what are stresses in transmission line??

When erecting your lines, you have a table of factors, Temperature when erecting, length of span, if it is suspended and how many spans, the size of cable, location, ie will it be prone to loading of ice, ice and wind! An example here in Spain:- a 70m span in 95Al at 32^oC, no ice is 230kg tension, if that line ices up, the tension can increase to a calculated 1200kg so, you have to get your sums right or you could break lines or even pylons! Pylons are also rated in height and strength for example if you are only suspending a line in the middle of a long span you would use a low strength pylon whereas if the pylon was at a corner you would use a stronger one! The height of the pylon depends on the voltage and minimum object clearance, for example a 32KV line in Spain is 7m min object clearance, this gives you pylons inbetween say 18m and 36m high, whereas a main 164KV power transmission line is somewhere in the 30m clearance zone with pylons of 56m to very high! Also your insulators, the glass or plastic hangers or cable anchors have specific voltages too a rule of thumb is for every 1KV you have 1cm of insulator therefore a 32KV line has insulators 32cm long and the bridges (isolator to isolator) cannot be less than 32cm at nearest point to the pylon!

I have hung HV lines in Spain for the last 5 years and I only know the basics, If you are hanging lines, I would look for professional advice and only use this as an idea of the things to take into account!

I hope this has got you off to a start!

If you are hanging lines, I would look for professional advice and only use this as an idea of the things to take into account!

Excellent reply Mr. Truman Brain, This is another post where only an on-site professional can analyze the requirements. As you said general weather conditions, length of span, size of cable, materials, soil condition for pylon (tower?) anchoring and on and on and on. On site experts are the only folks to determine the conditions and solutions for this type of project. If this poster needs to ask this question he/she should hire professional expertise. NOT AN INTERNET PROJECT.

NOT AN INTERNET PROJECT.

I strongly agree!

and right of way, and landowners ERCOT NERC FERC. and any of series of alpabet acronyms. Terribly stressful...

Illegitimi non carborundum

Excellent reply Mr. Truman Brain, This is another post where only an on-site professional can analyze the requirements. As you said general weather conditions, length of span, size of cable, materials, soil condition for pylon anchoring and on and on and on. On site experts are the only folks to determine the conditions and solutions for this type of project. If this poster needs to ask this question he/she should hire professional expertise.

OK being a car buff, my thoughts went straight to (Automobile) transmission lines.

And the stress being the flex that occurs when the motor torques.

Not gonna be much help here lol.

One stress I didn't notice any mention of is the stress that lightning can place on your transmission lines and anything connected to them.

By placing some additional lines above your transmission lines you can shield them from lightning. You need to have really good earthing of these lines to cope with the surge that a lightning strike causes.

It is an additional cost but it can save a fortune in damaged plant and overtime for breakdown repairs.

It is also a huge saving in personal discomfort if you are involved in emergency repair work.

Is lightning a problem in your area?

Every tower or pylon has to have an earth spike, a tower with furnature, eg isolators, aerial transformers, spider trip, fused isolators and the like have normally a copper cable ring with 4 spikes surronding the base, The ground transformers ie, 24KV/415V, 32KV/415V, are surrounded by a matrix of earth spikes connected together by minimum of 50mm^{2 (about 8mmdia)} Uninsulated Copper cable. Normally, only the large capacity lines eg 128KV, 164KV or the new MegV lines have an extra cable running above because as you say, it starts to get expensive repairing these lines! The other lines are a case of changing a fuse, or resetting the trip, It really depends on how many people will be affected by a line failure!

Stresses on Transmision lines. There are many components that make the line.Normally it is taken care at design stage.The foundation for the tower or Pylon is cast according to soil conditions.All other factors like Ice loading,Wind loading,Weights on towers are all estimated at design stage including the max and min temp and variation in Sag on account of that and tension to be used while stringing the conductor.These are all predictable. What is not possible to calculate exactly is the vibration due to gusts of wind leading to oscillations of the conductors termed as galloping or dancing which cause severe stresses leading to failure.The other problem is electromagnetic forces on conductors due heavy short circuits which if happens near a generating station can be severe.