Effect of power frequency on the stress state of disc actuator

This paper presents the concept of determining the optimum frequency of coil supply in inductive-dynamic drive. As a criterion to obtain the sought frequency, the smallest value of reduced stress in the disc was assumed while maintaining the desired dynamics. The disc stress is determined on the basis of solution of vibrating thin plate equation. Magnetic pressure acting on the disc is obtained from a hybrid circumferentially-field model (CI-FI). The observations made during the experiment with the physical model of the actuator show that in some extreme cases the disc is clearly deformed, as evidenced by the oscillations of its center (Fig. 2). Hence, it is necessary to determine the stress state of the disc, due to the possibility of not only elastic, but even plastic deformation of the disc. Even a slight deformation of the disc is unacceptable from the standpoint of repeatability of drive work in the hybrid circuit breaker (6). Therefore, to determine the stress state of the disc, a mechanical model for a circular plate energized by electrodynamic force, has been built. The force was calculatedin the program realising CI-FI modelpresented in the accompanying article (5). Electrodynamic actuators consist of two main parts: a coil supplied with capacitor banks and a movable disc. The disc in a hybrid circuit design solutions is also a movable contact (Fig. 1). Drive project is made individually depending on the properties of the circuit breaker to which it is to be used. It is based on the selection of actuator parameters such as the dimensions of the disc and the coil and the number of turns, and also the capacitance and initial voltage capacitors. The selection criteria for these parameters are usually determined by the set dynamics of the disc, that is contact (disc) must achieve sufficient distance in a specified time. This criterion is met by a suitable choice of initial energy of the capacitor in relation to the mass of the disc. By changing the dimensions of the disc, e.g. by reducing the thickness, one can improve its dynamics, but it should be kept in mind that its deflection can then grow. On the other hand, the initial energy of the capacitors depends on the voltage and capacitance. The change of capacitance will change the frequency of the transient coil current and hence it will change the force frequency that forms as a result of the electrodynamic interaction.