You are welcome to change the *DEFINITIONS* of the terms at your own
pleasure, but be advised that as soon as you do, you no longer have
any common ground for using the term in a discussion with others using
the definition you have chosen to disregard. The logical term for
this process is "equivocation."
Quote: Because simple arithmetic leads to an absurd answer and therefore
simply does not apply!
....not if simple arithmetic has been misapplied, as in your argument.
Quote: Can you show me *HOW* 2 x 92% = 96%? I don't think so.
By looking at the data. It's clear that if one system has half as
much loss as another the one with the greater loss is twice as
inefficient.
So, you turn the discussion from one of "efficiency" to one of "loss"
while pretending not to have changed anything. The phrase "it is
clear" is a standard pedagogical cop-out. It usually means "I haven't
bothered to work out the details, but I'm pretty sure this is the way
it is."
Quote: Hence it logically follows from the data that one is
twice as efficient as the other.
You apparently are not clear on the relationship of "efficiency" to
"loss," either.
Quote: If you want to play English word
games have at it, but language doesn't have to make sense either,
ESPECIALLY "muttish" English!
But "science" requires unambiguous communication wherever possible.
To support clear communications, rigorous definitions are established
and all parties agree to adhere to them. These definitions establish
the "playing field" for scientific discussions. If you wish to
discuss a subtly different concept with scientists, you must give your
concept a unique name and definition.
Quote: If you wish to make up equations that
have no basis in reality
They are not my "equations," but rather mathematical *definitions*
agreed upon by physicists for the study of physics.
Quote: and then claim that somehow it shows you are
"correct" because the laws of arithmetic are being followed, you can
say that, but you make no sense in a practical world. Say, how is
life up there in the Ivory Tower?
I imagine from your perspective a white fire hydrant would seem like
an ivory tower. I work in the real world.
Quote: So the REAL question is what is going on in the system?
This was answered in the Wiki articles which I have previously cited.
It isn't all that complicated.
Electrical power is typically transmitted at 110KV+. At one-thousand
times the voltage of household current, the current of a HV
transmission line is kept low, so the losses are kept low. I could do
the math for you, but by now I'm sure you could not follow it, or if
you could, you would not trust it simply because it is math.
Quote: Trying to
press mathematical dogma or the rules of English grammar upon any
situation in no way impresses the power transmission systems. They
don't listen to either mathematics OR English. If what is going on is
understood and described, that is sufficient for those people who deal
with these things. Goofy arguments by you don't make you look any
smarter.
Excellent words. You should heed them.
Quote: If you want to look smart then tell us what the best efficiency of
AC<>DC HV converters are these days... (only values under 100% will be
considered valid)
In the real world, AC to DC 'converters' are called "rectifiers," and
their efficiency depends on their operating voltage, frequency, and
other characteristics of the individual circuit (including the load!).
I have seen a claim (admittedly by 'marketing' types) for >= 97.7%:
http://www.chlorideups.com/Data%20Sheets/40%20kVA.pdf
although elsewhere they state "87% efficiency minimum."
....but here is a peer-reviewed article:
http://ieeexplore.ieee.org/Xplore/login.jsp?url=/iel3/4202/12369/00573386.pdf?temp=x
claiming "92% for a 12 kW rectifier for telecom applications ... for
a 380/480 V three phase AC input utilizing semiconductor devices with
commonly available breakdown voltages ... including predicted and
laboratory measurements of power train efficiency."
Perhaps you will find data in the links on this page informative:
http://category.alldatasheet.com/datasheet-pdf/category/rectifier/efficiency,.html
Tom Davidson
Richmond, VA |
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| tadchem |
| Posted: Thu Apr 24, 2008 2:06 pm |
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On Apr 24, 2:37 am, "Y.Porat" <y.y.po...@gmail.com> wrote:
Quote: On Apr 23, 1:17 am, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Tue, 22 Apr 2008 12:13:06 -0700 (PDT), Bret Cahill
BretCah...@aol.com> wrote:
Is there some low frequency radiation or hysterisis loss or what?
Bret Cahill
If you mean long-distance transmission lines, DC can be run at higher
average voltages (less corona losses, relatively) and has no skin loss
or inductive coupling to the world. I don't know about 10:1.
DC systems do need inverters and rectifiers on the ends, which have
losses.
John
----------------
i dont know what you mean by inverters
"Inverters" convert DC to AC.
Quote: AFAIK
DC cannot be transform to very high volages-
Not directly. Voltage dividers/multipliers are notoriously
inefficient ("lossy"), but via the sequence "inverter -> transformer -
Quote: rectifier" it can be done.
OTHOA
AC can be transformed to huge voltages by trasformers
yet transformers can work only on AC
and hight voltage AC is much more efficient than
any low voltage current
do i remember correctly ??
ATB
Y.Porat
---------------------------
Tom Davidson
Richmond, VA |
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| Bret Cahill |
| Posted: Thu Apr 24, 2008 5:03 pm |
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The trifling daffynition hair splitting bean counting nerds here will
never take me alive!
Bret Cahill |
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| Judge Mental |
| Posted: Thu Apr 24, 2008 6:49 pm |
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On Wed, 23 Apr 2008 16:11:47 -0400, Paul E. Schoen wrote:
Quote: "Bret Cahill" <BretCahill@aol.com> wrote in message
news:155f31ec-16a8-4bf3-a872-36772b553f99@i76g2000hsf.googlegroups.com...
you came up
with.
Never end sentences with prepositions.
But it sounds funny to say, "up with which you came."
A googlie netcop! ROFLMAOPIMP!!!!
Cheers!
Rich |
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