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