© The Institution of Electrical Engineers
In this paper the author discusses the various forces which give rise to stresses and deflections in large electrical machine frames. The mechanical or static loading is treated, and then the forces due to magnetic loading are examined. It is shown that the latter forces are by far the more important. The tendency for the rotors of induction motors to pullover to the stator is explained by means of a graph, and it is shown how a machine can be so designed as to avoid this trouble. It is pointed out that the frame of a machine is under the action of a total magnetic pull equal in most cases to 10 times the “unbalanced magnetic pull” calculated for a rotor displacement of 10 per cent of the radial air-gap. This particular problem is examined by means of photoelastic tests taken upon celluloid models, and the effect of the spread of the frame feet is very clearly demonstrated. A comparison is made between these tests and the calculated bending-moment diagram. In an Appendix the author gives a mathematical solution of the problem, the unbalanced magnetic pull being considered as a concentrated load, and a number of curves are included in order to simplify the calculation of stresses and deflections. The points of zero bending moment are also given, so that the complete bending moment diagram can be rapidly drawn for any case. In conclusion, an actual example is worked out in detail, and it is shown that an induction motor frame has to be so designed as to limit the deflection; the stresses are very low and of the order of 2 000 lb. per sq. in. or less. Machines with large air-gaps are designed on a basis of limiting stress, which occurs long before the limiting deflectionis reached.
References
-
-
1)
-
Edgar Knowlton
.
Magnetic Attraction in Dynamos Due to Armature and Field being Non-Concentric.
Electrical World and Engineer
-
2)
-
R.E. Hellmund
.
Series versus Parallel Windings for A.C. Motors.
Electrical world
-
3)
-
B.A. Behrend
.
The Mechanical Forces in Dynamos Caused by Magnetic Attraction.
Transactions of the American I.E.E.
-
4)
-
Charles R. Moore
.
A Study of Unbalanced Magnetic Pull.
Electrical review and western electrician
-
5)
-
B. Soschinski
.
Pull Due to Rotor Eccentricity.
Zeitschrift für Elektrotechnik
-
6)
-
F. Niethammer
.
Deflection of Stators of Electric Generators.
Electrical world
-
7)
-
(1927)
Transactions of the American Society of Mechanical Engineers.
-
8)
-
R.V. Picou
.
The Law of Magnetic Attraction.
Bulletin de la société internationale des Électriciens
-
9)
-
J.K. Sumec
.
Determination of Magnetic Pull on Rotor Due to Eccentricity.
Zeitschrift für Elektrotechnik
-
10)
-
F.W. Carter
.
Magnetic Centering of Dynamo Electric Machinery.
Proceedings of the Institution of Civil Engineers
-
11)
-
(1918)
Transactions of the American I.E.E..
-
12)
-
Miles Walker
.
(1915)
, Specification and Design of Dynamo-Electric Machinery.
-
13)
-
E.G. Coker ,
L.N.G. Filon
.
, Photo Elasticity.
-
14)
-
J. Fisher-Hinnen
.
(1899)
, Dynamo Design.
-
15)
-
E. Rosenberg
.
Magnetic Pull in Electric Machines.
Transactions of the American I.E.E.
-
16)
-
F. Niethammer
.
The Lateral Magnetic Pull of Dynamos and Motors.
Zeitschrift für Elektrotechnik
-
17)
-
J. Rey
.
Magnetic Pull Due to Eccentricity of Rotor in Induction Motors.
L'éclairage électrique
-
18)
-
H. Linsenmann
.
Mechanical Strength of Large Alternators.
Elektrotechnische zeitschrift
http://iet.metastore.ingenta.com/content/journals/10.1049/jiee-1.1935.0138
Related content
content/journals/10.1049/jiee-1.1935.0138
pub_keyword,iet_inspecKeyword,pub_concept
6
6