A-C. Elevator Motor Drive

There are very few data available on the problems of using alternating current when applied directly to a motor on an elevator. It is apparent, also, that eventually there will be no d-c. power transmitted for elevator service. Because of these facts and the size of this industry it seems that such data should be available. A paper covering the entire field in detail would be excessively long and it is therefore the aim of this paper to cover the subject in a general way, giving such outstanding facts as are felt to be of most interest at this time. It is hoped also to correct a false impression that is sometimes found to exist-that an a-c. elevator is not practical for car speeds above 350 ft. per min. Without question, this understanding was correct six or seven years ago but it is desired to call attention to the fact that for the past five years many a-c. elevators have been installed with car speeds in excess of 500 ft. per min. and today some are operating as high as 700 ft. per min., and nothing has appeared to indicate that there is a limit of car speed other than for any other type of control. A brief outline of the necessary requirements of the elevator machine is given because as yet the development of a-c. elevators has depended upon the success of this unit.