Power Plant Engineering

STEAM TURBINE 209

sion. Generator losses appearing as heat must be constantly removed to avoid damaging the windings.

Large generators have cylindrical rotors with minimum of heat dissipation surface and so they have

forced ventilation to remove the heat. Large generators generally use an enclosed system with air or

hydrogen coolant. The gas picks up the heat from the generator any gives it up to the circulating water in

the heat exchanger.

6.17 Steam Turbine Specifications

Steam turbine specifications consist of the following:

(i) Turbine rating. It includes :

(a) Turbine kilowatts

(b) Generator kilovolt amperes

(c) Generator Voltage

(d) Phases

(e) Frequency

(f) Power factor

(g) Excitor characteristics.

(ii) Steam conditions. It includes the following:

(a) Initial steam pressure, and Temperature

(b) Reheat pressure and temperature

(c) Exhaust pressure.

(iii) Steam extraction arrangement such as automatic or non-automatic extraction.

(iv) Accessories such as stop and throttle valve, tachometer etc.

(v) Governing arrangement.

SOLVED EXAMPLES

Example 1. In an impulse steam turbine, steam is accelerated through nozzle from rest. It enters
the nozzle at 9.8 bar dry and saturated. The height of the blade is 10 cm and the nozzle angle is 15°.
Mean blade velocity is 144 m/s. The blade velocity ratio is 0.48 and blade velocity coefficient is 0.97.
Find:

(1) Isentropic heat drop.

(2) Energy lost in the nozzles and in moving blades due to friction.

(3) Energy lost due to finite velocity of steam leaving the stage.

(4) Mass flow rate.

(5) Power developed per stage.

(6) Diagram and stage efficiency. Take: Nozzle efficiency = 92%

Blade angles at inlet = Blade angles at out let Speed = 3000 rev/min

Solution. V.R. =

1

V

V

b = 0.48