NHPC-JE'21 EE: Daily Practices Quiz 01-Oct-2021

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NHPC-JE’21 EE: Daily Practices Quiz

NHPC-JE’21 EE: Daily Practices Quiz 01-Oct-2021

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

Q1. A bipolar HVDC transmission line has two poles:
(a) One positive and other negative
(b) Both negative
(c) Both positive
(d) None of the above

Q2. A dc line carries
(a) Same power as an ac line
(b) More power than an equivalent ac line
(c) Less power than an ac line
(d) None of the above

Q3. Two capacitors C_1 and C_2 have C_1 =20μ F and C_2= 30μ F, are connected in parallel
across a 100V source. The net capacitance of the circuit is?
(a) 50 μ F
(b) 10 μ F
(c) 12 μ F
(d) 60 μ F

Q4. A 100mA meter has accuracy of +2%. Its accuracy while reading 50mA will be:
(a) +1%
(b) +2%
(c) +4%
(d) +20%

Q5. If a 3-phase, 40V, 50Hz, 4 pole induction motor is running at a slip of 5% then the
relative speed of rotor field with respect to stator filed is:
(a) Zero
(b) 75 rpm
(c) 142.5 rpm
(d) 1500 rpm

Q6. In ACSR conductors, steel is used for:
(a) Compensating skin effect
(b) Neutralizing proximity effect
(c) Reducing line inductance
(d) Increasing the tensile strength

SOLUTIONS

S1. Ans.(a)
Sol. The high voltage dc links may be classified into:
1. Monopolar Link: monopolar link has only one conductor and return path is provided by permanent earth or sea.
2. Bipolar Link: This is most widely used dc link for overhead long distance HVDC transmission systems and also for back-to-back HVDC system. This link has two conductors— one operating with positive polarity and the other with negative polarity with respect to the earthed tower structure.
3. Homopolar Link: A homopolar link has two or more conductors having the same polarity.

S2. Ans.(b)
Sol. A dc line carries more power as compared to ac line.

S3. Ans.(a)
Sol. C_eq=C_1+C_2
= 30μF + 20μF
= 50 μF

S4. Ans.(c)
Sol. Error = 100 mA ×(±2)/100= ±2mA
% Error = (±2mA)/50mA×100= ±4%

S5. Ans.(a)
Sol. Each field rotates at synchronous speed. So, they are stationary w.r.t each other.

S6. Ans.(d)
Sol. ACSR stands for aluminium conductor steel reinforced and steel is used for increasing the tensile strength.