Number of Suspension Insulators for a Given Voltage Level

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Discussion Overview

The discussion revolves around the determination of the number of suspension insulators required for different voltage levels in a substation design, specifically for 230-115kV terminals. Participants explore factors influencing this requirement, such as dry arcing distance and creepage distance, and whether a rule of thumb exists for estimating voltage levels based on insulator counts.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant questions the basis for determining the number of insulators needed for specific voltage levels, suggesting factors like dry arcing distance and creepage distance may play a role.
  • Another participant recalls a method from their experience, stating that counting insulators and multiplying by 10kV can provide an estimate of the voltage level of high tension power lines.
  • Links to manufacturers' specifications for high voltage insulators are provided, indicating a resource for further information.
  • A suggestion is made to consult manufacturers directly for confirmation on insulator choices, highlighting the importance of compliance with safety standards.

Areas of Agreement / Disagreement

Participants express differing views on the factors that determine the number of insulators needed, and while one method for estimating voltage levels is mentioned, it is not universally accepted or confirmed by all participants.

Contextual Notes

There is uncertainty regarding the specific factors that dominate the determination of insulator numbers, and the discussion does not resolve which factors are most critical or how they interact.

Who May Find This Useful

Engineers and designers involved in substation design, particularly those working with high voltage systems and insulator specifications.

jegues
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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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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.
 
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
 
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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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