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Niraj Joshi

Fri Oct 08 2010, 06:19PM

Registered Member #3291 Joined: Fri Oct 08 2010, 06:06PM
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Posts: 11

Hi frnz,

I wanna make an HV tester circuit. I am willing to design the HV transformer myself.

The test voltage is 0-5000 V AC. The transformer rating is 500 VA.

What would be the accurate volts per turn selection for this Xmer.

The input voltage to Transformer is 230 V AC.

radiotech

Sat Oct 09 2010, 01:01AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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Posts: 1546

What is the brand name of the core material you are going to use.
What percent impedance do you want the transformer to have.
Find out what flux level the core uses, if unavailable use 1T.
Work backwards from %Z to wire size based on 500 watt load
and find what ratio you will need for 5000 volts at that load.

Sulaiman

Sat Oct 09 2010, 10:01AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Nirai Joshi,
1) 500 W at 5000 V is 100 mA .... this is a potentially lethal device
2) 5000 V is well abve the voltage where corona starts to be a problem, winding your own is certainly possible but not simpe.

Your best bet woulkd be a variac followed by a step-up transformer,
check eBay for a suitable transformer.
If a 'normal' transformer is unavailable consider
- a Neon Sign Transformer (NST)
- an Oil Burner Ignition Transformer (OBIT)
- a pair of Mocrowave Oven Transformers (MOT)

Whichever option you choose, caution is required.

Niraj Joshi

Sat Oct 09 2010, 10:08AM

Registered Member #3291 Joined: Fri Oct 08 2010, 06:06PM
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Posts: 11

@sulaiman: yes sir, the way is as u said. A variac followed by a step up transformer.

But i want to make the transformer myself. I know the method to design. Just a bit confused about the accurate volts per turn

Adam Munich

Sat Oct 09 2010, 02:57PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

As Sulaiman said, corona will be a problem, and it certainly will. Fire up that xformer in air and it won't last too long. You'll need to put it under hot oil (canola or mineral) and pull a vacuum for a few hours. I recommend organic oils as they smoke heavily before they catch fire, giving you a big warning; mineral oil has a low flashpoint and will just catch fire without prior notice. You'll also want to separate the coil layers with cardboard too, not plastics as they are impermeable to oil. I'm not too keen on transformer design, and I'm sure the almighty knowledge god Proud Mary has something to add.

If you're winding your own primary too, then volts per turn won't be a problem; you would have to worry about turns ratio instead. You'll also have to pick a core that won't get saturated, and for a 500VA transformer it'll have to be a big laminated iron one. That's going to be hard to find, and your best bet would be making your own. I'm not sure if you have access to a cnc/laser cutter and soft iron sheet though, as well as a welder. In the end it'll be cheaper to buy a used potential transformer anyway.

Steve Conner

Sat Oct 09 2010, 03:48PM

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

Grenadier wrote ...

If you're winding your own primary too, then volts per turn won't be a problem; you would have to worry about turns ratio instead. You'll also have to pick a core that won't get saturated

This is wrong. Volts per turn is the same thing as saturation: a core of a given size will have a maximum volts per turn rating that it can stand before saturating. There are well known equations for calculating the volts per turn from the cross-sectional area, frequency and so on: if you plan to design your own transformer, you should already have seen them. (Hint: there's a 4.44 in there)

Nobody makes their own transformer cores like that. You just buy them or salvage them from an old transformer. The bigger the transformer, the more likely it is that the core is in several pieces that can be unbolted. The last one I dismantled was a 2.2kVA plate transformer that was scrapped because of shorted turns. After some persuasion with a blowtorch, mallet, and big old screwdriver, the core came apart into four C-shaped sections.

Niraj Joshi

Sat Oct 09 2010, 04:54PM

Registered Member #3291 Joined: Fri Oct 08 2010, 06:06PM
Location:
Posts: 11

Guys/// This is only a short time rating device. The applicaation of Transformer will be only until the HV test for checking leakage current in insulation. The test period will last only for a few minutes (max 180 sconds).

The core i will have to buy from vendors of CRNO steel of course. Only the design i am worried about.

The volts per turn will remain same for primary for secondary winding. The no of turns for high voltage winding increase if i assume a safe value of v/t.

So a compromise of insulation, copper and core will have to be made.

Thank u for ur replies. Keep them coming.

As soon as i make the design i will post it for sure.

Carl Pugh

Sat Oct 09 2010, 05:49PM

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

I did a dry type 10 kV hipot transformer in1973,
It worked great, no corona at 10 kV.
Drawing is C size. If you would like, can scan on four A size and send to you. Send your Email address as a private message.
Drawing is written in shop abbreviations and will be difficult for you to interpret.

My advice would be to not attempt to design or build this transformer. You will have problems that you cannot imagine.

Good Luck
Carl Pugh

Adam Munich

Sat Oct 09 2010, 07:15PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

Steve McConner wrote ...

This is wrong. Volts per turn is the same thing as saturation:

Thanks for correcting me.

radiotech

Sun Oct 10 2010, 07:14AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

Make your primary 460 turns. Use a core E with center leg area 16 square centimeters , 8 cM long., Make you secondary 10,000 turns.
Run calcs using these bogies and see how the core flux is.

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