Why do isolators have a sort of circular spring around?

[ChrisToffer]

Can someone Please explain to me how do these isolators works, i mean what about the parts? why does it look like this? and what's the purpose of the spring like thing around the isolators?

 

[dlgoff]

Can someone please explain to me how do these isolators works, i mean what about the parts? why does it look like this? and what's the purpose of the spring like thing around the isolators?

You can see how insulators differ here: http://en.wikipedia.org/wiki/Electrical_insulation

Suspension insulator - For voltages greater than 33 kV, it is a usual practice to use suspension type insulators shown in Figure. Consist of a number of porcelain discs connected in series by metal links in the form of a string. The conductor is suspended at the bottom end of this string while the other end of the string is secured to the cross-arm of the tower. The number of disc units used depends on the voltage.

 

[jim hardy]

The individual ceramic disks are umbrella shaped to shed rain. You want at least part of the insulator to stay dry in bad weather.

 

[ChrisToffer]

does the number of ceramic disk in the isolator matter??

 

[dlgoff]

does the number of ceramic disk in the isolator matter??

Yes. As the wikipedia page says,

The number of disc units used depends on the voltage.

For a good read on insulators, check out

http://www.myinsulators.com/acw/bookref/overvoltage/index.html#dies

 

[Windadct]

For these insulator there are two commonly referred to ratings, Creep and Strike.

Creep is the total distance along the surface of the insulator from one end ( conductor) to the other, Could be ground or energized conductor depending on the application. Creep is a measure of how resistant the insulator will be to contamination ( like salt ) or dust, that can lead to tracking, and ultimately a flash over, or tracking can also permanently damage the surface of the insulator itself. As you can visualize, this multiple mushroom shape, does shed off the water, but dramatically increases the distance on the surface of the insulator.

Strike - is the distance through the air - from one end ( conductor) to the other. The mushroom skirts could help with this in some cases, but typically the Strike is just the overall length of the insulator portion. ON some bushings ( an insulator that the conductor runs through) - you will often see the bottom skirt a little longer, to help add a few inches of strike distance.