Determine the amount of porcelain insulation

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In summary, the amount of porcelain insulation needed for electrical systems in a substation depends on the frequency and the issue of creepage, which is the current conduction across the surface of an insulator. The dielectric strength of most good insulators is about 400V/mil, so designing with 150V/mil is usually sufficient. Creepage is affected by factors such as humidity and dirt on the surface, and can be increased by creating longer paths on the insulator. Insulators used in high voltage systems are designed with mushroom-shaped ceramic discs to prevent moisture from building up on the surface and causing conductive deposits. Special systems are used to wash the insulators and remove these deposits.
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Ron_04
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hi everyone...i want to know tht how we determine the amount of porcelain insulation to be done in any electrical systems situated in a substation? please help
 
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For power line that is 60Hz, the important thing to worry is not the insulation strength first. Most problem is creepage. Creepage is the current conduct across the surface of an insulator. That's the reason you see the HV standoff on the power lines is not straight, they are shape such the diameter get bigger and then smaller and bigger and smaller along the length. This is to increase the length of the path from the HV point at the top to the anchor point at the base.

Back to your original question, dielectric strength of most good insulator is about 400V/mil give and take. If you design with 150V/mil, usually it is ok already. You want to be more conservative, lower the number. This is a very general statement, you need to look up the specific material you are using.

As I said before, unless you push the insulation thickness, most problem is the creepage. It is only when the frequency goes up, then the material make a big difference. That's where the whole topics of dielectric loss and loss tangent and all come in.
 
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  • #3


thank u very much for ur explanation...but i want to knw one thing tht is like in bushing of a transformer we do insulation to protect the transformer from surface current so why again creepage current...can u xplain me the creepage current please
 
  • #4


Ron_04 said:
thank u very much for ur explanation...but i want to knw one thing tht is like in bushing of a transformer we do insulation to protect the transformer from surface current so why again creepage current...can u xplain me the creepage current please

I don't think that's creepage, sound more like eddy current. Creepage is conduction on the surface due to potential difference. Dirt, moisture on the surface promote creepage. The distance depends on humidity and other factors. I don't remember the ball part distance. But it is a lot larger than insulation thickness.

I remember when I designed for CE requirement, say if I have a HV wire connect to one point. I need to prevent any human from touching even the insulation of the HV cable 3" from the exposed junction. From my experience, arcing in HV system was mostly from creepage. We trouble shoot where the arc was by turning off all lights and induced arcing. You can actually the lighting shoot across the surface.
 
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ok thanks for the xplanation...but one more foolish question is how can creepage current flow through insulation? i mean to say how can a insulator conduct a current?
 
  • #6


Ron_04 said:
ok thanks for the xplanation...but one more foolish question is how can creepage current flow through insulation? i mean to say how can a insulator conduct a current?

Creepage don't go through insulation. It only travel on surface of the insulator. When I design HV pcb, I lot of time, I route groove to create a longer path of creepage on the FR4.

I really have not look into the detail theory of creepage, I just know by real life experience. I believe is the stuffs deposit on the surface that break down and conduct. For example, solder flux residue, finger print oil, moisture in air all degrade the performance. I believe people use Teflon material not because of the insulation strength, it is still about 400V/mil. It's the surface of Teflon, things don't stick on the teflon so it's better to handle the creepage.
 
  • #7


I believe is the stuffs deposit on the surface that break down and conduct.



OP asked about electric utility insulators?

Yungman is exactly right.
The individual ceramic discs are mushroom shaped so that rain runs over top to edge and drips off leaving underside dry so it retains insulating capability.

Near the ocean or on a foggy morning inland you can hear high voltage insulators "sizzle" as the deposits absorb moisture and become conductive. A good rain will wash them clean.

search on 'insulator wash system'

there's some brave folks who wash them while energized..
http://www.wilorton.com/HotLineIns.htm [Broken]
 
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  • #8


jim hardy said:
OP asked about electric utility insulators?
That was my understanding, so it is likely to be 60Hz

Yungman is exactly right.
The individual ceramic discs are mushroom shaped so that rain runs over top to edge and drips off leaving underside dry so it retains insulating capability.

Near the ocean or on a foggy morning inland you can hear high voltage insulators "sizzle" as the deposits absorb moisture and become conductive. A good rain will wash them clean.

search on 'insulator wash system'

there's some brave folks who wash them while energized..

I can assure you I am not one of the brave one!:rofl:
http://www.wilorton.com/HotLineIns.htm [Broken]

I never look at an power line insulator close up, I hope they have smooth shinny surface so it is less susceptible to things sticking onto the surface.
 
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  • #9


got it...thnx
 

1. How is the amount of porcelain insulation determined?

The amount of porcelain insulation is determined by measuring the surface area of the object to be insulated and calculating the thickness of insulation needed to achieve the desired level of insulation.

2. What is the purpose of porcelain insulation?

The purpose of porcelain insulation is to provide thermal protection and prevent heat loss or transfer. It is commonly used in electrical equipment, such as wires and transformers, to prevent overheating and ensure safe operation.

3. What factors affect the amount of porcelain insulation needed?

The amount of porcelain insulation needed can be affected by the type of material being insulated, the temperature and environmental conditions, and the required level of insulation. The shape and size of the object may also play a role in determining the amount of insulation needed.

4. How is the thickness of porcelain insulation determined?

The thickness of porcelain insulation is determined by considering the thermal conductivity of the material, the desired level of insulation, and the environmental conditions. It can be calculated using mathematical equations or determined through testing and experimentation.

5. What are the different types of porcelain insulation available?

There are different types of porcelain insulation available, including mica, glass, and ceramic porcelain. Each type has its own unique properties and is suitable for different applications. It is important to choose the right type of insulation based on the specific needs and requirements of the object being insulated.

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