Day 3 ECET 2026 Night – Power Systems (Generation: Thermal & Hydel Stations)

Concept Notes

1. Thermal Power Stations

A thermal power station converts heat energy of fuel (mainly coal, oil, or gas) into electrical energy.

Main Process:

1. Fuel Combustion → Heat generated.
2. Boiler → Converts water into high-pressure steam.
3. Turbine → Steam expands and rotates turbine blades.
4. Alternator (Generator) → Mechanical energy converted into electrical energy.
5. Condenser & Cooling Tower → Steam condensed back to water.

Block Diagram Flow:
Fuel → Boiler → Steam → Turbine → Generator → Electricity

Advantages:

• Can be installed anywhere (close to load centers).
• High reliability, simple design.
• Cheaper initial cost compared to hydel.

Disadvantages:

• High fuel cost (coal/gas).
• Causes air pollution.
• Efficiency is low (~30–35%).

Example: NTPC Thermal Plants in India (Vijayawada, Ramagundam).

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2. Hydel (Hydroelectric) Power Stations

Hydel stations convert potential energy of water into electrical energy.

Main Process:

1. Water Reservoir → Stores water at high level.
2. Penstock → Large pipe carrying water to turbine.
3. Water Turbine → Converts water energy to mechanical energy.
4. Generator → Mechanical energy converted into electrical energy.

Block Diagram Flow:
Water Head → Penstock → Turbine → Generator → Electricity

Advantages:

• No fuel cost.
• Eco-friendly (no direct pollution).
• High efficiency (~85–90%).
• Long life.

Disadvantages:

• High initial cost (dam construction).
• Dependent on rainfall.
• Requires large area (flooding issue).

Example: Nagarjuna Sagar Dam, Srisailam Hydel Plant in Andhra Pradesh.

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3. Comparison of Thermal vs Hydel

Aspect	Thermal Station	Hydel Station
Fuel Requirement	Coal, Gas, Oil	Water (No fuel)
Efficiency	30–35%	85–90%
Initial Cost	Low	Very High
Running Cost	High (fuel + maintenance)	Very Low
Pollution	High (CO₂, SO₂, Ash)	Almost None
Location	Can be anywhere	Only at water sources

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⚙️ Formulas

• Hydropower Output:
  
  Where,
  = Efficiency,
  = Density of water (1000 kg/m³),
  = Acceleration due to gravity (9.81 m/s²),
  = Discharge (m³/s),
  = Head (m).
• Thermal Power Efficiency:

Steam Rate (kg/kWh):

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🔟 10 MCQs

Q1. The efficiency of thermal power stations is typically:
a) 20–25%
b) 30–35%
c) 50–60%
d) 80–90%

Q2. In a thermal station, the device used to convert steam energy into mechanical energy is:
a) Boiler
b) Turbine
c) Generator
d) Condenser

Q3. Hydel plants convert mainly:
a) Solar energy → Electrical energy
b) Kinetic + Potential energy of water → Electrical energy
c) Chemical energy → Electrical energy
d) Heat energy → Electrical energy

Q4. Which among the following has higher initial cost?
a) Thermal plant
b) Hydel plant
c) Diesel plant
d) Nuclear plant

Q5. The efficiency of hydroelectric power stations is approximately:
a) 25%
b) 50%
c) 85–90%
d) 100%

Q6. The largest hydroelectric power station in Andhra Pradesh is:
a) Srisailam
b) Nagarjuna Sagar
c) Machkund
d) Polavaram

Q7. In a thermal plant, flue gases are released from:
a) Boiler
b) Chimney
c) Turbine
d) Condenser

Q8. The main disadvantage of hydel stations is:
a) High running cost
b) Dependence on rainfall
c) Low efficiency
d) High pollution

Q9. The unit of water head (H) in hydro power formula is:
a) Newton
b) Pascal
c) Meter
d) Joule

Q10. Which plant is more eco-friendly?
a) Thermal
b) Hydel
c) Diesel
d) Gas

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✅ Answer Key

Q.No	Answer
1	b
2	b
3	b
4	b
5	c
6	a
7	b
8	b
9	c
10	b

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🧠 Explanations

• Q1: Efficiency of thermal plants is 30–35% → (b).
• Q2: Steam rotates turbine → (b).
• Q3: Hydel → Converts water energy → Electrical → (b).
• Q4: Hydel plants need dam, land, high cost → (b).
• Q5: Hydel efficiency ~90% → (c).
• Q6: Largest → Srisailam Hydel Station → (a).
• Q7: Gases exit through chimney → (b).
• Q8: Dependent on rainfall, seasonal → (b).
• Q9: Head measured in meters → (c).
• Q10: Hydel → eco-friendly → (b).

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🎯 Motivation / Why Practice Matters

Power Generation forms the backbone of Power Systems. In ECET 2026, questions on thermal vs hydel plants test your understanding of real-world energy systems. Remember:

• At least 1–2 direct questions come from this topic every year.
• Concepts like efficiency, cost, advantages, and formulas are simple but high-scoring.
• By mastering these, you strengthen your basics for Power Systems, Utilisation, and Smart Grids.

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