A hydro generator converts the motion of falling or flowing water into electrical energy. Water stored at a higher elevation has gravitational potential energy, and that energy becomes kinetic energy as it moves through a penstock. When the water strikes the turbine runner, it makes the runner and shaft spin.
This matters because hydropower can produce large amounts of renewable electricity with very low fuel cost during operation.
Inside the generator, the spinning shaft turns a rotor that carries magnets or electromagnets. As the rotor spins inside the stationary stator, the changing magnetic field induces an electric voltage in coils of wire. The electrical output is then controlled, transformed to a higher voltage, and sent to transmission lines for the grid.
The main physics links water flow, torque, rotational motion, electromagnetic induction, power, and energy conservation.
Key Facts
- Gravitational potential energy of stored water: E = mgh
- Water power available from height and flow rate: P = ρgQh
- Electrical power output is less than water power input because efficiency is below 100 percent: Pout = ηρgQh
- A turbine converts moving water into rotational motion and torque on a shaft.
- A generator produces voltage by electromagnetic induction: changing magnetic flux through coils creates an emf.
- For electric power delivery, P = IV, so raising voltage with a transformer can reduce current for the same power.
Vocabulary
- Penstock
- A large pipe or channel that carries high-pressure water from a reservoir or intake to the turbine.
- Turbine runner
- The rotating wheel with blades that is pushed by water and converts water motion into shaft rotation.
- Rotor
- The spinning part of a generator that creates a moving magnetic field.
- Stator
- The stationary part of a generator that contains coils where voltage is induced.
- Electromagnetic induction
- The process in which a changing magnetic field creates an electric voltage in a conductor.
Common Mistakes to Avoid
- Confusing the turbine with the generator is wrong because the turbine converts water energy into rotation, while the generator converts rotation into electrical energy.
- Using the total reservoir volume instead of flow rate in P = ρgQh is wrong because power depends on how much water passes through each second.
- Ignoring efficiency is wrong because friction, turbulence, heating, and electrical resistance mean the electrical output is always less than the water power input.
- Thinking voltage is created by water directly touching wires is wrong because the voltage is induced by a changing magnetic field inside the generator.
Practice Questions
- 1 A hydro plant has water density 1000 kg/m^3, flow rate 12 m^3/s, height 35 m, and efficiency 0.88. Using g = 9.8 m/s^2, calculate the electrical power output.
- 2 A generator sends 2.4 MW of power to a transformer at 6000 V. What current is flowing before the transformer, assuming P = IV?
- 3 Explain why a hydro generator needs both a spinning rotor and stationary stator coils to produce useful electricity for the grid.