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Arjan EMM

Tue Jul 29 2008, 11:01PM

Registered Member #149 Joined: Sun Feb 12 2006, 09:11AM
Location: Netherlands
Posts: 12

I designed and built a big charging reactor for a dc sgcoil. A 50kva 3fase core with the middle leg cut out and an air gap. After some testing it turns out the reactor will probably start saturating at full power.
As a test i dumped a big cap through the reactor and measured the current on a scope. It should hold out to 7 Amps but the expected sine shape starts to bend the wrong way slightly at 4.5 amps and sky rockets around 12 amps.
Will the reactor still store all the energy and charge the primairy cap to twice the voltage or can you expect large losses ?

i find this bit of magnetics a bit hard too grasp.

Bert

Wed Jul 30 2008, 06:27PM

Registered Member #118 Joined: Fri Feb 10 2006, 05:35AM
Location: Woodridge, Illinois, USA
Posts: 72

Have you tried increasing the air gap a bit? A small amount of nonlinearity should not be a problem - you'll charge up the tank cap a bit quicker, peak current will be a bit higher, but you'll still get approximately 2X Vsupply on the tank cap. However, if your charging inductor goes into hard saturation, you may develop power arcing in your spark gap, your charging choke may overheat, and your HV supply voltage may droop due from excessive loading. If you happen to be using an unballasted low impedance HV supply, you may even take out your HV rectifiers or trip the mains breaker/fuse.

Arjan EMM

Fri Aug 01 2008, 06:53AM

Registered Member #149 Joined: Sun Feb 12 2006, 09:11AM
Location: Netherlands
Posts: 12

Very clear, thank you. With a longer air gap, the non linearity starts at a higher current as expected.
From the tests it looks like we can run it in discontinuous mode at the highest bps with just a little bit of non linearity.
So we should not run in the the problems you mentioned.
The idea is to set the airsgap shorter with a lower max bps depending on the power available to keep the peak currents at a appropriate level. (And so a better power factor)

Dr. Drone

Fri Aug 01 2008, 02:15PM

Registered Member #290 Joined: Mon Mar 06 2006, 08:24PM
Location:
Posts: 1673

Herr Zapp

Sat Aug 02 2008, 02:11AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

Arjan -

Did I read your description of the core as being removed from a 50KVA (fifty-thousand volt-amps) transformer? And its saturating at 4.5 amps? Can you provide some additional details about this core, like:
Material: (laminated silicon steel, or tape-wound?)
External dimensions: (overall height-width-length)
Physical form: (E-I core, O-core, or something else?)

It seems difficult to understand how a core capable of handling 50KVA could saturate at 4.5A.

Regards,
Herr Zapp

Arjan EMM

Sat Aug 02 2008, 11:29AM

Registered Member #149 Joined: Sun Feb 12 2006, 09:11AM
Location: Netherlands
Posts: 12

Yes it's a core from a 3 fase 50kva transformer. Center leg is removed. We cut the core in two so you end up with two C's.
Laminated silicon steel.
The cross sectional area is 110cm2
Mangnetic length is about 200cm. outside dimensions 55x 55cm
1000 turns with 2,5mm2 in 20 sections.

I added some pictures of the whole powersupply
The reactor is standing in front of the 125kva 3 fase transformer with the fuse and relay box on the right. On the left you see a small part of the rectifier box. (black with ceramic white insulators)

In the second picture you seen more of the rectifier.
In the acrillic box sits a jennings hv relay that turns the coil on an off. It has it's own switching supply with a tranformer wound with hv wire for better galvanic isolation.
In the grey box sits a frequency inverter for the rsg and a motorized 3 fase variac to "softstart" the 125kva transformer.

Steve Conner

Sat Aug 02 2008, 11:30AM

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

wrote ...
It seems difficult to understand how a core capable of handling 50KVA could saturate at 4.5A.

Easy, with a large number of turns, such as you'd use to build a high voltage inductor.

Herr Zapp

Mon Aug 04 2008, 06:15AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

Arjan -

What is the dimension of the air gap you are currently using?

Herr Zapp

Arjan EMM

Mon Aug 04 2008, 07:14AM

Registered Member #149 Joined: Sun Feb 12 2006, 09:11AM
Location: Netherlands
Posts: 12

With two 2mm airgaps, so 4mm total. soft saturation seems to start around 4.5amps as in my first post. And gives around 3-4 henries.
With two 4mm gaps, 8 total, soft saturation seemes to start around 6 amps with aprox 2-2.5 henries.
Self induction was exptrapolated from the scooptrace while dumping 4800uF in it so it's not very accurate.
The numbers are not very far of from what we need so i guess we don't have a problem :)

After rectifiing we have 14kv, so we charge a 300nF tankcap two 28kv at max 600 bps.

Steve Ward

Mon Aug 04 2008, 05:48PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

After rectifiing we have 14kv, so we charge a 300nF tankcap two 28kv at max 600 bps.

That should be satisfying! Thats like 70kW, very cool! I hope you will actually finish this project and show us your results, im sure they will be stunning no matter what.

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