Clearance & barrier

[sgtan1]

Hi, been picking up bits of useful knowledge just reading the board.So wondering if you guys can help me.

On MV gears design, I have often come across barrier place between the phases or ph - earth. I am told that these are able to reduce the required air clearance. they act to prevent flashover.
Place incorrectly and these become another burning material

How do they work?
How do we decide on material, spacing needed.
Any good books or writeups?

Regards

 

[candu6]

The barriers are made of an insulating material such as fibreglass, mica, ect. They provide a higher resistivity per inch than air, therefore conductors may be placed closer together.
The material would be decided upon based on its electrical properties and the amount of room available between two conductors and ground.

 

[sgtan1]

Thanks candu6,

But I am interested in more details.
On how we can work out the space reduction and suitable material.

Material with dielectic rigidity 12kV/mm
System being 12kV
Add material 1mm thick around the conductor and we could have 2 conductors siting side by side ?

Should we be considering the current pssing through the insulator and so the heat generated. Effects on the material due to heat?

 

[ScottyUK]

You must consider the BIL level of the equipment - the basic insulation level - and the impulse withstand voltage. Also, what are the effects of contamination on the surface? Damp? Condensation? Airborne vapour? Smoke? None of these are ideal from the equipment point of view, but users expect equipment to work even in imperfect circumstances. The margins in the design are usually very generous, especially at low voltage like 12kV.


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