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Home > Archive > Electrical Engineering > February 2008 > Calculating Watt loss in a line
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Calculating Watt loss in a line
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|
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| Hi,
I am trying to figure the watt loss on a 3 phase power line. The line
is 30 miles long with .015 resistance per mile. There is 900 amps
across the line.
Could you please help me?
| |
| Palindrome 2008-01-30, 1:25 pm |
| Troy wrote:
> Hi,
>
> I am trying to figure the watt loss on a 3 phase power line. The line
> is 30 miles long with .015 resistance per mile. There is 900 amps
> across the line.
>
> Could you please help me?
Assuming that the phase loads are balanced and there is no neutral
current or ground current and that the resistance is that per conductor:
Then each line has 900 amps flowing through a total resistance of 0.015
x 30 ohm.
Thus each line loss is I^2(R) = 900x 900 x 0.015 x30
The total loss is three times that, ie 900 x900 x0.015 x30 x 3 watts.
--
Sue
| |
| charles 2008-01-30, 1:25 pm |
| In article
<adf3a786-3d50-46a6-8262-e79d9ee9f571@p69g2000hsa.googlegroups.com>,
Troy <paynetd@gmail.com> wrote:
> Hi,
> I am trying to figure the watt loss on a 3 phase power line. The line
> is 30 miles long with .015 resistance per mile. There is 900 amps
> across the line.
Ohm's law is quite useful here. power = current squares x resistance.
Power = 900 x 900 x 0.015 x 30
which my calculator gives as 364.5kW
(& probably 3 times that if there is 900 amps flowing in each line)
> Could you please help me?
--
From KT24 - in "Leafy Surrey"
Using a RISC OS computer running v5.11
| |
|
| On Jan 30, 11:29=A0am, charles <char...@charleshope.demon.co.uk> wrote:
> In article
> <adf3a786-3d50-46a6-8262-e79d9ee9f...@p69g2000hsa.googlegroups.com>,
> =A0 =A0Troy <payn...@gmail.com> wrote:
>
[color=darkred]
>
> Ohm's law is quite useful here. =A0power =3D current squares x resistance.=
>
> Power =3D 900 x 900 x 0.015 x 30
> which my calculator gives as 364.5kW
> (& probably 3 times that if there is 900 amps flowing in each line)
>
>
> --
> From KT24 - in "Leafy Surrey"
>
> Using a RISC OS computer running v5.11
Thanks Charles & Sue! I appreciate your quick response. I thought it
was this simple but I wanted to check with you guys first.
| |
| Gerald Newton 2008-01-30, 5:25 pm |
| On Jan 30, 8:01=A0am, Troy <payn...@gmail.com> wrote:
> Hi,
>
> I am trying to figure the watt loss on a 3 phase power line. =A0The line
> is 30 miles long with .015 resistance per mile. =A0There is 900 amps
> across the line.
>
> Could you please help me?
0.15 ohms per mile comes to 0.15/5280 x 1000 =3D 0.0284 ohms per 1000
ft.
This corresponds to 400 Kcmil at 75 degrees C copper using table 8 of
the NEC.
The ampacity of 90 degree C 400 kcmil is 380 amperes. Utility
overhead lines are run at 120 degrees and assume a 40 degree C
ambient.
Even at this higher temperature, it appears without further
calculations that 900 amperes is much too high of a current for this
conductor.
| |
| HapticZ 2008-01-30, 5:25 pm |
| hmmm, now we're thinking!
local nuke here (Dominion) wants nrc special dispensation to run the rods
higher to increase plant output beyond originally spec rating.
engineering says orginal specs were conservatively written to ensure
original permitting was accepeted without severe review.
safety measures were reviewed to assure any unusual incident occurence could
be met within nrc standard.
ok, so now somebody in newsgroups wants to know if some xmiss line can
handle more than it was designed for....
am i paranoid, or is the element of pure profit causing bending of rules and
compromise of safety??
ok, now lets find out if the BWR really can huff and puff its way over the
hil.......... :-))
"Gerald Newton" <electrician@electrician2.com> wrote in message
news:5dd37d6f-2c95-4772-be25-c8b1ba7b7f54@d21g2000prf.googlegroups.com...
On Jan 30, 8:01 am, Troy <payn...@gmail.com> wrote:
> Hi,
>
> I am trying to figure the watt loss on a 3 phase power line. The line
> is 30 miles long with .015 resistance per mile. There is 900 amps
> across the line.
>
> Could you please help me?
0.15 ohms per mile comes to 0.15/5280 x 1000 = 0.0284 ohms per 1000
ft.
This corresponds to 400 Kcmil at 75 degrees C copper using table 8 of
the NEC.
The ampacity of 90 degree C 400 kcmil is 380 amperes. Utility
overhead lines are run at 120 degrees and assume a 40 degree C
ambient.
Even at this higher temperature, it appears without further
calculations that 900 amperes is much too high of a current for this
conductor.
| |
| Gerald Newton 2008-01-30, 8:25 pm |
| On Jan 30, 1:14=A0pm, "HapticZ" <hapt...@sbcglobal.net> wrote:
> hmmm, now we're thinking!
>
> local nuke here (Dominion) wants nrc special dispensation to run the rods
> higher to increase plant output beyond originally spec rating.
>
> engineering says orginal specs were conservatively written to ensure
> original permitting was accepeted without =A0severe review.
>
> safety measures were reviewed to assure any unusual incident occurence cou=
ld
> be met within nrc standard.
>
> ok, so now somebody in newsgroups wants to know if some xmiss line can
> handle more than it was designed for....
>
> am i paranoid, or is the element of pure profit causing bending of rules a=
nd
> compromise of safety??
>
> ok, now lets find out if the BWR =A0really can huff and puff its =A0way ov=
er the
> hil.......... =A0:-))
>
> "Gerald Newton" <electric...@electrician2.com> wrote in message
>
> news:5dd37d6f-2c95-4772-be25-c8b1ba7b7f54@d21g2000prf.googlegroups.com...
> On Jan 30, 8:01 am, Troy <payn...@gmail.com> wrote:
>
>
>
>
> 0.15 ohms per mile comes to 0.15/5280 x 1000 =3D 0.0284 ohms per 1000
> ft.
> This corresponds to 400 Kcmil at 75 degrees C copper using table 8 of
> the NEC.
> The ampacity of 90 degree C 400 kcmil is 380 amperes. =A0Utility
> overhead lines are run at 120 degrees and assume a 40 degree C
> ambient.
> Even at this higher temperature, it appears without further
> calculations that 900 amperes is much too high of a current for this
> conductor.
Disregard my previous post. I used 0.15 ohms but should have used
0.015 ohms. Sorry about that.
| |
| Don Kelly 2008-01-30, 9:25 pm |
| ----------------------------
"charles" <charles@charleshope.demon.co.uk> wrote in message
news:4f695fbca0charles@charleshope.demon.co.uk...
> In article
> <adf3a786-3d50-46a6-8262-e79d9ee9f571@p69g2000hsa.googlegroups.com>,
> Troy <paynetd@gmail.com> wrote:
>
>
> Ohm's law is quite useful here. power = current squares x resistance.
>
> Power = 900 x 900 x 0.015 x 30
> which my calculator gives as 364.5kW
> (& probably 3 times that if there is 900 amps flowing in each line)
----------------------------
Except that "power = current squares x resistance. is not Ohm's Law even
though true.
--
Don Kelly dhky@shawcross.ca
remove the X to answer
| |
| Don Kelly 2008-01-30, 9:25 pm |
|
----------------------------
"Gerald Newton" <electrician@electrician2.com> wrote in message
news:5dd37d6f-2c95-4772-be25-c8b1ba7b7f54@d21g2000prf.googlegroups.com...
On Jan 30, 8:01 am, Troy <payn...@gmail.com> wrote:
> Hi,
>
> I am trying to figure the watt loss on a 3 phase power line. The line
> is 30 miles long with .015 resistance per mile. There is 900 amps
> across the line.
>
> Could you please help me?
0.15 ohms per mile comes to 0.15/5280 x 1000 = 0.0284 ohms per 1000
ft.
This corresponds to 400 Kcmil at 75 degrees C copper using table 8 of
the NEC.
The ampacity of 90 degree C 400 kcmil is 380 amperes. Utility
overhead lines are run at 120 degrees and assume a 40 degree C
ambient.
Even at this higher temperature, it appears without further
calculations that 900 amperes is much too high of a current for this
conductor.
------------------
I would suggest that the person who set this problem just extracted some
numbers out of the air. numbers together without considering that they were
not realistic. However they suffice to deal with the concept at a beginner
stage.
Also, I am not too sure that I would want to run ACSR (as opposed to copper
which no utility uses) at 120C. There will be an irreversible deterioration
in conductor life which will happen every time the conductor reaches this
temperature.
--
Don Kelly dhky@shawcross.ca
remove the X to answer
| |
| Paul Hovnanian P.E. 2008-01-31, 8:25 pm |
| HapticZ wrote:
>
> hmmm, now we're thinking!
>
> local nuke here (Dominion) wants nrc special dispensation to run the rods
> higher to increase plant output beyond originally spec rating.
>
> engineering says orginal specs were conservatively written to ensure
> original permitting was accepeted without severe review.
>
> safety measures were reviewed to assure any unusual incident occurence could
> be met within nrc standard.
>
> ok, so now somebody in newsgroups wants to know if some xmiss line can
> handle more than it was designed for....
>
> am i paranoid, or is the element of pure profit causing bending of rules and
> compromise of safety??
You are reading too much into this question. Odds are that its someone's
homework.
--
Paul Hovnanian mailto:Paul@Hovnanian.com
------------------------------------------------------------------
Don't hate yourself in the morning -- sleep till noon.
| |
| daestrom 2008-02-01, 8:25 pm |
|
"Don Kelly" <dhky@shaw.ca> wrote in message
news:LYaoj.26668$4w.11892@pd7urf2no...
>
> ----------------------------
> "Gerald Newton" <electrician@electrician2.com> wrote in message
> news:5dd37d6f-2c95-4772-be25-c8b1ba7b7f54@d21g2000prf.googlegroups.com...
> On Jan 30, 8:01 am, Troy <payn...@gmail.com> wrote:
>
> 0.15 ohms per mile comes to 0.15/5280 x 1000 = 0.0284 ohms per 1000
> ft.
> This corresponds to 400 Kcmil at 75 degrees C copper using table 8 of
> the NEC.
> The ampacity of 90 degree C 400 kcmil is 380 amperes. Utility
> overhead lines are run at 120 degrees and assume a 40 degree C
> ambient.
> Even at this higher temperature, it appears without further
> calculations that 900 amperes is much too high of a current for this
> conductor.
>
> ------------------
> I would suggest that the person who set this problem just extracted some
> numbers out of the air. numbers together without considering that they
> were not realistic. However they suffice to deal with the concept at a
> beginner stage.
>
> Also, I am not too sure that I would want to run ACSR (as opposed to
> copper which no utility uses) at 120C. There will be an irreversible
> deterioration in conductor life which will happen every time the
> conductor reaches this temperature.
>
And with such temperatures isn't there also a problem with sagging in the
line? ISTR that running very hot lines can lead to the expansion of the
line and sagging to dangerous levels.
But the OP had said 0.015 ohms per mile, so it must be larger than 400
kcmil...
daestrom
| |
| Paul Hovnanian P.E. 2008-02-01, 8:25 pm |
| daestrom wrote:
>
> "Don Kelly" <dhky@shaw.ca> wrote in message
> news:LYaoj.26668$4w.11892@pd7urf2no...
>
> And with such temperatures isn't there also a problem with sagging in the
> line? ISTR that running very hot lines can lead to the expansion of the
> line and sagging to dangerous levels.
IIRC, the big outage back in '03 began with a heavily loaded
transmission line (on a hot day) sagging into some trees.
'Dangerous levels' is somewhat ambiguous. All power lines sag more at
higher temperatures. Their design must take this into account when
allowing for clearances, insulator string swings, etc. Then, its up to
the maintenance folks to keep trees clear of the lines and operations
not to overload them beyond their thermal limits.
> But the OP had said 0.015 ohms per mile, so it must be larger than 400
> kcmil...
>
> daestrom
--
Paul Hovnanian mailto:Paul@Hovnanian.com
------------------------------------------------------------------
I think you left the stove on.
| |
| Don Kelly 2008-02-02, 8:25 pm |
| ----------------------------
"daestrom" <daestrom@NO_SPAM_HEREtwcny.rr.com> wrote in message
news:47a3b7bf$0$22854$4c368faf@roadrunner.com...
>
> "Don Kelly" <dhky@shaw.ca> wrote in message
> news:LYaoj.26668$4w.11892@pd7urf2no...
>
> And with such temperatures isn't there also a problem with sagging in the
> line? ISTR that running very hot lines can lead to the expansion of the
> line and sagging to dangerous levels.
>
> But the OP had said 0.015 ohms per mile, so it must be larger than 400
> kcmil...
>
> daestrom
In addition, with ACSR, there can be a problem with "birdcaging" due to
differential expansion of the steel core and the aluminum conductor. I don't
think that this is completely reversible- correct me if I am wrong. I am
going on memory of a long ago look into the effects of overloads
(particularly repeated ones) on overhead conductors.
You reminded me of a situation many years ago (over 50) in Quebec when, on a
hot day with well above normal loading due to a combination of things there
were repeated mysterious outages on a 240KV line.
Mysterious until a local farmer called in and complained that the wires were
hitting his barn roof.
This is an exercise in some circuits course where the intention was to find
out whether the student could apply I^2R to a 3 phase line- as opposed to a
single phase line. The realism of the actual numbers given isn't important
at this stage (sure, it would be nice to use data pertaining to a real
conductor just to say there is an real application for this) - the concept
(which Troy apparently hadn't grasped) is the point.
The side track is more interesting than the original question.
--
Don Kelly dhky@shawcross.ca
remove the X to answer
>
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