Power Plant Engineering

HYDRO-ELECTRIC POWER PLANTS 371

Pa

A

H 0

H

pa

h

B

C

D

E

hd

Fig. 11.26

Ea = Eb = H + hd +

pa

ρ

Ec = h +hd +

2

2

Vc

g

+ c

p

ρ

Ed =

2

2

Vd

g

+ d

p

ρ

.

WZ (work done per kg of water passing through the turbine) = Eb – Ec = Eb – (Ed + hf)

where Ec = Ed + hf where h is the head lost by water passing through the draft tube (friction and
other losses).

= d a

p

Hh



++

ρ

• 
  

2

2

dd

f

Vp

h

g



++

ρ

=

2

2

H Vd

g



−



+ hd ppad



+−

ρρ

• hf

The pressure at the point D and E must be same.

∴ d

p

ρ

= a

p

ρ

+ hd

Substituting this value in the above equation, we get

W 2 =

2

2

H Vd

g



−



• hf

= H –

2

2

Vd

g

in hf is taken as zero ...(b)