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NHPC-JE’21 EE: Daily Practices Quiz 27-Sep-2021

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NHPC-JE’21 EE: Daily Practices Quiz

NHPC-JE’21 EE: Daily Practices Quiz 27-Sep-2021

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

Q1. For an AC transmission line, the string efficiency is 80 %. If the DC voltage is supplied with the same set-up, the string efficiency will be:
(a) 75 %
(b) 80 %
(c) 92 %
(d) 100 %

Q2. Sheaths are used in cables to:
(a) Provide mechanical strength
(b) Provide proper insulation
(c) Provide ingress of moisture
(d) None of these

Q3. Which of the following represents the operating region slips of a 1-phase induction motor?
(a) 0<s<2
(b) -2<s<2
(c) 0<s<1
(d) -1<s<1

Q4. If the torque/weight ratio of an instrument is low, then it can be concluded that
(a) The meter will have a uniform scale
(b) The meter will have the non-uniform scale
(c) The sensitivity of the meter will be high
(d) The sensitivity of the meter will be low

Q5. The no-load current drawn by transformer is usually what percentage of the full-load current?
(a) 0.2 to 0.5 %
(b) 12 to 15 %
(c) 20 to 30 %
(d) 2 to 5 %

Q6. The secondary winding of which of the following transformers is always kept closed?
(a) Current transformer
(b) Voltage transformer
(c) Power transformer
(d) Step-down transformer


S1. Ans.(d)
Sol. In DC transmission line ground capacitance does not exist. Therefore, voltage across each disc is equal and string efficiency is 100 %.

S2. Ans.(c)
Sol. Provide ingress of moisture.

S3. Ans.(a)
Sol. In a 1-phase induction motor, due to both forward and backward torque slips, the operating region lies between 0 and 2. In motoring mode slip is 0 to 1 and breaking mode 1 to 2.

S4. Ans.(d)
Sol. The low torque/weight ratio signifies heavy weight of the moving system due to which the instrument incurs frictional losses hence the sensitivity will be low.

S5. Ans.(d)
Sol. Current required to set up magnetic flux in a magnetic material is rather low. Hence no-load primary current is a very small fraction of the rated full load current

S6. Ans.(a)
Sol. Because if CT secondary is not shorted then it can develop a very high voltage across secondary which may damage transformer insulation.

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