Kaplan Turbine MCQ Quiz - Objective Question with Answer for Kaplan Turbine - Download Free PDF

Explanation:

Kaplan Turbine

• A Kaplan turbine is a type of reaction turbine specifically designed for low-head and high-flow applications. It is a propeller-type turbine with adjustable blades, which allows it to operate efficiently under varying water flow conditions. It is one of the most commonly used turbines in hydroelectric power plants where the available water head is relatively low.

Working Head Range:

• The Kaplan turbine is best suited for a working head range of 5 to 70 meters. This is because it is designed to harness energy from water at low to medium heads while maintaining high efficiency. The adjustable blades of the Kaplan turbine allow it to adapt to changing water flow conditions, making it highly versatile for such applications.

Working Principle:

• The Kaplan turbine operates on the principle of reaction and dynamic action of water. Water enters the turbine through a scroll casing and is directed onto the runner blades by guide vanes. The adjustable guide vanes control the flow of water, ensuring optimal efficiency. The water’s pressure energy is converted into mechanical energy as it flows through the turbine, causing the runner to rotate. The rotation of the runner drives the generator, which converts mechanical energy into electrical energy.

Features of Kaplan Turbine:

• Adjustable Blades: The runner blades of the Kaplan turbine are adjustable, allowing the turbine to maintain high efficiency across a wide range of water flow conditions.
• Reaction Turbine: It operates as a reaction turbine, meaning the water’s pressure energy is partially converted into kinetic energy before it reaches the runner.
• Low-Head Application: It is specifically designed for low-head applications, making it ideal for rivers and dams with small elevation differences.
• High Flow Rate: The Kaplan turbine is capable of handling large volumes of water, making it suitable for high-flow conditions.

Explanation:

Kaplan Turbine

Definition: A Kaplan turbine is a type of water turbine that was developed by Austrian engineer Viktor Kaplan. It is a reaction turbine that is specifically designed for low-head and high-flow water applications. The Kaplan turbine is highly efficient and can handle a wide range of water flow conditions, making it suitable for various hydropower plants.

Working Principle: In a Kaplan turbine, water flows parallel to the axis of the rotation of the shaft. This axial flow design allows water to pass through the turbine blades with minimal resistance, converting the hydraulic energy of the water into mechanical energy. The turbine consists of adjustable blades that can be angled to optimize the efficiency based on the water flow conditions. The water enters the turbine through a spiral casing, flows through the guide vanes, and then passes through the turbine blades, causing them to rotate. The rotational energy is then transferred to a generator to produce electricity.

Advantages:

• High efficiency across a wide range of flow conditions due to the adjustable blades.
• Suitable for low-head and high-flow applications, making it versatile for various hydropower projects.
• Compact design, which can save space and reduce construction costs.

Disadvantages:

• Higher initial cost compared to other types of turbines due to the complexity of the adjustable blades.
• Requires regular maintenance to ensure the adjustable blades function correctly.

Applications: Kaplan turbines are commonly used in hydropower plants with low-head and high-flow water conditions. They are ideal for river-based power stations and tidal power plants.

Correct Option Analysis:

The correct option is:

Option 3: Kaplan turbine

This option correctly describes the Kaplan turbine, where water flows parallel to the axis of the rotation of the shaft. The axial flow design is a distinctive feature of Kaplan turbines, making them highly efficient for specific hydropower applications.

Additional Information

To further understand the analysis, let’s evaluate the other options:

Option 1: Old Francis turbine

The old Francis turbine is a mixed-flow turbine where water enters the turbine radially and exits axially. It is not characterized by axial flow throughout, as is the case with the Kaplan turbine. The Francis turbine is suitable for medium-head applications and cannot be described as having water flow parallel to the axis of the rotation of the shaft.

Option 2: Francis turbine

The modern Francis turbine, like the old version, is a mixed-flow turbine where water enters radially and exits axially. While it is highly efficient and widely used in medium-head hydropower plants, it does not have the axial flow design seen in Kaplan turbines. Therefore, it does not meet the criteria of water flowing parallel to the axis of the rotation of the shaft.

Option 4: Pelton wheel

The Pelton wheel is an impulse turbine designed for high-head and low-flow applications. In a Pelton wheel, water jets strike the buckets tangentially, causing the wheel to rotate. The flow of water is not parallel to the axis of the rotation of the shaft, making this option incorrect in the context of the given statement.

Conclusion:

Understanding the operational characteristics of different types of turbines is essential for correctly identifying their applications. The Kaplan turbine, with its axial flow design, is highly efficient for low-head and high-flow water conditions. This makes it distinct from other turbines like the Francis turbine and Pelton wheel, which have different flow characteristics and applications.

Concept:

The area of flow for a Kaplan turbine is determined by the annular area between the runner's outer diameter and the hub diameter.

Given:

• Outer diameter of runner, \( D_0 \)
• Diameter of hub, \( D_b \)

Key Points:

1. A Kaplan turbine is an axial-flow turbine where water flows parallel to the shaft.
2. The flow area is the annular region between the runner's outer edge and the hub.
3. The correct formula calculates the cross-sectional area of this annular space.

Derivation of Correct Formula:

The flow area is the difference between the runner's cross-section and the hub's cross-section:

\[ \text{Area of Flow} = \frac{\pi}{4} D_0^2 - \frac{\pi}{4} D_b^2 = \frac{\pi}{4} \left( D_0^2 - D_b^2 \right) \]

Explanation:

According to the direction of flow of fluid over the blades, turbines can be classified in the following categories:

• Axial flow turbine: The flow of water is in the direction parallel to the axis of the shaft.
  • Example: Kaplan turbine and propeller turbine.
• Mixed flow turbine: water flows through the runner in the radial direction but leaves in the direction parallel to the axis of rotation of the runner. In simple terms, Fluid flows both in radial as well as in axial direction.
  • Example: Modern Francis Turbine
• Radial flow turbines: In this type of turbine, the water strikes in the radial direction. accordingly, it is further classified as:
  • Inward flow turbine: The flow is inward from periphery to the center (centripetal type); Example: old Francis turbine
  • Outward flow turbine: The flow is outward from the center to periphery (centrifugal type); Example: Fourneyron turbine
• Tangential flow turbines: In this type of turbines, the water strikes the runner in the direction of the tangent to the wheel. Example: Pelton wheel turbine.

Concept:

Kaplan turbines are a type of axial flow reaction turbine, which are specifically designed for low head, high flow hydroelectric power plants. A key feature that contributes to their high efficiency in such conditions is their ability to adjust both the wicket gates and the runner blades.

In Kaplan turbines, the wicket gates are adjustable and are located before the runner blades. They control the flow of water entering the turbine, ensuring that the water hits the runner blades at the optimal angle. This adjustment helps in regulating the flow and maintaining efficiency under varying water flow conditions.

The runner blades in Kaplan turbines are also adjustable. These blades can change their pitch (angle) to adapt to the flow conditions. This means that the turbine can maintain high efficiency over a wide range of operating conditions, as the blades can be adjusted to the most efficient angle for the current flow rate and head.

Explanation:

To understand why the combination of adjustable wicket gates and runner blades contributes to high efficiency, let's delve into the mechanisms at play:

1. Adjustable Wicket Gates:

The wicket gates are positioned around the runner and control the flow of water that enters the turbine. By adjusting the position of these gates, the flow rate and direction of water can be optimized. This ensures that the water hits the runner blades at the best possible angle, maximizing the transfer of energy from the water to the turbine. The ability to adjust the wicket gates allows the turbine to adapt to varying water flow conditions, maintaining efficient operation even when the flow rate changes.

2. Adjustable Runner Blades:

The runner blades in a Kaplan turbine can change their pitch to match the water flow conditions. This is crucial because the optimal angle for the blades depends on the flow rate and head. By adjusting the pitch of the blades, the turbine can ensure that the water flow strikes the blades at the most efficient angle, maximizing energy extraction. This adjustability allows the Kaplan turbine to operate efficiently over a wide range of flow rates and heads, making it highly versatile and efficient in low head, high flow applications.

3. Combined Effect:

The combination of adjustable wicket gates and runner blades allows for fine-tuning of the turbine's operation. The wicket gates control the flow rate and direction, while the runner blades adjust to the optimal pitch. This dual adjustability ensures that the turbine can maintain high efficiency across a wide range of operating conditions. The ability to adapt to changing water flow and head conditions is what makes Kaplan turbines particularly suited for low head, high flow hydroelectric power plants.

In summary, the distinct feature of Kaplan turbines that contributes to their high efficiency in low head, high flow conditions is the combination of adjustable runner blades and wicket gates. This dual adjustability allows the turbine to optimize the flow of water and the angle of the blades, ensuring efficient energy extraction over a wide range of operating conditions.

Correct Option:

The correct answer is option 4: Both adjustable runner blades and wicket gates.

Solution Statement:

Kaplan turbines achieve high efficiency in low head, high flow hydroelectric power plants due to their ability to adjust both the wicket gates and the runner blades. The adjustable wicket gates control the flow rate and direction of water entering the turbine, while the adjustable runner blades change their pitch to match the optimal angle for energy extraction. This combination allows the turbine to maintain high efficiency across a wide range of operating conditions, making it highly effective in low head, high flow applications.

Non-dimensional specific speed is given by

\({N_S} = \frac{{N\sqrt P }}{{{{\left( {gH} \right)}^{\frac{5}{4}}} \cdot \sqrt \rho }}\)

The Francis turbine is a type of reaction turbine, and it can operate over a wide range of water flows and height differences, which makes it suitable for a specific speed value of 1. It is more flexible in terms of operation conditions compared to the Pelton wheel.

Explanation:

Specific speed: 

• It is defined as the speed of a similar turbine working under a head of 1 m to produce a power output of 1 kW. The specific speed is useful to compare the performance of the various type of turbines. The specific speed differs for the different type of turbines and is the same for the model and actual turbine.
• \({N_s} = \frac{{N\sqrt P }}{{{H^{\frac{5}{4}}}}}\)

Following are the range of specific speed of different turbines

• The specific speed of Pelton wheel turbine (single jet) is in the range of 10-35
• The specific speed of Pelton wheel turbine (multiple jets) is in the range of 35-60
• The specific speed of Francis turbine is in the range of 60-300.
• The specific speed of Kaplan/propeller turbine is greater than 300.

So the Kaplan turbine has the highest specific speed.

The classification of the turbine based on the basis of operating head

The specific speed of a turbine is in the range of

Explanation:

Turbines are hydraulic machines that convert hydraulic energy into mechanical energy.

Classification of turbines based on the energy at inlet:

Specific Speed of Turbines:

Head of turbines:

Concept:

Kaplan Turbine:

Kaplan Turbine is an axial reaction flow turbine and has adjustable blades. When the water flows parallel to the axis of the rotation of the shaft, the turbine is known as the axial flow turbine.

Flow ratio (ψ) for a Kaplan Turbine is given by:

\({\rm{ψ }} = \frac{{{{\rm{V}}_{\rm{f}}}}}{{\sqrt {2{\rm{gH}}} }}\)

Where V_f is the flow velocity at the inlet of the runner and 'H' is the head available.

Calculation:

Given:

ψ = 0.6, H = 20 m.

Taking g = 10 m/s²

\({\rm{ψ }} = \frac{{{{\rm{V}}_{\rm{f}}}}}{{\sqrt {2{\rm{gH}}} }}\)

\(0.6 = {\rm{\;}}\frac{{{{\rm{V}}_{\rm{f}}}}}{{\sqrt {2 \times 10 \times 20} }}\)

V_f = 12 m/s

∴ The velocity of flow at the inlet of the runner is 12 m/s.

Explanation:

where α₁ and α₂ are the guide vane angles, and β₁ and β₂ are runner blade angle.

Guide angle as per the aerofoil theory of Kaplan turbine blade design is defined as the angle between lift and resultant force.

Since the vertical component of the force on aerofoil is called lift so the guide angle is the angle between the lift and the resultant force.

Explanation:

Specific speed: It is defined as the speed of a similar turbine working under a head of 1 m to produce a power output of 1 kW. The specific speed is useful to compare the performance of the various type of turbines. The specific speed differs for the different type of turbines and is the same for the model and actual turbine.

\({N_s} = \frac{{N\sqrt P }}{{{H^{\frac{5}{4}}}}}\)

• Low specific speed turbine: The specific speed is less than 50. (varying from 10 to 35 for single jet and up to 50 for a double jet)
  • Example: Pelton wheel turbine
• Medium-specific turbine: The specific speed varies from 60 to 250.
  • Example: Francis turbine
• High specific turbine: the specific speed is more than 300.
  • Example: Kaplan or propeller turbine

The specific speed of a turbine is in the range of

Hence, the order of the turbines on the basis of specific speed is Kaplan > Francis > Pelton

Important Points

The classification of the turbine based on the basis of operating head

Additional Information

The specific speed of a centrifugal pump is defined as the speed of a geometrically similar pump which would deliver one cubic metre of liquid per second against a head of one metre.

\({N_s} = \frac{{N\sqrt Q }}{{H_m^{3/4}}}\)

Explanation:

Classification of turbines on the various basis is given in the table below:

Explanation:

Kaplan turbine:

• In Kaplan turbine, water flows parallel to the axis of rotation of the shaft, hence it is called axial flow turbine.
• Head at the inlet of turbine is the sum of pressure energy and kinetic energy.
• During flow of water through runner, a part of pressure energy is converted into kinetic energy.
• It indicates that Kaplan turbine is a reaction turbine. When the vanes on the hub are adjustable, the turbine is known as Kaplan turbine.
• When vanes are not adjustable, turbine is called propeller turbine. Kaplan turbine components are shown in the figure below.

Explanation:

• If the water flows parallel to the axis of rotation of the shaft, the turbine is known as an axial flow turbine.
• For the axial flow reaction turbine, the shaft of the turbine is vertical.
• The lower end of the shaft is made larger which is known as a hub or boss.
• When the vanes on the hub are adjustable then the turbine is known as the Kaplan turbine and when the vanes are fixed to the hub then the turbine is known as the Propeller turbine.
• Kaplan turbine is a low head axial flow turbine with an adjustable vane.
• In a Kaplan turbine, the velocity of flow through the rotor is constant along the radius.

Classification of turbines on various bases is given in the table below:

Explanation:

Kaplan turbine:

• In Kaplan turbine, water flows parallel to the axis of rotation of the shaft, hence it is called axial flow turbine.
• Head at the inlet of the turbine is the sum of pressure energy and kinetic energy.
• During the flow of water through the runner, a part of pressure energy is converted into kinetic energy.
• It indicates that the Kaplan turbine is a reaction turbine. When the vanes on the hub are adjustable, the turbine is known as the Kaplan turbine.
• When vanes are not adjustable, the turbine is called the propeller turbine. Kaplan turbine components are shown in the figure below.

• Kaplan turbine has adjustable runner blades. Kaplan Turbine has a very small number of blades 3 to 8.

​Important Points

• Francis Turbine has a very large number of blades 16 to 24