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Abstract
The driving of an induction machine faster than its synchronous speed, causing it to
generate electrical power, is described in most textbooks on electrical machines. The
principle of self-excitation, by which an induction generator can be excited from static
capacitors is not, however, obvious. Further, difficulties in controlling the voltage and
the frequency of an induction generator, have restricted its use for supplying electricity.
However, recent development of static var sources with power electronic controls,
combined with the depletion of non-renewable energy resources have revived interest in
the subject.
For microhydro electric schemes used in remote areas in developing countries, such as
Indonesia, stand-alone induction generators can have advantages over conventional
alternators. These include the ruggedness, low capital cost and low maintenance
requirements of the induction machine and the fact that short circuit currents are limited
by the excitation current only, thereby providing a self-protection scheme.
The thesis initially describes the mathematical modelling of an induction machine based
on generalised machine theory. The thesis then describes a new computer program that
was developed to simulate the transient behaviour of a capacitively self excited induction
generator. As self-excitation occurs in the saturated region of the magnetisation curve, a
comprehensive model of the saturation effect has to be included. The rotor parameter
variations of the machine are taken into account. Two simulations are performed, one
based on steady-state behaviour and the other based on transient behaviour. The
programs simulate the starting transient of an induction generator as well as the
switching transients associated with various combinations of loads.
It is shown that the calculated and measured results are in strong agreement for the two
types of induction generator studied. Small-slip parameters were required to give good
agreement for the loaded squirrel-cage generator.
Two common prime movers used in micro-hydro schemes are Pelton wheels and Cross-
Flow turbines. These two turbines are discussed and modelled. They could be included
in the simulation programs if parameters were available.
The simulation studies provide invaluable information on how the machine and load
parameters and excitation capacitance interact, as well as information on the stability
behaviour of the system during loading.
In exploratory investigations, a Pelton wheel was used to drive a squirrel-cage induction
generator. The use of an electronic controller on the installation was also investigated.
Control and protection strategies are suggested based on the laboratory investigations
and simulations.