I got some two-stranded litz wire for cheap. My plan was to easy wind a bifiliar interstage transformer, as the wire is just ready to use.
My worry is finding out how much voltage potential the wire might withstand.
The spool is labeled with a efficient wire diameter of 0.224mm
The thickness of the wire I measured is 0.25mm with a micrometer. That results in an enamel coating thickness of 13 microns.
What could be the worst quality enamel used, let's assume it is to stay on the safe side? What could be its dielectric breakdown voltage?
My intention is to use the built transformer in a DC voltage potential of 350V between the secondary and primary max.
My worry is finding out how much voltage potential the wire might withstand.
The spool is labeled with a efficient wire diameter of 0.224mm
The thickness of the wire I measured is 0.25mm with a micrometer. That results in an enamel coating thickness of 13 microns.
What could be the worst quality enamel used, let's assume it is to stay on the safe side? What could be its dielectric breakdown voltage?
My intention is to use the built transformer in a DC voltage potential of 350V between the secondary and primary max.
I'd doubt you would get a datasheet rating of insulation voltage rating for enamelled wire. The detailed one I have from litone doesn't go anywhere near that type of spec. Safety standards wouldn't either. I think you'd be looking for ad hoc failure with any such wound transformer. Perhaps trade one strand for an insulated wire with 'basic insulation' rating.
According to the CEI standard 317.1, a wire of 0.224mmm has to withstand 300V AC for a grade I insulation (normal insulation) and 750V AC for grade II (reinforced enamel).
The outer diameter for grade I is 0.256mm and 0.276mm for grade II, yours is thus grade I.
The outer diameter for grade I is 0.256mm and 0.276mm for grade II, yours is thus grade I.
Thank you Elvee. I'd like to add a further question if you don't mind. Is this voltage rating applied to wire-next to-bare metal conditions or wire-next to-wire conditions?
Litz wire is many strands of ultra thin wires wound in a format that brings the innermost wires out towards the outer of the bundle.
All the wires in the bundle swap repeatedly from outer to centre of core.
Typically the Litz wires <<0.1mm diameter.
Two wires each of 0.22mm diameter can't be Litz.
Maybe you just have two enamelled copper wires.
All the wires in the bundle swap repeatedly from outer to centre of core.
Typically the Litz wires <<0.1mm diameter.
Two wires each of 0.22mm diameter can't be Litz.
Maybe you just have two enamelled copper wires.
The two wires are held together using the same kind of silk insulation strands that other litz wire are held too with, this is why I assumed so. I guess you're right. It's just an enameled twisted pair.
It is for the wire wound on a bare metal mandrel 12mm in diameter, but this doesn't mean the wire-to-wire rating is 2 x 300V: first, the breakdown voltage does not increase linearly with insulation thickness, and second, the spec takes the defects into account: enamel has a number of defects/100m, and this figure is low enough to ensure that in a winding, the probability of having two defects in contact from adjacent turns is negligible, but there will be spots where only one layer of enamel takes all of the insulation task, meaning it is prudent to base your calculations on 300V.... but you are free to do whatever you think safe
Thank you. Well, safety is really important here. You mentioned 300V AC, while my maximum potential difference will be 350VDC. I suspect it should be okay, no?
Your OP says ...."DC voltage potential of 350V between the secondary and primary max"
If you separate primary from secondary with an appropriate layer of insulating tape or paper, that will take care of your requirement, surely?
If you separate primary from secondary with an appropriate layer of insulating tape or paper, that will take care of your requirement, surely?
Perhaps you need to think about vacuum impreg, as a method to improve creepage/clearance between existing and future pin-holes or insulation thickness variations or cracks due to winding, and use insulation resistance measurement at 500VDC as a measure of merit (as built and periodically over time).
The only advantage with this wire is what you say "to easy wind...." as you can continue the complete wind without interruption.
Disadvantage is, apart from the higher risk of failure, that a wire like this will take more winding space. It takes the width and heigth of two wires, and there is the additional insulation to make it "one" wire.
When you build up the coil the normal way, that is "one layer primary - thin sheet insulation - one layer secondary", and you repeat this process until you reach the needed number of primary/secondary turns, you will have an IT with the same quality without the disadvantages of the bifilar wound (breakdown risk; winding space).
But it takes more time 😀😀😀
An useful advice. I'm wondering if paraffin would work, or I definitely have to use a varnish compound?
Exactly! I'm trying the easy route! 😀😀 Layer by layer horizontal + vertical sectioning is going to last a lifetime. 😱
50 turns of this wire, roughly wound on a mandrel with sharp edges successfully resisted 1kV DC using a megaohmmeter 🙂 So I suppose 350Vdc will not be an issue.
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