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If mechanical efficiency of a Pelton Turbine is 80% and its hydraulic efficiency is 85%, its overall efficiency will be:


1. 50%
2. 75%
3. 68%
4. 72%

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Correct Answer - Option 3 : 68%

Concept:

The overall efficiency ηo of turbine = volumetric efficiency (ηv) × hydraulic efficiency (ηh) × mechanical efficiency (ηm)

ηo = η× η× ηm 

\({{\rm{η }}_{\rm{v}}} = \frac{{{\rm{volume\;of\;water\;actually\;striking\;the\;runner}}}}{{{\rm{volume\;of\;water\;actually\;supplied\;to\;the\;turbine}}}}\)

\({{\rm{η }}_{\rm{h}}} = \frac{{{\rm{Power\;deliverd\;to\;runner}}}}{{{\rm{Power\;supplied\;at\;inlet\;}}}} = \frac{{{\rm{R}}.{\rm{P}}}}{{{\rm{W}}.{\rm{P}}}}\)

\({{\rm{η }}_{\rm{m}}} = \frac{{{\rm{Power\;at\;the\;shaft\;of\;the\;turbine}}}}{{{\rm{Power\;delivered\;by\;water\;to\;the\;runner}}}} = \frac{{{\rm{S}}.{\rm{P}}}}{{{\rm{R}}.{\rm{P}}}}\)

Overall efficiency: \({η _o} = \frac{{S.P}}{{W.P}}\)

Water Power = ρ × Q × g × h 

Calculation:

Given:

hydraulic efficiency = 85% and mechanical efficiency = 80%

ηo = η× η× ηm 

ηo = 0.80 × 0.85 = 0.68 = 68%

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