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DFCCIL’21 EE: Daily Practices Quiz 24-July-2021

Each question carries 1 mark.
Negative marking: 1/4 mark
Total Questions: 06
Time: 08 min.

Q1. Which of the following NOT correct for sag in overhead lines?
(a) Proportional to weight per unit length of conductor
(b) Proportional to tension in the conductor
(c) Proportional to square of span length
(d) None of the above

Q2. 1 ampere-turn/metre=……………oersted.
(a) 4π×10^(-3)
(b) 4π×9.81×10^(-3)
(c) 4π×10^(-2)
(d) 4π×10^(-4)

Q3. If the load on an induction motor is increased from no-load to full load, its slip and power factor will, respectively.
(a) Decrease, decrease
(b) Increase, increase
(c) Decrease, increase
(d) Increase, decrease

Q4. The percentage resistance and reactance of a transformer are 2 % and 4 % respectively. The approximate regulation on full load at 0.8 pf lag is:
(a) 4 %
(b) 6 %
(c) 8 %
(d) 12 %

Q5. An R-L-C. series resonant circuit has a Q of 15 and a source voltage of 60 V. The voltage across the capacitor at resonance is __________
(a) 60 V
(b) 15 V
(c) 450 V
(d) 900 V

Q6. The system with open-loop transfer function G(s)H(s) = 1/(s(s+1)) is
(a) type 2 and order 1
(b) type 1 and order 1
(c) type 0 and order 0
(d) type 1 and order 2

SOLUTIONS

S1. Ans.(b)
Sol.
The difference in level between points of supports and the lowest point on the conductor is called sag.
In general, sag(s) α (Wl^2)/T
Where; W=weight per unit length of conductor
l=span lenght & T=tension

S2. Ans.(a)
Sol. Magnetic field strength:
SI unit: AT/m
CGS unit: oersted
1 AT/m=0.012566 oersted=4π×10^(-3) oersted

S3. Ans.(b)
Sol. slip(s)=(N_s-N_r)/N_s
If the load on an induction motor is increased, the rotor speed will decrease and consequently slip and power factor will increase.

S4. Ans.(a)
Sol. At lagging power factor: VR=%R cos⁡〖ϕ+%X sin⁡ϕ 〗
∴VR=2×0.8+4×0.6=4 %

S5. Ans.(d)
Sol. V_c=Q.V_in
= 15 × 60 = 900 V

S6. Ans.(d)
Sol. Comparing the open loop transfer function with G(s)H(s) = (K(1+sT_a )(1+sT_b )….)/(s^N (1+sT_1 )(1+sT_2 )…)
we get,
Type = N = 1
Order is 2.
Type of system=open loop pole at origin

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