I presume that you are referring to a live tank circuit breaker design.
"On live-tank circuit breakers, the interrupter chamber is arranged in the insulator, which can be either porcelain or of a composite material and is at high potential with the voltage level determining the length of the insulators for the interrupter chamber and the insulator column."
You can Google for "live tank breaker" vs. dead tank breaker design and check on image to see the insulator column.
Basic idea is to put a current transformer around the leg supporting the breaker in such a way as to detect fault currents and trip the equipment out of service. From here it just gets more sophisticated as this elemented is integrated into the larger protection scheme.
CR
"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]
The concept of using CT on the base of insulator it is common practice for dead-tank breakers design. However for live tank breakers LTB design virtually impossible difficult at best since there is not current flow at the base of the LTB breaker insulator.
If any one have information with LTB with CT as described above post please share that with us
This is more commonly known as Breaker Frame Leakage protection. Use a donut CT mounted on the bottom of the structure.... Run your ground connection plus any control cables through this CT and connect it to an overcurrent relay. Simple and effective.
