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Transformer not giving 10kV

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Member level 4
Sep 23, 2008
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I have a simple circuit where I just need to give a 7kV to a surge protector to see if it works.

However I dont seem to be able to ignite it. The transformer is 380VAC on the pri and 10kV on the secondary I am triggering the SCR at 30 deg. The trigger on scope it perfectly at 30 deg. but 0.38kVA transformer is not going more than 5kV and the surge protector is just 7kV. SCR_TX.png

Not sure if the 1kohm might be too much so I tried a 2k instead but that didnt help much.

A current leakage would be a likely situation if the insulation and internal stacking of the winding layers are not adequate. Although this level of tension is not yet the most critical, had you injected varnish on wire reel ?

Try connecting the transformer directly across the 380v supply without any of the capacitors and measure the secondary voltage.
Then try it with the two capacitors fitted.

Those capacitors look very suspicious, and are large enough to create a resonance, but the effects of that are difficult to guess, which is why some experimentation may be in order.

Is this a straight conventional transformer, or does it have a shunt magnetic air gap (like a neon sign transformer) ?

The maximum voltage on a transformer depends on the frequency being applied or rise time in the case of switched inductors and self capacitance.

It would be straight forward to use an old ignition coil which has a high turns ratio and drive it with audio 10~20V to get 10 to 20kV and expect 10kV to arc at approximately 10mm from sharp wire. then it can be measured from the primary side after the voltage ratio is confirmed at low voltage. V is not always L di/dt when there is stray winding capacitance involved.

\One must choose a suitable transformer.

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