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EXAM DATES: 26 SEPT TO 30 SEPT
DFCCIL’21 EE: Daily Practices Quiz 10-Sep-2021
Each question carries 1 mark.
Negative marking: 1/4 mark
Total Questions: 06
Time: 08 min.
Q1. In power transformers, it is found that the iron or core losses practically varies very less, this is because
(a) Constant leakage flux
(b) Constant core flux
(c) Constant load current
(d) Constant leakage and core flux
Q2. Which of the conditions is must be fulfilled for a satisfactory parallel operation of transformers?
(a) Correct polarity
(b) Same pu impedance
(c) Same voltage ratio
(d) Leakage impedance should be inversely proportional to KVA of the transformer
Q3. Condition of symmetry in Z-parameter representation is
(a) Z11 = Z12
(b) Z11 = Z22
(c) Z12 = Z21
(d) Z12 = Z22
Q4. To control the speed of an induction motor, the supply frequency is reduced by 10%. For the same magnetizing current to remain constant, the supply voltage must be
(a) Increased by 10 %
(b) Increased by 20 %
(c) Decreased by 10 %
(d) Decreased by 20 %
Q5. What is the maximum load that can be connected in a circuit containing only lighting points?
(a) 500 watts
(b) 750 watts
(c) 800 watts
(d) 1000 watts
Q6. The iron core in a transformer provides a _____path to the main flux
(a) Low reluctance
(b) High reluctance
(c) Low resistance
(d) High conductivity
Sol. Due to the constant core flux, the iron losses also remain constant.
Sol. out of all, polarity must be correct for the connected transformers.
Sol. A two-port network is said to be symmetrical if the ports of the two-port network can be interchanged without changing the port voltages and currents. This will hold good, if Z11 = Z22.
Sol. In an I/M, flux ∝V/f
Where; I_m= magnetizing current
To maintain magnetizing current constant, if frequency is reduced by 10 %, then voltage also to be reduced by 10 %.
Sol. The maximum load that can be connected in a circuit containing only lighting points is 800 watts.
Sol. The iron core in a transformer provides a low reluctance path to the main flux.