NHPC-JE’21 EE: Daily Practices Quiz 20-Oct-2021

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NHPC-JE’21 EE: Daily Practices Quiz

NHPC-JE’21 EE: Daily Practices Quiz 20-Oct-2021

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

Q1. If the Q-factor of a coil at resonant frequency of 1.5 MHz is 150 for a series resonant circuit, then the corresponding bandwidth is
(a) 225 MHz
(b) 1.06 MHz
(c) 50 kHz
(d) 10 kHz

Q2. In a synchronous motor, if β is the impedance angle and ? is torque angle, then the maximum developed mechanical power is obtained when
(a) δ=β
(b) δ=180^0-β
(c) δ=2β
(d) δ=180^0-2β

Q3. Load frequency control uses
(a) Proportional controllers alone
(b) Differential controllers alone
(c) Both a and b
(d) Either a or b

Q4. The connected load of a consumer is 2 KW and his maximum demand is 1.5 KW. The demand factor of the consumer is:
(a) 1.33
(b) 0.375
(c) 0.75
(d) None of the above

Q5. In a synchronous machine, salient pole construction has been found to suit best for ___________
(a) low speed prime movers
(b) high speed prime movers
(c) medium speed prime movers
(d) any of the mentioned

Q6. What is the equation for frequency of generated EMF?
(a) f = PN/120 Hz
(b) f = 120/PN Hz
(c) f = P/120 Hz
(d) f = N/120 Hz

SOLUTIONS

S1. Ans.(d)
Sol. Q-factor=ω0/(△ω)=f0/(△f)=f0/BW
∴BW=f0/Q=(1.5×10^6)/150=10 KHz

S2. Ans.(a)
Sol. Pm=(EVb)/Zs cos⁡(β-δ)-(Vb^2)/Zs cos⁡β
Condition for maximum power output: dP/dδ=0
On solving: β=δ

S3. Ans.(c)
Sol. P+I (proportional plus integral) controller is installed so as to bring the steady state error to zero in tie-line.
The load-frequency control (LFC) is used to restore the balance between load and generation in each control area by means of speed control. The main goal of LFC is to minimize the transient deviations and steady state error to zero in advance.

S4. Ans.(c)
Sol. Demand factor=max. demand/connected load=1.5/2=0.75.

S5. Ans.(a)
Sol. For accommodating large number of poles, the rotor diameter must be comparatively increased, and from mechanical considerations, salient pole construction has been found to suit best for low-speed prime movers.

S6. Ans.(a)
Sol. f= PN/120 Hz in India and many other countries, alternators feeding the power system generates at a frequency of 50 Hz.

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