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.

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