Number of Suspension Insulators for a Given Voltage Level

[jegues]

Hello all,

I'm currently designing all the structure, equipment and grounding for a 230-115kV terminal substation, and for our dead end connections consisting porcelain ball & socket type suspension insulators we are given the number of insulators required for each voltage level. (i.e. 14 for 230kV and 9 for 115kV)

On what basis do they determine that 'X' number of insulators are needed for a voltage level of 'Y'?

Is it the dry arcing distance? Is it the creepage distance? Is it a combination of multiple factors, or does one particular factor mostly dominate over the others?

Also I've often heard that there is a rule of thumb through which one can guess at the voltage level of a given transmission line by counting the number of insulators in a given insulator string, is this true?

Thanks again!

 

[skeptic2]

Forty years ago I worked with an engineer who had worked at a power station. He told me how to estimate the voltage of high tension power lines (in the US). He knew the standard transmission voltages, which I have long forgotten, and it was simply a matter of counting the number of insulators, multiplying by 10kV and "rounding" to the nearest standard voltage. All I still remember is the 10kV per insulator.

 

[Bobbywhy]

Here are three manufacturers that give descriptions and specifications of their high voltage insulators:

http://www.ceramic-insulator.com/showproduct.asp?id=80

http://sunelectric.en.alibaba.com/product/889748928-218648551/ANSI_52_3_ball_socket_type_suspension_insulators.html

http://electrical-engineering-portal.com/ceramic-porcelain-and-glass-insulators

 

[sophiecentaur]

I wouldn't make any final choices without asking the manufacturers themselves about this. I imagine you will need this installation checked by some insurance inspector and you'd hate to be told it was not adequate.