What are the thermal limit calculations in transmission?

Question

Hey everyone,

i'm supposed to be gathering information about electrical power transmission, and my instructor told me to research about thermal limit calculations. i know the thermal limit is the result of the heat that is produced in the cables as a result of electricity loss, but i can't find any more information on the net. can you guys give me some ideas on where to look / what to look for?

Answer 1

It changes according to geographical conditions of the country.Every country have their own sectioning according to the climate conditions.The transmission line will be designed according to the sectioning assumptions.E.g if it is a coastal area this means there will be no snow and ice load.In the design the wind load will be accepted and past 20 years wind loads will be gathered and the worst case will be selected for design calculation.But in some sections,like Canada or Alaska ice ,snow,wind load all wil be calculated according to worst cases.The sag is not always in hot weather sometimes with ice and snow load the the sag can be more.Sag calculations are made for all worst cases and the height and the span length of the towers are chosen accordingly.This was a very short and rough explanation for details look at" www.powerlinesystems.com " or you can search from the web as power transmission lines.

Answer 2

The thermal limits for an overhead transmission line are where the conductor sag is at the minimum allowable clearance (either to ground or a lower circuit)

The higher the load, the higher the temperature, the greater the expansion of the conductor and the greater the sag.

The National Electric Safety Code defines the minimum clearances depending on circuit voltage and what is under the lines (navigable waterways, highways, fields, etc)

If there are other transmission lines below this one, the NESC also defines the minimum clearance between circuits.