Overwinding protection devices are used to brake hoisting containers before these containers reach a limited height, thereby preventing the hoisting containers from impacting the hoisting system. However, in ultra-deep shafts (depth > 1000 m), traditional overwinding protection methods fail to protect the hoisting system, because this type of hoisting system has a greater mass, kinetic energy, and inertia than the traditional hoisting system, and also the environment of ultra-deep shafts is more complex. This paper presents a novel overwinding protection method that applies a linear permanent magnet eddy current brake (LPMECB) to the hoisting system in ultra-deep shafts. This paper also finds the optimum setting parameter of permanent magnets (PMs). First, an analytical model of the LPMECB is built, and the time-domain signals of the braking force are processed via fast Fourier transform, confirming the mechanism of the optimum setting parameter. Subsequently, the simulations are conducted by establishing a finite-element model of the LPMECB; the simulations prove the existence of the optimum setting parameter of PMs and demonstrate the influence of the air gap, velocity, and conductivity on this parameter. Finally, the experimental studies are carried out on a test bench of the LPMECB to validate the analytical model and the simulation results. The results show the existence of the optimum setting parameter of PMs and prove that the air gap has an effect on this parameter.INDEX TERMS Eddy current brake, linear permanent magnet, overwinding protection.
To improve the braking force of the Linear Permanent Magnet Eddy Current Brakes (LPMECB) under a large Air Gap (AG) length, this paper presents a novel structure of the LPMECB, named H-type Linear Permanent Magnet Eddy Current Brake (H-type LPMECB). To begin with, the analytical model of the LPMECB is established by using the equivalent magnetic circuit method, and it is found that the AG reluctance is greater than that of the other parts of the LPMECB. Based on this, a novel H-type LPMECB is proposed in order to compensate the influence of the AG. The H-type LPMECB adds Iron Foils (IFs) in the AG. These IFs are rectangular sheets made of pure iron. Furthermore, the finite element model of the H-type LPMECB is established to optimize the geometry parameter of the IFs, then the braking performance of the H-type LPMECB is measured. The simulations show that the optimal geometry parameter of the IFs of the H-type LPMECB is 0.25 ∗ L, and the braking performance of the H-type LPMECB is superior to that of the LPMECB, around three times. Finally, experiments were conducted, which validated the simulations.
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