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Image from page 714 of "The Bell System technical journal" (1922) | by Internet Archive Book Images
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Image from page 714 of "The Bell System technical journal" (1922)

Identifier: bellsystemtechni06amerrich

Title: The Bell System technical journal

Year: 1922 (1920s)

Authors: American Telephone and Telegraph Company

Subjects: Telecommunication Electric engineering Communication Electronics Science Technology

Publisher: [Short Hills, N.J., etc., American Telephone and Telegraph Co.]

Contributing Library: Prelinger Library

Digitizing Sponsor: Internet Archive



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Text Appearing Before Image:

type of generator is now being made available.The purpose of the filter is to make the current from the discharge POWER PLANTS FOR TELEPHONE OFFICES 709 leads of the power plant sufficiently quiet for talking batterysupply. It is also possible to use a somewhat higher speedmachine which is smaller than the present type. The usual slottedmica commutator construction and self-lubricating carbon brushes areemployed. While the mechanical noise tends to be greater because ofthe higher speed and the carbon brushes, it has been found that this isnot a factor of importance under present conditions where power plantscan usually be located more or less by themselves and well removedfrom the Wire Chiefs testing equipment. Filters A new type of choke coil has been developed foi the filter used with commercial type generators. It is of the enclosed shell type design having short air gaps, using the materials more economically and having a higher inductance than the coils which have been available


Text Appearing After Image:

Fig. 5—Part of power room for two large panel units as provided five years ago.Twelve motor-generators for both alternating-current and direct-current service withpower switchboard at left and battery control board in background. This was analternate arrangement to use of large motor-generator to make both kinds of poweravailable. heretofore. Associated with this coil is a group of electrolytic con-densers each of which has upwards of 1,200-mf. capacity on 24 volts, orroughly half this amount on 48 volts. 710 BELL SYSTEM TECHNICAL JOURNAL For one of the larger motor-generator sets the cost of the first set,including a filter, is about the same as that of the former telephonegenerator type outfit. The cost of the additional sets used in thepower plant, which under present conditions are not provided withindividual filters if a common filter is placed in the talking dischargecircuit, is about half that of the present type sets. Power Factor CorrectionIn connection with the new generat



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