No abstract

This paper describes a method for accurately predicting the miriimum value of capacitance necessary to initiate self-excitation with a. stand alone induction generator.Final steady-state self-excitation voltages and frequencies are also calculated, for loaded and unloaded operation, taking into account rotor parameter variations with frequency.

In this paper, some results of experiment on modification of induction motor into generator are described. Not as usually done on three-phase motor, the modification has been done on capacitor motors normally supplied with singlephase source. The resulted induction generator should be able to self-excite and has been intended for low-power, low-speed applications. These applications are prospective for example in rural renewable energy generations and as motors for some special electric vehicles. Machine modification instead of total design-production or new machine acquisition is considered more appropriate for remote rural electrification. Distance and transportation difficulties, unavailability of nearby machine industry, lack of human resources with 'high-tech savvy', besides the low purchasing power of population in remote rural areas are some reasons behind the consideration. Experiment results indicated that voltage generation up to nominal value is not always easy to attain in a capacitor motor, even when functioning beyond its synchronous speed. An additional pre-charged capacitor should be used to initiate voltage generation. During start-up, load and the pre-charged capacitor had to be removed from generator to avoid capacitor discharge. Load could then be added gradually once generator approached its nominal output value. It was also shown that in order to generate power the generator must be rotating over its synchronous speed. The resulted frequency values did not vary linearly to the rotation speed and the obtained efficiency was still low.

The increasing use of energy saving lamps provides additional benefits to the application of low-power low-speed self-excited induction generators resulted from capacitor motor modification. Reactive power requirement of the generator can be provided from the capacitive nature of the lamps, while at the same time it is delivering active power to loads. Any loading change will automatically increase or reduce reactive power supply to generator. Results of experiments show that low-power low-speed single-phase self-excited induction generator is more robust and suitable for this kind of loads. Generator does not lose its voltage when experiencing abrupt change of loads. This robustness makes the generator suitable for the use in low-capacity hydropower generation in remote areas being commonly not covered by national electricity grid.