Nuclear and coal-based thermal power plants produce nearly half of the world's power.
Steam turbines are essential for converting thermal energy in steam to mechanical energy.
Structure and Function of Steam Turbines
Blade Design: Steam turbine blades have an airfoil shape which creates a pressure difference when fluid passes over them, generating a lift force that rotates the turbine.
Energy Transfer:
Energy in fluid converts to mechanical energy of the rotor.
Key forms of fluid energy: speed, pressure, and temperature.
Fluid Energy Dynamics
As blades absorb energy, all three forms of energy (speed, pressure, temperature) decrease.
Low-velocity jets are ineffective for producing lift force.
Role of Stator
Stator Section: A stationary component attached to the turbine casing that reduces flow area, increasing fluid speed.
Acts like a nozzle to enhance kinetic energy.
No net energy transfer occurs; hence, pressure and temperature must decrease to maintain energy balance.
Rotor and Stator Interaction
The flow exiting the stator is optimized for the next rotor set.
Multiple stator and rotor sets are essential for steam turbine operation.
Degree of Reaction
Definition: Calculated by dividing pressure and temperature energy by the total energy change in the rotor.
This determines the type of steam turbine design.
Steam Behavior in Turbines
As steam pressure drops, its volume increases.
Longer blades towards the outlet accommodate the expanded steam; tips achieve higher velocities compared to roots.
Blades are twisted to maintain optimum angle of attack across cross-sections.
Configuration of High Capacity Power Plants
Utilize multiple stages:
High pressure turbine
Intermediate pressure turbine
Low pressure turbines
All units connect to a single rotating shaft, linked to a generator.
Efficiency Considerations
Greater steam temperatures improve power plant efficiency (Second Law of Thermodynamics).
Maximum temperature limit is 600 degrees Celsius due to material constraints.
Reheating: After the first turbine stage, steam is bypassed to the boiler for additional heating, enhancing output and efficiency.
Speed Regulation of Steam Turbines
Maintaining constant speed is crucial for consistent electricity frequency.
Speed varies based on load/power demand; managed by a steam flow governing mechanism:
If speed increases, control valve reduces steam flow.
If speed decreases, steam flow increases.
Conclusion
Understanding the degree of reaction and turbine operation is essential for optimizing turbine design and performance.
Additional resources available in subsequent videos.
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