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DC Machines MCQs – Motor Control by Static Power Converters ( DC Machines ) MCQs

DC Machines MCQs – Motor Control by Static Power Converters ( DC Machines ) MCQs

Latest DC Machines MCQs

By practicing these MCQs of Motor Control by Static Power Converters ( DC Machines ) MCQs – Latest Competitive MCQs , an individual for exams performs better than before. This post comprising of objective questions and answers related to Motor Control by Static Power Converters ( DC Machines ) Mcqs “. As wise people believe “Perfect Practice make a Man Perfect”. It is therefore practice these mcqs of DC Machines to approach the success. Tab this page to check ” Motor Control by Static Power Converters ( DC Machines )” for the preparation of competitive mcqs, FPSC mcqs, PPSC mcqs, SPSC mcqs, KPPSC mcqs, AJKPSC mcqs, BPSC mcqs, NTS mcqs, PTS mcqs, OTS mcqs, Atomic Energy mcqs, Pak Army mcqs, Pak Navy mcqs, CTS mcqs, ETEA mcqs and others.

DC Machines MCQs – Motor Control by Static Power Converters ( DC Machines ) MCQs

The most occurred mcqs of Motor Control by Static Power Converters ( ) in past papers. Past papers of Motor Control by Static Power Converters ( DC Machines ) Mcqs. Past papers of Motor Control by Static Power Converters ( DC Machines ) Mcqs . Mcqs are the necessary part of any competitive / job related exams. The Mcqs having specific numbers in any written test. It is therefore everyone have to learn / remember the related Motor Control by Static Power Converters ( DC Machines ) Mcqs. The Important series of Motor Control by Static Power Converters ( DC Machines ) Mcqs are given below:

DC Motor Control Through Converters

1. Half wave converters are used for controlling DC motor of ________________
a) Below 400 W
b) 400 W – 4000W
c) More than 4000W
d) Anywhere
Answer: a
Explanation: Half wave converter requires a single thyristor and a free-wheeling diode. In half wave converter circuit the motor current will always be discontinuous. Ultimately it results in poor motor performance. This type of converter is employed only for motors below 400W.

2. How many thyristors does we need in half wave converter?
a) 1
b) 2
c) 3
d) Many
Answer: a
Explanation: Only one thyristor is sufficient for the half wave converter purpose, this is employed for small motors only. This thyristor is connected to the single-phase AC supply and with parallel combination of free-wheeling diode with motor armature.

3.Semi-converters can’t be used when regeneration is required.
a) True
b) False
Answer: a
Explanation: According to the one-quadrant converter, it gives voltage and current of one polarity at DC terminals. Therefore, it does not provide support for regenerative braking, i.e. power flow from DC motor to the AC supply.

4. How many thyristors does we need in semi-converter?
a) 1
b) 2
c) 3
d) Many
Answer: b
Explanation: Semi-converter requires two thyristors. Thyristor Th1 is fired at angle of α and Th2 at angle π+α with respect to the supply voltage v and the process is repeated continuously. Circuit also requires two diodes and one free-wheeling diode.

5. When armature current becomes discontinuous?
a) Small firing angles
b) Large firing angles
c) Infinite firing angle
d) Does not depend on firing angle
Answer: b
Explanation: There are various reasons when armature current becomes discontinuous armature current, prominent reasons are large values of firing angle, high speed and sometimes low torque can also affect.

6. Which of the following is the effect of non-uniform armature current?
a) Ratio of peak to average and rms to average armature current decreases
b) Ratio of peak to average and rms to average armature current increases
c) Ratio of peak to average increases and rms to average armature current decreases
d) Ratio of peak to average decreases and rms to average armature current increases
Answer: b
Explanation: The armature current sometimes due to some reasons may become non-uniform. In this conditions motor performance deteriorates with discontinuous armature current. So, the ratio of peak current to average current increases. Also, rms to average armature current increases.

7. How many quadrants does full-converter work?
a) One
b) Half
c) Two
d) Can be any
Answer: c
Explanation: A full-converter is a two-quadrant converter in which the voltage polarity of the output can reverse, but the current remains unidirectional because of the unidirectional thyristors. It requires no free-wheeling diode.

8. How many thyristors are required for full converter?
a) 1
b) 2
c) 3
d) 4
Answer: d
Explanation: Full converter requires 4 thyristors. The only different thing about the full converter is, it does not require free-wheeling diode. A full converter can be used to feed a separately excited DC motor. Each thyristor is fired accordingly.

 

Synchronous Machines MCQs

 

9. Full-converter can be used in DC motor for regenerative braking in ______________
a) Constant operation
b) Variable operation
c) Inversion operation
d) Opposite operation
Answer: c
Explanation: When α is greater than 900, the average motor voltage becomes negative. If the motor terminals are reversed, then the circuit will act as a generator in order to feed power back to the AC supply. This is the inversion operation of the converter and used in regenerative braking.

10. Dual converter operates in _________________
a) 1
b) 2
c) 3
d) 4
Answer: d
Explanation: The dual-converter is the modified one and can operate in all the four quadrants. Its circuit contains two full-converters converting to the DC in either direction. The dual converter provides virtually instantaneous reversal of voltage at DC terminals.

11. Which converter/s can be used for DC series motor control?
a) Semi-converters
b) Half-wave converter
c) Full-converter
d) Semi converters and full converter
Answer: d
Explanation: Semi-converters and full-converters are also employed for control of a DC series motor. The total circuit inductance is high because of the series field, as a consequence of which the armature current is mostly continuous.

12. Three phase converters are employed for _______________
a) Large kW motors
b) Small kW motors
c) In all motors
d) Never used
Answer: a
Explanation: Three phase converters are employed when DC motor of very high ratings is used. In three phase converters, the advantage is the ripple frequency of the motor terminal voltage is generally higher than that in single-phase converters.

DC Motor Control Through Choppers

1. Which of the following method is adopted for controlling a DC motor?
a) Resistance control
b) Motor-generator set
c) Inverter Rectifier
d) DC chopper
Answer: d
Explanation: All methods listed above are the methods which can be used to control DC motor, but resistive method makes lots of wastage of energy, while motor-generator set and inverter rectifier set are bulky and costly.

2. Which of the following method is employed when regenerative braking is necessary?
a) DC chopper
b) Variable resistor
c) Inverter rectifier
d) Motor-generator
Answer: a
Explanation: A chopper is essentially an electronic switch that turns on the fixed-voltage DC source for short time intervals and applies source potential to motor terminals in series of pulses. This process controls the average voltage applied to the motor.

3. Which of the following statement is not true regarding to DC chopper?
a) Cheap
b) Fast response
c) Regeneration
d) AC to DC control
Answer: d
Explanation: The chopper provides stepless and efficient control of DC voltage and it is less expensive. It is having another advantage of faster response and regeneration. The chopper is relatively new technology and equivalent to DC-DC transformer.

4. Which of the following correctly suits with chopper?
a) Thyristor in series with load
b) Thyristor in parallel with load
c) Thyristor switch in series with load
d) Thyristor switch in parallel with load
Answer: c
Explanation: A chopper is essentially a thyristor switch in series with the load. A shunting diode is provided across the load because free-wheeling the load current when thyristor is off. The thyristor can be shown enclosed by a dotted square can be turned-off over a time period and the cycle is repeated.

5. The average value of chopper output waveform is given by _____________
a) αV
b) V/α
c) α2V
d) V/α2
Answer: a
Explanation: Here the average value of the chopper output voltage waveform is given by Va=V tON/(tON+tOFF) = V (tON/T) =αV. So, by varying duty cycle α one can vary the average voltage at output.

6. How output voltage of chopper can be varied?
a) By using constant frequency system
b) By using variable frequency system
c) By using constant and variable frequency systems
d) By using constant or variable frequency systems
Answer: c
Explanation: The average voltage of the chopper output depends on α, thus, α can be varied by either changing the complete time period or by changing an on time or off time. These two methods are named as constant and variable frequency system.

7. What is the formula for step up chopper?
a) V(1-α)
b) V/(1-α)
c) αV
d) v/α
Answer: b
Explanation: With the help of conventional chopper one can reduce the average voltage, so by doing slight modification in the circuit one can use chopper method to increase the average voltage applied, by the formula V/(1-α).

8. Which of the following is not the method of auxiliary commutation?
a) Voltage commutation
b) Resistance commutation
c) Current commutation
d) Load commutation
Answer: b
Explanation: Thyristor in a chopper has to be turned off by auxiliary commutation. This can be done by two methods-Forced commutation and Load commutation. Forced commutation can also be done by two ways, current and voltage.

9. In voltage commutation, in chopper circuit we use _____________
a) 2 auxiliary thyristors
b) 2 diodes
c) 1 auxiliary thyristor
d) Many diodes
Answer: a
Explanation: Two auxiliary thyristors are connected in the chopper circuit along with one diode, one inductor, one capacitor in series with the voltage supply which is then connected in parallel with diode and DC motor armature.

10. In current commutation, in chopper circuit we use _____________
a) 2 auxiliary thyristors
b) 2 diodes
c) 1 auxiliary thyristor
d) 2 auxiliary thyristors and 2 diodes
Answer: d
Explanation: Two auxiliary thyristors are connected in the chopper circuit along with two diodes, one inductor, one capacitor in series with the voltage supply which is then connected in parallel with diode and DC motor armature.

DC Machines MCQs – Motor Control by Static Power Converters ( DC Machines ) MCQs