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8/9/2019 Proceedings of the Institution of Electrical Engineers Volume 121 Issue 10 1974 [Doi 10.1049%2Fpiee.1974.0259] R
1/5
Performance analysis of diecast multicage induction
motors:
a
comparative study of two approaches
M. Ramakrishna Rao, M.Tech., Mem .I.E.E.E., V . Subba Rao, M.Tech., Ph.D., Mem .I.E.E.E., and
B.G. Desai, M.E., P h.D., Sen. Mem .I.E.E.E.
Indexing terms: Machine theory, Skin effect,Squirrel cagemotors
Abstract
The paper presents a comparative study of the analysis of diecast double-cage induction motors by
single-cage/deep-bar approach^nd.multicage-approach method s. In both the m ethods, saturation of
leakage flux p aths and m ain flux p aths have been considered. The performance of individual cages and
saturation effects have been clearly brought out. The skin-effect ratios for the rotor, obtained by both
the methods, are compared. The validity of the equations is ascertained by comparison with the
experimental results.
List of symbols
B = flux density , T
/ = frequency, Hz
G = current density, A/m
2
H field intensity, A/m
/ = inductance, H
r = resistance, S7
H
= permeability
p
= resistivity , 2m
OJ = angular frequency =2irf
1 Introduction
During the diecasting process of double-cage induc-
tion motors, the portion separating the top and bottom
cages is also filled up with aluminium and this provides an
electrical contact between top and bottom cages all along
their length. The filling up of the neck of the rotor slots
enables one to view it either as a multicage or a single-cage
rotor.
Although solutions for a.c. impedance of straight and
tapered bars have been developed to some extent, there is
no published literature dealing exclusively with conductor
sections encountered in the present analysis. Babb and
Williams
1
have approached the impedance of single-cage
conductors of complicated shape by analogy with trans-
mission lines in which the accuracy depends on the number
of T orITsections u sed. But in the present case, the single-
cage/deep-bar approach has been extended to multicage
rotors.
Many authors, e.g. Alger and Wray,
2
Lee,
3
Goodman
4
and Jacobs,
s
have suggested methods for double-cage rotors.
Alger
2
has extended his method of analysis to triple-cage
rotors, but his method of analysis pertains to unskewed
rotors with rectangular sections. In the discussion of his
paper, Lee has suggested a better way of representing the
triple cage, and in the present paper, this suggested method
has been adopted.
Results of analysis obtained by both the methods have
been compared with each other under saturated and
Paper
7 37
P
first
received
8 th May 1973 and in
revised
form
12th June 1974
Mr. R amakrishna Rao and Dr.
Desaia re
with the
Research