Question Bank SSD EaswariEngg
Question Bank SSD EaswariEngg
Question Bank SSD EaswariEngg
VI Sem EEE
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VI Sem EEE
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Fig. (1)
Fig. (2)
10. Explain in detail the multi quadrant dynamics in the speed torque plane.
11. A motor drives two loads. One has rotational motion. It is coupled to the motor
through a reduction gear with a = 0.1 and efficiency of 90%. The load has a
moment of inertia of 10 Kg-m2 and a torque of 10 N-m. The other load has
translational motion and consist of 1000 Kg weight to be lifted at a uniform speed
of 1.5 m/sec. Coupling between this load the motor has an efficiency of 85%.
Motor has inertia of 0.2 Kg-m2 and runs at a constant speed of 1420 r.p.m.
Determine the equivalent inertia referred to the motor shaft and power delivered
by the motor.
12. (i) Give in brief the different types of loads.
(ii) Explain in detail constant HP and constant torque operations.
13. Develop an expression for power rating of an electric motor when it is
intermittently loaded.
14. Develop a relation between the temperature rise and time of an electric motor.
There from show that the heating and cooling curves are exponential in nature.
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Unit II
Converter / Chopper Fed DC Motor Drive
PART A
1. Write the expression for the average output voltage of a full converter fed DC drive.
2. What are the advantages in operating choppers at high frequency?
3. Is a sine- wave output current possible from a chopper circuit.
4. What are the two types of current controllers used in motor drive system?
5. When is discontinuous conduction mode expected with the operation of converter
fed DC drive?
6. Explain whether discontinuous conduction will occur in the operation of chopper
fed DC drives.
7. State the conditions for continuous current conduction mode for DC motor.
8. Mention the three methods of breaking of a DC motor.
9. What is meant by multi quadrant operation of DC motor?
10. Give the condition under which the DC motor operates under continuous current
mode.
11. Draw the diagram of a regenerative chopper fed separately excited D.C. motor
drive.
12. Why thyristors are not preferred now a days for chopper fed DC drives?
13. What do you understand by constant torque drive and constant power drive?
14. State the advantages of chopper fed dc drives.
15. What are the types of control strategies in a dc chopper?
16. What are the advantages in operating choppers at high frequency?
17. What are the advantages using PI controller in closed loop control of dc drive?
18. Mention the drawbacks of rectifier fed dc drives.
19. What is static Ward Leonard drive?
20. Define and mention different types of breaking in a dc motor.
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PART B
1. Explain using a power circuit the working of a single phase semi converter fed
separately excited motor drive.
2. A separately excited DC motor operating from a single phase half controlled bridge at
a speed of 1400 rpm has an input voltage of 330 sin 314t and a back emf of 80 V. The
SCR are fired symmetrically at = 30 in every half cycle. The armature has a
resistance of 4 ohms. Calculate the average armature current and the motor torque.
3. Describe DC shunt motor can be made to both run as a motor and operate in the
breaking mode using a chopper.
4. A DC shunt motor fed from 400 V DC source through a chopper has the following
parameters. Ra = 0.02 ohms Rf = 0.04 ohms and k = 5X10-3 Nm/Amp2. . The average
armature current of 50% determine
a. Input power from the source,
b. Motor speed and
c. Motor torque.
5. Discuss the control circuit design for a two- quadrant chopper circuit.
6. Evaluate the instantaneous steady state armature current and electromagnetic torque
including harmonics for continuous current conduction mode for a chopper controlled
DC motor drive.
7. Explain in detail the operation and steady state analysis of 1 phase fully controlled
converter fed dc drive with neat waveforms in continuous and discontinuous
conduction modes.
8. Explain the operation of four quadrant chopper control in dc motor drives.
9. A 250V separately excited dc motor has an armature resistance of 2.5 ohms. When
driving a load at 600 RPM with constant torque, the armature takes 20A. This motor
is controlled by a chopper circuit with a frequency of 400 HZ and an input voltage of
250 V.
(1) What should be the value of the duty ratio if one desires to reduce the
speed from 600 to 540 rpm with the load torque maintained constant
(2) Find out the value of duty ratio for which the per unit ripple current will
be maximum.
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10. A separately excited DC motor with constant field current has an armature source
whose pd is 400 V and the speed of the motor is 1600 rpm, if all the losses in the
motor are neglected.
a. What is the armature current when the load torque is 420 Nm?
b. If the armature pd is held constant at 600 V and field current is reduced
until the motors at 4000 rpm. Determine the torque that the motor may
exert this speed.
c. What is the required power rating of the source?
11. Explain the Ward Leonard method of speed control of DC shunt motor.
12. A DC shunt motor is connected to a constant voltage main. It drives load torque
which is independent of speed. Prove that if E < 1/2 V, increasing the air gap flux per
pole decreases the speed. While if E < 1/2 V, decreases the air gap flux increases the
speed. (E Induced EMF , V Supply voltage)
13. A 220 V, 1500 rpm, 50 A separately excited DC motor with armature resistance of 0.5
Ohm is fed from a three phase fully controlled rectifier. Available Ac source has a lie
voltage of 440 V, 50 Hz. A star Delta connected transformer is used to feed the
armature so that motor terminal voltage equals rated voltage when converter firing
angle is zero.
a. Calculate transformer turns ratio
b. Determine the value of firing angle when
1.
2.
(2)
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Unit V
Design of Controller for Drives
PART A
1. Give the transfer function relating speed and armature current of a DC motor.
2. What are the functions of feed back loops in an electric drive?
3. What is current controller and how it is represented in the form of simple
equation?
4. Write the transfer equation for a DC motor.
5. List out the factors concerned with selection of converters.
6. What is a closed loop control system?
7. What are the advantages of closed loop speed control?
8. What are the two types of feedback in DC drive?
9. What is Current and Speed feedback?
10. What are the design procedures for a closed loop speed control system?
PART B
1. Discuss using a diagram the operation of a closed loop scheme for speed control
of a DC motor, below and above the base speed.
2. Derive the transfer function of the speed controller.
3. Explain how the converter power output and controller characteristics are related.
4. Draw and explain a close loop speed control system of a BLDM drive with the
inverter operating in PWM feed back mode.
5. Explain with diagram a control schematic of the four quadrant dc motor drive.
6. Derive the transfer function of DC motor load system.
7. Give the design procedure of current controller.
8. Explain the armature voltage control of DC motor with constant field and field
weakening modes.
9. Describe the closed loop speed control of separately excited dc motor by
proportional control.
10. Draw the circuit diagram and explain the operation of closed loop control with
inner current loop and field weakening.
PREPARED BY
Question Bank EE2352 Solid State Drives
APPROVED BY
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K.V.Thilagar, AP/EEE
P.Pushpakarthick, AP/EEE
(HOD/EEE)
Unit III
Induction Motor Drives
PART A
1. Name the methods of speed control applicable on the rotor side of a three phase
induction motor.
2. State the advantages of closed loop systems.
3. Write any two applications of slip- power recovery drives in induction motor.
4. What is the meaning of voltage- fed inverter locomotive drive with parallel
machines?
5. State the advantages of PI controller used in closed loop control of induction motor
drives.
6. Compare voltage source and current source inverter fed drives.
7. Draw the per phase equivalent (approximate) circuit of induction motor referred to
stator and also give the final torque expressions.
8. Mention the different methods of speed control of induction motor drive.
9. What is the influence of harmonics over induction motor?
10. List out the advantages disadvantages of regenerative breaking in induction motor.
11. Why speed control (3 phase induction motor) with constant supply voltage and
reduced supply frequency is not preferred?
12. Name the methods of speed control applicable on the stator side of a three-phase
induction motor.
13. When is an induction motor said to be working in the field-weakening mode?
14. What is a static Kramer drive?
15. List the demerits of the rotor resistance control using SCR switching with external
resistance.
16. Show the slip power recovery scheme for slip ring induction motor. Offer both sub
synchronous and super synchronous range of speeds.
Question Bank EE2352 Solid State Drives
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PART B
1.
(i) Discuss how the speed of a three phase induction motor can be controlled by
varying the frequency of the applied voltage.
(ii) Draw the speed torque characteristics of the motor with the constant supply
voltage and variable frequency.
2. A three phase 400 V, 15 KW, 1440 rpm 50 Hz star connected induction motor has
rotor leakage impedance of (0.4 + j1.6) ohms. The stator leakage impedance and
rotational losses are assumed negligible. If the motor is energised from a 120 Hz,
400 V, 3 phase source, then calculate
(1) The motor speed at rated load.
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(2) The starting torque and rotor current in term of their values at the rated
frequency.
12. Describe the closed loop control with VSI fed induction motor and compare CSI
and VSI fed induction motor.
13. With necessary diagram, explain the theoretical principles of stator voltage
control.
14. Describe the slip power recovery scheme in both static Scherbius and static
Kramer drives.
15. Explain static rotor resistance control in closed loop speed control.
16. A 3 phase induction motor at rated voltage and frequency has maximum torque of
225 % and starting torque of 150 percent of full load torque. Neglect stator
resistance and rotational losses. Assume constant rotor resistance. Calculate the
following
(1) Slip at maximum torque
(2) Slip at full load
17. Describe the closed loop control with CSI fed induction motor
18. A 440 V, star connected 3 phase, 6 pole, 50 HZ induction motor has following
parameters referred to the stator Rs = Rr = 1 ohm, Xs = Xr = 2 ohm. For
regenerative braking operation of this motor determine the maximum over
handling torque it can hold and range of speed for safe operation.
19. Explain the sub synchronous static converter cascade and discuss the methods of
improving power factor for the same.
20. A three phase squirrel cage induction motor drives a blower type load. The no
load rotational losses are negligible. Show that the rotor current is maximum
when the motor runs at a slip equal to 1/3. Find the expression for maximum rotor
current.
21. Derive an expression for the torque of an inverter fed three phase Induction motor
when it is operated with vlf control. Show that the maximum torque remains
unaltered in this scheme.
22. Explain the mechanical characteristics of a three-phase induction motor with
stator current control.
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23. A 400 V 4 pole 50 Hz three phase star connected induction motor has
r l = 0,
Xl,= X2 = 1 ohm, r2 = 0.4 ohm, Xm = 500 ohms. The induction motor is fed from
(1) a constant voltage source of 231 volts per phase and (2) a constant current
source of 28 Amps. For both the cases calculate the slip at which maximum
torque occurs and the starting and maximum torques.
24. A three phase 420 V, 4 pole 50 Hz star connected slip ring induction motor has its
speed controlled by means of a GTO chopper in its rotor circuit. The effective
phase turns ratio from rotor to stator is 0.8. The filter inductance enables the
inductor current tc be ripple free losses in the rectifier inductor, GTO chopper and
no load losses of the motor arc neglected. Load torque proportional to speed
squared is 450 N-M.
(i). For a minimum motor speed of 1000 rpm, calculate the value of
chopper resistance R.
(ii) For the calculated value of R, if the speed is raised to 1.320 rpm,
calculate
(2) The inductor current
(3) The duty cycle of chopper
(4) Rectified output voltage
(5) Efficiency in case per phase resistances for stator and rotor are 0.015 ohms
and 0.02 ohms respectively.
25. A static Kramer drive is used for speed control of a 4 pole 3 phase slip ring
induction motor fed from a 415 V, 50 Hz supply. The inverter is connected
directly to the supply. If the motor is required to operate at 1200 rpm, find the
firing advance angle of the inverter. The voltage across open circuited slip rings at
stand still is 700 volts. Allow a voltage drop of 0.7 V and 1.5 V across each of the
diodes and thyristors respectively. The voltage drop across the inductor may be
neglected.
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Unit IV
Synchronous Motor Drives
PART A
1. What are the different modes are employed to achieve variable frequency control
in synchronous motors?
2. When can a synchronous motor be load commutated?
3. Write any two applications of synchronous motor drives.
4. Write any four special features of self controlled synchronous machine.
5. Mention any two advantages of self control of synchronous motor.
6. Write down the torque equation of synchronous motor.
7. What is meant by brushless excitation?
8. Give the application of self controlled synchronous motor.
9. Mention the different types of synchronous motor.
10. What are the modes of speed control of a synchronous motor?
11. What is self control mode of synchronous motor?
12. Why a self controlled synchronous motor is free from hunting operation.
13. Write any four special features of self controlled synchronous machine.
14. What is constant margin angle control of synchronous motor drive?
15. What are the advantages of constant margin angle control of synchronous motor
drive fed by an inverter?
16. Why a synchronous motor without damper winding is used in the drive system
employing a cycloconverter?
17. What are the major applications of cycloconverter fed synchronous motor?
18. What is commutator less dc motor?
19. What are the classifications of permanent magnet synchronous motor?
20. What are the advantages and disadvantages of PMSM?
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PART B
1. Explain the control characteristics of an open loop V/f controlled synchronous
motor.
2. A 7 MW three phase 12 KV star connected 6 pole 50 Hz 0.9 Leading power factor
synchronous motor has Xs = 10 Ohms and Rs = 0 Ohms. The rated field current is
40 A. The machines controlled by variable frequency controlled at constant V/f
ratio up to the base speed and at constant V above base speed. Determine
(1) Torque and
(2) The field Current for the rated armature current 750 rpm and 0.08 leading
power factor.
3. Show that the torque of a synchronous motor is independent of speed, when it
operates in the controlled current mode.
4. Explain using a power circuit, the working of a trapezoidally excited permanent
magnet synchronous motor, operating in the self controlled mode.
5. Draw the open loop volts/HZ speed control of multiple PM synchronous motors
and volts/HZ speed control characteristics in torque- speed plane.
6. Explain the special features of self- controlled synchronous motor with diagram
and write the difference between this and a dc motor.
7. Explain power factor control of synchronous motor with relevant vector diagram.
8. Explain the self control of synchronous motor in detail.
9. Write short notes on permanent magnet synchronous motor.
10. Write short notes on regenerative breaking in synchronous motor.
11. With diagram, explain the closed loop control synchronous motor drive.
12. A synchronous motor is controlled by load commutated inverter, which in tern is
fed from a line commutated converter. Source voltage is 6.6 KV, 50 Hz. Load
commutated inverter operate at a constant firing angle 1 of 140 degrees and
when rectifying 1 = 0 degrees, DC link inductor resistance Rd = 0.1 Ohm. Drive
operates in self controlled mode with a constant (V/f) ratio. Motor has the details:
8 MW, 3 Phase, 6600 V, 6 poles, 50 Hz, unity power factor, star connected Xs =
Question Bank EE2352 Solid State Drives
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2.8 Ohms, Rs = 0 Ohm. Determine source side converter firing angles for the
following :
a. Motor operation at the rated current and 500 rpm. What will be the power
developed by the motor?
b. Regenerative breaking operation at 500 rpm and rated motor current. Also
calculate power supplied to the source.
13. Explain the operation of self controlled synchronous motor employing
cycloconverter.
14. Discuss using a block diagram the operation of a voltage source inverter fed
synchronous motor in the true synchronous mode.
15. A 6 MW 3 phase 11 kV star connected 6 pole 50 Hz 0.9 (lagging) power factor
synchronous motor has synchronous reactance equal to 9 ohms and armature
resistance equal to 'zero ohms. The rated field current is 50 Amps. The machine is
controlled by variable frequency control at constant v/f ratio up to the base speed
and at constant voltage above base speed. Determine
(1) Torque and field current for the rated armature current, 750 rpm and
0.8 leading power factor.
(2) Armature current and power factor for half the rated motor torque,
1500 rpm and rated field current.
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1) dc drives 2) ac drives
6. What are the advantages of electric drives?
1) They have flexible control characteristics. the steady state and
dynamic characteristics
of electrical drives can be shaped to satisfy load requirements.
2) Drives can be provided with automatic fault detection systems,
programmable logic
controllers and computers can be employed to automatically
ctrl the drive operations in a
desired sequence.
3) They are available in which range of torque, speed and power.
4) It can operate in all the four quadrants of speed-torque plane.
Electric braking gives
smooth deceleration and increases life of the equipment
compared to other
forms of braking.
5) Control gear required for speed control, starting and braking is
usually simple and easy
to operate.
7. What are the functions performed by electric drives?
Various functions performed by electric drives include the
following.
a. Driving fans, ventilators, compressors and pumps etc.
b. Lifting goods by hoists and cranes
c. Imparting motion to conveyors in factories, mines and
warehouses and
d. Running excavators and escalators, electric locomotives, trains,
cars, trolley
buses, lifts and drums winders etc.
8. What are the disadvantages of electric
drives?
The disadvantages of electric drives.
a. Electric drives system is tied only up to the electrified area.
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Where the motors drive loads with intermittent type duty, such as
cranes, ore or coal unloaders, skip hoists, mine hoists, lifts, etc.
slip-ring induction motors with speed control by variation of
resistance in the rotor circuit are frequently used. This method of
speed control is employed for a motor generator set with a
flywheel (Ilgner set) used as an automatic slip regulator under
shock loading conditions.
105. What are the advantages and disadvantages of rotor
resistance control?
Advantage of rotor resistance control is that motor torque
capability remains unaltered even at low speeds. Only other
method which has this advantage is variable frequency control.
However, cost of rotor resistance control is very low compared to
variable frequency control. Major disadvantage is low efficiency
due to additional losses in resistors connected in the rotor circuit.
106. What is mesnt by soft start?
The AC voltage controllers allow a stepless control of supply
voltage from zero to rated volt. They are used for soft start of
motors.
107. How is the resistance in the output terminals of a chopper
varied?
The resistance connected across the output terminals of a chopper
can be varied form O to R by varying the time ratio of the chopper.
When the chopper is always OFF, the supply is always connected
to the resistance R. The time ratio in this case is zero and the
effective resistance connected in R. Similarly when the chopper is
always ON, the resistance is short circuited. The time ratio in the
case is unity and the effective resistance connected is 0. Hence by
varying the time ratio from 0 to 1, the value of resistance can be
varied from R to O.
108. What is the function of inductance L and resistance R in
the chopper resistance circuit?
Question Bank EE2352 Solid State Drives
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