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UPRVUNL’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 statement is true for no-load current of the transformer?
(a) has high magnitude and low power factor
(b) has high magnitude and high-power factor
(c) has small magnitude and high-power factor
(d) has small magnitude and low power factor

Q2. For a linear B-H relationship, which option is correct?
(a) The exciting current is equal to core loss current
(b) The exciting current is equal to magnetizing current
(c) The exciting current is equal to de-magnetizing current
(d) The exciting current is equal to cross-magnetizing current

Q3. ____________ is equal to the current passing through short circuit output terminals.
(a) Thevenin’s voltage
(b) Load current
(c) Load resistance
(d) Norton’s current

Q4. ______________ of measurement is a measure of the change in instrument output that occurs when the quantity being measured changes by a given amount.
(a) Sensitivity
(b) Linearity
(c) Hysteresis
(d) Resolution

Q5. In a split phase machine, the, main winding has low resistance but high reactance where as the starting winding has a _____________ resistance, but ____________ reactance
(a) Low, High
(b) High, Low
(c) Low, Low
(d) High, High

Q6. Current chopping usually occurs in
(a) Oil circuit breaker
(b) Minimum OCB
(c) MCB
(d) Air blast circuit breaker

SOLUTIONS
S1. Ans.(d)
Sol. The no load current is about 2-5% of the full load current and it accounts for the losses in a transformer. Since no-load current lags voltage by the angle of nearly 90⁰. Thus, power factor will be low.

S2. Ans.(b)
Sol. For a linear B-H relationship it is assumed that, there are no losses present in the core like eddy current losses and hysteresis losses are neglected. Thus, core loss current is equal to 0, which ultimately confirms exciting current is purely magnetizing one.

S3. Ans.(d)
Sol. Norton’s current is equal to the current passing through short circuit output terminals.

S4. Ans.(a)
Sol. Sensitivity
• It is the ratio of change in output (or response) of the instrument to change in input or measured variable
• A higher sensitivity indicates that the system can respond to even the smallest input

S5. Ans.(b)
Sol. The Split Phase Motor is also known as a Resistance Start Motor. It has a single cage rotor, and its stator has two windings known as main winding and starting winding. Both the windings are displaced 90 degrees in space. The main winding has very low resistance and a high inductive reactance whereas the starting winding has high resistance and low inductive reactance.

S6. Ans.(d)
Sol. Current chopping usually occurs in Air blast circuit breaker.
• Current Chopping in circuit breaker is defined as a phenomenon in which current is forcibly interrupted before the natural current zero.

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