Springs are widely used components in circuit breaker spring operating mechanisms, and springs at critical locations have a significant impact on circuit breaker performance. This paper takes an energy-based approach, considering the spring's installation space and utilizing existing spring calculation formulas to solve for unknown quantities from known quantities, obtaining the required spring parameters, and ultimately creating the spring design drawings.
Springs are widely used components in the spring mechanism of circuit breakers. Various types of springs, such as cylindrical or spiral springs, disc springs, leaf springs, and torsion springs, are used in the mechanism. Springs at critical points have a significant impact on the performance of circuit breakers. For example, improper design of the opening and closing springs will cause the circuit breaker to fail to open or close properly or to fail to meet the required opening and closing speeds.
This paper starts with the overall energy layout of the circuit breaker, combines the installation space of the spring, uses known conditions to solve the spring parameters, and then combines factors such as the surface treatment, strength verification, and reinforcement of the spring to design a spring that meets the requirements.
When designing a spring operating mechanism, the first step is to understand the overall energy distribution of the circuit breaker, that is, to determine the energy of the contact springs by using the rated current, rated voltage and other electrical parameters of the circuit breaker; then, to determine the energy of the opening spring based on the speed, mass of the moving parts and frictional resistance when the circuit breaker is opening; and finally, to determine the energy of the closing spring based on the speed, mass of the moving parts and friction when the circuit breaker is closing.
Based on the known energy of the opening and closing springs, and combined with the known conditions, the parameters of the springs are solved. Then, by combining the spring manufacturing process and strength verification, a spring that meets the requirements is designed.
Design of the trip spring
The functions of the tripping spring are mainly twofold: first, to meet the requirements of the circuit breaker's tripping speed; and second, to ensure that the circuit breaker is fully tripped. The former is necessary to break the electric arc, while the latter is to ensure that the moving and stationary contacts have sufficient opening distance after tripping.
The following design of the opening spring is based on a vacuum circuit breaker. The opening spring is a cylindrical helical tension spring. This type of spring is widely used and does not require a guide when it is working, and its structure is simple.
Design of closing spring
The design of the closing spring must also start from energy. The energy of the closing spring is mainly distributed to the contact spring, the opening spring, the work done by the electrodynamic force when closing, the work done by the gravity of the moving parts, and the energy consumed by the friction of the moving parts. Among them, the load energy generally accounts for 30 to 50% of the closing energy. Since the energy of the contact spring and the opening spring has been obtained, the energy of the closing spring can be roughly estimated.
Springs are widely used in circuit breaker mechanisms, and springs at critical locations have a significant impact on circuit breaker performance. For springs at critical locations, the design must ensure that the spring's working pressure P2 ≤ 80% Plim to prevent plastic deformation due to fatigue during operation. Furthermore, springs can be strengthened through shot peening, high-pressure treatment, etc., increasing their Plim value by approximately 20%.
Of course, depending on the application, using appropriate materials can also improve the spring's Plim value. After galvanizing the spring surface, a dehydrogenation treatment is necessary to prevent hydrogen embrittlement. In summary, when designing springs for circuit breaker mechanisms, both the requirements of the circuit breaker mechanism and the general design specifications of the spring itself must be considered to ensure that the designed spring better meets the operational requirements of the circuit breaker.
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