The delay is created by forcing the core to move through a cylinder filled with silicone fluid. When the overcurrent occurs, the magnetic field created pulls the core. The core has to pass through a cylinder filled with silicone fluid. This introduces the time delay.
Thus if the overcurrent is momentary, the core goes back after the current comes back to normal. If the overcurrent persists, the core travels towards the coil.
When the core reaches the coil, the reluctance of the magnetic circuit changes. This creates sufficient flux to attract the armature which causes the protecting device to trip and the contacts to separate.
Once the contacts separate, the current becomes zero. The magnetic field ceases and the core returns to its original position.
The advantage of the magnetic hydraulic circuit breakers is that they can be reset immediately after tripping unlike thermal overcurrent elements which require a cooling period.
Magnetic Hydraulic Circuit Breakers provide accurate, relatively inexpensive and reliable overcurrent protection. They are independent of ambient temperature.
Magnetic Hydraulic Circuit Breakers are available both for AC and DC applications.