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UPRVUNL’21 EE: Daily Practices Quiz 21-July-2021

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

Q1. Match List-I (Types of motors) with List-II (Characteristics) and select the
appropriate response.
List-I List-II
A. dc series motor 1. Constant speed
B. dc shunt motor 2. High starting torque
(a) A → 1, B → 2
(b) A → 2, B → 1
(c) A → 1, B → 1
(d) A → 2, B → 2

Q2. For enhancing the power transmission in a long EHV transmission line, the most preferred method is to connect a
(a) Series inductive compensator in the line
(b) Shunt inductive compensator at the receiving end
(c) Series capacitive compensator in the line
(d) Shunt capacitive compensator at the sending end

Q3. Copper shading is provided in the energy meter to
(a) Bring flux exactly in quadrature with applied voltage
(b) To increase speed of the aluminum disc
(c) To count the rotation
(d) To balance the system from vibration

Q4. Laminated cores in electrical machines are used to reduce
(a) copper loss
(b) eddy current loss
(c) hysteresis loss
(d) all of the above

Q5. If coper loss of transformer at 7/8th full load is 4900 W, then its full load copper loss
would be
(a)5600 W
(b) 6400 W
(c) 373 W
(d) 429 W

Q6. In a series L-C-R circuit, resistance R = 20 Ω and the impedance Z = 20Ω. The phase difference between the current and the voltage is
(a) 0⁰
(b) 30⁰
(c) 45⁰
(d) 60⁰

SOLUTIONS
S1. Ans.(b)
Sol. DC series motor: Starting torque is high.
DC shunt motor: better speed regulation or constant speed.

S2. Ans.(c)
Sol. Power flow in line ⍺1/(reactance of the line)
Series capacitive compensation reduces the reactance of the line.

S3. Ans.(a)
Sol. Copper shading is provided on the shunt magnet’s central limb to make the phase angle displacement between the magnetic field set up by the shunt magnet and supply voltage Approx. 90°

S4. Ans.(b)
Sol. To reduce eddy current loss laminated cores are used.

S5. Ans.(b)
Sol. Copper loss at fractional load=x² full load copper loss
⇒4900=(7/8)^2×P_(F.L.)
⇒P_(F.L).=6400 W

S6. Ans.(a)
Sol. For series resonant circuit: Z=R(i.e.X_L=X_C)
So, a circuit is basically resistive in nature. Hence, the phase difference between V and I is 0⁰.

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