Difficulties in the Path of Constructing Giant Generators Discussed by Stone--Queer Problems of Vibration Arise

"The problems raised in constructing increasingly large water wheel and turbo-generators are for the most part mechanical," declared Morris Stone '23 research engineer for the Westinghouse Company, in a recent interview with a CRIMSON reporter. "Seven years ago the largest generator was capable of producing only 20,000 kilowatts; but recently a 95,000 kilowatt generator has been built and at present one is under construction which will produce 160,000 kilowatts. In increasing the size of these generators, the electrical companies have been facing mechanical rather than electrical difficulties."

"Several examples will serve to illustrate the methods of dealing with vibration difficulties. In the western part of the country there is a large power plant to which water is brought from a great head by huge pipes. The residents of the vicinity were considerably disturbed by a high pitched sound which seemed to be produced by the water pipes. After thorough investigation it was found that the noise was due to the number of blades in the rotors of the turbines and their relation to the speed of propagation of vibrations through water. A mere modification of the rotor allowed the disturbed people to sleep comfortably.

"Another example is offered by the vibration of buildings in the wind. A certain building which engineers were called upon to deal with was swinging to an appreciable degree. It was found that by the construction of a flagpole of proper flexibility on top of the building, and by suspending a weight of several hundred pounds from this pole, that the vibration period of the entire building was altered and the swinging stopped."

In regard to the determination of stress and the development of more resistant metals, Mr. Stone said that whereas in 1910 the greatest stress which could be allowed in a generator was 10,000 pounds per square inch, at present it is 20,000 pounds per square inch. "This improvement," he said, is due to the work of metallurgists and to the photoelastic determination of stress. This latter method, which is very complex, involves the rotation by mechanical stress, of a light beam in a plane of polarization. The effect is similar to that of double refraction. Straining the medium between the polarizers, which in our case is a celluloid model of the machine we are working on, increases the transmission through the second polarizer and a color scale is produced similar to that produced by the passage of light through a prism. By photographing the display of colors and their form, we can determine the amount of stress applied to the model and the limit of stress which can be applied."