Innovative application of induction and synchronous generators in autonomous small hydropower plant Prof. M.T.E. Kahn NeuroMorphoGenics/NMG Africa Abstract Conversion elements Proposed power plant Hydropower is the most important of the renewable for Hydro energy is based on the flow of naturally circulating water and its drop from electrical power generation. The potential of small a higher level to a lower land surface. Conversion of the energy to electricity hydropower has not been exploited due to economies of takes place in electro-mechanical generating units consisting of hydraulic scale of large plants and cost of the equivalent fossil fuel turbines and electric generators. powered plants. The current principal elements of energy conversion are hydraulic turbines and synchronous The turbines convert water power into mechanical power through the rate of generators. Effective exploitation of a hydropower requires change of angular momentum of the water. The effect of this change in angular two or more generating units to be employed in a plant. In momentum is to induce torque on the shaft on the runner coupled to the this study, a two unit small hydropower plant is proposed, a generator. The speed of rotation is the rate at which this angular momentum is Schematic diagram of the Equivalent diagram of the synchronous generator driven by a governor regulated changed and if the driven is synchronous generator, determines the frequency plant plant turbine and an induction generator coupled with of power generated. The general formula for hydro system power output is unregulated hydraulic turbine. The synchronous generator Pm gqh determines the generation voltage and power frequency, The plant consists of a synchronous generator driven by a also it adjusts its output accordingly to plant load For frequency regulation, the turbines are individually equipped with governors. The function of a governor is to measure the governor regulated hydraulic turbine operating in parallel requirements. Induction generator power output is constant rotational speed of the generator; to compare it to the reference value (50Hz) and based on the error signal, to instruct the with an induction generator coupled to uncontrolled and proportional to slip. Static compensator incorporated hydraulic actuator to open or close wicket gates or needles which control water flow into the turbine. hydraulic turbine supplying a constant mechanical power. generates reactive power to meet magnetizing power The incorporated static compensator supply reactive requirements of the induction generator and part of that power to meet the magnetizing power requirement of the demanded by the load. The proposed techniques have induction generator and part of that demanded by load so succeeded to exclude a governor and the of synchronizing Turbine-governor characteristics Induction generator as the synchronous generator is not over loaded equipment. Implementation of the proposed plants can help electrifying communities in off grid remote areas with hydro Governors are designed to operate as proportional control systems Induction generators commonly used are induction potential at a relatively low cost. characterized by a wide spread droop of 4% across the operational range. There is an inbuilt facility within a governor that allows an machines with cage rotors; the attractive features of these machines are simplicity and ruggedness in construction and Conclusions operator to adjust the set point frequency. hence low cost. The preliminary investigation indicates the possibility of Introduction For line A, the set point is 1.04 p.u and the frequency As a generator, the induction machine is driven by a prime mover at a speed above the synchronous speed. Part of the implementing small hydropower plant at low cost by employing synchronous-induction generator combination rotor shaft power is transferred across the air gap and whose operation requires neither synchronization nor Hydropower, large and small remains by far the most will be 1.00 p.u when the governor for the hydraulic turbine driving the induction important of the renewable source for electrical power increased to rated generator delivered to the system as generated power. generator. In addition, the combination offer chances of generation worldwide. Because of economies of scale of power. Changing the set lowering capacities of switchgears and sizes of current large hydro schemes and relatively low investment costs of point to 1.02 p.u moves the carrying equipment of the plant due to short circuit equivalent fossil fuel powered plants, small hydropower line to B. Set point characteristics of the induction generator. potential (not exceeding 10MW) is under exploited. Power adjustment allows the Ruggedness of induction generator and its governor less in small hydropower plant is generated by natural run-off operator to decide on how turbine prime mover further reduces maintenance cost of without flow regulation therefore generation capacity varies the demand is shared by the the generating unit. The generation of reactive power Frequency/power characteristics according to weather conditions. generators on the system. of turbine-governor generated by STATCOM change the main role of the Equivalent circuit of an induction generator synchronous generator in the plant to determinant of The effective exploitation of available generation capacity generation frequency and the common bus voltage. of a plant is effected by applying two or more generating Synchronous generator For small slip, the power transferred across the air gap can The application of induction generators in micro units even of different types and capacities. be estimated as A single synchronous generator supplying power to 2 hydropower plants has been widely reported; therefore Achievements in research and development on machines V s the function ability of the proposed small hydropower and power electronics show possibilities of implementing an impedance load acts as a voltage source whose Pg frequency is determined by its prime mover speed. rr plants cannot be doubted. However, further work on competitive small hydropower plants at low costs. The modelling of the plant and simulation of its operation in In power system modelling, a synchronous introduction of cheap induction generators in some micro both normal and faulty conditions has to be undertaken to generator is represented by its direct axis jx m hydro plants and the development and operation of static Where V Vt I o (rs jx s ) Vt determine capacity of switchgears and sizes of reactance x in series with a constant voltage E rs jx11 VAR sources with power solid state controls has enhanced equipment required in a specific plant and their cost the opportunity for use of large scale induction generators. Ignoring rotor saliency effects, the power transferred by the implications. generator to external system is determined by the power angle x11 xs xm and Io is zero-load exciting current Implementation of the proposed autonomous plants can This study proposes the implementation of cheaper small characteristic as EVt help electrifying communities in off grid remote areas with hydropower plants employing the large scale induction P sin The exciting current absorbed from the system x hydro potential at a relatively low cost. generators and synchronous generators simultaneously. Ea Im The active power is limited by the capability of the prime mover. jx m When the active power loading and voltage are fixed, the allowable reactive power loading is limited by either armature or field heating.
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