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.

 

[alphy]

I would like to provide some insight into the factors that determine the number of suspension insulators needed for a given voltage level. First, let's define what suspension insulators are. These are devices that support and insulate high voltage conductors in overhead transmission lines. They are typically made of porcelain or glass and are designed to withstand high electrical and mechanical stresses.

Now, to answer the question of how the number of insulators is determined for a specific voltage level, it is important to consider the main factors that affect the performance of these insulators. These include the dry arcing distance, the creepage distance, and the electrical and mechanical stresses that the insulators will be subjected to.

The dry arcing distance is the shortest distance between two conductive parts that can cause an electrical arc to form. This distance is critical in determining the number of insulators needed, as a shorter dry arcing distance means a higher number of insulators are required to ensure proper insulation and protection against electrical arcing.

The creepage distance, on the other hand, is the distance along the surface of an insulator that is required to prevent a flashover (an electrical breakdown) from occurring. This distance is also important in determining the number of insulators needed, as a longer creepage distance means that fewer insulators may be needed to achieve the same level of insulation.

In addition to these factors, the electrical and mechanical stresses that the insulators will be subjected to also play a role in determining the number of insulators needed. These stresses can vary depending on the design and location of the substation and transmission lines, and must be carefully considered in order to determine the appropriate number of insulators.

Regarding the rule of thumb for guessing the voltage level of a transmission line based on the number of insulators in a string, this is not entirely accurate. While the number of insulators may provide some indication of the voltage level, it is not a reliable method as other factors, such as the design and spacing of the insulators, can also affect the number needed.

In conclusion, the number of suspension insulators needed for a given voltage level is determined by a combination of factors, including the dry arcing distance, creepage distance, and electrical and mechanical stresses. It is important to carefully consider these factors in order to ensure proper insulation and protection in a substation and transmission line.