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Registered Member #57520
Joined: Thu Oct 15 2015, 11:21PM
Location:
Posts: 15
Hi there, I need some advice with a transformer I'm winding. It's an ETD59, with 211 secondary turns of 0.27mm wire.
I have wound from left to right all the 41.2mm of the coil former and I'm at 156/211 turns, so I have to wind 55 more turns from right to left.
This means a second layer of wire although just a bit. This transformer is 5kV so I have calculated the voltage between the two layers of wire to be 3kV max @ 110kHz. I have left 3 layers of epoxy dry before starting the second layer of wire, but I'm not confident that this will work because this is the second attempt. In the first one, the transformer died instantly because of the voltage between the two layers of wire, so I'm trying again and need something else.
I was thinking about applying some Scotch 23 on the first layer of wire that already has 3 layers of epoxy, and then winding those 55 turns that will only take 1.4cm from right to left.
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
You might want to think about winding the second layer in the same direction as the first. Bringing the return wire back requires insulation both above and below it, but you can choose a point not constrained in height by the return limbs.
There are several advantages. The first is that it halves the peak voltage between the layers, and makes it consistent at Vlayer, rather than being 0 at one end and 2Vlayer at the other, so gives you more efficient use of your interlayer tape thickness.. The second is that it reduces the self capacitance of the secondary, by the same mechanism of reducing the peak voltage between the layers.
Registered Member #2939
Joined: Fri Jun 25 2010, 04:25AM
Location:
Posts: 615
You might want to reassess that statement. If the second layer was going to cover the entire bobbin I'd agree with you, but as its only going to be 1/3 of the bobbin width there will be less voltage stress, by about 500V, just winding back from the end of the first layer.
I'd second using Kapton tape over Scotch 23. The Scotch tape needs to be stretched and lapped, so its not going to be easy to achieve uniform or controlled thickness. Preferably use Kapton tape wide enough to cover the bobbin in one wrap, without lapping.
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HV transformer isolation
