Power Plant Engineering: Load Analysis and Site Selection

1. Base Load and Peak Load Analysis

Base Load:

• Base load is the minimum continuous load demanded by consumers throughout the day.
• It remains almost constant for a large part of the 24-hour period.
• Base-load power plants operate continuously and supply the basic electricity demand.
• Thermal, nuclear, and large hydroelectric power plants are commonly used for base-load operation.
• Base-load plants generally have high efficiency and low operating costs but may have higher initial costs.

Peak Load:

• Peak load is the maximum electrical load occurring during certain periods of the day when electricity demand is high.
• It occurs mainly during morning and evening peak hours due to increased domestic and industrial consumption.
• Peak-load plants are designed to start and stop quickly according to variations in demand.
• Diesel, gas-turbine, and pumped-storage hydroelectric plants are commonly used as peak-load plants.
• Peak-load plants generally have higher operating costs but lower starting times and are used only when required.

2. Advantages of Interconnected Grid Systems

• Improved reliability: If one generating station fails, power can be supplied from other interconnected stations.
• Continuity of supply: It reduces the possibility of complete power failure and ensures continuous electricity supply.
• Economical operation: Power can be generated by the most economical power station according to the load requirement.
• Reduced reserve capacity: Stations can share reserve capacity, reducing the need for separate standby generating units.
• Better utilization of generating plants: Different types of power plants can be operated according to their suitability, such as base-load and peak-load requirements.
• Handling of peak load: Peak demand in one area can be supplied by surplus power available from another area.
• Improved load factor: Interconnection helps combine different load patterns, resulting in a better overall load factor.
• Reduced cost of generation: More efficient plants can supply power to other areas, thereby reducing the overall cost per unit of electricity.
• Easy maintenance: A generating station can be taken out for maintenance while other stations continue to supply the load.
• Better system stability: Interconnection improves the stability and flexibility of the overall power system.

3. Daily Load Cycle Calculation

Data: Time (0-6, 6-10, 10-12, 12-16, 16-20, 20-24); Load (40, 50, 60, 50, 70, 40).

1) Maximum Demand: The maximum demand is the highest load on the generating station during the day. Maximum demand = 70 MW = 70,000 kW.

2) Units Generated Per Day: Energy generated in 24 hours = (40x6) + (50x4) + (60x2) + (50x4) + (70x4) + (40x4) = 240 + 200 + 120 + 200 + 280 + 160 = 1,200 MWh = 1,200,000 kWh (units).

3) Average Load: Average daily load = Energy generated in 24 hours / 24 = 1,200,000 / 24 = 50,000 kW = 50 MW.

4) Load Factor: Load factor = Energy generated in 24 hours / (Maximum demand x 24) = 1,200,000 / (70,000 x 24) = 0.714 = 71.4%

4. Site Selection Criteria for Thermal Power Plants

1. Fuel availability: The plant should be located near the source of coal or other fuel to reduce transportation costs and ensure a continuous supply.
2. Water supply: A large quantity of water is required for steam generation and cooling; the site must have a reliable water source.
3. Transportation: Good railway, road, or waterway facilities should be available for transporting fuel and equipment.
4. Load center proximity: The plant should be located near major load centers to reduce transmission losses.
5. Land availability: Sufficient land should be available at a reasonable cost for the plant, storage, and future expansion.
6. Ash disposal: Adequate space and arrangements must be available for the safe disposal or utilization of ash.
7. Ground conditions: The site should have suitable soil and drainage to provide a stable foundation for heavy equipment.
8. Environmental impact: The plant should be located away from densely populated areas to mitigate pollution.
9. Labor availability: Skilled and unskilled labor should be readily available near the site.
10. Future expansion: Sufficient space should be available for installing additional generating units.

5. Importance of Hydrological Curves

1) Hydrograph

• Shows the variation of river discharge with time during a storm or rainfall event.
• Helps determine the peak discharge of a river and estimate runoff volume.
• Useful for designing spillways, bridges, and drainage structures.
• Used in flood forecasting and studying watershed response.

2) Mass Curve

• Used for determining the storage capacity of a reservoir.
• Helps determine the amount of water that can be supplied continuously.
• Indicates periods of surplus and deficit water supply.
• Assists in planning irrigation and water-supply systems.

3) Flow Duration Curve

• Used to study the flow characteristics of a river.
• Helps estimate water availability for different percentages of time.
• Essential for the planning and design of hydroelectric power plants.
• Useful for selecting turbine capacity and comparing river flow characteristics.