Dielectric breakdown

[gar]

171117-2354 EST

A fairly good discussion on dielectric breakdown is at:
https://en.wikipedia.org/wiki/Electrical_breakdown

.

 

[gar]

171117-2514 EST

Comparison of some materials:http://chemistry.mdma.ch/hiveboard/rhodium/pdf/chemical-data/diel_strength.pdf

.

 

[Sahib]

One interesting property, perhaps not covered in the above papers, is the breakdown strength decreases with increase in thickness of a dielectric medium.

 

[rian0201]

Depends on the properties of the material i think @ sahid.

Sent from my vivo 1606 using Tapatalk

 

[rian0201]

It's Sahib sorry

Sent from my vivo 1606 using Tapatalk

 

[gar]

171118-2121 EST

I believe from general information I have seen in the past that Sahib's comment is probably correct. I don't know what the reason is for this effect.

It may result from a nonuniform field intensity, and/or imperfections. See BertHickman's comment at
http://cr4.globalspec.com/thread/69395/Does-Dielectric-Strength-Depend-On-Thickness .

Magnet wire for high power compact motors have "enamel" insulation made up of many separate layers. Like 15 layers adding up to 50 microns (about 0.002") in total thickness. A major problem with magnet wire is that it has to be bent. This mechanically stresses the insulation.

The following reference may not relate, but is of interest:
https://en.wikipedia.org/wiki/Partial_discharge .

.

 

[Sahib]

I stated dielectric breakdown strength decreases with increase in thickness based on H.Cotton Advanced Electrical Technology. He states poor heat dissipation in thicker dielectrics may be a reason.

 

[junkhound]

171118-2121 EST

... reason is for this effect.

Can become a very complicated subject.

50 years ago I was shown a piece of a fly wing embedded in the paper of a paper/foil oil filled capacitor and was told that imperfections were the main reason volts/mil dielectric withstand decreased with thickness.
As mentioned in your referenced, once polymers come into the equation the question of electric fields and length of polymers comes into play, but imperfections still are the main reason. Damage due to assembly is alos considered and imperfection.

Occasionally, the converse is true. Had 3 kapton insulation layers in a high voltage high frequency (1 kV, 100 kHz) transformer. Unfortunately the vacuum potting procedure was flawed and there were air gaps between a layer next to the winding . A stress riser led to partial discharges eating thru the outer layer (and thru wire insulation), and the other 2 kapton layers 'zippered'. In this case, one thicker dielectric would have probably not failed as kpotting would have been able to eleiminate the air voids, but that is a secondary effect.