250+ TOP MCQs on Countercurrent Braking of DC Shunt Motors and Answers

Advanced Electric Drives Questions and Answers on “Countercurrent Braking of DC Shunt Motors”.

1. Plugging is suitable for __________ type loads.
A. Gravitational
B. Electrostatic
C. Weightless
D. Leading
Answer: A
Clarification: Plugging is suitable for gravitational type loads. It halts the motor operation. It can reverse the direction of rotation of the motor. It can hold the motor at zero speed.

2. In DC shunt machine ∅ is directly proportional to I_a.
A. True
B. False
Answer: B
Clarification: In shunt DC machine, the field winding is in parallel with the armature winding. The armature current flows through the armature winding. I_F∝∅∝V_t.

3. Braking resistance should be selected in order to limit the braking current.
A. True
B. False
Answer: A
Clarification: During braking, a high current flows in the armature circuit. To limit the braking current a proper value of braking resistance should be selected.

4. Torque developed in the motor is ___________
A. K_mΦI_a
B. K_mΦI_a³
C. 2K_mΦI_a
D. K_mΦI_a²
Answer: A
Clarification: The torque developed in the motor is directly proportional to the flux, machine constant, armature current. It is mathematically represented as T= K_mΦI_a.

5. Full form of TVR is _________
A. Terminal voltage reversal
B. Total voltage reversal
C. Terminal voltage redirect
D. Total voltage reversal
Answer: A
Clarification: TVR stands for terminal voltage reversal. It is one of the methods of countercurrent braking of the DC shunt motor. It halts the motor rapidly and reverses its direction of rotation.

6. Calculate the current in DC shunt field winding using the following data: I_a=15 A, I_L=21, R=22, N=484.
A. 4 A
B. 2 A
C. 7 A
D. 6 A
Answer: D
Clarification: In DC shunt motor, field windings are connected in parallel with the armature circuit. I_F=I_L-I_a=11-5=6 A. Motor current is the sum of field and armature current.

7. Calculate the flux produced by the DC shunt field winding using the following data: I_a=5 A, I_L=11, R=2, N=4.
A. 14 Wb
B. 12 Wb
C. 17 Wb
D. 18 Wb
Answer: B
Clarification: In DC shunt motor, field windings are connected in parallel with the armature circuit. I_F=I_L-I_a=11-5=6 A. F=NI_F=R∅. I_F∝∅. ∅=F÷R=12 wb.

8. The shape of the speed-armature current characteristics in DC shunt motor is __________
A. Hyperbolic
B. Parabola
C. Negative slope linear line
D. Ellipse
Answer: C
Clarification: The shape of the speed-armature current characteristics in DC shunt motor is negative slope linear line. The motor equation is E_b=V_t-I_aR_a=K_m∅ω_m. N=(V_t-IR_a)/K_m. N vs I_a is a negative slope line with slope = -R_a/K_m.

9. The shape of the speed-torque characteristics in DC shunt motor is __________
A. Rectangular Hyperbolic
B. Whole x-y plane
C. Circle
D. Ellipse
Answer: A
Clarification: The shape of the speed-torque characteristics in the DC shunt motor is a rectangular hyperbola. The motor equation is E_b=V_t-I_aR_a=K_m∅ω_m. N=(V_t/K_mI_a)-R_a/K_m. I_a∝√T .N∝1÷√T.

10. DC shunt motors are used where the high _________ is required.
A. Starting torque
B. Maximum torque
C. Minimum torque
D. Breakdown torque