1. Conclusions Innovative application of induction and synchronous generators in autonomous small hydropower plant Prof. M.T.E. Kahn NeuroMorphoGenics/NMG Africa Induction generator The preliminary investigation indicates the possibility of implementing small hydropower plant at low cost by employing synchronous-induction generator combination whose operation requires neither synchronization nor governor for the hydraulic turbine driving the induction generator. In addition, the combination offer chances of lowering capacities of switchgears and sizes of current carrying equipment of the plant due to short circuit characteristics of the induction generator. Ruggedness of induction generator and its governor less turbine prime mover further reduces maintenance cost of the generating unit. The generation of reactive power generated by STATCOM change the main role of the synchronous generator in the plant to determinant of generation frequency and the common bus voltage. The application of induction generators in micro hydropower plants has been widely reported; therefore the function ability of the proposed small hydropower plants cannot be doubted. However, further work on modelling of the plant and simulation of its operation in both normal and faulty conditions has to be undertaken to determine capacity of switchgears and sizes of equipment required in a specific plant and their cost implications. Implementation of the proposed autonomous plants can help electrifying communities in off grid remote areas with hydro potential at a relatively low cost. Introduction Abstract Hydropower is the most important of the renewable for electrical power generation. The potential of small hydropower has not been exploited due to economies of scale of large plants and cost of the equivalent fossil fuel powered plants. The current principal elements of energy conversion are hydraulic turbines and synchronous generators. Effective exploitation of a hydropower requires two or more generating units to be employed in a plant. In this study, a two unit small hydropower plant is proposed, a synchronous generator driven by a governor regulated turbine and an induction generator coupled with unregulated hydraulic turbine. The synchronous generator determines the generation voltage and power frequency, also it adjusts its output accordingly to plant load requirements. Induction generator power output is constant and proportional to slip. Static compensator incorporated generates reactive power to meet magnetizing power requirements of the induction generator and part of that demanded by the load. The proposed techniques have succeeded to exclude a governor and the of synchronizing equipment. Implementation of the proposed plants can help electrifying communities in off grid remote areas with hydro potential at a relatively low cost. Hydropower, large and small remains by far the most important of the renewable source for electrical power generation worldwide. Because of economies of scale of large hydro schemes and relatively low investment costs of equivalent fossil fuel powered plants, small hydropower potential (not exceeding 10MW) is under exploited. Power in small hydropower plant is generated by natural run-off without flow regulation therefore generation capacity varies according to weather conditions. The effective exploitation of available generation capacity of a plant is effected by applying two or more generating units even of different types and capacities. Achievements in research and development on machines and power electronics show possibilities of implementing competitive small hydropower plants at low costs. The introduction of cheap induction generators in some micro hydro plants and the development and operation of static VAR sources with power solid state controls has enhanced the opportunity for use of large scale induction generators. This study proposes the implementation of cheaper small hydropower plants employing the large scale induction generators and synchronous generators simultaneously. Conversion elements Hydro energy is based on the flow of naturally circulating water and its drop from a higher level to a lower land surface. Conversion of the energy to electricity takes place in electro-mechanical generating units consisting of hydraulic turbines and electric generators. The turbines convert water power into mechanical power through the rate of change of angular momentum of the water. The effect of this change in angular momentum is to induce torque on the shaft on the runner coupled to the generator. The speed of rotation is the rate at which this angular momentum is changed and if the driven is synchronous generator, determines the frequency of power generated. The general formula for hydro system power output is For frequency regulation, the turbines are individually equipped with governors. The function of a governor is to measure the rotational speed of the generator; to compare it to the reference value (50Hz) and based on the error signal, to instruct the hydraulic actuator to open or close wicket gates or needles which control water flow into the turbine. Turbine-governor characteristics Governors are designed to operate as proportional control systems characterized by a wide spread droop of 4% across the operational range. There is an inbuilt facility within a governor that allows an operator to adjust the set point frequency. Frequency/power characteristics of turbine-governor For line A, the set point is 1.04 p.u and the frequency will be 1.00 p.u when the increased to rated generator power. Changing the set point to 1.02 p.u moves the line to B. Set point adjustment allows the operator to decide on how the demand is shared by the generators on the system. Synchronous generator A single synchronous generator supplying power to an impedance load acts as a voltage source whose frequency is determined by its prime mover speed. In power system modelling, a synchronous generator is represented by its direct axis reactance x in series with a constant voltage E Ignoring rotor saliency effects, the power transferred by the generator to external system is determined by the power angle characteristic as The active power is limited by the capability of the prime mover. When the active power loading and voltage are fixed, the allowable reactive power loading is limited by either armature or field heating. Induction generators commonly used are induction machines with cage rotors; the attractive features of these machines are simplicity and ruggedness in construction and hence low cost. As a generator, the induction machine is driven by a prime mover at a speed above the synchronous speed. Part of the rotor shaft power is transferred across the air gap and delivered to the system as generated power. Equivalent circuit of an induction generator For small slip, the power transferred across the air gap can be estimated as and I o is zero-load exciting current Where The exciting current absorbed from the system Proposed power plant Schematic diagram of the plant Equivalent diagram of the plant The plant consists of a synchronous generator driven by a governor regulated hydraulic turbine operating in parallel with an induction generator coupled to uncontrolled hydraulic turbine supplying a constant mechanical power. The incorporated static compensator supply reactive power to meet the magnetizing power requirement of the induction generator and part of that demanded by load so as the synchronous generator is not over loaded