# Hydraulic Machines Questions and Answers – Efficiency of Kaplan Turbine

This set of Hydraulic Machines Multiple Choice Questions & Answers (MCQs) focuses on “Efficiency of Kaplan Turbine”.

1. For a Kaplan turbine, the whirl velocity at inlet of the turbine is given to be 18 m/s. The blade velocity is given as 25 m/s. What is the hydraulic efficiency for a head of 50 m. Take g = 10 m/s2?
a) 80%
b) 90%
c) 70%
d) 98%

Explanation: The hydraulic efficiency of a Kaplan turbine is given by ηh = Vw1.u1/ gH. Substituting the values of the given parameters in the equation, we get hydraulic efficiency = 90%.

2. Which of the following efficiencies for Kaplan Turbine is described as the ratio between the power produced by runner to the power supplied by water at the inlet?
a) Hydraulic efficiency
b) Volumetric efficiency
c) Mechanical efficiency
d) Overall efficiency

Explanation: The definition of Hydraulic efficiency in a Kaplan turbine states that it is the ratio between the Runner power to the shaft power. Hence, the correct option is Hydraulic efficiency.

3. The desired hydraulic efficiency of a Kaplan turbine is 98% at a whirl velocity of 20 m/s and a head of 60 m. What should be the blade velocity of the turbine at inlet in m/s? Take g = 10 m/s2.
a) 40
b) 60
c) 80
d) 30

Explanation: The hydraulic efficiency of a Kaplan turbine is given by ηh = Vw1.u1/ gH. Substituting the values of the given parameters in the equation, we get blade velocity at the inlet as 29.4 m/s which can be roughly approximated to 30 m/s.

4. It is given that the input water power of the Kaplan turbine is 1.10 times the runner power. What would be the hydraulic efficiency of the turbine (in %)?
a) 60.61
b) 70.71
c) 80.81
d) 90.91

Explanation: The definition of Hydraulic efficiency in a Kaplan turbine states that it is the ratio between the Runner power to the shaft power. If input water power is 1.10 times the runner power, the runner power is 1/1.10 = 0.90909 Times the water power. Hence, hydraulic efficiency = 90.91%.

5. Which of the following efficiencies for Kaplan Turbine is described as the ratio between total quantity of water over runner blades to total quantity of water supplied to turbine?
a) Hydraulic efficiency
b) Volumetric efficiency
c) Mechanical efficiency
d) Overall efficiency

Explanation: The definition of volumetric efficiency in a Kaplan turbine states that it is the ratio between the total volume of water flowing over the runner blades to the volume of water entering the turbine. Hence, the correct option is volumetric efficiency.

6. The volume flow rate into a Kaplan turbine is Q m3/s. 0.10Q m3/s volume of water do not flow over the runner blades. What further information is required to find the volumetric efficiency (numerical value) of the Kaplan turbine?
a) The numerical value of Q
b) The available head of the turbine
c) The RPM or the blade velocity of the turbine
d) No further information is required

Explanation: The volumetric efficiency of the Kaplan turbine is given by Q – ΔQ/ Q. In this problem, ΔQ = 0.1Q. Thus, Q – ΔQ = 0.9Q. Hence, we get volumetric efficiency as 90%. The problem can be solved with the available information.

7. A student reports the volumetric efficiency of a Kaplan turbine to be 95%. If he measures the volume flow rate through the turbine is 40 m3/s. What is the flow rate of water over the runner blades (in m3/s)?
a) 38
b) 40
c) 42.11
d) 45

Explanation: The definition of volumetric efficiency in a Kaplan turbine states that it is the ratio between the total volume of water flowing over the runner blades to the volume of water entering the turbine. Hence, if Q = 40 m3/s, the volume of water over runner blades = 0.95*40 = 38 m3/s.

8. In a Kaplan turbine experiment, the volumetric efficiency of a given turbine is 91%. If volume flow rate of water in given to be 35 m3/s, find the volume of water (m3) NOT flowing over the runner blades per second?
a) 4.05
b) 3.15
c) 3.30
d) 2.55

Explanation: The volume of water flowing over runner blades = 0.91*35 = 31.85 m3/s. The volume of water NOT flowing over the runner blades would then be 35 – 31.85 = 3.15 m3/s.

9. Which of the following efficiencies for Kaplan Turbine is defined as the ratio between the power available at the shaft of the turbine to the power produced by the runner?
a) Hydraulic efficiency
b) Volumetric efficiency
c) Mechanical efficiency
d) Overall efficiency

Explanation: The definition of Mechanical efficiency in a Kaplan turbine states that it is the ratio between the Shaft power to the Runner power. Hence, the correct option is Mechanical efficiency.

10. The power available at the shaft of a Kaplan turbine is 0.75 MW. The volume flow rate of water in 15 m3/s, whirl velocity at inlet is 12 m/s and blade velocity is 5 m/s. Find the mechanical efficiency (in %)?
a) 66.66
b) 75.00
c) 83.33
d) 91.33

Explanation: Mechanical efficiency of a Kaplan Turbine is given by ηm = shaft power / ρQVw1u1. Substituting the given values into this equation, we get mechanical efficiency = 83.33%.

11. The whirl velocity at inlet of a Kaplan turbine is 7.5 m/s and blade velocity is 5 m/s. The volume flow rate of water in 20 m3/s. Find the power output available at the shaft if the mechanical efficiency is 93% (in MW)?
a) 0.831
b) 0.697
c) 1.362
d) 0.298

Explanation: Mechanical efficiency of a Kaplan Turbine is given by ηm = shaft power / ρQVw1u1. Substituting the given values into this equation, we get shaft power = 697500 W = 0.697 MW.

12. In a Kaplan Turbine experimental setup, the power output of the shaft is 4.325 MW. The volume flow rate of water in 15 m3/s at an available head of 50 m. Find the overall efficiency of the turbine in % (g = 10 m/s2)?
a) 57.66
b) 83.63
c) 81.33
d) 79.95

Explanation: The overall efficiency of a Kaplan turbine is given by ηo = shaft power/ ρQgH. Substituting the given values in this equation, we get overall efficiency = 57.66 %.

13. The hydraulic efficiency of a Kaplan turbine is 95%, the mechanical efficiency is 93% and the volumetric efficiency is assumed to be 100%. Fine the overall efficiency (in %)?
a) 80.05
b) 93.15
c) 87.55
d) 88.35

Explanation: For a Kaplan Turbine, the overall efficiency is also given by ηo = ηh*ηm*ηv. So, ηo = 0.95*0.93*1 = 0.8835 = 88.35%.

14. Which of the following efficiencies for Kaplan Turbine is defined as the ratio between the power available at the shaft to the power supplied by water at the inlet?
a) Hydraulic efficiency
b) Volumetric efficiency
c) Mechanical efficiency
d) Overall efficiency

Explanation: The definition of Overall efficiency in a Kaplan turbine states that it is the ratio between the Shaft power to the Water power. Hence, the correct option is Overall efficiency.

15. In Kaplan turbine apparatus, the volume flow rate of water in 15 m3/s at an available head of 55 m (g = 10 m/s2). Find the shaft power (in MW) if the overall efficiency of the turbine is 95%.
a) 78.3
b) 7.83
c) 783
d) 0.783

Explanation: The overall efficiency of a Kaplan turbine is given by ηo = shaft power/ ρQgH. Substituting the given values in this equation, we get shaft power = 7.83 x 106 W = 7.83 MW.

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