Power Plant Fundamentals: Types and Hydroelectric Systems
Power Plants Producing Energy
The need for electricity in large quantities requires power plants, installations that convert primary energy into electricity. These facilities use machines and equipment to generate power.
Types of Power Plants
Based on the overall network consumption, power plants are classified as:
- Basic or Main Power Plants: Supply electricity continuously (e.g., nuclear, large thermal, hydroelectric).
- Peaking Power Plants: Meet peak-time demands.
- Reserve Power Plants: Replace base production during outages or repairs.
- Pumped Storage Power Plants: Use excess energy during off-peak hours to pump water to an upper reservoir, releasing it during peak hours.
Hydroelectric Power Plants
Hydroelectric plants leverage the energy of flowing water to turn turbines coupled to alternators. The energy transformation process is: Potential Energy > Kinetic Energy > Rotational Kinetic Energy > Power > Utilization.
There are two main types:
1) Run-of-River Hydro Plants
Built where hydraulic energy can directly drive turbines.
2) Impoundment Hydro Plants
Water accumulates in a reservoir and is used based on electricity needs.
a) Diversion Power Plants
The river is diverted into a channel with a minimal slope difference from the river, increasing with channel length.
b) Storage Power Plants
Located in a river stretch with a significant slope, a dam obstructs water flow, creating a reservoir. Potential energy increases with the dam’s height.
Hydroelectric Components
- Dam: A structure (usually concrete) across a river, raising water level to form a reservoir.
- Gravity Dams: Resist water force with their weight.
- Arch Dams: Curved structures anchored to the river walls.
- Water Intake: Gates and channels regulate water flow to turbines, protected by metallic grids.
- Machine Room: Houses turboalternator groups (Pelton, Francis, Kaplan turbines).
- Transformers and Distribution Park: Increase voltage (from ~20kV) for transmission to consumers.
Hydroelectric Operation
The dam creates a reservoir, increasing water level. Water flows through a forced pipe to the turbines, converting potential energy to kinetic energy. This rotates the turbine and alternator, generating electricity. Water returns to the river via drainage channels. The system is designed for maximum energy transfer. A DC generator creates a magnetic field in the rotor coils, producing AC voltage in the stator. Transformers increase voltage for transmission.
Pumped Storage Power Plants
These plants optimize energy production by consuming surplus power during off-peak hours and providing energy during peak hours.
- Pure Pumped Storage: Electricity production requires prior water pumping to the upper reservoir.
- Mixed Pumped Storage: Can produce energy with or without pumping, as the upper reservoir is also fed by a river.
Mini-Hydropower
Power plants with a capacity between 250 and 5000 kW, historically supplying electricity to small rural villages and factories near rivers.