Automation of mine hoisting with asynchronous drive at skips with bottom unloading
Abstract
Lift automation at skips with bottom unloading in the period of deceleration can be realized by application of dynamic braking mode of asynchronous lifting motor. In Fig. 1 the calculated diagram of velocity during the deceleration period t₃ is shown by the dotted line λr. During the unloading period t₄', a constant velocity v₃ (line ρϕ) is assumed, which drops to zero during the period t₄ along the line ϕф. According to the force diagram of the induction machine shown in Fig. 2, the acceleration of the hoisting motor during the start-up period occurs along the broken line BCDEFGHIKLT, varying about the given (design) force value F₁ as about the average value between the extreme limits F₁' and F₁". At the end of the start-up period, there is a full stroke period during which the driving force follows all changes in the static force. Assuming a statically unbalanced lifting system, let the static force, and hence the driving force developed by a motor operating on the natural characteristic R₂, vary from the value of F's₂ at the beginning of the full stroke period (point N') to the value of F"s₂ at the end of this period (point N). At the end of the full stroke period, there comes a deceleration period t₃, during which a braking mode is assumed, which is implemented in the form of dynamic braking. An asynchronous machine from the motor mode on characteristic R₂ at speed vₙ is switched to dynamic mode by switching the stator from alternating current to direct current.
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