Current transformer with air gap for power supply

[AnIlin]

Hello everyone!
This is current transformer for supply electronic devices.
Does anyone know why it is like this?
Are there any books on designing such transformers?

A few questions:
1. Why is the right leg of the magnetic circuit narrow?
I think to limit secondary current and power.
2. Why do we need a middle leg with an air gap?
I think to increase leakage inductance. But why?

I ask for help with articles, books, links.
Thank you!

 

[waross]

As the current increases, the magnetic flux increases.
When the thin section saturates, The magnetic flux is forced across the air gap.
Flux is the product of the Amp Turns over the length of the magnetic path.
The ratio of air path to iron path may be over 1000:1
That is 0.001 inches of air path may be equal to 1 inch of iron path.
As a result, once the thin core saturates, the magnetic path is through the air gap and the flux density and the current are limited.
Cores such as that are very common in mercury vapour ballasts to limit the lamp current.

 

[AnIlin]

As the current increases, the magnetic flux increases.
When the thin section saturates, The magnetic flux is forced across the air gap.
Flux is the product of the Amp Turns over the length of the magnetic path.
The ratio of air path to iron path may be over 1000:1
That is 0.001 inches of air path may be equal to 1 inch of iron path.
As a result, once the thin core saturates, the magnetic path is through the air gap and the flux density and the current are limited.
Cores such as that are very common in mercury vapour ballasts to limit the lamp current.

thank you so much