Permanent magnetic actuator（PMA）for vacuum circuit breaker is always powered by the energy storage electrolytic capacitor

which has a significant influence on the dynamic behaviour of the actuator. But at present there’s no specific theoretical method to evaluate the capacitance. Therefore

an evaluation method for the capacitance value of the energy storage used in PMA is proposed

i.e. the capacitance can be calculated under the condition that the first peak value of the discharged current equals to the critical moving current

based on the corresponding analysis of the excitation characteristic and the dynamic performance. By taking a certain PMA as example

the process of the evaluation for the capacitance is discussed. In the end

the dynamic behaviour of the PMA excited by the obtained capacitance is studied. The result reveals that the evaluation method for the capacitance value can not only ensure the breaker operating reliably but also ensure the capacitance getting the minimum value

which optimizes the design of PMA.