Transient Performance of Electric Elevators

The investigation of transient conditions is vitally important in elevator engineering, both electrical and mechanical. In no other method of human transportation are traveled distances so short and speeds and loads so frequently varied. Passengers mutst be hoisted and lowered safely and expeditiously. Landings must be accurately made. The elevator is consequently a machine that is very sensitive to transient effects and the entire apparatus must therefore be designed on the basis of transient analysis. Pure mathematical determination of elevator transients is evidently both difficult and laborious. In some cases it is impossible because the functions are unknown. Graphic methods of analysis lead to a much clearer understanding of the reasons for transient conditions, thus considerably aiding development. Interdependent mechanical and electrical transients of a hoist system are first developed in the following. Then separate mechanical and electrical transients are considered. Finally, temperatures of the electrical apparatus, resulting from elevator operation in service are determined. The basic method of transient determination used in this paper is to plot one or more curves representing integrals which each contain a single variable and which, when integrated, will give the desired solution. These integrals are evaluated between limits by measurement of the areas defined by these curves. Methods of determining elevator transients of speeds, distances, currents, voltages, powers, forces and fluxes, are developed in this paper by means of this system of graphic integration.