Selection of Turbine for Hydro Power Plant

• From the study of large number of generating power stations, it is found that there is a particular range of head and specific speed for which a particular turbine is most suitable.
• Figure A, Figure B and Figure C are the curves drawn from the results obtained in these studies on various turbines and different specific speeds.
• These curves are useful for preliminary selection of turbines. From these curves, it is seen that Pelton wheel is suitable for head varying between 90 m to 1100 m and specific speed between 10 to 40 r.p.m. Refer Figure A.

Figure A

Figure B

Figure C

• Francis turbine is suitable for specific speed 95 to 440 and the suitable head of water being 14 m to 300 m and is represented in Figure B.
• The Kaplan turbine is essentially a low head turbine, the head of water used lies between 3 m to 30 m, but they operate at a high specific speed varying between 550 rpm to 830 rpm, hence they are selected for low head and high discharge purpose. Refer Figure C as a reference.
• The generators selected with all these turbines are the salient pole type synchronous generators, developing 3-phase, 50 Hz voltage at 3.3 kV, 6.6 kV or 11 kV depending upon the design and requirements of supply agency.
• The construction of all these generators is similar to that explained in article 3.4.6, the only change will be in the number of poles of the rotor and stator. As the specific speed of turbines changes, for producing a 50 Hz frequency of supply the number of poles should be in accordance with the relation.

N= 120
f/P

     Where,

N=
Specific speed  of tubine

F=
No of pole of geerator

P= 50
Hz, frequency of e.m.f