The non-monotonic voltage sag tolerance characteristics may lead to the wrong evaluation of voltage immunity of AC contactors. To analyze the non-monotonic voltage sag tolerance characteristics of AC contactors

this paper developes a detailed mathematical model including the electrical performance of the control coil. By solving the model

the current of control coil and the spring compression distance of AC contactor can be calculated. The voltage sag tolerance characteristics of the AC contactor are analyzed in theory. The non-periodic current will appear in the control coil during the voltage sag. The non-periodic component decides the electromagnetic force produced by the control coil

which determines the voltage sag tolerance characteristics. The research shows that the non-periodic current in the control coil is dependent on the voltage sag starting angle. It is the root cause of non-monotonic voltage sag tolerance characteristics. Finally

the experimental results show the correctness of the theoretical analysis.