Power Plant Engineering

SOLVED EXAMPLES
Example 1. A nuclear fission reaction power plant converts energy in matter to electrical energy
by following energy chain
Energy in
Thermal
Mechanical
Electrical
Matter
Energy
 Energy
Energy
Neglecting losses, how much matter is converted into electrical energy per day by a 10 mW
power plant ?
Solution. Matter converted = Electrical Energy delivered
Energy delivered = Power × Time
E
e
= (10 mW × 10
6
) × (24 hr × 3600)
= (10
7
W) × (8.64 × 10
4 
s)
E
e 
= 8.64 × 10
11 
J
Electrical energy delivered = Matter converted into energy
E
0
= m
0
C
2
m
0
= E/C
2
= 
11
8
2
8.64 10
J
(3 10 m/s)
×
×
= 9.6 × 10
–4
kg
→
→
→

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110
POWER PLANT ENGINEERING
The dimensional relationship of [E/C
2
] is
2
J
(m/s)
= 
2
2
N.m.s
m
= 
N
m
s
2
= kg.
Example 2. A turbine generator unit has output of 150 mW and efficiency of 0.80. Calculate
energy supplied per hours by steam generator.
Solution. Output of turbine generator = 150 mW
Input to turbine = 
150
0.8
= 187.5 mW
Energy input for 1 hour operation
= 187.5 (mW) × 1 (hr) = 187.5 mW-hr
1 mW hr = 3.6 × 10
9 
J
187.5 mW hr = 675 × 10
9
 J.
Example 3. A 100 mW geothermal power plant is operated for 11 months in a year. 1 month is
for maintenance shutdown. The cost of electrical energy supplied is Rs. 2.5/- per kW-hr. Calculate the
total earning by the power plant neglecting losses.