The economical speed control of alternating-current motors driving rolling mills

For reasons which need not be discussed in this paper the induction motor has been adopted almost exclusively for driving rolling mills where electrical equipments have been installed. One of the most difficult problems to be solved with this type of motor when electrifying rolling mills is the speed regulation required for the merchant and hand mills, owing to the fact that this type of motor is normally a constant speed machine. It is also one of the requirements on which it is almost impossible to obtain reliable information and one which invariably leads to a great deal of discussion, not only between the electrical engineers and the mill operator, but also amongst the operators themselves. Although the principal types of mills requiring adjustable speed are the merchant and hand mills, it is occasionally necessary to run the mills rolling heavy sections at various speeds. In the latter case, however, the problem is usually fairly simple because as a rule only two speeds are asked for.