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NHPC-JE’21 EE: Daily Practices Quiz 14-Oct-2021

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NHPC-JE’21 EE: Daily Practices Quiz

NHPC-JE’21 EE: Daily Practices Quiz 14-Oct-2021

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

Q1. Hot wire ammeters are used for measuring:
(a) only AC
(b) only DC
(c) neither AC nor DC
(d) both AC and DC

Q2. Power transfer capability of a power system can be improved by?
1. Using series compensations
2. Using parallel transmission lines
3. Reduce voltage of transmission
Which of the above statement(s) is/are correct?
(a) 1 only
(b) 2 only
(c) 2 and 3
(d) 1 and 2

Q3. The minimum phase-neutral voltage at which corona starts occur in power transmission lines is called
(a) Knee voltage
(b) Visual critical voltage
(c) Critical disruptive voltage
(d) Flash voltage

Q4. Which of the following is used to neutralize the Ferranti effect in the medium and long transmission lines?
(a) Shunt capacitor
(b) Series resistor
(c) Series capacitor
(d) Shunt reactor

Q5. In the induction motors the torque is directly proportional to the
(a) Higher slip values
(b) Voltage slip
(c) Lower slip values
(d) None of the above

Q6.In a differential amplifier an ideal CMRR is
(a) infinity
(b) zero
(c) –1
(d) +1

SOLUTIONS

S1. Ans.(d)
Sol. Hot wire instruments works on the heating effect of the current. The length of the wire increases because of heating effect of the current flowing through it. It is used for measurement of both ac and dc.

S2. Ans.(d)
Sol. Power transfer capability of a power system can be improved by using series compensations and parallel transmission lines.
As, P=EV/X sinδ.
So, by series compensations X can be minimized and power transfer capability will be increased.

S3. Ans.(c)
Sol. Critical disruptive voltage: – it is the minimum phase neutral voltage at which the corona occurs in power transmission line.
g_o=V_c/(r loge e d/r)
g_o=Potential gradient at conductor
V_C=critical disruptive voltage
VC=go r log⁡e d/r)
go=30kv\/cm(max)@=21.2kv\/cm(rms) )]→at 76 cm of Hg and 25°C

S4. Ans.(d)
Sol. Ferranti effect: – Receiving end voltage (V_R) > Sending end voltage (V_S) i.e., V_R > V_S and this is due to no-load or light load condition.
Ferranti effect can be neutralized by using shunt reactor.

S5. Ans.(c)
Sol. for lower slip values, torque in an induction motor is directly proportional to it.
For lower slip values, T ⍺ SLIP(S)
For higher slip values, T ⍺1/SLIP.

S6. Ans.(a)
Sol. Infinity

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