UTS of Conductor And Insulator

UTS (ultimate tensile strength) would pertain to how much one can pull on conductors/insulators until they break. Perhaps worth considering.

which should be higher conductor UTS and insulator UTS ? and why?

This is only a guess, but I think they should be nearly equal.

Maybe the insulators should be stronger? If an insulator breaks first, a live conductor would fall to the ground. If the conductor breaks first, either the live or dead part of the conductor could fall to the ground. But in this formulation, 50% seems better than 100%.

If standard do not suggest anything and you want to specify it, Then better way is to conduct a What if analysis or Failure Mode and Effect Analysis on the subject items.

It depends upon each item's cross-sectional area and the loads applied to them.

If you use a catenary wire you do not have to worry about tensile strength.

That is completely wrong!

OHL cable and disc insulators, multiple questions of Mr Amithabha0107 concerning transmission lines design, including calculation of strength, disc insulators, etc..The question about UTS of a disc insulator is considered to be answered dy someone else (forgive me to have forgotten his name...).

2_Selection procedure of a disc insulator ---> Leads to: What is an overhead line (for short, called an OHL). A quick answer to the question of UTS choice is ALWAYS the insulator rating. It is the weakest part of the chain including:

_A beam as support, in the source substation (for short, so called Subst),

_A clamp between the beam and the string of insulators,

_A string of disc insulators (from 1 to generally 24, according to level of voltage)

_A clamp between the string and the OHL bare cable. This clamp has, also, to comply with the metal of OHL cable.

_A conductor by OHL (up to 6 may be laid in parallel - which complexify any problems)

_In target Subst, the same gear in a mirror...

Clamps have to be designed to a certain heavy load, generally 15 or 30 metric tons of strength, never less (May be 10 metric tons in your country, you have to see that with your manufacturer).

A disc insulator has much less resistance than clamps. They are generally designed to resist to an effort of, say, 5 metric tons, or so. It's due to porcelain or glass resistance which is less than metal inserts in them. It's a ratio between the weight of disc (consequently the weight of the string) and its tensile strength. Anyway, you have no choice in mechanical strength of your disc: it is a choice of your manufacturer (He can't do any type of insulator, this is required by his standards). Your only choice is the dielectric length which is the course of a spark along the profile of your disc (V nominal divided by square two to have voltage between phase and ground...)

║#[[[[[[-#-----___sag___----#-]]]]]]#║ This will represent your OHL with :

Sag is only one part of OHL weight (See following)

1 beam, 1 clamp, 1string, 1 clamp, in source Subst.,one cable with its sag, 1 clamp, 1 string, 1 clamp, 1 beam in target Subst will represent any charge which are totalised in the weight of OHL, but not only, that is to say:

_Effect of wind (in same direction (so called directional) and perpendicular to line). You have to have the wind signature of each component: 1 for the whole string including clamps, 1 for the cable and 1 for the other string. You have to include the directional effect for the strings, not for the cable -only perpendicular for this -) Ask to manufacturers, they are accustomed to that question.

_Sand effect or ice effect or snow effect or salt effect (close to seas),

_Short-circuit effect or surge effect (the hightest one),

_Self attraction due to weak distance between different phases on a same tower,

_Link clamps or OHL connections laying down to devices on the route of line,

_Weight of branches or falling leaves accumulations, (about x times 10 kg)

_Weight of a man on the line (with his complete toolbox) (about 150 kg)

_Weight of 2 complete strings and 1 cable (or more, if any...)

Sag will represent the given effect of tensile strength beared onto the beam (on each side of OHL) which is the total of above described loads, plus a traction exercised, in order to have a convenient sag in the middle of OHL.

The distance between the horizontal between the attaching points and the middle of the line is called the sag. That value is determinating for the strength and the design of each string (i.e. each insulator disc): The less is the sag, the more you pull up to the beams (and the strings).

Sag is function of your towers, your subst. beam height, your land, its obstacles, and so on...

It is tremendous to calculate, particularly, when tower and/or subst. have different levels. Generally a value of 0.5, 1, 1.5 % is acceptable, according to level of voltage.

For instance: Voltage: 33 kV, distance between supports 150 meters, sag will be:

0.75 or 1.5 or 2.25 meters. 0.5 will be the worst case, with a tensile strength probably above unitary mechanical resistance of one disc (generally 2.5 metric ton, depending of manufacturer),

Preferable value will be 1.5 meters which allows an height above land of 7.5 = 6+1.5 meters at a minimum. This will represents the height of the lowest phase. You have to add a safety value of one height of a man (generally 1.75 meters) So you have to tie your cable up to 9.25 meters above land minimum.

You can't go down to 6 meters (+1.75m) because of circulation of trucks, lorries, trains, people, etc...)

You have to anticipate the life of your OHL, at least 10 years after its erection, depending on any sort of cultivation, any type of superstructures growing and, for sure, any type of trees and plants.

After your sag calculation, you will see that choice of your disc insulators will be very a minor thing! Good luck, man (Ask for a consultant!). BRZK