The simulation of induction generators for microhydro systems: with application to developing countries

The driving of an induction machine faster than its synchronous speed, causing it togenerate electrical power, is described in most textbooks on electrical machines. Theprinciple of self-excitation, by which an induction generator can be excited from staticcapacitors is not, however, obvious. Further, difficulties in controlling the voltage andthe 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 inthe subject.For microhydro electric schemes used in remote areas in developing countries, such asIndonesia, stand-alone induction generators can have advantages over conventionalalternators. These include the ruggedness, low capital cost and low maintenancerequirements of the induction machine and the fact that short circuit currents are limitedby the excitation current only, thereby providing a self-protection scheme.The thesis initially describes the mathematical modelling of an induction machine basedon generalised machine theory. The thesis then describes a new computer program thatwas developed to simulate the transient behaviour of a capacitively self excited inductiongenerator. As self-excitation occurs in the saturated region of the magnetisation curve, acomprehensive model of the saturation effect has to be included. The rotor parametervariations of the machine are taken into account. Two simulations are performed, onebased on steady-state behaviour and the other based on transient behaviour. Theprograms simulate the starting transient of an induction generator as well as theswitching transients associated with various combinations of loads.It is shown that the calculated and measured results are in strong agreement for the twotypes of induction generator studied. Small-slip parameters were required to give goodagreement 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 includedin the simulation programs if parameters were available.The simulation studies provide invaluable information on how the machine and loadparameters and excitation capacitance interact, as well as information on the stabilitybehaviour of the system during loading.In exploratory investigations, a Pelton wheel was used to drive a squirrel-cage inductiongenerator. The use of an electronic controller on the installation was also investigated.Control and protection strategies are suggested based on the laboratory investigationsand simulations