11. Reluctance motor operates at power factor of __________
A. .8
B. .2
C. .3
D. .9
Answer: A
The reluctance motor operates at a power factor of .8. The Reluctance motor works on the principle of an Induction motor.
12. Calculate the reactive power in a 24.5 Ω resistor.
A. 0 VAR
B. 5 VAR
C. 8 VAR
D. 9 VAR
Answer: A
The resistor is a linear element. It only absorbs real power and dissipates it in the form of heat. The voltage and current are in the same phase in the case of the resistor so the angle between
V & I is 0°. Q = VIsin0 = 0 VAR.
13. Calculate the value of the duty cycle if the system is on for 1 sec and off for 17 sec.
A. .055
B. .781
C. .484
D. .947
Answer: A
The duty cycle is Ton÷Ttotal. It is the ratio of the time for which the system is active and the time taken by the signal to complete one cycle.
D = Ton÷Ttotal=1÷18=.055.
14. Calculate mark to space ratio if the system is on for 4 sec and off time is 9 sec.
A. .54
B. .44
C. .45
D. .46
Answer: B
Mark to space is Ton÷Toff. It is the ratio of the time for which the system is active and the time for which is inactive.
M = Ton÷Toff = 4÷(9) = .44.
15. Calculate the value of the frequency if the inductive reactance is 60 Ω and the value of the inductor is 4 H.
A. 2.38 Hz
B. 5.54 Hz
C. 4.65 Hz
D. 9.42 Hz
Answer: A
The frequency is defined as the number of oscillations per second. The frequency can be calculated using the relation
XL = 2×3.14×f×L. F
= XL÷2×3.14×L
= 60÷2×3.14×4 = 2.38 Hz.
16. The Hall effect sensor is used as the rotor position sensor for the BLDC motor.
A. True
B. False
Answer: A
The Hall effect sensor is used as the rotor position sensor for the BLDC motor. It is used to measure the strength of the magnetic field.
17. In BLDC motor armature windings are placed on the stator side.
A. True
B. False
Answer: A
In BLDC motor armature windings are placed on the stator side. It is more economical and less maintenance is required. Permanent magnets are placed on the rotor side.
18. BLDC motor is analogous to ______________
A. Permanent magnet synchronous motor
B. DC motor
C. Rotating Transformer
D. Single-phase Induction motor
Answer: A
BLDC motor is analogous to Permanent magnet synchronous motor. In BLDC motor armature windings are placed on the stator side. It is more economical and less maintenance is required. Permanent magnets are placed on the rotor side.
19. The speed of a BLDC motor can be controlled by __________
A. Changing input DC voltage
B. Changing temperature
C. Changing wind direction
D. Cannot be controlled
Answer: A
The speed of a BLDC motor can be controlled by changing the input DC voltage or the current using PWM. It can be achievable by using a transistor and chopper.
20. What are the advantages of BLDC motors?
A. Low cost
B. Simplicity
C. Reliability
D. All of the above
Answer: A
The BLDC motor is used in low-power applications. They have many advantages like low cost, simplicity, reliability, good performance, and long life.
