Electromechanical modeling of a contactor with dc coil

The purpose of this article is to model a contactor with dc coil using simple electromechanical equations. These models do not need a detailed description of internal characteristics of the contactor, and the parameters are estimated from external measurements (current in main coil, and operation time of contacts). Four models are formulated to obtain the operation time of contacts and to describe the current in contactor coil. Two ways for modeling the contactor have a constant equivalent area for airgap (with and without considering friction). The other two ways for modeling the contactor have a variable equivalent area for airgap; these two ways only have different parameters for models. The results of these models are compared with experimental measurements. Although the proposed models include several simplifications, these models are very accurate for obtaining the operation time of contacts for eight different values of the dc source voltage. The three transient stages of the current in contactor coil are obtained with these models, with good accuracy for the time of occurrence of the local minimum of the current. These facts are important, because they imply a good representation of the behavior of the contactor. The obtaining of the three transient stages of current in contactor coil, using the electromechanical models, had not been shown in the literature. This article shows the feasibility of obtaining such computed results, which are in agreement with experimental measurements.