. Electrical world. beconnected in parallel with the first. Imaginethat the first set is carrying full load andthat the second set is to divide the load withit. The motor can be synchronized in theusual manner by adjusting the field currentso that the potential difference between thebus-bars and the synchronous motor van-ishes. If the generator is synchronized inthe same way it is not possible to put a loadon the machine. If the field current of thegenerator is diminished or increased theload of the frequency changer remains un-altered and the effect of changing the ex-citation results only in
. Electrical world. beconnected in parallel with the first. Imaginethat the first set is carrying full load andthat the second set is to divide the load withit. The motor can be synchronized in theusual manner by adjusting the field currentso that the potential difference between thebus-bars and the synchronous motor van-ishes. If the generator is synchronized inthe same way it is not possible to put a loadon the machine. If the field current of thegenerator is diminished or increased theload of the frequency changer remains un-altered and the effect of changing the ex-citation results only in an increase of thecross currents between the two sets. Nowthen, in order to make the second frequency-changer divide the load w-ith the first, it be-comes essential to abandon the usual way of paralleling. The follow-ing reasoning will at once give us a solution of the problem. Let usassume that both sets are in operation and are dividing the loadequally. The saturation curves of the machines being the same, it is. FIG. 4.—OUTLINE OF IO65-KW. FREQUENCY CHANGERS. clear that the exciting currents of the machines must also be the sameif the load be distributed uniformly between them. As juggling thefield currents after the marlnne has been thrown in parallel has no On account of the high peripheral speed of 8,000 ft. per minuteof the revolving fields, the mechanical construction of the rotatingparts has to be made solid and reliable. The rotor spiders are madeof cast steel with dove-tailed slots milledinto them. The pole pieces are held bymeans of wedges in these slots. The spideris designed with a central web, which isthe best construction for high-speed rotat-ing wheels. These machines were tested atthe shops of the Bullock Company at asurface speed of 12,000 ft. per minute. The high combined efficiency of the setsis shown in the curves represented in and 8. Fig. 7 shows the combined effi-ciency for 100 per cent, power factor onj both machines for an output of 800 kw a
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectelectri, bookyear1883
