This set of Electric Drives Multiple Choice Questions & Answers (MCQs) focuses on “Regenerative Braking of DC Shunt Motors”.

1. A circuit consists of 3 F capacitor and 5 H inductor. Determine the order of the circuit.

a) 2

b) 1

c) 3

d) 0

View Answer

Explanation: The order of the circuit is the number of memory/storing elements which are non-separable present in the circuit. In mathematics, the order is defined as the highest order derivate in the differential equation. The order of the circuit is 2.

2. The forced response is due to a source present in the circuit.

a) True

b) False

View Answer

Explanation: The steady-state response is a part of the forced response. The forced response is due to the electrical source present in the circuit. Its mathematical equation involves the source present in the circuit.

3. Full form of DTC.

a) Direct torque control

b) Digital torque control

c) Discrete torque control

d) Distribution torque control

View Answer

Explanation: DTC stands for Direct torque control. DTC and IFOC are the techniques used for controlling the speed and torque of a 3-phase induction motor.

4. The characteristics shown by an element in the I-V curve is V=I^{2}. The nature of the element is _______

a) Non-linear, Bilateral, Passive

b) Linear, Unilateral, Active

c) Linear, Bilateral, Passive

d) Non-linear, Unilateral, Active

View Answer

Explanation: The nature of the element is non-linear, unilateral and active. The shape of the characteristic is parabolic. For bilateral nature, it should be symmetrical in the first and third quadrant. Its slope is negative in the second quadrant which determines its active nature.

5. Transient response is a temporary response.

a) True

b) False

View Answer

Explanation: Transient response is a primary response in the circuit. It is a temporary response which dies out at t=infinity. It consists of exponential decaying functions.

6. Calculate the steady state value for x(t)=4(1-e^{-3t}).

a) 5

b) 4

c) 3

d) 2

View Answer

Explanation: The steady state value is obtained at t=∞. The value of x(t) at t=∞ is 4(1-e

^{-∞})=4(1-0)=4. The term e

^{-3t}is an exponentially decaying function.

7. The natural response is due to _________ conditions present in the circuit.

a) Initial

b) Final

c) Zero

d) Negative

View Answer

Explanation: The natural response is due to the initial conditions present in the circuit. The natural response is a complete part of the transient response. It is mathematically represented as y(t)=y

_{o}×e

^{-at}.

8. Calculate the value of the coefficient of coupling for the isolated coils.

a) 0

b) 1

c) 5

d) 7

View Answer

Explanation: The coefficient of coupling expresses how the two coils are magnetically coupled. It is mathematically represented as K=M÷√L

_{1}.L

_{2}. For the isolated coils, the value of the mutual inductance is 0. The value of the coefficient of coupling is 0.

9. Calculate the value of equivalent inductance for series aiding of two coils whose self inductances are 5 H, 2 H, and mutual inductance value is 4 H.

a) 15 H

b) 12 H

c) 13 H

d) 11 H

View Answer

Explanation: The equivalent inductance for series aiding of two coils is L

_{eq}=L

_{1}+L

_{2}+2M=5+2+8=15 H. The value of equivalent inductance increases due to mutually induced e.m.f in case of the magnetically coupled circuit.

10. Calculate the value of equivalent inductance for series subtracting polarity of two coils whose self inductances are 14 H, 5 H, and mutual inductance value is 1 H.

a) 15 H

b) 17 H

c) 12 H

d) 10 H

View Answer

Explanation: The equivalent inductance for series subtracting of two coils is L

_{eq}=L

_{1}+L

_{2}-2M=14+5-2=17 H. The value of equivalent inductance decreases due to negatively mutually induced e.m.f in case of the magnetically coupled circuit.

11. Calculate the value of the capacitive reactance during resonance if the value of the inductor is 5 H and supply frequency is 20 rad/sec.

a) 100 Ω

b) 200 Ω

c) 300 Ω

d) 700 Ω

View Answer

Explanation: Resonance is defined as the phenomenon in which energy of any element changes from one form to another. During resonance condition X

_{c}=X

_{l}=ΩL=20×5=100 Ω.

12. Calculate the quality factor for the R-L circuit if R=28 Ω and L=2 H.

a) 14

b) 16

c) 10

d) 17

View Answer

Explanation: The quality factor is defined as the ratio of the reactive power to the active power consumed. The resistor always absorbs active power and inductor absorbs the reactive power. Quality factor=R÷L=28÷2=14.

13. The quality factor is calculated for ___________

a) Power factor loads

b) Inductive coils

c) Lagging loads

d) Leading loads

View Answer

Explanation: Quality factor is calculated for inductive coils, not for power factor loads. Its value determines the quality of the inductor or capacitor. It shows how good an inductor or capacitor can absorb reactive power.

14. Calculate the equivalent resistance when two resistances are connected in parallel of values 8 Ω, 8 Ω.

a) 3 Ω

b) 2 Ω

c) 4 Ω

d) 7 Ω

View Answer

Explanation: When two resistances are connected in parallel their equivalent resistance is equal to the harmonic mean of the individual resistances. R

_{eq}=R

_{1}.R

_{2}÷(R

_{1}+R

_{2})=8×8÷(8+8)=4 Ω.

15. Calculate the quality factor for the R-C circuit if R=2 Ω and C=1 F.

a) 0.2

b) 0.4

c) 0.6

d) 0.5

View Answer

Explanation: The quality factor is defined as the ratio of the reactive power to the active power consumed. The resistor always absorbs active power and capacitor absorbs the reactive power. Quality factor=1÷RC=1÷2=.5.

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