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ELIMINATION OF COMMUTATOR RIPPLE FROM DIRECT CURRENT GENERATORS
O. K. BUCK AND J. C. ALBERT*
The large electric utilities of today are interested not only in the kilowatt hour sales, but also in the most efficient use of that energy by its consumers. The Department of Water and Power of Los Angeles endeavors to identify itself with the industries it serves by cooperation with its consumers to the fullest extent. This department has established very low rates for energy and also has assisted in solving technical problems which arise in the utilization of that energy.
One of these problems which we have been able to render assistance in solving is undoubtedly of considerable interest to this group. This is the elimination of the commutator ripple from the direct current generator in order that high intensity arcs may be used in the production of talking pictures.
When the studios first started making talking pictures it was, of course, necessary to eliminate all outside noises from the sets. In using the high intensity arc it was found that a high pitched squeal was emitted therefrom, a pitch near the middle of the audible range and therefore very objectionable. It was found upon investigation that this noise was caused by an alternating current wave superimposed upon the direct current. This was readily traced to the generator and determined as a function of commutation. It has been termed "commutator ripple." The frequency is directly proportional to the speed of the generator times the number of commutator bars. We therefore have to deal with frequencies ranging from 900 to 1800 cycles.
Several of the studios have been more or less successful in cutting the noise down to a minimum. The first method employed was the use of impedance choke coils, either on the lamp, on the feeder, or, perhaps, upon the generator itself. The small "whistle boxes" installed
* Dept. of Water and Power, Los Angeles, Calif.
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