Corona Inseption Voltage at 80kHz

[Vladpl]

Hello All

I have a requirement to design an Isolation transformer(oil filled) with secondary being 15kV at 80kHz.

To isolate the transformer I have looked into teflon, glass and other isolating materials. When looking at material specification I noticed that manufacturers always give corona inseption voltages at 50/60Hz and nothing at 80kHz. I have tryd to get information form manufacturers but there was no luck there.

Does anyone out there knows the type and amount of insulatiuon I need(kV/micron) to have at 80kHz 15kV. Some graphs would be of great help.

Thank you all in advance

 

[Skogsgurra]

I have no curves or other data saying how CIV is related to frequency. If there is a time/frequency aspect, I would guess that CIV is higher at higher frequencies. So, designing for same CIV at 80 kHz as for 50/60 Hz seems to be a safe strategy.

But - and this is where I have first-hand experience - Partial Discharge (PD) in voids and air gaps in insulation systems and cables is much more pronounced at higher frequencies. This can be seen in cables and motor windings connected to PWM inverters.



Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[itsmoked]

Boy.. I don't know skogs... I think the CIV drops at higher frequencies. I offer a Tesla coil as an example. The higher the frequency the farther away from the conductor surface the current wants to flow. Skin effect. So I think corona would occur much easier. That is a lower CIV.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Skogsgurra]

I do not think so. Corona is a ionization effect. And if, as I said, time is involved at all, the higher frequency *ought to* reduce corona. The skin effect is something quite different and is a result of magnetic fields from heavy currents pushing current to the perifery of a conductor. Also, 80 kHz - not Tesla frequencies? Or is it?

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[itsmoked]

I believe my big Tesla ran at about 200kHz - 14 inch sparks.

200kHz isn't too far off from 80kHz. But who knows maybe someone who actually knows will come along. LOL

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Skogsgurra]

Let's hope so.

You have a Tesla coil with foot+ sparks?

Are you running a science park?

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[scottf]

Certainly in the range of power-frequencies (50-300 Hz), it is generally understood that corona and partial discharge measurements are unaffected by frequency.

 

[itsmoked]

No I built it for my 8th grade science fair. Took a while to wrap the 5 foot secondary by hand. As is typical of science fairs I only got an honorable mention because the lame brain judges refused to believe I made the entire thing without a shred of adult assistance. They insisted I was lying and that someone wound the secondary with a lathe. Sheesh.

It was explained to me that its current because of its frequency traveled over one's skin instead of thru ones body. You could hold fluorescent tubes in one hand and something metal in the other. When you approached the output it would be attracted to your piece of metal. The current would travel through you to fully light the tubes. You never felt a thing proving to me that we were talking surface currents. You sure would feel one of those sparks if they hit you!

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com