The operating mechanism creates and stores energy to operate the circuit breaker.

Spring; a spring-operated mechanism is one driven by the mechanical energy stored in springs. Typically, the “closing spring” is mechanically charged by a motor and is held in its compressed position by a closing latch. When a close signal releases this latch, this spring pushes against a mechanical linkage to force the breaker contacts closed and, at once, charges the trip spring. The closing spring is then immediately recharged by the motor. Another latch will hold the tripping spring in the compressed position until an open signal releases this latch.
https://uk.megger.com/applications/circuit-breakers/operatin...

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Note added at 1 hr (2020-03-19 12:48:00 GMT)
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What is spring charging of circuit breaker?
A spring charged motor mechanism is most popular. It consists a separate springs for Opening and Closing. You can see the below image for reference:
https://www.quora.com/What-is-spring-charging-of-circuit-bre...
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The braking device of the circuit breaker spring energy storage mechanism is applied in circuit breakers of gas insulated metal closed composite apparatuses, breaks a spring energy storage mechanism, and prevents energy of a spring from being stored in excess.
https://patents.google.com/patent/CN202796700U/en
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A Stored Energy Mechanism (SEM) is a mechanism that opens and closes a device (Switch) by compressing and releasing spring energy. The operating handle compresses a set of closing springs and a separate set of opening springs. These springs store the mechanical energy of this movement and are held in the compressed state by close and open latches. (In other words, the springs are pre-charged). The springs will release their energy when the close or trip latches are moved and will close or trip the device. The close or trip latches can be moved by local mechanical push buttons or by the plunger of close or trip electrical coils. The speed of operation is independent of the speed of the operator. The operating time of the SEM mechanisms is approximately 100 milliseconds. The motor operator will recharge the springs in approximately 3 seconds.
https://www.se.com/us/en/faqs/FA108257/