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Turbine.

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Turbines used in industry.

Turbines used in industry.

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  • 1. Principle It changes thermal energy to mechanical energy.  Heat (thermal energy) produces steam pressure, and the steam pressure is converted to steam velocity by the nozzle. After steam strikes the buckets, steam velocity decrease.  The rotor turns and produces mechanical work. Means Rotation of rotor.
  • 2. Operation principle  The flow of steam into the steam chest is controlled by the governor valve. By controlling the amount of steam, the governor valve controls the output of mechanical energy.  For the steam to flow into the casing through the nozzle, the steam pressure in the casing must be lower than the steam pressure in the steam chest..  The high – velocity steam directed toward the buckets is an impelling force (impulse) which causes the rotor to turn. The buckets are mounted on a wheel rather than directly on the shaft and the nozzle or nozzles are located in the wall of the steam chest.
  • 3. Classification of Steam turbines: Based on exhaust condition: CONDENSING BACK- PRESSURE EXTRACTION INDUCTION Based on stage design: Impulse Reaction Based on steam flow: Axial flow Radial flow Mixed flow Based on stages: Single stage Multi stage
  • 4. Condensing Turbines  condenser at the exhaust  low pressure at the exhaust by heat removal  Utilize all of the available thermal energy present in the steam.  Since large pressure drops are common in condensing turbines, the steam pressure is usually reduced in steps. Condensing turbines are usually multi-stage turbine.
  • 5. BACK- PRESSURE TURBINE # Back pressure turbine is operated in back pressure which is higher pressure than atmospheric pressure. # The exhaust steam can be used effectively in any other machine and finally steam converted to condensed water which returns to boiler.
  • 6. Extraction and Induction Extraction: Steam removed from a stage can be used for processes that need steam at pressures and temperature above the pressure and temperature of the exhaust. Removing steam at intermediate stage is Extraction. Induction: Some times excess steam is available in the plant, at the pressure of a turbines intermediate stage. This steam can be induced into the turbine at that stage. Some steam may be removed from or added to a stage before it reaches the exhaust.
  • 7. Impulse The high – velocity steam directed toward the buckets is an impelling (impulse) force which causes the rotor to turn. 1. All the steam expansion occurs through a stationary nozzle. 2. Steam dose not expand to a great extent in the bucket.
  • 8. Reaction turbines Reaction turbine: The steam expands as it flows through the bucket. 1. All expansion occurs in the buckets mounted on the rotor. 2. Require more stages than impulse turbine
  • 9. Single-stage Single stage 1. One wheel. 2. Pressure is reduced in one stage
  • 10. Multi -stage Multi stage 1. More than one wheel. 2. Pressure is reduced in stages (Turbine having large pressure drops between inlet and exhaust are usually multi-stage turbines)
  • 11. Look at the drawing:  All the wheels are mounted on one shaft.  Each stage is isolated by a diaphragm which holds the nozzles.  Instead of one large nozzle, a row of smaller nozzles can be used. There is row of nozzles per stage.
  • 12. Governors The governor valve: 1. Regulates the amount of steam AS REQUIRED into the turbine. 2. It is used to control turbine speed. LET US SEE---- HOW
  • 13. First … What is the governor? It is a mechanism which opens and closes the governor valve. For example, fly ball governor. The drawing shows a fly ball governor:  As the governor turns, the centrifugal force moves the fly balls further apart.  At low speed, the force of the spring keeps the fly balls together.  At higher speeds, the fly balls move further apart. The faster the governor turns, the fly balls moves further away from the center.
  • 14. Second … Operation of the governor valve 1- When the turbine is not operating, the spring holds the fly balls close to the shaft. Before the turbine is started, the governor valve is wide open.
  • 15. 2- As the shaft approaches operating speed, spring tension is overcome by the centrifugal force, and the balls move away from each other, the governor valve is Pushed to closed. When the turbine reaches operating speed, the governor valve allows less steam in than at startup, and turbine stops accelerating.
  • 16. 3- If the turbine speed is too fast, the governor valve will be closed.
  • 17. Over speeds Trip  If all loads are suddenly removed from a fully-loaded turbine, the turbine may over speed.  Some times the governor reacts too slowly or fails to respond at all.  If the steam is not shut off promptly, the turbine over speeds until it flies apart. A trip pin in the turbine shaft is used to shut off the steam flow in the shaft.
  • 18. 1. At normal speeds the trip pin remains inside the shaft by a spring. 2. If the turbine over speeds, the pin is ejected from the shaft by centrifugal force. The drawing shows a trip pin in the shaft.
  • 19. Look at the drawing 1. When the turbine over speeds, the extended pin strikes the over speed trip. 2. The trigger releases a latch holding the trip lever, which is then pulled down by a spring. The force of the spring closes the trip valve which closes and cuts off the steam flow to the steam chest. 3. The turbine stops.
  • 20. Main Parts of steam turbine Rotor Steam chest Casing Over speed trip system Governor system

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