D. C. drives for winders

It is generally accepted that the type of control obtainable with the Ward-Leonard drive is the most suitable for mine winder operation and all developments on other electrical drives for winder have striven to achieve a similar control. There are, however, a number of other factors which affect the decision on the type of drive to use on any particular installation. The most important of these, viz power consumption, voltage regulation, maximum demand, capital cost, heat dissipation and harmonics, are considered in the paper and a comparison is made between Ward-Leonard, rectifier and a.c. drives in relation to these factors. For many years, open-loop control of winders has provided adequate control characteristics but the more stringent operational requirements for modern electric winders have resulted in the development of closed-loop control systems. Two such systems, one for a Ward-Leonard drive and the other for a rectifier drive, are described and the arrangements for obtaining automatic retardation of the winder as the conveyances approach the terminal points of the shaft are discussed. Operational results obtained on winders employing these systems arc given and attention is given to the means for stopping the winder in emergencies. It is concluded that the results obtained with the closed loop Ward-Leonard system are sufficiently accurate to meet present requirements but that some improvement is still desirable on the rectifier winder. Future developments would, therefore, appear to be aimed mainly at the application of new techniques to achieve similar results.