Power line sag/tension calcs
Power line sag/tension calcs
(OP)
Hello All
From time to time I have done calcs to determine the changes in conductor tension under differing wind loads and temperatures. But for a new job I'm starting, I need to consider the effects on sag and tension when lines are subjected to radial ice, of which I have no experience (I live in a warm area). I've performed manually calcs using an old (1940s) British text as basis ... answers seem to be reasonable, but ideally I'd like them checked.
Might be a bit cheeky here, but would it be possible for someone to run the required calcs (including ice) through a line design program to check my results if I provide all the details for a base set of conditions?
Thanks for any response.
Graeme
From time to time I have done calcs to determine the changes in conductor tension under differing wind loads and temperatures. But for a new job I'm starting, I need to consider the effects on sag and tension when lines are subjected to radial ice, of which I have no experience (I live in a warm area). I've performed manually calcs using an old (1940s) British text as basis ... answers seem to be reasonable, but ideally I'd like them checked.
Might be a bit cheeky here, but would it be possible for someone to run the required calcs (including ice) through a line design program to check my results if I provide all the details for a base set of conditions?
Thanks for any response.
Graeme
RE: Power line sag/tension calcs
It has a full explaination of the Overhead sag calcs and the calcs themselfs. Overhead sag calcs are on page IV-7.
If someone does the calc for you on this tread you will still need this information to know how, why and check if it correct.
good luck
RE: Power line sag/tension calcs
I actually have this doc and Bull 1724E-152 which I believe supersedes it in part. As far as I can tell at a glance the basic S/T maths are pretty much the same as that which I've used.
My concern is really to see if I've correctly applied the formulae when using ICE (having had no prior experience with ice), so I'm hoping someone will be able to check my results.
Thanks
Graeme
RE: Power line sag/tension calcs
http://www.aerocomp.com/tldesign.html
http://www.kougakukishou.co.jp/gijyutuhiroba/bunken/IWAISrist.htm
etc. for more info
RE: Power line sag/tension calcs
RE: Power line sag/tension calcs
1. C.L. Wadhwa "Electrical Power Systems," John Wiley & Sons, 1991,
Chapter 7 Mechanical Design of Transmission Lines includes ice coating with thickness t beside wind pressures, etc.
RE: Power line sag/tension calcs
Looks like just what I need! I'm in New Zealand and haven't managed to find any commonality between any US and NZ conductors [you're in the US?] so I've included parameters. Hope metric OK, but I can convert for you if need be ...
WOLF ACSR:
A = 195.0319 mm2
Effective Overall Dia = 18.13 mm
Weight = 7.11963 N/m
Coeff of Expansion (final) = 1.782 * 10E-5 /deg C
E (final) = 79.979 MPa
UTS = 67.44 kN
Stranding = 30/2.59 Al + 7/2.59 GS
Ruling span = 130 m
Ice = 12.7 mm radial thickness @ 8.959 kN/m3.
RESULTS:
Using a starting point of 14.3 kN at 10 deg C (no ice; no wind) ...
* 8.38 kN at 50 deg C (no ice; no wind)
* 16.42 kN at 0 deg (no ice; no wind)
* 22.04 kN @ 15 deg C (no ice; 1 kPa transverse wind [includes conductor Cd = 1.2])
* 21.90 kN @ 0 deg C (WITH ICE; no wind)
I think that's it! I really appreciate your help and time. If there's anything else you need, please advise.
Thanks again
Graeme
RE: Power line sag/tension calcs
The SAG10 computations would have to be made with an approximation of the Wolf ACSR conductor; there is really no single coefficient of expansion or elasticity for ACSR. Maybe 336.4 kcmil 30/7 Oriole which has strand diameters of 2.69 mm for both steel and aluminum.
RE: Power line sag/tension calcs
You're probably correct, but for our purposes the figures stated will be OK. We have used manufacturers' composite E and coeff data (also scheduled in engineering handbooks) for many years and as far as I know, have never caused a problem. In any case, the Wolf ACSR used is just an example ... I can redo for AAC or other materials if alehman prefers.
Regards
Graeme
RE: Power line sag/tension calcs
Using AAC would not be a good test of the method if it is also going to be used on composite conductors.
RE: Power line sag/tension calcs
50°C no ice or wind - 7.08 kN initial, 5.8 kN final vs your 8.38 kN
0°C no ice or wind - 16.2 kN initial and final vs your 16.42 kN
15°C no ice, 1 kPa wind - 15.02 kN initial and final vs your 22.40 kN
0°C, 12.7 mm ice, no wind - 17.27 kN initial and final vs your 21.9 kN
The differences are quite significant for loading conditions much different from the initial.
The program uses the same area, diameter, and weight for the conductor. Coefficients of expansion and elasticity are not given because stress-strain curve data is used instead.
RE: Power line sag/tension calcs
50C no ice, no wind - 8.44 kN
0C no ice, no wind - 16.4 kN
15C no ice, 1kPA wind - 20.2 kN
0C, 12.7mm ice, no wind - 21.8 kN
Re-running assuming your "starting point" values are initial tension, I get the following final tensions:
10C no ice, no wind - 13.3 kN
50C no ice, no wind - 7.97 kN
0C no ice, no wind - 15.3 kN
15C no ice, 1kPA wind - 19.5 kN
0C, 12.7mm ice, no wind - 20.6 kN
I'm not sure why there is such a difference with jghrist's results.
My SAG10 WOLF spec:
dia: 18.14 mm
area: 195.0 sq mm
wt: 7.14 N/M
RTS: 71.6 kN
RE: Power line sag/tension calcs
My input was as follows (all English units):
Conductor Type 2 - ACSR BRITISH
Codeword WOLF
Area, Dia, Wgt, RTS - .30230 .7140 .4890 16100
Chart #1-773
TEMP ICE WIND TENS CODE
32.0 0.50 2
59.0 20.9 2
32.0 2
50.0 3215 1
60.0 2
122.0 2
I assumed ICE to be in radial inches, WIND to be in lb/ft², and TENS to be in lb.
RE: Power line sag/tension calcs
With the correct ruling span I get:
50°C no ice or wind - 9.84 kN initial, 8.63 kN final vs your 8.38 kN and alehman's 7.97 kN
0°C no ice or wind - 15.72 kN initial, 14.83 kN final vs your 16.42 kN and alehman's 15.3 kN
15°C no ice, 1 kPa wind - 21.01 kN initial and final vs your 22.40 kN and alehman's 19.5 kN
0°C, 12.7 mm ice, no wind - 21.78 kN initial and final vs your 21.9 kN and alehman's 20.6 kN
I converted to English units and back again instead of using the SAG10 SI unit option because I couldn't figure out what units they wanted.
RE: Power line sag/tension calcs
Input data:
LOADINGS
Deg C Mm Nsm % or N
TEMP ICE WIND TENSION CODE
═══════════════════════════════════════
0.0 12.70 2
15.0 1000.00 2
0.0 2
10.0 14300 2
50.0 2
And I get the following output:
Conductor WOLF ACSR/British
AREA= 195.0319 Sq.Mm.
Data from Chart No. 1-773
Metric N Units
SPAN= 130.0 Mtrs Special Loading
Creep is NOT a Factor
Design Points Final Initial
TEMP ICE WIND K WEIGHT SAG TENSION SAG TENSION
C Mm Nsm N/M N/M Mtrs N Mtrs N
0. 12.70 .00 .00 18.156 1.76 21787. 1.76 21787.
15. .00 ****** .00 19.489 2.04 20230. 2.04 20230.
0. .00 .00 .00 7.136 .92 16377. .89 16939.
10. .00 .00 .00 7.136 1.05 14300.* .98 15318.
50. .00 .00 .00 7.136 1.79 8444. 1.53 9875.
RE: Power line sag/tension calcs
alehman, your figures especially are very close to mine ... I'd double-counted my drag coeff hence my error during wind. Now reset Cd to 1.0 at 1 kPa and get 20300 N at 15 deg. And it seems I've done the ice part OK too. So I'm rapt with correlation.
jghrist, I'll go over your answers more closely and see if I can figure why we have significant differences.
Thanks again for your time, both of you. Much appreciated!
Regards
Graeme
RE: Power line sag/tension calcs
RE: Power line sag/tension calcs
RE: Power line sag/tension calcs
Another case to consider is birds. What is the loading for a line densely populated with large birds? Also what is the wind loading on the birds? When something scares them all away, sometimes there is a very noticable uplift of the span which tells me the birds are a fairly significant load.
RE: Power line sag/tension calcs
RE: Power line sag/tension calcs
Visit
http://www.timesfreepress.com/2000/JAN/24JAN00/NEWS0424JAN.html
for:
In Georgia, more than 10,000 residents in Catoosa County and more than 1,000 in Walker County awoke to cold and dark homes due to power outages, as iced-over trees fell onto already-sagging power lines drooping with icicles.
http://www.americanlifelinesalliance.org/pdf/IceStormSummaries.pdf
for: Storm on 1/1/1952 when:
Ice on wires 2" in diameter with 6" long icicles in MO
RE: Power line sag/tension calcs
Another consideration: I live in the midwestern U.S. where I have personally experienced several extended outages due to ice storms. The last one was in December of 2001, when electicity at my home was off for six days. The vast majority of the damage is normally caused by trees and limbs burdened with ice which break and fall on lines (and houses and cars). The fireworks from arcing lines and damage in general was quite amazing and took several months to clean up. Thousands of trees were destroyed. One utiltiy pole in my back yard was broken in two when a large tree limb fell on a line it supported.
As a side note, my company recently completed a study for several communities in my area on the costs and possible benefits of relocating overhead lines underground. Needless to say the costs would be rather substantial.