Steam entering from a small opening attains a very high velocity. The velocity attained during expansion depends on the initial and final content of the steam. The difference in initial and final heat content represent the heat energy to be converted to kinetic energy.
There are two types of steam turbines:
Compounding of steam turbines:
Single stage turbines are of low efficiency. In compounding, a number of rotors are connected or keyed to the same shaft. Two types of compounding are used: Velocity compounding and pressure compounding.
|Expansion happens in a nozzle||Expansion happens in turbine blades|
|High speed||Low speed|
|Sufficient number of impulse stages are provided|
Governing of steam turbines
Governing signifies the process of controlling the volume of steam to meet the load fluctuation.
The function of the condenser is to condense the steam exiting the turbine. The condenser helps maintain low pressure at the exhaust.
Two types of condensers are used:
Jet condenser (contact type)
Exhaust steam mixes with cooling water. Temperature of the condensate and cooling water is same while leaving the condenser. Condensate cannot be recovered.
Heat exchanged by direct conduction Low initial cost. High power required for pumping water.
Surface condenser (non-contact type)
Steam and water do not mix. Condensate temperature higher than the cooling water temperature at outlet. Condensate recovered is fed back to the boiler.
Heat transfer through convection. High initial cost. Condensate is not wasted so pumping power is less.
|Title:||Lecture notes on power station engineering for students – Department of Electrical Engineering, Veer Surendra Sai University of Technology Burla|
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