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Drives and Control TE Electronics Unit -1
1. 2. 3. 4. 5. 6. State essential part of electric drives and state its functions.[8] What is a drive? Explain different types of drives and procedure for selection of it.[8] What are the parameters to be varied for speed control of DC Series motor? What are the parameters to be varied for speed control of separately excited DC motor? Explain with neat diagram how the speed control is achieved by a 3-phase fully controlled converter. Draw o

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Question Bank
Drives and ControlTE ElectronicsUnit -1
1.
State essential part of electric drives and state its functions.[8]
2.
What is a drive? Explain different types of drives and procedure for selection of it.[8]
3.
What are the parameters to be varied for speed control of DC Series motor?
4.
What are the parameters to be varied for speed control of separately excited DC motor?
5.
Explain with neat diagram how the speed control is achieved by a 3-phase fully controlled converter. Drawoutput voltage waveforms for
α= 30
0
.Write output equations for the converter.[10]
6.
A 220V, 1200rpm, 15A separately excited DC motor has a armature resistance and inductance of 1W and 52mH respectively. This motor is controlled by a single phase full converter with a Ac voltage source of 230V
50 Hz. Find Speed at α= 30
0
and
α= 60
0
.[8]
7.
Why are dual converters important? With the help of a neat circuit diagram and relevant waveforms, explainthe operation of a single-phase dual mode dual converter.
8.
Why are dual converters important? With the help of a neat circuit diagram and relevant waveforms, explainthe operation of a three-phase dual mode dual converter.
9.
With the help of a neat circuit diagram and relevant waveforms, explain the Symmetrical Angle Control(SAC) technique for power factor improvement in AC-DC converters.10.
With the help of a neat circuit diagram and relevant waveforms, explain the Symmetrical Angle Control(EAC) technique for power factor improvement in AC-DC converters.11.
With the help of a neat circuit diagram and relevant waveforms, explain the Symmetrical Angle ControlPWM technique for power factor improvement in AC-DC converters.12.
What is input power factor of the converter? Explain various methods used to improve input power factorand compare them.13.
With the help of a neat circuit diagram and relevant waveforms, explain the operation of a single-phase semiconverter-based separately excited DC motor drive. Derive expressions for the motor armature current andtorque in terms of the firing angle, motor speed, field current and motor parameters.14.
With the help of a neat circuit diagram and relevant waveforms, explain the operation of a single-phase fullconverter-based separately excited DC motor drive. Derive expressions for the motor armature current andtorque in terms of the firing angle, motor speed, field current and motor parameters.15.
With the help of a neat circuit diagram and relevant waveforms, explain the operation of a single-phase Dualconverter-based separately excited DC motor drive. Derive expressions for the motor armature current(circulating current) and torque in terms of the firing angle, motor speed, field current and motor parameters.16.
With the help of a neat circuit diagram and relevant waveforms, explain the operation of a three-phase semiconverter-based separately excited DC motor drive. Derive expressions for the motor armature current andtorque in terms of the firing angle, motor speed, field current and motor parameters.17.
With the help of a neat circuit diagram and relevant waveforms, explain the operation of a three-phase fullconverter-based separately excited DC motor drive. Derive expressions for the motor armature current andtorque in terms of the firing angle, motor speed, field current and motor parameters.18.
With the help of a neat circuit diagram and relevant waveforms, explain the operation of a Three-phase Dualconverter-based separately excited DC motor drive. Derive expressions for the motor armature current(circulating current) and torque in terms of the firing angle, motor speed, field current and motor parameters.19.
Draw a neat circuit diagram of 1 semiconverter drive for separately excited dc motor. Explain its operationwith suitable wave forms. [10]20.
Draw a neat circuit diagram of chopper fed dc drive. Explain its operation with suitable waveforms. [8]21.
What are the advantages and disadvantages of 3phase dc drive over 1 phase dc drive? [6]22.
Draw a neat circuit diagram of 3 phase full converter dc drive. Explain its operation with suitablewaveforms. [10]
23.
What are the effects of discontinuous armature current for dc motor drive.[4]
24.
Explain over voltage and over current protection for D.C. motor. 25.
Explain ‘Field failure and under voltage protections for D.C. motor.
[4] 26.
Write short note: a) DC motor performance parameters.b) PWM converter drive.c) Digital control of DC motor27.
A 230V, 1000rpm, 10A separately excited DC motor is fed from a single-phase semiconverter operatingfrom the 230V, 50Hz mains. If Ra = 0.75, calculate the firing angle to obtain rated torque for a motor speedof 500rpm. [6]
28.
The Speed of a separately excited motor is controlled by a single phase semi converter. The Field currentwhich is also controlled by a semi converter is set to the maximum possible value. The ac supply voltage tothe armature and field converters is 1-phase 208 V, 60 Hz. The armature resistance R
a
= 0.25Ω, the field
resistance R
f
= 147Ω and the motor voltage constant K
v
= 0.7032 V/A rad/sec. T he load torque is T
L
= 45 Nmat 1000 rpm. The viscous friction and no-load losses are negligible. The inductances of the armature andfield circuits are sufficient enough to make the armature and field currents continuous and ripple free.Determine: [10]a)
The field currentb)
The delay angle of the converter in the armature circuits
α
a
and c)
The input power factor of the armature circuit converter. 29.
The Speed of a separately excited motor is controlled by a single phase semi converter. The Field currentwhich is also controlled by a semi converter is set to the maximum possible value. The ac supply voltage tothe armature and field converters is 1-phase 208 V, 60 Hz. The armature resistance R
a
= 0.1
2Ω, the field
resistance R
f
= 220
Ω and the motor voltage constant K
v
= 1.055V/A rad/sec. T he load torque is T
L
= 75 Nmat 700 rpm. The viscous friction and no-load losses are negligible. The inductances of the armature and fieldcircuits are sufficient enough to make the armature and field currents continuous and ripple free.Determine: [10]a)
The field currentb)
The delay angle of the converter in the armature circuits
α
a
and c)
The input power factor of the armature circuit converter. 30.
The Speed of a separately excited motor is controlled by a single phase Full converter. The Field currentwhich is also controlled by a full converter is set to the maximum possible value. The ac supply voltage tothe armature and field converters is 1-phase 208 V, 60 Hz. The armature resistance R
a
= 0.
5Ω, the field
resistance R
f
= 345
Ω and the motor voltage constant K
v
= 0.71 V/A rad/sec. T he load torque is T
L
= 45 Nmat 1000 rpm. The viscous friction and no-load losses are negligible. If delay angle of the armature converteris
α
a
= 45
0
and the armature current I
a
= 55 ADetermine: [12]a)
Torque developed by the motor T
d
b)
The speed ω
c)
The input power factor of the drive. d)
If the polarity of the motor back emf is reversed find
α
a
to maintain the armature current constant atsame value of I
a
= 55 Ae)
Power fed back to supply during regenerative braking.31.
The Speed 20 HP, 300 V, 1800 rpm of a separately excited motor is controlled by a three phase fullconverter drive. The Field current which is also controlled by a full converter and is set to the maximumpossible value. The ac supply voltage to the armature and field converters is 3-phase;
Υ connected
208 V, 60Hz. The armature resistance R
a
= 0.35
Ω, the field resistance R
f
= 250
Ω and the motor voltage constant K
v
=1.15V/A rad/sec. The viscous friction and no-load losses are negligible. The inductances of the armature andfield circuits are sufficient enough to make the armature and field currents continuous and ripple free.Determine: [10]a)
The delay angle of the converter in the armature circuits
α
a
if motor supplies rated power at rated speed
b)
The no load speed if the delay angles are the same as in (a) and armature current at no-load is 10 % of the rated value. c)
Speed regulation32.
The Speed 20 HP, 300 V, 1800 rpm of a separately excited motor is controlled by a three phase semiconverter drive. The Field current which is also controlled by a semi converter and is set to the maximumpossible value. The ac supply voltage to the armature and field converters is 3-phase
; Υ connected
208 V, 60Hz. The armature resistance R
a
= 0.35
Ω, the field resistance R
f
= 250
Ω and the motor voltage consta
nt K
v
=1.15V/A rad/sec. The viscous friction and no-load losses are negligible. The inductances of the armature andfield circuits are sufficient enough to make the armature and field currents continuous and ripple free.Determine: [10]a)
The delay angle of the converter in the armature circuits
α
a
if motor supplies rated power at rated speed b)
The no load speed if the delay angles are the same as in (a) and armature current at no-load is 10 % of the rated value. c)
Speed regulation33.
The Speed 20 HP, 300 V, 900 rpm of a separately excited motor is controlled by a three phase full converterdrive. The Field current which is also controlled by a full converter and is set to the maximum possiblevalue. The ac supply voltage to the armature and field converters is 3-phase
; Υ connected
208 V, 60 Hz. Thearmature resistance R
a
= 0.15
Ω, the field resistance R
f
= 145
Ω and the motor voltage constant K
v
= 1.15V/Arad/sec. The viscous friction and no-load losses are negligible. The inductances of the armature and fieldcircuits are sufficient enough to make the armature and field currents continuous and ripple free.Determine: [10]a)
The delay angle of the converter in the armature circuits
α
a
if the field converter is operated atmaximum field current and the developed torque is T
d
= 106 Nm at 750 rpm. b)
If the field converter is operated at maximum field current and the developed torque is T
d
= 106 NmThe delay angle of the converter in the armature circuits
α
a
=0 determineSpeedc)
For the same load as in (b) determine delay angle of the field circuit converter if the speed is increasedto 1800 rpm34.
The Speed 20 HP, 300 V, 900 rpm of a separately excited motor is controlled by a three phase semiconverter drive. The Field current which is also controlled by a semi converter and is set to the maximumpossible value. The ac supply voltage to the armature and field converters is 3-phase
; Υ connected
208 V, 60Hz. The armature resistance R
a
= 0.15
Ω, the field resistance R
f
= 145
Ω and the motor voltage constant K
v
=1.15V/A rad/sec. The viscous friction and no-load losses are negligible. The inductances of the armature andfield circuits are sufficient enough to make the armature and field currents continuous and ripple free.Determine: [10]d)
The delay angle of the converter in the armature circuits
α
a
if the field converter is operated atmaximum field current and the developed torque is T
d
= 106 Nm at 750 rpm. e)
If the field converter is operated at maximum field current and the developed torque is T
d
= 106 NmThe delay angle of the converter in the armature circuits
α
a
=0 determineSpeedf)
For the same load as in (b) determine delay angle of the field circuit converter if the speed is increasedto 1800 rpm35.
A 210 V, 1200 rpm, 10A separately excited motor is controlled by a single phase fully controlled converter
with an a.c. source ‘voltage of 230 V, 50Hz. Assume that sufficient inductance is present in the armature
circuit to make the motor current continuous and ripple free for any torque greater than 25 percent of ratedtorque Ra = 1.5i)
What should be the value of the filing angle to get the rated torque at 800 rpm?ii)
Compute the filing angle for the rated braking torque at
–
1200 rpm.iii)
Calculate the motor -
speed at the rated torque and α = 165º for the regenerative braking in the
second quadrant. [10]
Unit -2
36.
Write short note: a)
PWM converter drive.
b)
Digital control of DC motorc)
Phase locked loop control of DC drived)
Microcomputer control of DC Drivee)
Mechanical time constant and electrical time constant of DC motors37.
What are the advantages of closed loop control of DC Drives?38.
Derive and explain the principle of closed loop control of DC drives using suitable block diagram forseparately excited DC Motor.39.
Derive and explain the principle of closed loop control of DC drives using suitable block diagram for DCSeries Motor.40.
Draw and explain the operation of closed loop control of separately excited DC Motor with inner-currentloop and field weaking.41.
Explain the principle of Phase locked loop control of DC drive using suitable block diagram for separatelyexcited DC Motor.42.
Explain the principle of Microcomputer control of DC drive using suitable block diagram and flow chart forseparately excited DC Motor.43.
Explain briefly the braking methods of dc motor.44.
Explain the operation of closed loop control of separately excited DC Motor with inner-current loop.45.
Problems 15.21 to 15.27 from power electronics circuits, devices and applications- M H Rashid46.
Example 15.12 from power electronics circuits, devices and applications- M H Rashid.
Unit-3
47.
Explain any two of the following methods for speed control of induction motors : [16]a) Variable frequency PWM-VSI drive.b) Stator voltage control.c) Slip power.48.
With the help of the appropriate torque-speed characteristics, explain how electromagnetic braking isachieved for 3-phase induction motors fed from a constant V/f variable voltage variable frequency drive. [8].49.
Draw the torque- speed characteristics of the polyphase induction-motor. Also explain the followingoperating regions.i)
Motoring regionii)
Generating regioniii)
Braking region [6]50.
Explain PWM techniques for the speed control of IM.[8]51.
Draw circuit diagram of transistorized stator control of IM. Draw waveform for output voltage, current andsequence of pluses.[8]52.
A 4 pole, 415V, 50Hz, three-phase induction motor has a rated speed of 1460rpm. Calculate its speed, slipand slip frequency under constant V/f control for a stator frequency of 40Hz, the load torque being equal to60% of rated motor torque. [8]
53.
What is static Kramer drive and static Scherbius drive? [6]54.
What are the different speed control methods of Induction motor? Explain it in brief. [12]55.
Draw the circuit diagram and explain the operation of rotor resistance control using chopper. [8]56.
Explain with suitable block diagram the control of induction motor using microprocessor.57.
With the help of a circuit diagram and the motor torque
–
speed characteristic, explain stator voltage speedcontrol of induction motors.[8]58.
What do you understand by soft start? State and explain the soft start methods employed for motors. [4]59.
Justify “The speed range of an induction motor is restricted to above 30%
of full range while operating withslip power regulation system. [4].60.
What is V/f control in speed control of IM? Explain its limitations.[8]61.
Compare VSI and CSI for IM drive.[8]62.
Explain the induction motor operation, when the V/f ratio is held constant. Also derive the expression formaximum torque.
[8]
63.
Explain various protection circuits used for AC motors.[8]64.
Explain Vector control of IM drive.[8]65.
Explain Briefly the braking method of Induction motor.[8]

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