133 / 2024-04-14 16:44:43

Simulation and optimization of bimetal multifield coupling of micro DC circuit breaker

micro circuit breaker; Bimetal sheet; Heat trip; Temperature field simulation; Multiple physical field coupling

Low voltage micro DC circuit breaker is widely used in low voltage DC power system, when the DC system has a long overload current, the bimetal sheet will bend because of the overload current heat accumulation, and push the traction bar to make the circuit breaker trip, break the overload current. In this paper, aiming at the instability of bimetal thermal trip time of micro DC circuit breaker, simulation software is used to simulate and optimize the operation characteristics of thermal trip process.

In order to determine whether the bimetal sheet of a certain specification can achieve stable thermal trip in a certain type of miniature circuit breaker, this paper determines the thickness and metal composition of the bimetal sheet of different current specifications through the microscope and element spectrum, establishes a three-dimensional model of the bimetal sheet, and connects the bimetal sheet model with the metal terminal model in the miniature circuit breaker. In order to simulate the operating environment of the bimetal sheet heating and heat dissipation in the micro circuit breaker. Through the coupling simulation of electric field-temperature field-structure field, the thermal deformation process of bimetal sheet is simulated, and the shape variables and output characteristics generated by bimetal heating under different power distance are calculated. And through the transient field simulation, the thermal trip time of bimetal sheet is determined to meet the standard requirements.

The simulation results show that the bimetal sheet of 16A, 20A and 25A can reach the trip distance of the product design under the corresponding overload current, while the bimetal sheet of 10A, 32A, 40A and 50A cannot reach the trip distance of the product design. In order to make the micro DC circuit breaker stable trip in the specified current and specified time, this paper reduces the cross-sectional area of the deformable end of the 10A bimetal sheet, and improves the end-shape variable of the bimetal sheet by changing cross-section and other technical means. For the original design of 32A, 40A, 50A bimetal sheet of the miniature circuit breaker, the bimetal sheet specifications are replaced by 25A, 32A, 40A, and control the bimetal sheet power distance so that the miniature circuit breaker can be smoothly tripping.

In order to verify the feasibility of the simulation, the bimetal pieces with different current specifications were installed to the micro circuit breaker for thermal trip research test verification, and the optimization scheme was adopted for the micro circuit breaker that failed to trip, in order to prove the feasibility of the simulation analysis and optimization scheme.