construction and working principle of pelton wheel turbine
• The Pelton turbine is impulse turbine. Water coming out of nozzle with total kinetic energy strikes the bucket along the tangent of the runner. a tangential flow It was designed by Pelton, an American engineer in 1880. It works under high head and small quantity of water.
• Figure 1.1 shows the layout of a hydroelectric power plant with Pelton wheel as turbine. The water from reservoir flows through pipe called penstocks at the outlet of which nozzle is fitted.
•Nozzle is used to convert pressure energy into kinetic energy. At the outlet of the nozzle, the water comes out in the form of a jet and strikes the buckets (vanes) of the runner wheel.
specification:
Type impulse (free jet) turbine.
Type of flow -tangenional
Head - more than 250 m.
Runner shaft - generally horizontal
Specific speed - 10 to 60 rpm.
Discharge - low Power developed diameter of wheel number of buckets.
Main Parts of Pelton Turbines are shown below.
1. Nozzle:
with flow regulating arrangement: A nozzle is fitted at the end of penstock to convert pressure energy of water into kinetic (velocity) energy. To regulate flow of water, a spear mechanism is fitted inside the nozzle. For small units, it is operated manually by rotating wheel fitted at the end of spear rod which is threaded, conical needle increases or decreases cross-sectional area of nozzle available for flow of water. Refer Figure 1.2
2. Effective Head:
It is also called as Net Head and is defined as the head available at the inlet of the turbine. When water is flowing from head race to the turbine, a loss of head due to friction between the water penstocks occurs. Though there are other losses also such as loss due to bend, pipe fittings, loss at the entrance of penstock etc., yet they are having small magnitude as friction. If hr is the head loss due to friction penstocks and water then net heat on turbine is given by,
head loss H = Hg - hr
3. Runner and Buckets:
A circular disc with number of buckets evenly spaced on its periphery constitutes runner of Pelton wheel. The shape of the buckets is double hemispherical. Each bucket is divided into two symmetrical parts by dividing wall which is known as splitter. Shape of bucket is shown in figure 1.3.
Jet of coming out of nozzle strikes on the splitter. Splitter divides the jet into two equal parts without shock and flows over the both portion of the bucket. The bucket is shaped in such a manner that the jet is defleeted through an angle of about 160° to 170°. The surface of the bucket is made very smooth. It is made of Cast iron, Cast steel, Bronze or other alloys. The advantage of having double cup-shaped buckets is that the axial thrust is neutralised. At the lower tip of bucket, a notch is cut which prevents the jet striking the preceding bucket being intercepted by the next bucket very soon.
4. Casing:
A casing made of cast iron or fabricated steel plates is provided for a Pelton wheel. It has no hydraulic function to perform. It is provided only to prevent splashing of water, to lead water to the tail race and also to act as a safeguard against accidents.
5. Braking jet:
Larger Pelton wheels are having small brake nozzle which when opened directs a jet of water on the back of the buckets, thereby bringing the wheel quickly to rest after it is shut down. Larger wheels are having large moment of inertia due to which after closing jet of water, it starts rotating for long time
• The Pelton turbine is impulse turbine. Water coming out of nozzle with total kinetic energy strikes the bucket along the tangent of the runner. a tangential flow It was designed by Pelton, an American engineer in 1880. It works under high head and small quantity of water.
• Figure 1.1 shows the layout of a hydroelectric power plant with Pelton wheel as turbine. The water from reservoir flows through pipe called penstocks at the outlet of which nozzle is fitted.
•Nozzle is used to convert pressure energy into kinetic energy. At the outlet of the nozzle, the water comes out in the form of a jet and strikes the buckets (vanes) of the runner wheel.
Type impulse (free jet) turbine.
Type of flow -tangenional
Head - more than 250 m.
Runner shaft - generally horizontal
Specific speed - 10 to 60 rpm.
Discharge - low Power developed diameter of wheel number of buckets.
Main Parts of Pelton Turbines are shown below.
1. Nozzle:
with flow regulating arrangement: A nozzle is fitted at the end of penstock to convert pressure energy of water into kinetic (velocity) energy. To regulate flow of water, a spear mechanism is fitted inside the nozzle. For small units, it is operated manually by rotating wheel fitted at the end of spear rod which is threaded, conical needle increases or decreases cross-sectional area of nozzle available for flow of water. Refer Figure 1.2
It is also called as Net Head and is defined as the head available at the inlet of the turbine. When water is flowing from head race to the turbine, a loss of head due to friction between the water penstocks occurs. Though there are other losses also such as loss due to bend, pipe fittings, loss at the entrance of penstock etc., yet they are having small magnitude as friction. If hr is the head loss due to friction penstocks and water then net heat on turbine is given by,
head loss H = Hg - hr
3. Runner and Buckets:
A circular disc with number of buckets evenly spaced on its periphery constitutes runner of Pelton wheel. The shape of the buckets is double hemispherical. Each bucket is divided into two symmetrical parts by dividing wall which is known as splitter. Shape of bucket is shown in figure 1.3.
Jet of coming out of nozzle strikes on the splitter. Splitter divides the jet into two equal parts without shock and flows over the both portion of the bucket. The bucket is shaped in such a manner that the jet is defleeted through an angle of about 160° to 170°. The surface of the bucket is made very smooth. It is made of Cast iron, Cast steel, Bronze or other alloys. The advantage of having double cup-shaped buckets is that the axial thrust is neutralised. At the lower tip of bucket, a notch is cut which prevents the jet striking the preceding bucket being intercepted by the next bucket very soon.
4. Casing:
A casing made of cast iron or fabricated steel plates is provided for a Pelton wheel. It has no hydraulic function to perform. It is provided only to prevent splashing of water, to lead water to the tail race and also to act as a safeguard against accidents.
5. Braking jet:
Larger Pelton wheels are having small brake nozzle which when opened directs a jet of water on the back of the buckets, thereby bringing the wheel quickly to rest after it is shut down. Larger wheels are having large moment of inertia due to which after closing jet of water, it starts rotating for long time
No comments:
Post a Comment