The Chapter 4 covers various types of governors and load controllers used for governing the speed of the turbine, and act as speed sensitive servomechanism. Its function is to restore the speed by exciting the flow of water to the turbine to suite the new conditions. Two factors influence the governing of water turbines when compared with other prime movers. Firstly, hydraulic and frictional loads which have to be overcome are much higher, requiring the use of oil operated servomotors with high energy potential. Secondly the water column associated with the turbine has considerable inertia and changes in guide-vane opening (which results in changes of water velocity) leading to variations in pressure across the turbine runner.
Governing is required when electricity is generated by a synchronous generator at an isolated power plant. Its frequency is determined by the speed of the generator and the number of poles. If this speed increases or decreases, the frequency generated increase or decreases proportionately in more competitive systems the governors sense unit speed and adjust water flow through the turbine to obtain the desired speed through mechanical or electronic device. Therefore various types of governors and combination of the systems for various types of turbines have been diagrammatically explained.
Similarly the load controller is an electronic device that maintains a constant electric load on a generator in spite of change in user load there by promoting the use of turbine with low flow regulator devices. The principal advantage of load controller is that over all system becomes simpler and less costly. It not only eliminates the need for intricate governor and actuating mechanism but it allows design of the turbine to be simplified. A less sophisticated system increases the chances for long term viability and reduces equipment cost considerably for plants in the micro-hydropower plant. If electronic components fail in the field, they probably cannot be repaired on the spot, however, a well-designed unit is composed of separate printed circuit boards that can be replaced easily with soar boards kept for that purpose.
The Chapter also describes low cost load control for head men made canals. This has been taken specifically as we have very large canal system of about 3,000 km. and many more systems are under plan. There is a possibility of using the canal heads for generation of some power at economic rates as that total canal system at each distance of one or two km could be utilized for the generation of energy. In some cases we have lift canal system used for lifting the water to certain height and finally the water goes through gradient. Part of energy used for lifting the water could be regenerated at different locations during the course of canal. Therefore, to establish such micro energy system it is essential that cost of generation and total investment should be within the limit and feasible for authorities to sanction them such systems can only function and can be financed when feasibility looks good therefore, technology which helps reduction of the cost are very important. In this context neighboring countries experience and their research finds use in the development good for 50kW schemes. Blade angle control and use of by-pass techniques have been described for cost control purposes.
Chapter 5 describes various alternators which are to be coupled with the turbine to convert mechanical energy and to electrical energy. Synchronous alternators have been the principal electric power source in utility system ever since A.C. current became preferred from of power supply. Synchronous alternators have undergone an impressive evaluation in terms of creating controlling methods and parameters but in their basic structure they have remained the same as they were first introduced.
Induction generators exhibit different dynamic characterstics which can affect the dominant type of stability problems i.e. break up of net and induction of power supply. Induction generators are incapable for controlling voltage. In this chapter both types of generators, advantages disadvantages and comparisons have been discussed and as a result, relevance of induction generators for MMH station have been presented. Use of induction generator with turbine eliminates the requirements of governors, to induction generatotrs run with a wide range of rotor speeds over synchronous speed depending upon the power demand on the unit. The variation in speed can be simply obtained by regulating the turbine gate opening which could be done either manually or automatically by remote control.
Induction generator has an advantage that it requires no excitor in governing mechanism and no synchrounous equipment. This results in saving of up to 20% in the cost of electric plant. Moreover, with small and variable amounts of water, which does not justify the erection of a normal power station, it is simple enough to arrage for a water wheel to drive an induction machine having a cage rotor. This shows why induction generators could be used for micro schemes where cost reduction is more important. Back
