1.1 Hydro mechanical installation in powerhouse
Hydro mechanical equipment:
- Those equipment that convert either hydraulic energy into mechanical energy or mechanical energy into hydraulic energy.
Turbine:
- Turbine are the hydro-mechanical equipment that convert hydraulic energy into mechanical energy.
Classification of hydraulic turbine
A. Based on nature of energy head possessed by water at inlet
1. Impulse or velocity turbine
- A turbine in which water entering runner possess kinetic energy only.
- Pressure is atmospheric at inlet and outlet of the turbine.
- Example: Pelton turbine.
2. Reaction turbine
- The turbine in which water entering the runner possess pressure as well as kinetic energy.
- Enclosed by tight casing.
- Example: Kaplan turbine, Francis turbine etc.
B. Based on direction of flow
1. Tangential flow turbine
- The flow in turbine is in tangential direction of rotation of runner.
- Example: Pelton turbine.
2. Radial flow turbine
- Water moves toward the axis of rotation of runner or away from it.
3. Axial flow turbine
- Water flows parallel to the axis of rotation.
- Example: Kaplan turbine
4. Mixed flow turbine
- Water enters radially inward at inlet and discharges water at outlet in direction parallel to axis of rotation of runner.
- Example: Francis turbine
C. Based on head
1. Low head turbine (15m-60m)
- Example: Kaplan turbine
2. Medium head turbine (60m -250m)
- Example: Francis turbine
3. High speed turbine (>250m)
- Example: Kaplan turbine
D. Based on specific speed
1. Low specific speed turbine (8-30)
- Example: Pelton turbine
2. Medium specific speed turbine (50-250)
- Example: Francis turbine
3. High specific speed turbine (250-850)
- Example: Kaplan turbine
Selection of turbine:
1.Available head and its fluctuation
- Very high head (H>350m): Pelton turbine
- High head (150-350m): Pelton or Francis
- Medium head (60-150m): Francis turbine
- Low head (<60): Kaplan and Francis turbine
2. Efficiency
- Turbine that gives highest overall efficiency for various operating condition should be selected.
3. Specific speed
- High specific speed is required where head is low and output is large.
4.Rotational speed
- Depends upon specific speed but in practice it should have higher value.
5. Water quality
- Quality of water is more important for impulse turbine than reaction turbine.
6. Conveyance or maintenance
- Impulse turbine has less cost of maintenance that reaction turbine.
7. Deposition of turbine shaft
- Vertical shaft arrangement is better for large size turbine.
- Horizontal shaft arrangement is preferred for large size impulse turbine.
Scroll case, draft tube and tail race canal:
Draft tube:
- It is a pipe of gradually increasing area which connects the outlet of runner to the tail race.
- Used for discharging water from the exit of the turbine to the tail race.
Function of draft tube:
- Helps to recover the velocity head of the water out the runner.
- Helps to reduce turbulence and minimize cavitation.
- Increase efficiency of turbine.
- Reduce velocity of water exiting the turbine.
- Reduce noise and vibration from turbine.
Types of draft tube:
- Conical draft tube
- Simple elbow tube
- Moody spreading tube
- Draft tube with circular inlet and rectangular outlet
1.2 Electro-mechanical installation
Introduction to generator and their types:
Generator:
- Device that converts mechanical energy into electrical energy.
Types of generator:
1.Synchronous generator
- Used to maintain a constant frequency in the electricity grid.
- More expensive than asynchronous generator.
2.Asynchronous generator
- Used to provide additional power during peak demand.
- Cannot generator AC power when disconnected from grid.
1.3 Pumps
Centrifugal pumps:
- A centrifugal pump is a mechanical device used to more water by converting rotational energy into kinetic energy.
- Used in hydropower to transfer water from a low pressure area to a higher pressure area.
Reciprocating pump:
- A pump uses piston to move water.
- Create pressure to move water through pipeline.
References:
- Dandekar, M. M., & Sharma, K. N. (2010). Water Power Engineering. Vikas Publishing House.
- Punmia, B. C., Pande, B. B. L., Jain, A. K., & Jain, A. K. (2016). Irrigation and Water Power Engineering. Laxmi Publications.
- Singh, Bharat (2018). Fundamentals of Hydrology and Hydropower Engineering. Nem Chand & Bros.
- Central Water Commission, Government of India (2019). Handbook on Hydroelectric Engineering.
- International Energy Agency (IEA) (2021). Hydropower Status Report. Retrieved from www.iea.org
- Nepal Electricity Authority (NEA) (2022). Annual Report on Hydropower Projects in Nepal. Retrieved from www.nea.org.np
- United States Bureau of Reclamation (2020). Design of Small Dams. U.S. Government Printing Office.