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Why is dielectric breakdown damaging?

by iScience
Tags: breakdown, damaging, dielectric
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iScience
#1
May26-13, 03:48 PM
P: 334
Dielectric break down... i understand that there is current passing through the insulator but why is this damaging to the insulator? please go as deep as you can. thankyou
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yungman
#2
May26-13, 04:57 PM
P: 3,898
One thing I can think of is the current surge that heat and burn the material. You are talking dielectric break down which usually require higher voltage. Once breaking down, current surge and W=IV produce heat and burn. I am sure there are other reasons, this is one I can think of.
davenn
#3
May26-13, 08:41 PM
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its not so much that its damaging to the insulator... it is initially damaged with the breakdown.
its what ever the 2 things that the dielectric (insultator) is separating that get damaged.

take a capacitor, the plates of which have a dielectric separating them, be it paper, plastic, ceramic etc
once that dielectric has been breached ( breakdown occurred) you then are likely to have a short circuit between the 2 plates and its no longer a capacitor

same thing in cables with a dielectric separating the conductors. or say with hi voltage power lines ... you get an insulator breaks down ... then you have an earth fault ... imagine the damage that could be caused on a 220kV transmission line system if that happens, not to mention the huge loss of power

Dave

iScience
#4
May26-13, 10:07 PM
P: 334
Why is dielectric breakdown damaging?

@ Davenn , i understand that during the short, the component no longer functions as a capacitor... but my confusion was why this causes damage to the cap component. is it because the short messes up the cap plates via the heat?
OCR
#5
May26-13, 10:08 PM
P: 124
Just some interesting stuff, if you care to look...

http://205.243.100.155/

http://www.capturedlightning.com/frames/longarc.htm

http://www.youtube.com/watch?v=PXiOQCRiSp0



OCR
davenn
#6
May26-13, 10:18 PM
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Quote Quote by iScience View Post
@ Davenn , i don't understand. Are you saying that the current surge due to the short will mess up the capacitor plates due to heat?
no, once the dielectric between the plates breaks down, the capacitor can no longer act like a capacitor due firstly, the probability of a short circuit between the plates. Secondly, at the very least ( minimum damage), the value of capacitor will change dramatically. Either would make it useless for its intended purpose

Dave
BertHickman
#7
May27-13, 10:25 AM
P: 8
Quote Quote by iScience View Post
Dielectric break down... i understand that there is current passing through the insulator but why is this damaging to the insulator? please go as deep as you can. thankyou
Dielectric breakdown is not always damaging. For example, when it occurs in gases and many liquid dielectrics, the dielectric can recover all (or most) of its previous insulating capability once the arc or spark is extinguished. In gases, the conductive plasma channel taken by the discharge cools and dissipates, and the gas recovers its full dielectric strength. In liquids, the gaseous extinguished channel breaks up and if the gaseous byproducts of breakdown can fully dissipate, the liquid will recover most, or all, of its dielectric strength.

However, in a solid, a permanent breakdown channel is created, and the resulting hollow tube/fracturing now contains gases that have a much lower breakdown strength than the solid dielectric. In addition, heat from the electrical discharge may also reduce the dielectric strength of solid dielectric surrounding the channel, such as charring of organic dielectrics. The damaged dielectric can no longer withstand as much voltage, so it more easily breaks down along the damaged path and never regains its original dielectric strength.
iScience
#8
May27-13, 10:36 AM
P: 334
Quote Quote by BertHickman View Post
Dielectric breakdown is not always damaging. For example, when it occurs in gases and many liquid dielectrics, the dielectric can recover all (or most) of its previous insulating capability once the arc or spark is extinguished. In gases, the conductive plasma channel taken by the discharge cools and dissipates, and the gas recovers its full dielectric strength. In liquids, the gaseous extinguished channel breaks up and if the gaseous byproducts of breakdown can fully dissipate, the liquid will recover most, or all, of its dielectric strength.

However, in a solid, a permanent breakdown channel is created, and the resulting hollow tube/fracturing now contains gases that have a much lower breakdown strength than the solid dielectric. In addition, heat from the electrical discharge may also reduce the dielectric strength of solid dielectric surrounding the channel, such as charring of organic dielectrics. The damaged dielectric can no longer withstand as much voltage, so it more easily breaks down along the damaged path and never regains its original dielectric strength.
Now that was a satisfying answer; thank you very much :)


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