Modeling of overloads of raising mechanism in metallurgical overhead cranes

Electromechanical processes occurring when the load is lifted by an overhead crane are considered. The main idea of the work is to identify emergency mode (crane overload) by a method based on control of stator current of lift motor. To obtain stator current diagrams of electric motor, mathematical model of overhead crane (three-mass circuit) has been developed, which includes equations describing elastic properties of crane beams and its rope. A system of (α, β) coordinates, fixed relative to electric motor stator, is adopted to describe the drive asynchronous motor. Lifting cycle is considered as sequence of three steps: choice of the rope “slack”; rope tension; separation of cargo lifting. For each stage, a system of differential equations has been compiled describing motion of masses of overhead crane elements and electrical parameters of electric motor. Initial and boundary conditions for each of the stages were determined. Preliminary transformations of the system of equations to their solution by numerical methods and subsequent modeling of stages of lifting loads were carried out for different weights. Sequential solution of three boundary value problems allows obtaining values of stator currents at time of load separation. Diagrams of stator phase currents of an electric motor were obtained for loads of different mass. Simulation results indicate the presence of fixable difference in magnitudes of stator currents after the load is separated from the support surface. On basis of the developed model and the study results, a functional diagram of crane overload protection device is proposed and its principle of operation is described. It consists in controlling lifted load mass and stator current when lifting
the load. Conclusion is made about feasibility and effectiveness of monitoring electrical values of lifting motor for development of overhead crane protection against overloads. Effectiveness of the proposed system was evaluated.

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