Traditional transmission or distribution lines use porcelain insulator or glass insulator, when repair, some power grid prefer to change into composite insulators, especially in polluted area, since the composite insulators have more advantage on the electrical performance, decrease flashover, and then decrease the damage of the lines.

Then the problem is, how to design so that the new composite insulators can replace the original porcelains, and no need revise the tower or link fittings?
 

If it is suspension type, it is much easier. Since the suspension insulators mostly requires tension strength, and epoxy resin fiber glass core can provide better.
 
Such as 110kv transmission lines, the original porcelain suspension insulator string has 10pcs insulators, the standard creepage distance is 295mm per one, then 10pcs are 2950mm. The length of the string is 146mm per one, total section length of the composite insulator will be 1460mm, if it is 70KN, and socket and ball type. Then the composite insulator design will be 1460 length, 70KN, with creepage distance 2950mm, this is enough for the design.

If it is post type porcelain insulators, then the composite insulators should consider how to choose the fiber glass core diameter to meet the cantilever strength.
 
Porcelain insulator is rigidity, but the polymer insulator has flexibility, when design a 10KN failing load porcelain post insulator, when it change into polymers, this 10KN will be specified mechanical load (SCL), and consider MDCL parameter to choose the core size.
 
Some post insulator need to measure deflection when bend, when they are used on substations and railways, and some equipment.
 
How to choose the core size, there is the formula on the standard, but the manufacturers should do tests on 90h, and calculate their own formula, make this value as their own formula to design insulators when need.
End fittings of the post type should consider the porcelain fittings, and allow changes under the condition that the final composite post insulators can be amounted and totally replace the original insulators.
 
This article is a simple introduction, if you want to know more, please contact us, we will respond more details.