Optimization on magnetic trip used in hydraulic-magnetic circuit breakers based on Taylor approximation

Insufficient unlocking torque provided by the magnetic trip in circuit breaker at low over-current may lead to a certain probability of trip failure in a batch of breakers, which lowers the qualified rate and the quality consistency. The existing solutions to improve the unlocking torque of product batches are mostly based on single factor analysis and optimization, but the impact of multiple factor interactions on product performance are neglected. In this paper, finite element model of the magnetic trip is firstly established, and the key dimensions that affect the unlocking torque are determined and parameterized. Then, a fast approximating model for calculating the unlocking torque is established based on Taylor expansion method in their possible varying ranges, considering the influence of independent term, interactive term and error term for improving the accuracy. Signal-to-noise ratio and sensitivity of each dimension are analyzed by using the orthogonal test method to determine their significance, and the optimized dimensions of key parts in the magnetic trip are obtained. Finally, a batch of the circuit breakers with both the original and the optimized dimensions are manufactured, and the effectiveness of the optimized design method is verified by comparing the median and standard deviation of both the unlocking torques and the tailored time delays under a series of overload current multiples.