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NHPC-JE’21 EE: Daily Practices Quiz 17-Sep-2021

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NHPC-JE’21 EE: Daily Practices Quiz

NHPC-JE’21 EE: Daily Practices Quiz 17-Sep-2021

Each question carries 1 mark.
Negative marking: 1/4 mark
Total Questions: 06
Time: 06 min.

Q1. In series resonant circuit the impedance of the circuit is
(a) Minimum
(b) Maximum
(c) Zero
(d) None of these

Q2. Proximity effect is more in case of
(b) Power cable
(c) DC transmission
(d) None of the above

Q3. XLPE cable is one type of H.T. cable. The full form of XLPE is:
(a) Cross lead polyethylene cable
(b) Cross linked paper ethylene cable
(c) Cross line paper ethylene cable
(d) Cross linked polyethylene cable

Q4. Which of the following is not a reaction turbine?
(a) Francis turbine
(b) Kaplan turbine
(c) Pelton wheel turbine
(d) Propeller turbine

Q5. The power input to a 3-phase induction motor is 50 KW. If the stator losses are 800 W, then copper losses of rotor phase for 0.5 % slip will be:
(a) 492 W
(b) 246 W
(c) 200 W
(d) 100 W

Q6. The value of current (I) in the following figure is

(a) 3A
(b) 4A
(c) 5A
(d) 6A

SOLUTIONS

S1. Ans.(a)
Sol. At the resonant frequency, the net reactance is zero because X_L=X_C. The circuit impedance Z becomes minimum and is equal to the resistance R. “Since the impedance is minimum, the current will be maximum”.

S2. Ans.(b)
Sol. The alternating magnetic flux produced in the conductor due to the current flowing through the neighbouring conductor gives rise to the circulating current which increases the resistance of the conductor. This phenomenon is called the proximity effect.
The proximity is more in the case of power cable and underground line where the distance between the conductor is small.

S3. Ans.(d)
Sol. XLPE: cross linked polyethylene cable.

S4. Ans.(c)
Sol.
Francis, Kaplan and propeller turbines are reaction turbines.
Pelton wheel turbine is an impulse turbine.

S5. Ans.(b)
Sol. Air gap power or rotor input power (P_g )=stator input power-stator loss
∴P_g=50000-800=49200 W
Rotor copper loss (P_cu )=sP_g=0.005×49200=246 W

S6. Ans.(a)
Sol. According to Kirchhoff’s 1st law (KCL)
Σi=0
ie,3+4+I+(-8)+(-2)=0
⇒I =10-7
=3A

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