The electricity generated inside the generator is not of sufficient voltage. The transformer converts the alternating current produced from within the generator to the high voltage current. The transformer comprises of two coils: the supply coil and the outlet coil. Current is supplied to the supply coil, from where it passes to the outlet coil. The number of turns in the outlet coil decides the voltage of output electricity from the transformer. If the numbers of turns in outlet coil are double of supply coil, the voltage produced is also double.
The power supply from the transformer is connected to the nation grid, from where the power is distributed for the domestic and industrial use. The voltage supplied by the main transformer is very high, while the voltage required for various applications is 110V or 230V. To reduce the voltage a number of transformers are installed at various locations that reduce the high voltage from the main wirings to the voltage required for domestic and industrial applications.
The water that has been used to rotate the turbine blades and turbines shaft leaves the power generation unit entering the pipeline called as the tailrace. From here the water flows into the main river. The height of water in the tailrace is much below the height of water in the water reservoir behind the dam. The potential energy of water in the tailrace has been used to generate electricity.
The water flowing out from the tail race joins the natural flow of water. During the rainy seasons when there is excess water in the dams, it is allowed to overflow through the gates in water reservoir to the low level natural flow of water. If the river is very large, then multiple dams can be constructed across the river at various locations.