100+ TOP THERMAL & HYDRO LAB VIVA Questions and Answers

Thermal and hydro VIVA Questions :-

1.Why efficiency in Thermal Power Plant is Low?
Almost 50% of the heat generated is lost at the condenser as heat rejection. It is unavoidable as with out 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%.

2.On What Cycle does Thermal Power Plant operate?
Thermal Power plant works on the principle of Rankine cycle

3.Why Generation Voltage in Thermal Power Plant is between 11kV to 33kV?
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.

4.What are the different circuits in Thermal Power Plant?
Some of the major circuits in the thermal power plant are:

  • Coal and Ash circuit
  • Air and gas circuit
  • Cooling water circuit
  • Feed water and steam flow circuit

5.How efficiency of Thermal Plant can be improved?
Some of the methods by which the efficiency of the thermal plant can be improved are:

  • By increasing the temperature and pressure of the steam entering the turbine
  • By reducing the pressure in the condenser
  • By reheating the steam between different stages between the turbine

6.Advantages and Disadvantages of Thermal Power Plant?


  1. Thermal Power Plants can be operated near the load centers unlike hydro and nuclear plants
  2. Requires less space compared to hydro plants and cost of construction is less
  3. Running or operating costs are less compared to diesel or gas plants
  4. Can able to handle over load for certain period of time


  1. Emits green house gases and causes pollution
  2. Coal and Ash handling requires large area
  3. Efficiency is low

6.What are the advantages of Hydropower?
• A renewable source of energy – saves scarce fuel reserves.
• Non-polluting and hence environment friendly.
• Long life – The first hydro project of India completed in 1897 is still in operation at Darjeeling.
• Cost of generation, operation and maintenance is lower than the other sources of energy.
• 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.
• Has higher efficiency (over 90%) compared to thermal (35%) and gas (around 50%).
• Cost of generation is free from inflationary effects after the initial installation.
• Storage based hydro schemes often provide benefits of irrigation, flood control, drinking water supply, navigation, recreation, tourism, pisciculture etc.
• Being located in remote regions leads to development of interior backward areas (education, medical, road communication, telecommunication etc.)

7.Why hydropower is called renewable source of energy?
Hydropower is called renewable source of energy because it uses and not consumes the water

8.What is the classification of Hydro Projects based on Installed Capacity?
Micro: up to 100 KW
d capacity >= 500 MW

9.How energy is generated in Hydroelectric Power Plant?
for generation of electricity, and the hydropower leaves this vital resource available for other uses
Mini: 101KW to 2 MW
Small: 2 MW to 25 MW
Mega: Hydro projects with installe
Thermal Projects with installed capacity >=1500 MW

10.Which is the largest Hydropower station in the world?
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.

11.How does cost of generation from Hydropower Plant compare with other sources of electricity?
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.

12.Which is the oldest Hydropower Plant in India?
The oldest Hydropower power plant is in Darjeeling District in West Bengal. It’s installed capacity
is 130KW and was commissioned in the year 1897.

13.What is the estimated total Hydropower potential of India?
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.

14.How much of the total Hydro power potential has been exploited so far in India?
Around 19.9% of Hydropower potential has been exploited in India.

15.What are the different types of dams?
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.

16.Why the unit sizes of hydro generating machines are not standardized as in case of thermal powerplants?
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.

17.What are the different types of Hydro Schemes?
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.

18.What are the major reasons for balancing Hydro-thermal mix?
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.

19.Why Hydropower stations are preferred solution for meeting peak loads in grids?
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.

20.What are approaches to tackle sedimentation problem of reservoir?
The following are some approaches to tackle sedimentation problem of reservoir:-

  • Catchment Area Treatment (CAT) for reduction of silt load includes afforestation of the
    catchment area and Environmental works such as construction of check dams.
  • Effective de-silting arrangements for prevention of silt.
  • Silt resistant equipment for withstanding the silt.

THERMAL & HYDRO LAB VIVA Questions and Answers Pdf ::

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