I just stumbled across this picture a while back and wanted to ask: Why are there spaces in the secondary windings? What purpose does it serve?

 

Must be separation for high voltage.

Don't know offhand the insulation value of the coating on magnet wire, but it's not terribly high.

By adding spacers between the windings, the effective insulation value is increased.

 

They also improve the voltage rating by using a different winding technique - if you compare to a single spool of the same overall size, the windings typically run back and forth in layers. The start & finish of each pair of layers are a lot of turns apart but directly on top of each other so minimal insulation between them.

The segmented former is wound one section at a time, then working from one end to another. The narrow segments mean only a few turns between any two wires in contact, so a vastly higher voltage rating is possible with the same wire insulation.

 

Thanks for the answers. Just a few more things I would like to know?

I was curious because I've never seen any HV transformers with secondary spacing like that....

Is it just used when the transformer is not insulated with oil or when the wire coating is not strong enough?

Is there a name for it? Is it very common?

Do the spaces create capacitance within the transformer?

 

It's a coil bobbin.

The flanges are there to effectively increase the voltage rating of the secondary.

It would also help to delay the onset of core saturation.

The extra spacing caused by the flanges would actually help to reduce the capacitance.

 

I do believe many automotive and aeromotive high tension magnetos were bobbin wound.

There are certainly some patents on such bobbins.