Breaker closing and tripping mechanism

The breaker closing and tripping mechanism is complicated mechanical system called Breaker Operating Mechanism. This mechanism primarily contains Close spring, Trip spring, Close coil, Trip coil, Spring charge motor (or solenoid mechanism) etc. The close spring is much stronger than the trip spring. The breaker is closed with the force applied by releasing the close spring and at the same time the trip spring is charged automatically. The close spring should be strong enough to close the breaker contacts and charge the trip spring simultaneously.

The operating mechanism has basically 4 states:

(1) Breaker opened state with close spring discharged, trip spring discharged

(2) Breaker opened state with close spring charged, trip spring discharged

(3) Breaker closed state with close spring discharged, trip spring charged

(4) Breaker closed state with close spring charged, trip spring charged

Let's start from the sate 1. The breaker remains in this state generally after the first installation or after the maintenance. The first thing that needs to do is 'charge the closing spring either manually or electrically'. Most of the breaker has both options to charge the spring. After the maintenance or new installation, as soon as you apply the control power, the close spring is charged electrically. There is a limit switch which stops the charging when the spring is fully charged. The charged close spring is locked and hold by a latching mechanism. The breaker now moves to state 2.

At this state, the latching mechanism is released electrically by close coil or manually (most of the breakers has both options). The close spring is then released and closes the breaker contacts and charge the trip coil with the releasing force. The trip spring is now locked and hold by another latching mechanism. It now goes to state 3.

State 3 remains very short time. Once the close spring get discharged, the limit switch closes and the close spring is electrically charged again. It then moves to state 4 and remains in this state as long as the breaker keeps closed.

The trip coil is electrically operated either by protection relay or manually from breaker open signal and releases the trip latching mechanism. The force of releasing the trip coil opens the breaker contacts. The breaker now goes to back to state 2 and remains in this state until the next close operation.

If the breaker needs to do any maintenance, it must be in the sate 1 first.

The change of state from 2 to 3 and 4 to 2 happens very quick. I am not sure I could explain it because the breaker operating mechanism is one of the most complicated mechanical system that I ever seen.

-MS