I’m going to use 230 kV as the reference voltage for the example below;
I know if I put a piece of metal too close to a 230 kV source it will breakdown the air and jump to the piece of metal causing a visible spark, even if the piece of metal is floating in air and not completing a visible circuit.
I also know that when a dielectric breaks down it drastically reduces its resistive properties and can act like a conductor.
Let’s say the dielectric breakdown of air in 230 kV is 7 inches.
If I put a grounded piece of metal 8 inches away from the source then nothing will happen other than negligible small currents from capacitive induction.
If I put a floating ungrounded piece of metal 4 inches away from the source then it will breakdown the air and cause a visible spark, energizing the piece of metal.
Now what if I put one ungrounded floating piece of metal (piece “A”) 4 inches from the source and another grounded piece of metal (piece “B”) 4 inches from the previous piece A. Together the total distance piece B is from the source is 8 inches. Would the 230 kV breakdown the air from the source to piece A (visible spark), causing piece A to become energized and then breakdown the air from piece A to piece B (visible spark) causing piece B to be energized at 230 kV and causing a fault?
Can this cycle continue if I were to put another floating ungrounded plate (piece “C”) 4 inches from A then put B 4 inches from C? (Source <-4”-> A <-4”-> C <-4”-> B) Then air to A would breakdown then air to C would breakdown then air to B would breakdown causing B to be energized and a fault?
If the above is true then here’s my following question;
If I have rubber gloves rated for 20 kV and dielectric boots rated for 20 kV, does that combine to make a total rating of 40 kV safe to touch?
Or if I had say a 35 kV source would the voltage breakdown my gloves destroying their dielectric properties and then break down my boots as well? Meaning the total rated voltage safe to touch would be 20 kV since that’s the highest of any single dielectric.
I understand if we were to build a circuit with capacitors acting as insulators there would be a voltage drop across each capacitor causing the layering effect to work, making the gloves and boots a total rated voltage of 40 kV when worn together. But this does not incorporate the concept of dielectric breakdown of the insulators causing a significant change in its resistivity.
Thanks for the help, please provide details and reasons for why your answer is what it is and if possible please explain the theory behind it.
Thanks!
Best Answer
HV is trickier than simple addition, but in your first question, when breakdown happens between A and B, due to the air becoming a conductor, B is now roughly at A's potential, which means that breakdown will also occur between B and C.
To put it clearly, in your question, B is a stepping stone for the voltage.
Now for the second question, PLEASE DO NOT DO THAT
and for two reasons :
To elaborate a bit, in your question, you are B, what do you think will happen when (i said "when", not "if") the insulator breaks down?
Regarding your circuit with capacitors as insulators, your reasoning is only theoretically valid. In the real world, the capacitors have parasitic parallel resistance whose value can vary wildly, which means that the voltage will not be shared evenly between them, which can lead to failure.
As a conclusion, I do not know what you are trying to achieve, but please seek professional training and advice.