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Number of Suspension Insulators for a Given Voltage Level

by jegues
Tags: insulators, number, suspension, voltage
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Jul4-13, 10:05 AM
jegues's Avatar
P: 1,089
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!
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Jul4-13, 10:34 AM
P: 1,815
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.
Jul4-13, 08:59 PM
PF Gold
P: 1,909
Here are three manufacturers that give descriptions and specifications of their high voltage insulators:


Jul8-13, 10:19 AM
Sci Advisor
PF Gold
sophiecentaur's Avatar
P: 12,203
Number of Suspension Insulators for a Given Voltage Level

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.

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