DFCCIL’21 EE: Weekly Practice Quiz-01

Each question carries 1 mark.
Negative marking: 1/4 mark
Total Questions: 12
Time: 12 min.

Q1. The speed regulation of a motor falls from 1100 rpm at no-load to 1050 rpm at rated load. The speed regulation of the motor is:
(a) 6.77 %
(b) 2.33 %
(c) 8.84 %
(d) 4.76 %

Q2. In ACSR conductors, steel is used for:
(a) compensating skin effect
(b) neutralizing proximity effect
(c) reducing line inductance
(d) increasing the tensile strength

Q3. Why are conductors for high voltage transmission lines suspended from towers?
(a) for increasing ground clearance
(b) for reducing effect of wind
(c) for reducing ground clearance
(d) for countering the lengthening of conductor during summer.

Q4. In a star connected three-phase balanced system. If the line current is 125A then the phase current is?
(a) 216.5 A
(b) 72.16 A
(c) 250 A
(d) 125 A

Q5. A Schrage motor can run on:
(a) Zero slip
(b) Positive slip
(c) Negative slip
(d) Zero, positive or negative slip

Q6. The value of demand factor is:
(a) less than one
(b) greater than one
(c) equal to one
(d) Zero

Q7. Load factor during a period is defined as:
(a) (Average Load)/(Maximum Load)
(b) (maximum Load)/(Average Load)
(c) (Average Load)/(Installed Capacity)
(d) (Maximum Load)/(Installed Capacity)

Q8. Zener Diode is mostly used as ____________
(a) Half-wave rectifier
(b) Full-wave rectifier
(c) Voltage Regulator
(d) LED

Q9. The frictional loss in a transformer is
(a) 10 %
(b) 50 %
(c) 0 %
(d) More than 50 %

Q10. A single-phase induction motor, rotating in the direction of forward field, the slip of the rotor with respect to forward and backward rotating fields are respectively:
(a) s and s
(b) s and (1-s)
(c) s and (2-s)
(d) (1-s) and s

Q11. A series RLC circuit has R=4 Ω, X_L=12 Ω,X_C=9 Ω and is supplied with 200 V, 50 Hz. Calculate the power.
(a) 8000 W
(b) 6400 W
(c) 19,200 W
(d) 14,400 W

Q12. The pressure coil of an energy meter is…….
(a) Purely resistive
(b) Purely inductive
(c) Highly resistive
(d) Highly inductive

SOLUTIONS
S1. Ans.(d)
Sol. %Speed regulation=(N_nl-N_fl)/N_fl ×100=(1100-1050)/1050×100=50/1050×100=4.76 %.

S2. Ans.(d)
Sol. ACSR stands for aluminium conductor steel reinforced and steel is used for increasing the tensile strength.

S3. Ans.(a)
Sol. for increasing ground clearance, conductors for high voltage transmission lines suspended from towers.

S4. Ans.(d)
Sol. for star (γ) – connection: –
Line current (I_L) = Phase current (I_ph )
Line voltage (V_L )=√3×Phase voltage (V_ph )
Or, phase voltage = (Line voltage)/√3
⇒ ▭(V_ph=V_L/√3) – For star connection

S5. Ans.(d)
Sol. Schrage motor:
Can run on all values of slip, therefore it can work on all power factor.
This motor has three types of windings, out of three windings, two are placed in the rotor and the remaining one is placed in the stator.
The primary and tertiary are housed in the same rotor slots.
3-phase supply is given to the primary with the help of 3-slip rings.

S6. Ans.(a)
Sol. Demand factor is always less than 1.
Demand factor = (maximum demand)/(connected load)

S7. Ans.(a)
Sol.
Load factor = (Avg.load)/(Max.load)

S8. Ans.(c)
Sol. The Zener diode is a specifically designed diode to operate in the breakdown region and keeps the voltage in the circuit to which it is connected as constant. Thus, it is widely used as a voltage regulator.

S9. Ans.(c)
Sol. As we know, the transformer is a static device based on the principle of mutual
induction with no rotating part, so there is no frictional loss.

S10. Ans.(c)
Sol. For 1-phase Induction motor: s_f=s & s_b=(2-s).

S11. Ans.(b)
Sol. |Z|=√(R^2+(X_L-X_C )^2 )=√(4^2+(12-9)^2 )=5 Ω
∴I=V/|Z| =200/5=40 A
∴P=I^2 R=1600×4=6400 W

S12. Ans.(d)
Sol. The pressure coil of an energy meter is highly inductive while for wattmeter it is highly resistive.

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