## Variable frequency performance of the single phase capacitor run induction motor

thesis

posted on 05.12.2013 by Abdul S.K. Muslih#### thesis

In order to distinguish essays and pre-prints from academic theses, we have a separate category. These are often much longer text based documents than a paper.

A capacitor-run motor is often necessary where silent
running, low starting current, high efficiency and power factor
and overload capacity are required. When a capacitor· motor is
used in control or similar applications a knowledge of the variation in performance over a range of supply frequency is often
important, and this has been investigated by previous workers
using analyses of varying validity. For example, in early studies
it was common to base performance calculations on the revolving field
theory, when a general lack of agreement was found between
calculated and test values. This occurred particularly in the
starting wlnding under running conditions, and was attributed
usually to saturation and to space harmonics of mmf. The crossfield
theory provides a useful alternative to the revolving-field
theory for analyses of single-phase motors, and when applied to the
capacitor motor it is found that a much more accurate prediction of
the machine performance is obtained.
This thesis investigates the behaviour of a small singlephase
capacitor-run induction motor with relation to variable
frequency supplies and different capacitor values. The performance
of the capacitor motor is calculated, using an equivalent circuit
developed from basic cross-field theory considerations. However,
before calculating the performance of the motor, the experimental
determination of the parameters involved is necessary. From the
equivalent circuit for no-load and locked rotor conditions, a
set of voltage/current equations was obtained. Use of these equations requires a very complicated set of mathematical
procedures to determine the required parameters, and no solution
could be found. This difficulty was overcome by the
extensive use of a digital computer, enabling the parameters
to be obtained by the Newton-Raphson method of numerical
iteration. Using these parameters, the predicted performance
of the machine was compared with that obtained from an extensive
experimental investigation. The agreement which was found
to exist confirms both the validity of the theoretical analysis
and the accuracy of the measurement from which the parameters
were derived.

### History

#### School

- Mechanical, Electrical and Manufacturing Engineering