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after how many turn on a HV transfomer you start insulation

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LAN_403

genious 7

Tue Oct 16 2012, 09:22PM

Registered Member #2887 Joined: Sat May 29 2010, 11:10PM
Location: Panama City, Panama
Posts: 107

Well, the thing is, it is very hard to do the transformer you want, specially at on your first try. Tesla didn't start with the Wardenclyffe tower either, he started with smaller coils. At least for the transformer you are aiming to make, buying it is by far the best shot you have.

If you want to go through the theory and practice of making a transformer, start with a more conservative option; search the forum for the fryback transformer. It is smaller and runs on high freq, but it is way more forgiving in terms of layers, extra turns, wire size, etc.

Andre

Tue Oct 16 2012, 10:27PM

Registered Member #6921 Joined: Wed Sept 26 2012, 07:47PM
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Posts: 109

thanks but I'm looking to learn how it works and building according to correct calculation, not looking to buy.
that's why I wanted to know if the calculation I did previewsly were ok, and also seems like it was not since it has less turns only 174 turns on primary and is runnig at 60hz, and it has a ratio of 1:400 and ouputs 70KV

Where is Dr. Dark Current? he seems to know transfomers very well, I got this formula N = V / (4*f*B*Ae) from him

GrantX

Wed Oct 17 2012, 04:20AM

Registered Member #4074 Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335

If you are determined to build a 40 kV low frequency transformer by yourself, then you need to aware of the prices involved. First, the spool of wire for the secondary is going to be a killer, since you are going to need a couple of kilometres of continuous wire with a fairly high quality thin insulation, this could range from $500-$1000 (AUS) depending on quality and length. Next, the core, which will probably cost several hundred or more, depending on size and whether it is iron laminations or wound steel tape. The primary wire will be fairly cheap, and if you go for a dry insulation you will probably end up spending only a couple of hundred on polymer sheeting and varnish/epoxy. Oil insulation will be a bit harder, since you will have to construct a tough, air-tight container that can maintain a high vacuum for a couple of hours while doing the oil impregnation process. Vacuum epoxy potting is a possibly a bit cheaper than oil (in terms of container construction), but is very fiddly, plus you only have one shot and any mistakes will result in an unreliable secondary.

So in the end, you should set aside about $2,000 to $3,000 AUS for a GOOD, reliable HV transformer. On the other hand, I bought that X-ray transformer for about $200 minus oil and container, and I have an 8.2 kV, 2 kVA dry type transformer that I bought from work for only $600... Copper wound components are just expensive full stop.

I'm not trying to dissuade you, contrary, I'm trying to give you an idea of what you need to research in terms of materials and production processes if you want to end up with a decent transformer. But, be aware, this is a vary ambitious project. In the future I wish to wind a transformer for a VTTC, and I plan to aim for 50Hz, 5 kV, 3 kVA, but I think even that's quite ambitious for me, as I only have experience winding LV transformers at work, and I'm still a part time student.

Dr. ISOTOP

Wed Oct 17 2012, 07:43AM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

Andre wrote ...

thanks but I'm looking to learn how it works and building according to correct calculation, not looking to buy.

I will reiterate what others have said: building an SMPS for 40KV is not easy, even if you don't want any significant current. HF, HV AC is the destroyer of insulation, and winding a secondary for 40KV on anything less than a big TSC core is not feasible. The driver will have to switch at hundreds of kilohertz, so you'll need a proper gate drive and at least a half-bridge with fast transistors. All in all, not a good idea unless you've built SMPS'es before.
And for the love of god don't try to build an iron transformer for 40KV...

Pinky's Brain

Wed Oct 17 2012, 05:08PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
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Posts: 837

Why not make a 4kV core first but with primary to secondary/core insulation of >40 kV? If it works make 9 more.

Because of the relatively low power requirements multiple small cores seem to make more sense than one massive one (with multiple small scores your effective volume will scale linearly with effective area, which you can't do with a single core).

Steve Conner

Wed Oct 17 2012, 07:29PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Pinky, the paper linked earlier shows that multiple cores give no advantage, unless they're combined into a fractional turn transformer.

The only calculation you really "need" is the universal transformer equation, E=4fNBmax (4.4 for a sine wave). As far as I know, professional transformer designers use a fair bit of trial and error, and extrapolation from the last similar transformer they built. A newbie trying to design his first transformer can't do this.

Andre

Wed Oct 17 2012, 08:19PM

Registered Member #6921 Joined: Wed Sept 26 2012, 07:47PM
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Steve Conner wrote ...

The only calculation you really "need" is the universal transformer equation, E=4fNBmax (4.4 for a sine wave).

is E suppose to be the voltage, do you consider the core area(Ae) in the calculation?
how would you use this formula with the 70KV transformer running at 60hz transformer in the video?
here are the specifications

I know this was a very very very very hard question so I think I might not get an answer I just though to try anyways :)

just to help a bit
N =171 turns
F= 60Hz
B = 1.82T
Ae = 0.001420mÂ²

using that formula and applying this number you would get the input voltage (110V)?

Dr. ISOTOP

Wed Oct 17 2012, 08:23PM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

Andre wrote ...

Steve Conner wrote ...

The only calculation you really "need" is the universal transformer equation, E=4fNBmax (4.4 for a sine wave).

is E suppose to be the voltage, do you consider Ae in the calculation?
how would you explain this formula with the 70KV running at 60hz transformer in the video?
here are the specifications

I know this was a very very very very hard question so I think I might not get an answer I just though to try anyways :)

N, f, and V determine the flux, and given the core are you can compute B (the flux density).

Pinky's Brain

Wed Oct 17 2012, 08:36PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837

wrote ...

Pinky, the paper linked earlier shows that multiple cores give no advantage

Theoretically you can have a highly anisotropic transformer core with a relatively large area for a relatively small volume ... practically you're stuck with cores you can get off the shelf ... and you end up with a distribution transformer if you want an area large enough for 30 Hz 40 kV.

PS. of course a large enough distribution transformer could do what he wants to do as is ... it would be a shame to rewind it just to use smaller gauge windings.

Carl Pugh

Wed Oct 17 2012, 08:42PM

Registered Member #1064 Joined: Tue Oct 16 2007, 05:04PM
Location:
Posts: 42

Why re-invent the wheel.
There are good books on transformer design. Some of them are
Electronic Transformers and Circuits by Reuben Lee, Leo Wilson & Charles E. Carter.
Transformer Engineering by Blume, Boyahuab, Camilli, Lenox, Minneci & Montsinger. (General Electric)
Transformers for the Electric Power Industry by Richard L. Bean, Nicholas Chackan, JR, Harold R. Moore & Edward C. Wentz (This book is very similar to Transformer Engineering, but is by Westinghouse Engineers)
There is also some transformer design information in the book Reference Data for Radio Engineers, Fifth Edition
There is a brochure "The Technique of Transformer Design" Distributed by the Arnold Engineering Company (Reprinted from the January 1961 issue of Electro-Technology)
All of these books/literature are quite old and may not be availiable.
The specifications for this transformer are not intirely clear and it may not be possible to build a transformer to the specifications given. If it is possible, the design is very complicated and the manufacture of this transformer will be difficult and expensive.

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