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Different Types of Losses in Steam Turbine

Types of losses in steam turbine:

Steam Turbine being work producing device running at a high speed has number of losses occur in it, This losses results in to a Substantial loss of energy when they all combine together.
 In Steam Turbine some losses are within the turbine itself and some are external.

1.Internal losses
2.External losses

1) Internal losses:

There are different types of internal losses they are explained as follows:

a. Leakage Losses at Tip and Diaphragm:

  • Steam leakage may occur across the turbine shaft and in between the stages.
  • Leakage loss is occurred between the turbine shaft and bearings, and in between the blade tips and glands.
  • Due to the leakage losses in steam, the work done by this leakage stage is low because steam is not fully utilized for doing work.
  • to reduce this loses drum type construction is useful to diaphragm and a wheel type construction is needed in reaction turbine. 

b.   Wetness of Steam:

  • This type of loss is occurred due to the liquid particles present in the steam, in this liquid particles has less velocity than
  • vapor particles this gives less efficiency, these losses can be reduced by reheating the steam.
  • When a Steam causes wetness by this the water droplets on blades is formed, to throw off the water drops on blades there is a loss occur in mechanical work and erosion is also formed on the blades of last stage.

c. Radiation and Convection losses:

  • this type of losses is occurred due to the temperature difference between turbine casing and surroundings.

d. Nozzle friction losses:

  • These losses are occurred due to the friction in the nozzle. losses occurred in this can be reduced by using a better design.
  • Steam turbine nozzle is designed to get isentropic expansion, by this we can get an increasing in velocity from inlet to exit. but in practically the steam leaving in a nozzle does not have a velocity equal to designed velocity value, this is occur due to non-isentropic expansion. there is a friction losses in between the steam and nozzle by this it occurs in non-isentropic expansion.

e. Carry-over losses:

  • This loss occurs in between the nozzles gap and moving blade. by this kinetic energy of steam gets the loss.

2. External losses:

There are different types of external losses they are explained as follows:

a. Mechanical friction losses. 

  • This type of losses occurs due to the shaft and bearings friction.
  • This can control by using better lubrication.

 b. Shaft gland leakage:

     * Steam Leakage takes place through Main valve and regulating valve.
     * Seals and Glands.
     * Space between Nozzle and Moving Blades.

c. Governing losses.

  • This loss occur at the main valve of governing by throttling of steam.
  • A good design of governor can reduce the losses.

d. Thrust and journal bearing:

     * This losses is depend on the bearing load, shaft speed, oil viscosity and film thickness etc..

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