. Electrical world. ronger field, so thatthe induced from this external field will counterbalance of self-induction. The author points out that all designershave arranged to have the field at the point where they place thebrush nearly constant or at least increasing only slightly. Forspecial machines which run at very high speed, like those coupledto steam turbines, this remedy is, of course, not sufficient, and itis then necessary to provide a special commutating field at theplace where the commutation takes place, and of such a size thatthe induced by it in the short-
. Electrical world. ronger field, so thatthe induced from this external field will counterbalance of self-induction. The author points out that all designershave arranged to have the field at the point where they place thebrush nearly constant or at least increasing only slightly. Forspecial machines which run at very high speed, like those coupledto steam turbines, this remedy is, of course, not sufficient, and itis then necessary to provide a special commutating field at theplace where the commutation takes place, and of such a size thatthe induced by it in the short-circuited coil exactly counter-balances the of self-induction induced in the same. This may be done by means of special commutation poles, as shown inFig. I for a bipolar machine. They are supplied with the armaturecurrent, and by a suitable design it is easy to insure that the com-mutation field is constant over the whole commutation zone. Forcalculating the of self-induction the author recommends the. formula of Parshall and Hobart. and one of the main results ofhis paper is that the so-called reactance voltage (which, accordingto older theories, should be below a certain limit) may assume anyvalue whatever as long as a commutating field of such a size is pro-vided that it counterbalances the reactance voltage. In the discus-sion which followed, Deri remarked that the theory of the authorexactly corresponds with what he has done for years in his direct-current dynamos in which he annuls the armature reaction and alsoprovides a commutating field for counteracting the reactance voltagein the short-circuited coil. He states that many machines of hissystem are in practical use, and that direct-current dynamos drivenby steam turbines, and running at 4,000 , with a capacity of1,500 kw, have proven practically successful. He also mentionedexperiments in which he found that by means of the improved com-mutation device, it is possible to produce in shunt machines w
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectelectri, bookyear1883
