Document Type: 
Document Number (FOIA) /ESDN (CREST): 
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Document Creation Date: 
December 22, 2016
Document Release Date: 
August 12, 2011
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Publication Date: 
May 10, 1950
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PDF icon CIA-RDP80-00809A000600310057-4.pdf98.88 KB
Sanitized Copy Approved for Release 2011/08/17: CIA-RDP80-00809A000600310057-4 C ONFIDENTIA CENTRAL INTELLIGENCE AGENCY REPOR INFORMATION FROM FOREIGN DOCUMENTS OR RADIO BROADCASTS CD NO. DATE OF INFORMATION i osn HOW DATE DIST. 16 May 1950 PUBLISHED Monthly periodical WHERE PUBLISHED Moscow NO. OF PAGES 2 DATE PUBLISHED Feb 1950 SUPPLEMENT TO LANGUAGE Russian REPORT NO. THIS DOCUMENT CONTAINS INFO RYATIOM AFFECTING TNl RATIONAL DEFENSE OF THE UNITED STATES WITHIN THl MEANING OF E3PIOMAGE ACT EO U. S. C.. SI AND SZ. AS AMENDED. ITS TRAXSMISSIOH ON THE REVELATION OF ITS CONTENTS IN ANY MANNER TO AN UNAUTHORIZED PERSON IS PRO- 0111TED ET LAW. REPRODUCTION OF THIS FORM IS PROHIBITED INFLUENCE CF VARIATIONS IN THE AIR GAP ON THE NO-LOAD CURRENT OF INDUCTION MOTORS Docent L. V. Litvak Cand Tech Sci STATE ARMY OONFIOENTIAL Sanitized Copy Approved for Release 2011/08/17: CIA-RDP80-00809A000600310057-4 In induction motors the reluctance of the air gap amounts to 70-80 per- cent of the total reluctance of its magnetic circuit. Hence, it may be assumed that 70-80 percent of the no-load reactive power taken by an induction ;aotor is due to the reluctance of the air gap. Since, on an average, this reactive power constitutes 60 percent of the total reactive power supplied to industrial enterprises, it may be concluded that the air gaps of induction motors account for about half the total reac- tive power balance. This is a very imposing figure. It indicates the neces- sity of introducing into maintenance and operating procedures strict control over the dimensions of the air gap, inasmuch as it predetermines the amount of reactive power in the motor. To obtain the best operating characteristics (power factor and efficiency) modern induction motors of low or average power -- which constitute a majority' of present-day electric motors -- are built with as small an air gap as possible depending upon various mechanical factors: shaft vibration; permissible shaft deflection; accuracy in surfacing the rotor and stator; and allowances for wear and sag of the beax_ngs.' This "design" size of the air gap in various types of motors with different powers and with rated rpm's of 3,000, 1;500, 1,000, and 750, varies within wide limits -- 0.25 to 1.75 millimeters. Consequently, in regulating the air gaps in each concrete case, one must be guided by the "design" size of the gap and not by "average" values which - often exceed these "design" sizes. Sanitized Copy Approved for Release 2011/08/17: CIA-RDP80-00809A000600310057-4 ,1O!FIOEHTIAE It should be noted that, in practice, motors are often found in which the air gaps are ccnsi3erabiy enlarged as a result of wear on the rotor surface, and the "permissible' wear in these cases is largely based upon the "averae" values for air gaps. Analysis of carve:; showing the variation in no-load current as a func- tion of air gap reveals that reactive no-load power increases quite rapidly as the gea enlarges. Therefore, in view of the importance of this factor to power economy, and the general lack of systematized published data on the various motors in use, ar, extensive table of air-gap dimensions has been compiled to serve as P. 3uide. [Note: nominal. air Kap, motor type, rpm, and power range for over 100 induction motors, the majority for two or three rated speeds, are available in original document in CI.A_7 At the Scientific and Technical Session of the Moscow Scientific and Technical Society of Power Engineering on Maintainance of Electric Equip-' meat of industrial Enterprises, held in Moscow in 1946, it was pointed out that the advisability of repairing motors whose air gaps had increased by more than 15 percent. was open to question. Undoubtedly, this statement is too cautious. The operation of motors with sharply increased air gaps leads to a correspondingly inadmissible deterioration in the technical and economic characteristics of lectric power utilization, and should, therefore, be per- mitted only in special cases. CONFIDE aTm t Sanitized Copy Approved for Release 2011/08/17: CIA-RDP80-00809A000600310057-4