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Statement (I): The effective head of a turbo-machine is equal to: Gross head minus the head loss in penstock and the velocity head at the turbine inlet.

Statement (II): A turbo-machine becomes susceptible to cavitation if pressure falls below the vapour pressure of the liquid. 


1. Both Statement (I) and Statement (II) are individually true and Statement (II) is the correct explanation of Statement (I)
2. Both Statement (I) and Statement (II) are individually true but Statement (II) is not the correct explanation of Statement (I)
3. Statement (I) is true but Statement (II) is false
4. Statement (I) is false but Statement (II) is true

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Correct Answer - Option 2 : Both Statement (I) and Statement (II) are individually true but Statement (II) is not the correct explanation of Statement (I)

Statement I: True

The net head for a turbine is

\(\Rightarrow H_{Net}= H_{g}-H_{L}-\frac{V^{2}}{2g}\)

Where

Hg is the gross head i.e. energy available at the inlet of the turbine when ideal conditions of flow are considered.

HL is head loss. It is the friction loss in the penstock pipe.

V2/2g = Velocity head at the turbine inlet.

Statement II: True

Cavitation occurs when the liquid in a penstock (water delivery pipe in the turbine) turns to a vapor at low pressure.  When Cavitation takes place, air bubbles are formed at low pressure. As the liquid passes from regions of low pressure to higher pressure, the air bubbles explode. This creates a shockwave that hits the penstock and leading to the development of cracks in the pipe surface.

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