DYNAMIC BEHAVIOUR OF HYDRO POWER PLANT WITH AND WITHOUT SURGE TANK

Abstract

The prime source of electric energy supplied by electric- utilities is the potential energy of water which is converted into kinetic energy in case of hydro power plant. The hydraulic turbine converts this source of energy into mechanical. energy that, in turn, is converted into electrical energy by synchronous generator. The prime-mover governing system provides a means controlling power and frequency. Hence, the performance of hydraulic turbines, synchronous generator, penstock with and without surge tank greatly determines the dynamic behaviour of hydroelectric plant. The Performance of hydraulic turbines is influenced by the characteristics of the water column feeding the turbine and these include the effects of water inertia, water compressibility and pipe wall elasticity in the penstock. The effect of water inertia is to cause changes in turbine flow to lag behind changes in turbine gate opening. The effect of elasticity is to cause travelling waves of pressure and flow in the pipe & this Phenomenon is commonly referred to as "Water hammer". The effect of water hammer in the penstock pipe is sometimes taken care of by installing a surge tank near the turbine to reduce the rapid closure of gates. The prime-mover governing system also plays a critical role in determining the behaviour of the hydroelectric plant. The basic function of a governor is to control speed and/or load. The primary speed/load control function involves feedback speed-error signal to control the gate position. In order to ensure satisfactory and stable parallel operation of multiple-units, the speed governor is provided with droop characteristics. In view of the background mentioned above, this study presents the models of hydraulic turbine and penstock system without travelling wave effects and assuming that there is no surge tank. Finally, the study is extended to the models of hydraulic turbine and penstock system including the effects of water hammer and surge tank. Then, the models developed is simulated for varying conditions of load using Metlab/Simulink software with an aim to establish the overall dynamic behaviour of hydroelectric power plant.