Thermal & Hydro Lab Viva Questions and Answers

Question No. 01: Which is the largest Hydro-power station in the world?
Answer: Three Gorges project in China on Yang-Yang River is the largest power station in the world having installed capacity of around 22,500 MW.

Question No. 02: Why the unit sizes of hydro generating machines are not standardized as in case of thermal power plants?
Answer: Since the size of hydro generating machines are based on availability of water in river and the water head available at a particular project site, the size of the machines keeps varying from location to location and river to river. The sizes are also based on logistics and variation of water in river during the year.

Question No. 03: How many hydroelectric dams are in the world?
Answer: FERC regulates approximately 2,300 hydroelectric producing dams. In addition, there are approximately 240 federal dams that produce hydroelectric power. Thus, there are a total of approximately 2,540 hydro-power dams.

Question No. 04: How does cost of generation from Hydropower Plant compare with other sources of electricity?
Answer: The hydro power generation is highly capital-intensive mode of electricity generation but being renewable source of energy with no consumables involved; There is very little recurring cost and hence no high long term expenditure. It is cheaper as compared to electricity generated from coal and gas fired plants. It also reduces the financial losses due to frequency fluctuations and it is more reliable as it is inflation free due to not usage of fossil fuel.

Question No. 05: How much of the total Hydro power potential has been exploited so far in India?
Answer: Around 19.9% of Hydropower potential has been exploited in India.

Question No. 06: Why hydropower is called renewable source of energy?
Answer: Hydropower is called renewable source of energy because it uses and not consumes the water.

Question No. 07: What are the different circuits in Thermal Power Plant?
Answer: Some of the major circuits in the thermal power plant are:
  1. Coal and Ash circuit
  2. Air and gas circuit
  3. Cooling water circuit
  4. Feed water and steam flow circuit

Question No. 08: Why efficiency in Thermal Power Plant is Low?
Answer: Almost 50% of the heat generated is lost at the condenser as heat rejection. It is unavoidable as without heat rejection it is not possible to convert heat energy into mechanical energy and drive the turbine without drop in temperature. Therefore majority of the loss takes place in the condenser. Thus efficiency of the thermal power plant is between 30-35%.

Question No. 09: Which is the oldest Hydropower Plant in India?
Answer: The oldest Hydropower power plant is in Darjeeling District in West Bengal. It is installed capacity is 130 KW and was commissioned in the year 1897.

Question No. 10: What are the major reasons for balancing Hydro-thermal mix?
Answer: Seasonal load curves of our regional grids match with the pattern of hydro power generation. During summer/monsoon season when the generation at hydro power plants is high, the load factor of the system is high due to heavy agricultural load. During winter, the thermal stations operating at base load and hydro stations working as peak load stations will take care of weather beating loads. Thus the operational needs of hydro & thermal stations are complimentary and the balanced mix helps in optimal utilization of the capacity.

Question No. 11: How the electricity is generated from water?
Answer: Hydropower plants capture the energy of falling water to generate electricity. A turbine converts the kinetic energy of falling water into mechanical energy. Then a generator converts the mechanical energy from the turbine into electrical energy.

Question No. 12: On What Cycle does Thermal Power Plant operate?
Answer: Thermal Power plant works on the principle of Rankine cycle

Question No. 13: Advantages and Disadvantages of Thermal Power Plant?
Answer: The Advantages and Disadvantages of Thermal Power Plants are:
Advantages: Thermal Power Plants can be operated near the load centers unlike hydro and nuclear plants
  • Requires less space compared to hydro plants and cost of construction is less
  • Running or operating costs are less compared to diesel or gas plants
  • Can able to handle over load for certain period of time
Disadvantages: Emits green house gases and causes pollution Coal and Ash handling requires large area Efficiency is low.

Question No. 14: What are the different types of Hydro Schemes?
Answer: Different types of Hydro Schemes are:
  1. Purely Run-of-River Power Station.
  2. Storage type Power Station.
  3. Run-of-River Stations with Pondage.

Question No. 15: What is a hydro energy?
Answer: Hydroelectricity is the term referring to electricity generated by hydropower; the production of electrical power through the use of the gravitational force of falling or flowing water.

Question No. 16: Why Hydropower stations are preferred solution for meeting peak loads in grids?
Answer: Due to its unique capabilities of quick starting and stopping of hydro machines, hydropower stations are found to be economical choice to meet peak load in the grid.

Question No. 17: What is the classification of Hydro Projects based on Installed Capacity & Applicability?
Answer: The Hydro Projects Capacity & Applicability are as the following:
Large: > 100 MW = Large urban population centres
Medium: 10 – 100 MW = Medium urban population centres
Small: 1 – 10MW = Small communities with possibility to supply electricity to regional grid.
Mini: 100 kW – 1MW = Small factory or isolated communities.
Micro: 5 – 100kW = Small isolated communities.
Pico: <5kW = 1-2 houses.

Question No. 18: Why Generation Voltage in Thermal Power Plant is between 11 kV to 33 kV?
Answer: The current carrying conductor cross section depends upon the magnitude of the current it is carrying and insulation strength of the conductor depends on the maximum voltage it can withstand. Therefore while designing the generator an optimum value is chosen between the amount of the current and voltage conductor can withstand.

Question No. 19: What are the advantages of Hydropower?
Answer: The advantages of Hydropower are:
  1. A renewable source of energy – saves scarce fuel reserves.
  2. Nonpolluting and hence environment friendly.
  3. Long life – The first hydro project of India completed in 1897 is still in operation at Darjeeling.
  4. Cost of generation, operation and maintenance is lower than the other sources of energy.
  5. Ability to start and stop quickly and instantaneous load acceptance/rejection makes it suitable to meet peak demand and for enhancing system reliability and stability.
  6. Has higher efficiency (over 90%) compared to thermal (35%) and gas (around 50%).
  7. Cost of generation is free from inflationary effects after the initial installation.
  8. Storage based hydro schemes often provide benefits of irrigation, flood control, drinking water supply, navigation, recreation, tourism etc.
  9. Being located in remote regions leads to development of interior backward areas (education, medical, road communication, telecommunication etc.)

Question No. 20: How efficiency of Thermal Plant can be improved?
Answer: Some of the methods by which the efficiency of the thermal plant can be improved are:
  1. By increasing the temperature and pressure of the steam entering the turbine
  2. By reducing the pressure in the condenser
  3. By reheating the steam between different stages between the turbine

Question No. 21: What is the estimated total Hydropower potential of India?
Answer: The hydro power potential of India is around 1,48,701 MW and at 60% load factor, it can meet the demand of around 84,000 MW.

Question No. 22: What are approaches to tackle sedimentation problem of reservoir?
Answer: The following are some approaches to tackle sedimentation problem of reservoir:
  1. Catchment Area Treatment (CAT) for reduction of silt load includes Afforestation of the catchment area and Environmental works such as construction of check dams.
  2. Effective de-silting arrangements for prevention of silt.
  3. Silt resistant equipment for withstanding the silt.

Question No. 23: What are the different types of dams?
Answer: Different types of dams are conventional concrete dam, Roller compacted concrete dam, rock fill dam, Concrete Faced Rock fill Dam (CFRD), Earth fill dam, arch dam, barrages etc.
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