Discussion on “high-speed turbo-alternators — designs and limitations” (Lamme), New York, January 10, 1913)

Henry G. Reist: The author has treated this subject so fully that it leaves even those of us who have spent a good part of our lives on this work very little to add. He has weighed the different methods of construction so carefully, accurately and fairly that there is very little room for controversy, so what I have to say will be very brief and a part of it, at any rate, will be in the way of a slight further explanation of some of the methods of construction. The author limits the size of a two-pole machine of 3600 rev. per min. with a through shaft to about 600 kv-a. That is probably near the limit, if a solid shaft is used; but by the use of a flexible shaft, that is, a shaft which allows the rotor to run above the critical speed, the limits of output may be very materially increased. This is similar to the operation of the de Laval turbine, which in starting runs through a preliminary stage where it is not quite as steady as afterward, and then gets down to a perfectly quiet state. This construction does not require so large a shaft as if the machine were operated below the critical speed, and it is possible considerably to increase the limit of size. There are today a great many machines running constructed on this plan, of from 1000 to 2000 kw. in capacity, at 3600 rev. per min.