ANALYSIS OF PELTON TURBINE. •••••••••••••••••••••••••••••••••••••••••• ★ Points of Pelton Turbine:- * It is tangential flow impulse Turbin. * It is high head low discharge turbine. * The bucket of a Pelton wheels is double semi-ellipsoidal in shape. The jet of water impinge at the centre of the bucket & deflects through 160-170°. * The advantage of having double cup shaped buckets is that the axial thrust neutralizes each other. * If P is power developed by the Pelton wheels when working under head (H)& having one jet only the power developed by the same wheel will be (n.P) if n jet are used under the same head. ★ Work done per second = pQ ( Vw1+Vw2) u. = pQ ( V1-u)(1+k cos¤) u. = paV1 (V1-u)(1+k cos¤) u. V1 = Velocity of jet coming out of nozzle. u 1 = u2=u=Tangential velocity of vane. K = Bucket friction coefficient. ★ Efficiency of Pelton Wheel:- n Nozzle = K.E.of jet per sec/Water power at the base of nozzle. * Hydraulic Efficiency n hyd = Runner Power/Kinetic Energy per sec. n hyd = 2 (V1-u)(1+k cos¤) u/V2 1. n hyd max = {1+kcos¤/2}[when u =v1/2]. K = Friction factor for blades. * Mechanical efficiency n mech = shaft power/runner power. * Overall Efficiency no = nN×nh×n mech. * Velocity of jet V1 = Cv/^2gH. Cv = coeff of velocity = 0.97-0.99. * Speed ratio Ku = u//^2gH, Where u = rDN/60. Ku = 0.43-0.47 * Jet ratio (m)=dia of wheel (D)/jet dia (d). A jet ration of 12 is normally adopted. * No. of Buckets (z)= D/2d+15=m/2+15 = 18 to 25. This formula is called Tygun Formula.
Posted on: Sat, 13 Sep 2014 15:51:45 +0000
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