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Philips Optimus 65 X-Ray Transformer Saturation

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dude_500

Mon Feb 08 2010, 11:45PM

Registered Member #2288 Joined: Wed Aug 12 2009, 10:42PM
Location: Cambridge, MA
Posts: 179

I have the opportunity to purchase a Philips Optimus 65 X-Ray Transformer at a good price and am wondering about saturation problems. It is stated to operate at 7000hz, 150kV at up to 65kW. I'll be using it at fractions of 1kW, so basically no load as far as the core is concerned. I've had x-ray transformers in the past that have saturated and are useless without full load. Does anyone have experience with this transformer to know if it will work without full load?

Sulaiman

Tue Feb 09 2010, 01:14AM

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

I have no experience whatsoever with x-ray transformers, but a fair bit with other types,
basic principles;
Current capbility is determined by heating of the wires so is (mostly) independant of voltage,
so whatever the voltage, your transformer can supply 65kW/150k = 433 mA.

For a given core cross-section and number of turns, V.F is constant for a constant magnetic flux,
so at 60Hz you can get 150kV x 60/7000 = 1.3 kV

dude_500

Tue Feb 09 2010, 01:45AM

Registered Member #2288 Joined: Wed Aug 12 2009, 10:42PM
Location: Cambridge, MA
Posts: 179

I plan to run it at 7000hz not 60

rp181

Tue Feb 09 2010, 03:05AM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

Is there any chance your talking about the ones on fusor.net?
I live less than 20 min. from that guy, so I second the questions.

I think dude is trying to ask if there would be any problem running it at 1kW rather than the rated 65kW.

dude_500

Tue Feb 09 2010, 03:09AM

Registered Member #2288 Joined: Wed Aug 12 2009, 10:42PM
Location: Cambridge, MA
Posts: 179

Yes I am... I asked him to test it but always nice to get a second opinion. All he has is an audio amp driving them so I'm not sure how comprehensive of a test he can do. I live where it would have to be shipped so I'd rather not just hope it'd work.

And yes, I want to run at 1kW not 65 (actually probably far less than even 1kW)

klugesmith

Tue Feb 09 2010, 03:16AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

dude_500 wrote ...
...I've had x-ray transformers in the past that have saturated and are useless without full load.

Not sure what you mean by "saturated". The permissible maximum flux density in the core can be translated to a limit on "volt-seconds per cycle" or "volts per hertz". I don't see how reducing the secondary current can increase the magnetic flux density, IF the high-frequency driver maintains a fixed voltage and frequency. Unless there is a large I*R voltage drop in the primary winding under full-load conditions, enough to keep the volt-seconds below saturation.

There might be an issue with x-ray systems using self-rectification by the x-ray tube.
That results in significant DC current in the secondary loop, when tube is conducting.
So the primary winding is generally in series with a (diode in parallel with a resistor) to allow appropriate DC current to flow in primary & avoid saturation.

dude_500

Tue Feb 09 2010, 03:31AM

Registered Member #2288 Joined: Wed Aug 12 2009, 10:42PM
Location: Cambridge, MA
Posts: 179

Klugesmith wrote ...

dude_500 wrote ...
...I've had x-ray transformers in the past that have saturated and are useless without full load.

The last x-ray core I had which was 60hz was useless because if it was driven up to 110V primary, it would draw >2000W from the wall with zero secondary. This is what I mean by saturation. It couldn't be used effectively below it's dozens of KW rating.

...

Tue Feb 09 2010, 04:03AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

This is not saturation, for reasons that are probably not worth getting into. The current you are seeing is called the 'magnetizing' current, and is mostly reactive (or you could say has a power factor of about .01, or is drawing very little 'real' power, most of that 2KVA is being reflected back to the power company). Note the distinction between VA and W, a watt implies 'real' power, where as VA is just rms current multiplied by rms voltage--depending on the phase of the voltage and current these numbers are only the same for a power factor of 1.

That being said, it is a solvable problem, and the solution in the case of the large 60Hz transformer was probably as simple as adding a capacitor bank in parallel with the primary to help balance out all of the reactive power.

In the case of the 7000Hz transformer, you just need to design your driver correctly, there is no reason a large transformer can't be used at well under its rating (but you have to deal with the added cost/size of an oversized transformer, so it is rarely done)

Good luck!

Proud Mary

Tue Feb 09 2010, 02:46PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

dude_500 wrote ...

The last x-ray core I had which was 60hz was useless because if it was driven up to 110V primary, it would draw >2000W from the wall with zero secondary. This is what I mean by saturation. It couldn't be used effectively below it's dozens of KW rating.

The Philips Optimus 65 requires a 3-phase ~400V supply Ipk 190A, but Islowblow <50A. An up-convertor to enable operation from 230V single phase is available as a costly optional extra.

The Optimus 65 has 111 user selectable 1kV steps ranging from 40kV/100uA, through to user selected permutations of 65kW i.e. 900mA @ 65kV and 433mA @ 150kV.

dude_500

Tue Feb 09 2010, 08:14PM

Registered Member #2288 Joined: Wed Aug 12 2009, 10:42PM
Location: Cambridge, MA
Posts: 179

Proud Mary wrote ...

I won't be using the big 3-phase 400V driver though, I already have a small MOSFET driver based on the IRS2453 chip that can drive up to about a kilowatt max. The sale is only for the transformer, not all the driver circuitry.

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