Power Systems Interview Questions and Answers -2

Below are the concise answers to your questions:

1. What is a power generating station?

A power generating station is a facility where energy is converted from various forms (like chemical, nuclear, or mechanical) into electrical energy for distribution and use.

2. What is a steam power station? Discuss its advantages and disadvantages.

A steam power station uses steam to drive turbines connected to generators for producing electricity.
Advantages:

Low operating cost.
Can utilize low-grade fuels.
Reliable for base-load power.

Disadvantages:

High initial cost.
Produces pollution.
Requires large quantities of water.

3. Draw the schematic diagram of a modern steam power station and explain its operation.

(Unable to draw here; I can generate a diagram for you. Let me know.)
Operation: Fuel is burned in a boiler to produce steam, which drives a turbine. The turbine rotates the generator to produce electricity. Exhaust steam is condensed and reused in the boiler.

4. Explain the important components of a steam power station.

Boiler: Generates steam by burning fuel.
Turbine: Converts steam energy into mechanical energy.
Generator: Converts mechanical energy into electrical energy.
Condenser: Condenses exhaust steam into water.
Cooling tower: Removes waste heat.
Chimney: Releases flue gases.

5. What factors are taken into account while selecting the site for a steam power station?

Availability of fuel and water.
Transportation facilities.
Proximity to load centers.
Land cost and availability.
Environmental regulations.

6. Discuss the merits and demerits of a hydro-electric plant.

Merits:

No fuel cost.
Environmentally friendly.
Long life and low maintenance.

Demerits:

High initial cost.
Affected by seasonal water availability.
Requires large land areas, leading to displacement.

7. Draw a neat schematic diagram of a hydro-electric plant and explain the functions of various components.

Let me know if you'd like a generated diagram.
Components:

Dam: Stores water and creates potential energy.
Spillways: Prevent overflow during floods.
Turbine: Converts water energy into mechanical energy.
Generator: Converts mechanical energy into electricity.
Tailrace: Returns water to the river.

8. Essential factors influencing the site selection for a hydro-electric plant:

Availability of water resources.
Geological and topographical conditions.
Distance from load centers.
Environmental and social impact.

9. Functions of the following:

Dam: Stores water and regulates flow.
Spillways: Discharge excess water.
Surge tank: Reduces water hammer effect.
Headworks: Direct water into channels or turbines.
Draft tube: Recovers pressure from exiting water.

10. Flow diagram of a diesel power station and its operation:

Let me know for a diagram.
Operation: Diesel burns in an engine, driving an alternator to produce electricity.

11. Advantages and disadvantages of a diesel power station:

Advantages:

Quick start-up.
Low water requirements.

Disadvantages:

High operating cost.
Limited capacity.

12. Schematic diagram of a nuclear power station and its operation:

Let me generate a diagram if needed.
Operation: Nuclear fission produces heat to generate steam, which drives turbines connected to a generator.

13. Explain with a neat sketch the various parts of a nuclear reactor:

Core: Contains fuel rods.
Moderator: Slows down neutrons.
Control rods: Regulate reaction.
Coolant: Transfers heat.
Shielding: Protects from radiation.

14. Factors for the choice of site for a nuclear power plant:

Availability of water.
Distance from populated areas.
Geologically stable location.
Efficient waste disposal system.

15. Explain the working of a gas turbine power plant with a schematic diagram:

Working: Compressed air mixes with fuel and burns in a combustion chamber. The hot gases expand through a turbine to generate electricity.

16. Comparison of power plants:

Parameter	Steam	Hydro-electric	Diesel	Nuclear
Operating Cost	Low	Very low	High	Low
Initial Cost	High	Very high	Low	Very high
Efficiency	Medium	High	Low	Very high
Maintenance Cost	Medium	Low	High	Medium
Source Availability	High	Seasonal	Limited	High

Let me know if you need more details or diagrams for specific questions!

1. Why is the overall efficiency of a steam power station very low?

The overall efficiency of a steam power station is very low (around 30-35%) because:

A large amount of energy is lost as heat in the condenser.
Energy losses occur in boilers, turbines, and other components due to friction, incomplete combustion, and heat transfer limitations.

2. Why is a condenser used in a steam power station?

A condenser is used to:

Convert exhaust steam from the turbine back into water for reuse in the boiler, saving water.
Lower the pressure of exhaust steam, increasing the turbine efficiency.
Reduce environmental impact by recycling the water.

3. Why do hydro-electric stations have high transmission and distribution costs?

Hydro-electric stations are often located in remote areas near rivers and dams, far from load centers. This requires long transmission lines and infrastructure, increasing the cost of transmission and distribution.

4. Why are nuclear power stations becoming very popular?

Nuclear power stations are gaining popularity due to:

High energy output with minimal fuel consumption.
Reliable base-load power generation.
Low greenhouse gas emissions compared to fossil fuels.
Long operational life, making them cost-effective in the long run.

5. Why is hot gas at high pressure, not at atmospheric pressure, used in gas turbine power plants?

Hot gas at high pressure is used in gas turbines because:

High-pressure gas increases the turbine's efficiency and power output.
It provides more energy to drive the turbine.
Expanding gas at high pressure maximizes the mechanical energy extracted.

6. How do the various devices protect the penstock?

Devices protecting the penstock include:

Surge tanks: Absorb sudden pressure changes to prevent water hammer.
Air valves: Prevent vacuum formation during sudden flow changes.
Relief valves: Release excess pressure to prevent structural damage.
Anchors and supports: Maintain the stability and alignment of the penstock.

7. Why cannot diesel power stations be employed to generate bulk power?

Diesel power stations are unsuitable for bulk power generation due to:

High operating and fuel costs.
Limited capacity of diesel engines.
Inefficiency and high maintenance requirements for large-scale power generation.

8. Why is a regenerator used in a gas turbine power plant?

A regenerator is used to:

Recover waste heat from exhaust gases to preheat the compressed air entering the combustion chamber.
Improve the thermal efficiency of the plant by reducing fuel consumption.
Lower the overall operational cost by utilizing residual heat.

1. Why is the load on a power station variable? What are the effects of variable load on the operation of the power station?

Variable load: The load on a power station fluctuates throughout the day due to changes in demand (e.g., residential, industrial, and commercial usage patterns).

Effects of variable load:

Fluctuating efficiency: Generators operate less efficiently under partial loads.
Increased wear and tear: Frequent changes in load lead to mechanical and thermal stresses.
Higher operating costs: Standby units or load-following equipment may be required.

2. What do you understand by the load curve? What information is conveyed by a load curve?

A load curve is a graphical representation of the variation of electrical load with time (e.g., daily, monthly, or yearly).

Information conveyed:

Maximum, minimum, and average loads.
Peak load duration.
Energy demand patterns.
Helps in system planning and economic operation.

3. Define and explain the importance of the following terms in generation:

(i) Connected load: The total rated capacity of all electrical equipment connected to a system. It determines the potential maximum demand.

(ii) Maximum demand: The highest load recorded during a specified period. It is crucial for sizing generators and infrastructure.

(iii) Demand factor: Ratio of maximum demand to connected load. It indicates the utilization level of installed capacity.

\text{Demand Factor} = \frac{\text{Maximum Demand}}{\text{Connected Load}}

(iv) Average load: The total energy consumed divided by the time period. It helps in assessing the overall system load.

\text{Average Load} = \frac{\text{Total Energy}}{\text{Time}}

4. Explain the terms load factor and diversity factor. How do these factors influence the cost of generation?

Load factor: Ratio of average load to maximum demand during a given period.

\text{Load Factor} = \frac{\text{Average Load}}{\text{Maximum Demand}}

Higher load factor reduces generation costs by ensuring steady operation.

Diversity factor: Ratio of the sum of individual maximum demands to the overall maximum demand.

\text{Diversity Factor} = \frac{\text{Sum of Individual Max Demands}}{\text{System Max Demand}}

A high diversity factor reduces infrastructure costs as not all loads peak simultaneously.

5. Explain how load curves help in the selection of size and number of generating units.

Load curves help in:

Identifying base and peak load requirements.
Selecting the optimal capacity of generating units for efficient operation.
Deciding the number of units to match load variations and maintain reliability.

6. Important points to consider while selecting the size and number of units:

Nature of load (base or peak).
Future demand growth.
Load curve characteristics.
Efficiency and cost of operation.
Flexibility for maintenance and reliability.

7. What do you understand by (i) base load and (ii) peak load of a power station?

(i) Base load: The minimum continuous load over a period. It is met by efficient and reliable units like steam or nuclear power plants.

(ii) Peak load: The additional load during high-demand periods. It is usually met by hydro or gas turbine units due to their quick start-up capability.

8. Discuss the method of meeting the peak load of an electrified area.

Peak load can be met by:

Using quick-start plants like gas turbines or hydro plants.
Utilizing energy storage systems like pumped storage or batteries.
Load management techniques like demand-side management.
Interconnected grid systems for power sharing.

9. Advantages of interconnected grid systems:

Improved reliability and stability.
Efficient utilization of generation resources.
Sharing of reserve capacity.
Reduced overall generation cost.
Flexibility to meet varying load demands.

10. Write short notes:

(i) Load curves: Represent the variation of load with time and help in planning and operating power systems efficiently.

(ii) Load division on hydro-steam system: Hydro plants handle peak loads, while steam plants operate as base load units due to their efficiency and slower response.

(iii) Load factor: Indicates the efficiency of power usage. A higher load factor means better utilization of installed capacity and lower costs.

(iv) Plant capacity factor: Ratio of actual energy generated to the maximum possible energy. It reflects the efficiency of power plant utilization.

\text{Capacity Factor} = \frac{\text{Actual Energy Generated}}{\text{Plant Capacity} \times \text{Time}}

1. Why are load curves drawn?

Load curves are drawn to:

Analyze variations in electrical load over time.
Determine the maximum demand, average load, and peak load duration.
Assist in capacity planning for generating units.
Optimize scheduling and operation of power plants.
Aid in economic evaluation and efficient resource allocation.

2. How will you improve the diversity factor of a power station?

The diversity factor can be improved by:

Encouraging staggered usage of electrical appliances among consumers (e.g., shifting industrial loads to non-peak hours).
Promoting off-peak usage with time-of-use tariffs.
Connecting diverse types of loads (e.g., residential, commercial, and industrial) to the grid.
Utilizing interconnected grids to distribute load variations across regions.

3. What is the importance of load factor?

Load factor is important because:

It indicates the utilization efficiency of the power station.
A higher load factor reduces the cost of generation per unit by ensuring steady operation of generating units.
It helps optimize the sizing of infrastructure, such as generators, transformers, and transmission lines.
Ensures better resource utilization, reducing waste.

4. What is the importance of diversity factor?

Diversity factor is important because:

A high diversity factor allows designing systems with lower capacity, reducing initial and operational costs.
It ensures that not all loads peak simultaneously, improving system reliability.
Helps in balancing the supply and demand effectively in an interconnected grid.

5. The values of demand factor and load factor are always less than 1. Why?

Demand Factor:
The demand factor is always less than 1 because the maximum demand is always less than the connected load. Not all equipment or loads operate simultaneously at full capacity.
Load Factor:
The load factor is less than 1 because the average load over a period is always less than the maximum demand due to fluctuations in load throughout the day or season.

Power Systems Interview Questions and Answers -2