Solid State Drives (EE1351) S6 EEETwo Marks Questions and Answers Two Marks Questions Solid State Drives Answers and 1. What is meant by electrical drives? Systems employed for motion control are called drives and they employ any of the prime movers such as diesel or petrol engines, gas or steam turbines, hydraulic motors and electric for supplying mathematical energy for motion control. Drives employing electric motors mo tion are called electric drives. 2. Draw the electric drive system. Mai n Power Sourc Electric e Drive Fig. An system electric-drive Mai n Power Sourc e Comman d Workin g Machin e Power Controller Working Moto r Machin e Power Controlle r Moto r Rotor position or sp eed sensor Fig. Mo dern Electric Drive system using power electronic converter 3. Specify the functions of power modulator. modulator p erforms one or more of the following four Power functions. a. Modulates flow of power form the source to the motor in such a manner that motor is imparted speed-torque characteristics required by the load. b. During transient operations, such as starting, braking and speed reversal, it restricts source and motor currents within permissible values; excessive current drawn from source may overload it or may cause a voltage dip. 4. Mention the different types of drives. 1)Group drive 2)Individual drive 3)Multimotor drive 5. List the different types of electrical drives. 1)d c d rives 2)ac drives 6. What are the advantages of electric drives? Examples of such machines are single d rilling machines (Universal motor is used) and lathes. In many pumps. cars. f. electric locomotives. 7. 11. What are etc. trolley buses. Space requirement : Less space is required in group drive as compared to individual drive . ventilators. Write short notes on individual electric drives. 9. Low maintenance cost : It req uires little maintenance as compared to individual drive. d. . breakdown of conductor may lead to fatal overhead accidents. Power r Efficiency : Group drive system when used and if all the machines are not b. Sequence of operation : Group drive system is useful because all the operations are stopped simultaneously.ility : Such arrangement is not possible in group drive i. lifts and drums winders 8. operate in all the four quadrants of speed-torque plane. working together the main motor shall work at very much reduced lo ad. this arrangement d. disadvantages of electric the drives? The disadvantages of electric drives. Speed r. factor : Group drive has low power facto a. Electric braking 4) It can givesoth deceleration and increases life of the equipment compared to other smo forms of braking . In a lathe. leakage from conductors and b. moves the feed and also with the help of gears. speed and 3) They power. the motor rotates spindle the spindle. Initial cost : Initial cost of group drive is less as compared to that of the individual drive. Types of machines : Group drive is not suitable fro driving heavy machines such cranes. transmits motion to lubricating and cooling A three phase squirrel cage induction motor is used as the drive. compressors and pumps etc. Although the initial cost of group drive is less but yet this system is not used extensively because of following disadvantages. programmable 2) Drives can logic controllers and computers can b e emp loyed to automatically ctrl the drive operations in a desired sequence. Imparting motion to conveyors in factories. the steady state and dynamic characteristics drives can be shaped to satisfy load of electrical requirements. Reliability : In group drive if the main motor fails who le industry will come to stand still. What the group drive is not used extensively. What are the functions performed by electric drives? Various functions performed by electric drives include the following. Electric drives system is tied only up to the electrified a. each individual machine is driven by a sop arate motor.. Lifting goods by hoists and b. such applications the electric motor forms an integral part of the machine. Driving fans. 10. trains.are available in which range of torq ue. This motor In also imparts motion to various other parts of the machine.The condition arising und er the short circuits. Control gear req uired for speed co ntrol. starting and braking is usually simple and 5) easy to operate. Flexib is notsuitable for the place where flexibility is the prime facto : e.1) They have flexible co ntrol characteristics. lifts and hoists as etc. mines and warehouses andRunning excavators and escalators. a. area. cranes c. Group drive d oes not provide constant speed.e. c. Failure in supply for a few minutes may paralyses the whole system. c. be provid ed with automatic fault detection systems. c. What are the advantages of group drive over individual drive? advantages of group d rive over ind ividual drive The are a. individual drive. d. b. Mention the applications of electrical drives Paper mills Electric traction Cement mills Steel mills 15. braking is suitable for reversing the Which motor? Plugging is suitable for reversing the motor. 2) Power modulato r 3) Sources 4) Control unit Sensing 5) unit 14. maintenance needs. is critical What speed? is the speed that sep arates continuous conduction from discontinuous conduction It 21. Mention the types of enclosures Screen projected type Drip proof type Totally enclosed type Flame proof type 16.12. 6) Environment and location. mode. 1) Electrical motors and load. life. region. When phase sequence of supply of the motor running at the speed is reversed by interchanging connections of any two phases of stator with respect to supply terminals. . 4) Capital and running cost. Mention the different types of classes of duty Continuous duty Discontinuous duty Short time duty Intermittent duty 17. 13. 7) Reliability. 18. What is meant by plugging? It is one method of braking of IM. Mention the different factors for the selection of electric drives? 1) Steady state operation requirements. This method of braking is known as which regenerative braking . Space 5) and weight restriction. What is meant by regenerative braking? Regenerative braking occurs when the motor speed exceeds the synchro nous speed. In this case the IM runs as the induction m\c is converting the mechanical power into electrical power is delivered back to the electrical system. 2) Transient operation requirements. Mention the parts of electrical drives. This requires a motor to operate as a gen. What is meant by dynamic braking? Dynamic braking of electric motors occurs when the energy stored in the rotating dissipated mass is in an electrical resistance. operation shifts from motoring to plugging 20. 3) Requirements related to the source. 19. to convert the stored energy into electrical. drives. 26. Give some applications of D. a. Define four quadrant operation. Frequent starting. converting mathematical energy into electrical energy and thus opposes the motion. Coolng time constant is denoted as Tau Tau = C/A unt of heat required to raise the temp of the motor body by 1 degree Where C=amo Celsius A=amount of heat dissipated by the motor per unit time per degree Celsius. What is the use of flywheel? Where it is used?It is used for load equalization. it converts electrical energy into mechanical energy which supports its motion. 24. Define cooling time co nstant It is defined as the ratio between C and A.C. In motoring. 23. The reliability ad simple control. braking and The reversing. drives is the p resence of a mechanical co mmutator which limits the maximum power rating and the speed. It is mounted on the mo tor shaft in compound motor. 30. What are the advantage and disadvantages of D. Cranes. a. Paper mills c. This method of determining the power rating of the is known as equivalent current motor method.C. Excavators mils i. In braking. What are the advantages of series motor? . 27. Printing presses h. Machine tools f. Mine winders d. Why the variable speed applications are dominated b y D.C. The applications of D. Traction g. Mention the types of braking Regenerative braking Dynamic braking Pluggin g 28. Adjustable speed b.C. drives The are. This characteristic is called mechanical characteristics . Rolling mills b. it works as a generator. drives? advantages of D. Define equivalent current method motor selected should have a current rating more than or equal to the current. It is The also necessary to check the overload of the motor. Motor can pro vide motoring and braking operations for both forward and reverse directions. 32.C.22. drives are. drives because of lower cost. What are the methods of operation of electric drives? Steady state acceleration including starting deceleration including starting 25.C.C. 29. Hoists e. 31. disadvantage of D. drives? variable speed applications are dominated by D. The motor o perates in two mode: motoring and braking. What is meant by mechanical characteristics? The curve is drawn between speed and torque. Textile j. Good speed regulation c. High starting torque b. 41. How is the stator winding changed during constant torque and constant horsepower operations? For constant torque operation...c. voltage from an a. 34.C.C.. Mention the methods of armature voltage controlled dc motor? When the supplied voltage is ac. motor is started with full supply voltage across its terminals.. 33.... Write the expression for average o/p voltage of full converter fed dc drives? Vm=(2Vm/pi)cospi. Required frequent maintenance. 36. What is static Ward-Leonard drive? Controlled rectifiers are used to get variable d. Heavy torque o verload s. the change of stator winding is made form series – star to – star.. . What is a line commutated inverter? Full converter with firing angle delay greater than 90 deg. Regenerative braking takes place during changeover from higher to lower speeds. What are the disadvantages of conventional Ward-Leonard schemes? Higher initial cost d ue to use of two additional m\cs. source of fixed voltage controlled rectifier fed dc drives are also known as static Ward-Leonard drive. Needs more flo or space and pro per foundation. such an operation is used in regenerative braking mode of a dc motor in which case back a emf is greater than applied voltage. while fo r constant horsepower operation the change is made from seriesparallel delta to parallel-star.. Ward-Leonard schemes Transformer with taps and un controlled rectifier bridge Ward-Leonard scheme or controlled Static When therectifiers is supply dc: Chopper co ntrol 39.The advantages of series motors are.. 37. 40. dynamic or rheostat braking and plugging or reverse voltage braking.. How the D..c. Positive lo ad torque is negative if it produces change deceleration. may damage the motor due to heavy sparking at commuter and heating of the which winding. is called line commutated inverter...... a. it is necessary top limit the current to a safe value during Therefore. a very high current will flow. Define and mention different types of braking in a dc motor? In braking the motor works as a generator developing a negative torque which opposes the motion. 35..... Types are regenerative braking. since it is an inefficient method of speed control it was in intermittent load applications where the duration of low speed operations forms o used nly a proportion of total running small time.. Define positive and negative motor torque.continuous conduction Vm=[Vm(cos alpha-cos b eta)+(pi+alpha+beta)]/pi]. motor is affected at the time of starting? A D. Heavy weight and size.discontinuous conduction 42. Positive motor torque is defined as the torque which produces acceleration or the positive rate of of speed in forward direction. List the drawbacks of armature resistance contro l? In armature resistance control speed is varied by wasting power in external resistors that are connected in series with the armature. 38.. starting. What is meant by stator voltage control. . Mention the applications of ac drives. 51. What are the advantages in o perating choppers at high frequency? The operation at a high frequency improves motor performance by reducing current ripp le and eliminating discontinuous conduction. control r Roto resistance control power Slip recovery control. le in motor Ripp current 44. GTOs IGCTs areand preferred over thyristors for building choppers because they can be commutated by a power control signal and don’t need commutation low circuit. Current limit control. What are the advantages of closed loop c of dc drives? Closed loop control system has the adv. What are the types of control strategies in dc chopper? Time ratio control. Mention the application of stato r voltage control. What are the adv. which points towards its suitability for fan and pump drives. 45. small size.? The speed of the IM can be changed by changing the stator voltage. light weight. State the advantages of dc chopper drives? Dc chopper device has the advantages of high efficiency. What are the different methods of speed control of IM? Stator voltage control Supply freq.Higher noise and higher loss. quick response and regeneration down to very low speed. Low power factor. Mention the drawbacks of rectifier fed dc drives? Distortion of supply. of d c d rive? Stabilize the drive the damping ratio at the desired Adjust value the steady state speed error close to zero by integral action and filters out Makes noise due to the integral again action. This method is suitab le fo r applications where torque demand reduced with speed. IGBTs. What are the different methods of braking applied to the induction motor? Regenerative braking Pluggin g Dynamic braking. 48. 54. fast dynamic response and reduced effects of disturbance and system nonlinearities. 43. 50. 52. 47. 53. flexibility in control. Why self commutated devices are preferred o ver thyristors for chopper circuits? self commutated devices such as power MOSFETs power transistors. 46. of using PI controller in closed loop ctrl. of improved accuracy. 49. Because the pro portiotorque to the square of the nal is voltage. cranes. slip Define The difference between the synchro nous speed (Ns)and actual speed(N)of the rotor known as is speed. What are the adv. This motor. 63. The stator current be variedcan using current source by inverter. 61. List the adv of squirrel cage IM? Cheap er light in weight Rugged in construction More efficient Require less maintenance operated in dirty and explosive It can be environment 59. What is meant by frequency control of IM? The speed of IM can be controlled b y changing the supply freq because the speed is directly proportional to supply frequency. of stator voltage control method? The ctrl circuitry is simple Compact size Quick resp onse time is considerable savings in energy and thus it is economical method as There compared to other methods of speed ctrl. traction etc. %slip s=[(Ns-N)/Ns]x 100 Define base The synchro nous speed corresponding to the rated freq is called the base speed. Small start Higher starting torque for lo w case resistance 64. What is meant by soft start? The ac voltage controllers show a stepless control of supply voltage from zero to volt. theyrated used for soft start for are motors. 56. What are the advantages of V/F control? Smooth speed ctrl i/p current and improved power factor at low freq. of applications such as fans. the % of slip is gn slip by. What are the 3 modes of region in the adjustable-freq IM drives characteristics? Constant torque region . 55. 60. What is meant by V/F control l? When the freq is reduced the i/p voltage must be reduced proportionally so as to maintain constant flux otherwise the core will get saturated resulting in excessive iron loss and magnetizing type of IM behavior is similar to the working of dc series current. blowers. What is meant by stator current control? The 3 phase IM speed can be controlled by stator current control. What are the three regions in the speed-to rque characteristics in the IM? Motoring region (0<=s<=1) Generating region(s<0) Plugging region (1<=s<=2) where s is the slip. mill run-out tables. This method o f speed ctrl is called freq control. 57. 62. 65.AC drives are used in a no. speed. conveyors. 58. a. Give some advantages of Ward-Leonard drive. Regenerative braking. are. B. Inherent regenerative barking capability . They a. High initial cost b. Plugging or reverse voltage braking. How will you select the motor rating for a specific application? When operating for a specific application mo tor rating should be carefully chosen insulation that the temperature never exceed the prescribed limit.Constant power region speed series mo toring High region 66. c. control Armature resistance c. 69. It is of three types. a. ward Leonard scheme or controlled rectifiers when the supply in c. control.C. Chopper co d. What are the advantages of armature voltage control? advantages of armature voltage control The are. Otherwise either it will lead to its immediate thermal breakdown causing sho rt circuit and damage to winding. which supports its motion. a. Leonard drive are. 68. Give some drawbacks and uses of Ward-Leonard drive The drawbacks of Ward . In braking. What are the three types of speed control? three types of speed control The as. High efficiency b. Low efficiency The Ward-Leonard elevators. 70. it converts electrical energy to mechanical energy. it works as a generator converting mechanical energy to electrical energy and thus opposes the motion. The advantages of Ward-Leonard drive are. The mo tor works as a generator developing a negative torque which oppo ses the motion is called barking. motoring. a. What are the methods involved in armature voltage control? When the supply in A. What is braking ? Mention its types. In 73. Good transient response Good c. Armature voltage control Field flux b. Static D. tools machine etc. motoring and braking. paper mills. What are the two mod es of operation in the motor? The two modes of op eration in the motor are. a. 67. drive is used in rolling mills . or it will lead to deterioration of its quality resulting into thermal breakdown in near future. Ward-Leonard schemes b. ntrol. Transformer with taps and an uncontrolled rectifier bridge. Dynamic o r rheostat b b.C. raking. 71. 72. mine winders. speed regulation. mill run-out tables. What are the advantages of induction motors over D. The rectifiers allow D.C. the series motor must be designed with its base speed equal to the highest desired speed of the drive.C.C. The two intervals present in fully controlled rectifier are a. 76. A D. 74. How is the speed controlled in ind uction motor? The inductio n motor speed can be controlled by sup plying the stator a variable voltage. 80. Power factor improvement. interval. lighter. voltage in either direction and therefore. there are a number of problems with regenerative braking of a series motor.C. Give environments. On the other hand. allow motor control in quadrants I and IV. What is called continuo us and discontinuous conduction? motor is fed from a phase controlled converter the current in the armature may A D. What is the use of controlled rectifiers? Controlled rectifiers are used to get variable D. cranes. conveyors. separately excited motors are now preferred for even traction applications. flow in pulses in called continuous discrete conduction. If field contro l is not emp loyed. current interval. 77. What is known as half-controlled rectifier and fully controlled rectifier? The rectifiers provide control of D. moto rs is the presence of commutate and brushes. 82.b. 2. induction motors. Because of the limitations of series motors. mo tors? The main drawback of D. What are the limitations o f series motor? Why series motor is not used in traction applications now a days? 1. a.C. require lower maintenance and can operate in dirty and explosive 81. drives. 79. variable frequency supply using static frequency converters. 78.C. smaller.C. moto r is fed fro m a phase controlled converter the current in the armature may flow continuously with an average value superimposed on by a ripple is called discontinuous cond uction. and explosive and dirty involved are environments. Duty intervalZero b. because of the advantages of induction motors. particularly squirrel-cage are rugged.. What is called inversion? Rectifier takes power from D. which require frequent maintenance and make them unsuitable for explosive and dirty environments. 75. cheaper. more efficient.C. The field of series cannot be easily controlled. they are used in a number of applications such as fans. traction etc. Further. They are known as fully-controlled rectifiers. Speed control is also possible by feeding the slip . Voltage control only in one direction and motor quad rant control in They are known as half-controlled I only. terminals and transfers it to A. interval Zero current c. Source of voltage fixed .C. the applications of induction motors drives. Voltage form an A.C. What are the three intervals present in discontinuous conduction mode of single phase half and fully controlled rectifier? intervals present in half controlled rectifier The three are. rectifiers.C. Other applications underground and underwater installations. Duty interval Free. Although variable speed induction motor drives are generally expensive than D. wheeling b. mains is called inversion. blowers. The motor p ower factor is poor. Basically one distinguishes two different metho ds of speed co ntrol. if it o perates at very small The speed of the motor is therefore.C. 84. 85. c. b. versus speed metho d is suitable only for the following Torque cases. A stable operating a. The voltage controlled must be capable of withstanding high starting currents. Torque varying preoperational to the square of the speed. Roto r circuit. a. c. resistance control using a chopper controlled resistance in the rotor b. For short time operations where the duration of speed control ids defined.power to the supply system using co nverters in the rotor circuit. 83. type of load driven by the motor influences the current d rawn and losses of the motor as the The slip various. a. This is not suitable for constant torque loads due to increases and heating. poor efficiency ad poor power factor at low speeds.0. Classify the type of loads driven b y the motor. For speed control of motor having poor efficiencies under normal operation. Stator voltage control using a three-phase voltage controller. 88. Speed control by varying the slip frequency when the stator is fed from a co nstant voltage. This is due difficult to . Further the operation of the motor is eco nomical and efficient. How is the speed control by variation of slip frequency obtained?control by variation of slip frequency is obtained by the following Speed ways. The control of a three-phase induction motor. c. How is the speed of a sq uirrel cage induction motor controlled? The speed of a squirrel cage induction motor can be controlled very effectively by varying the stator frequency.C. maintaining the at the rated value or a value corresponding to the required torque on the linear rotor frequency portionto of rque-speed the curve. motors. What are the disadvantages of constant torque loads? constant torque loads are not favored due to increase in the losses linearly with slip and The becoming at s= 1 . To maintain constant torque the motor draws heavy current resulting in poor torque/ampere. torque curve beyond the maximum torque point has a negative shape. particularly when the dynamic p erformance is more involved than D. The normally occurring loads are a. The point in this region is not possible for constant torque load. b. Torque varying proportional to speed. 87. d. Using a cyclconverter in the rotor circuit. Speed co ntrol of the motor using a variable frequency variable voltage motor operating at constant rotor frequency. Why the control of a three-phase indication motor is more difficult than D. varied by varying the supply frequency and slips. Using a converter cascade in the rotor circuit to recover slip energy. The range of speedcontrol is rather limited. c. motors. a. Mention the effects of variable voltage supply in a cage induction motor. Constant torque loads. 89. speed control of blowers or pumps having parabolic or cubic variations of torque with b. constant frequency mains. 86. a cage induction motor is fed from a variable voltage for speed control the following When observations may be made. In which cases. torque versus speed method is suitable. This is obvio us form the variation of flux as the vo ltage is varied for speed maximum control. For speed. b. link voltage available at these frequencies cannot charge the commutating capacitors sufficiently enough to commutate the thrusters. To extend the frequency towards zero. By making the slip negative (i. as the D. These harmonics are also responsible pulsations. a D. special charging circuits must be used. decreasing the output freq uency of the The machine may be made to operate as a generator and the energy of the rotating parts fed inverter) back to the mains by an additional line side converter or dissipated in a resistance for dynamic barking. 93. What is slip controlled drive? When the slip is used as a controlled quantity to maintain the flux co nstant in the motor the drive is called slip enrolled drive. 97.C.C. What is the purpose of inductance and capacitance in the D. the torque varies as the square of the speed . 92.C. What is voltage source inverter? Voltage source inverter is a kind of D. To compensate for the resistance drop in the stator. link circuit provides smoothing whereas the capacitance maintains voltage. . What are the effects of harmonics in VSI fed induction motor drive? The motor receives sq uare wave voltages. What are the disadvantages of square wave inverter in induction motor drive? Square wave inverters have commutation problems at very low frequencies. Therefore at small the required torque is also small and V/f control would be sufficient to drive these leads speeds with no compensation required for resistance drop . with the rang of operating frequencies of the inverter. What are the components of the applied voltage to the induction motor? applied voltage to the induction motor has two components at low frequencies. motor. These vo ltage has harmonic co mponents. Thus braking is also fast. The link voltage is a controlled constancy of linkthe quality. braking at constant torque and current can be achieved . compressors and fans. 95. What is indirect flux control? The method of maintaining the flux co nstant by providing a voltage boost proportional to slip frequency is a kind of indirect flux co ntrol . Relatively large internal resistance of the converter causes voltage fluctuations following load fluctuations because the capacitor cannot be ideally b.. Where is the V/f control used? V/f control would be sufficient in some ap plicatio ns requiring variable torque. link circuit? The ind uctance in the D. 96.C. Inlarge. The second comp onent deepens on the load on the motor and hence on rotor frequency.e. This method of flux control is not desirable if very good dynamic behaviour is required. In these. such as The centrifugal pumps. They can be ind ependently controlled.a. Those puts a limit on the lower frequency of operation. This is true also for the case of the liquid being pumped with minimal solids. 91. 94.C. The harmonics of the stator current cause additional losses and heating. c. which is a two stage conversion device. By keeping the slip frequency constant. The reaction of the fifth and seventh harmonics with the fundamental gives for to rque rise seventh harmonic pulsations in the torque developed. An induction motor is very poorly damped compared to a D. motor there is a decoupling between the flux producing magnetizing current and torque ro ducing armature current. The They are a. For a given induction motor fed from a the to square wave inverter the harmonic content in the current tends to remain constant independent of input frequency. Proportional to stator frequency. This is not the case p with induction motors. link converter. b.C. 90. 98. In plugging? the barking torque is produced by interchange any two sup ply terminals. lifts. 101 How is the braking action produced in . lifts. The motor voltage is almost sinusoidal with superimposed spikes. A matching is therefore required between the inverter and the motor. Only other method which has this advantage is variable frequency control.f. However. mine hoists. This method of speed control is emplo yed resistance in for a generator set with a flywheel (Ilgner set) used as an automatic slip regulator under motor shock loading co nditions. 99. variable voltage supp ly is independent of stator frequency if the air gap flux is maintained constant. Only other method which has this advantage is variable frequency control. if the D. 100 Give the features from which a slip controlled drive is develo . etc. ore or coal skip unloaders. mine hoists. 105. The electromagnetic torque developed provides the braking action and brings the ro tor to a q uick stop. link current is controlled. This method of speed control is employed resistance in for a generator set with a flywheel (Ilgner set) used as an automatic slip regulator under shock motor loading cond itions. direction of rotation of the rotating magnetic field is reversed with respect to the ro tation of the motor. The commutation of the inverter is load dependent. The torque developed is also a function of rotor frequency. hoists. What is a current source inverter?D. slip-ring induction moto rs with speed control by variation of the rotor circuit are frequently used. 104. the inverter is called a current In a source inverter. . Where is rotor resistance control used? Where the moto rs drive loads with intermittent type duty. 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. cost resistance control is very low compared to variable frequency rotor of control. Major disadvantage is low efficiency due to additional losses in resistors co nnected in the rotor circuit . The developed is also a function of rotor frequency only. cost o f rotor resistance control is very low compared to variable frequency control. slip-ring induction mo tors with speed control by variation of the rotor circuit are frequently used. hoists.C. The stator current of an induction moto r operating on a variable frequency. Using these features a slip torque controlled be developed employing a current source inverter to feed an induction drive can motor. ore or coal skip unloaders. link is kept constant by a high inductance and he capacitance of the is dispensed with . Where is rotor resistance control used? Where the motors drive loads with intermittent type duty. ped. However.C. Major disadvantage is low efficiency due to add itional lo sses in resistors connected in the rotor circuit. such as cranes. What are the advantages and disadvantages of rotor resistance control? Advantage of rotor resistance contro l is that motor torque capability remains unaltered even at low speeds. A current so urce inverter is suitable fo r loads which present a low filter impedancecurrents and have unity harmonic to p. The inverter must necessarily be a force commutated one as the induction motor cannot p rovide the reactive power for the inverter. link converter. Multimotor operation is not possible. so that the plugging. Explain about the commutation of the current source inverter. The load parameters form a part of the commutation circuit. it is a function of the rotor frequency.C. The current in the D. However. such as cranes. 103. 102. etc. the p ower factor is better. This mains. Therefore. The performance of the drive improves with respect to add itional losses and torque pulsations. 109. 113. the static scherbius drive has a poor power factor? Drive input power is difference between motor input power and the power fed back. made possible by replacing the converter cascade by a cycloconverter. a slip ring rotor with external rotor resistance can be used when stator voltage control is used for controlling the 111. How is super synchro nous speed achieved? Super synchronous speed can be achieved if the power is fed to the rotor from A. the resistance is short circuited. The ratio in the case is unity and the effective resistance connected is 0. input Reactiveis the sum of motor and inverter reactive power. The rotor current is non-sinusoidal. Similarly when the chopper is always ON. S’ = S R’ +R’ 2 ex R’ 2 Where . What are the disadvantages and advantages of chopper controlled resistance in the rotor circuit method ? The method is very inefficient because of losses in the resistance. The time ratio in this case is zero and the effective resistance connected in R. Because of the increased rotor resistance. The value of R connected across the chopper is effective for all phases and its value be relatedcan the resistance to be connected in each phase if the conventional method has to been The speed control range is limited b y the used. 110. 108. in the chopper do es not beco me effective due to circuit L. drive has a poor power power throughout the range of its optio factor ns. R’ 2 R’ = Rotor resistance ex = Resistance included The external resistance can be added very conveniently to the phases of a slip ring rotor. It is suitable for intermittent loads such as elevators. in particular the motor has very poor efficiency.106 Give the equation of slip of the motor . 107. A smooth transition is possible . the supply is always connected to the resistance R. Give the features of static scherbius drive The torque pulsations and other reactions are minimal. How is the range of speed control increased? The range of speed control can be increased if a combination o f stator voltage control rotor and resistance control is employed. They harmonics of the rotor current producepulsations. Hence by varying time the ratio from 0 to 1. When the chopper is always OFF. At low speeds. How is the resistance in the output terminals of a chopper varied? The resistance connected across the output terminals o f a chopper can be varied form O to R by varying the time ratio of the chop per. Instead of using a high resistance rotor. These have a frequency which is six times the slip torque frequency.C. Whyspeed. What is the function of inductance L and resistance R in the chopper resistance circuit? A smoothing inductance L is used in the circuit to maintain the current at a constant Any short value. resistance. 112. the value of resistance can be varied from R to time O. can be A cycloconverter allows power flow in either direction making the static sherbets drive operate at and supper synchronous both sub speeds. additional slip power is injected into the rotor circuit . in applications requiring one quad rant operation. The additional advantages are that the drive system has D. of speed control is limited near. What are the causes of harmonic currents in static Kramer drive? The rectification of slip power causes harmonic currents in the rotor. 114. 117. large air blowers. step-down transformer has essentially two functions: besides improving the The line power factor. What is the use and functions of step down transformer is static Kramer drive? For a restricted sp eed range closer to synchro nous speed. the power rating becomes lower with a more restricted range of speed control. it also helps to reduce the co nverter power ratings. and60 sub synchronous range of speed control through a converter cascade is know as static Kramer drive. mine ventilators. where as for the case of speed above synchronous speed.C.C. using suitable switching . The range drive system is very efficient and the converted p ower rating is low because t has to handle only the slip power.C. Give the four modes of operation of a Scherbius drive The four modes of operation of static Scherbius drive are. the machine losses are increased and some of harmonic torque is produced. line by the inverter. the Kramer electrical drive system is used . A step up transformer may be interposed between the lines and the converter. 119. centrifugal pumps and any other mechanisms including pump s drives of hydraulic dredgers require speed adjustment from 15 to 30% below or above normal . If the induction motor is of the range in comparatively big KW) it becomes uneconomical to adjust speed by mean’ s pf external size (100 to 200 resistances due to copper losses as slip power is wasted as heat in the retort circuit resistance. the system power factor can be further improved by using a step –down transformer. and these harmonics are reflected to the stator by the transformer action of the machine. machine like characteristics and the control is very simple. How is the speed co ntrol obtained in static Kramer drive? For sp eed control below synchronous speed. Each harmonic current in the rotor will create a amount reading filed and its direction of rotation will depend on the order pf the magnetic harmonic. is 118.What drive? static Kramer Instead of wasting the slip power in the rotor circuit resistance.from sub to sup er synchronous speeds without any commutation problems. These can be employed for drives where at least one electrical barking is required. What are the advantages of static Kramer drive? The static Kramer drive has been very popular in large power pump and fan-type where thedrives. to reduce the voltage rating of the converter.Where is Kramer electrical drive system used? Some continuous rolling mills. Sub synchronous regeneratio n Super synchronous motoring Super synchronous regeneration . 121. 120. As a result. In fact. Sub synchronous motoring. 115. till now. What is the use of sub synchronous converter cascades? Sub synchronous converter cascades have been used. but b elow the synchronous speed. it can be converted to pumped back to the line. The harmonic currents are also injected into the A. In these case . the slip power is pumped back to the sup ply. where slip power recovery takes places. Speed reversal is not possible. The slip power controlled drive that permits only a Hz A. 116. A four quadrant operation can also be made possible in these cascades. D. can operated at any power factor by controlling the field be current. The line therefore supplies slip power into stator input power. motor. What is the difference between an induction motor and synchronous motor? An induction motor operates at lagging power factor and hence the converter supplying the same must invariable is a force commutated one. the phase sequence of slip frequency is addition reversedslip current – induced rotating magnetic filed is opposite to that of the that the so stator. c. servo drives. Synchronous motors were mainly used in constant speed app lications. synchronous True mode Self-controlled b. High power factor Low sensitivity to supply voltage d. Give the use of synchrono us motors. When a wound filed mo tor is started as an induction motor. Sometimes rotor may also be free from slid ing contacts (slip rings). on the other hand. through slip rings. their use 124. advantages of PMSM The b. A synchronous motor. In case of a permanent magnet motor. depending upon the situation. the low starting current. 128 Give the advantages and applications of . At this condition. such as inverters and cycloconverters. The slip power supplements the air gap power for the total mechanical power output. High efficiency c. using the information of rotor position or thrusters stator . in which rotor is fed from a rectifier rotating with case the rotor. It is supplied with D. Wound field synchronous b. the field cannot be ‘turned off’ . control Variable frequency control may employ and of the two a. 129 Give the uses of a hysteresis synchronous . motors. lled ? A machine is said to be self controlled if it gets its variable frequency from an whose inverter are freed in a sequence.C. 125. mode 131 Which machine is said to be self contro . has allowed in draft fane. Small hysteresis motors are extensively used in tape recorders. List out the commonly used synchronous motors. Permanent magnet synchronous motors d.C. 130 Mention the two modes emplo yed in variable frequency .122. The development of semiconductor variable frequency sources. fans and compressors. motors. Howetc. it finds application in high inertia application of such as gyrocompasses and small centrifuges. The rotor. Commonly used synchronous motors are. Synchronous reluctance synchronous motors. Hysterias e. the shaft speed increases beyond the synchronous speed. The ap plicatio n of PMSM is that it is preferred of industrial applications with large duty cycle as such pumps. field is kept off. PMSM. 127 Mention the main difference between the wound field and permanent magnet . the stator and rotor of the synchronous motor are supplied? The stator of the synchronous motor is supplied from a thyristor power converter capable of pro viding a variable freq uency supply. 126. main line traction. office equipment and Becausefans. may be constructed with slip rings. variations. modes. motors. 123. How is the static Scherbius drive operated in super synchronous motoring mod e? In super synchronous motoring mode. are. where it confo rms to a conventional rotor. the slip becomes negative and the slip power is absorbed by the rotor. in which case regeneration is straight forward.C. In this case an ad ditional phase controlled converter is required line on the side. 139 What are the disadvantages of VSI fed synchronous moto r . main-line traction and aircraft test facilities. drive. 137 How the machine op eration is performed in self-controlled . 132 What is Commutator Less Motor . When a PWM inverter is used. frequency supply. . frequency supply. 135 List out the advantages of load commutation over forced . variable voltage. A self controlled synchronous motor is a substitute for a D. link converter and . rotating filed speed should be the same as rotor speed. If this angle of the thyristor. 134 Define load . blowers. Motors bo th under steady state and dynamic conditions and therefore is called commutator less motor(CLM).C. motor. In the former a rotor p osition sensor is employed which measures the rotor position with respect to the stator and sends pulses to the thyristors. motor drive and finds application where a D. supply to the inverter may source be obtained form a diode rectifier. A normal VSI with system conduction of thyristors required 180 forced commutation and lo ad commutation is not possible. 140 How is PNM inverter supplied in VSI fed synchronous . Safe commutation is assured if this angle has a minimum value eq ual to the turn off angle f the thyristor.C. Cycloconverter is a single stage conversion device which provides a Variable variable voltage. steel rolling mills. mode? For machine operation in the self-controlled mode. These machines have stability behaviors. commutation has a number of advantages over forced Load commutation It does not require commutation circuits Frequency o f operation can be higher operate at power levels beyond the capability of forced It can commutation.C. which limits the speed range and power output. The D.C. They d o no t fall o ut of step and do no t have oscillatory better behaviors. commutation failure occurs. drive? VSI synchronous motor drives might impose fewer problems both on machine as o on the well as design.C. Thus frequency of the inverter is decided by the rotor output speed. This condition is relaised by making frequency of voltage induced in the armature. cycloconverter? link co nverter is a two stage conversion device which provides a variable D. commutation? between the lead angle of firing and the overlap angle is called the margin The difference of angle commutation. two cases may arise the inverter may be fed from a constant motor? D. commutation n of thyristors by induced voltages pf load is known as load Commutatio commutation. application o f self controlled synchronous 133 Give the . 141 What is D. Firning pulses are therefore generated either by comparison o f motor terminal voltages or by rotor position sensors. ( CLM)? The self controlled motor has properties of a D. commutation. motor is objectionable due to its mechanical commutator. Some prominent applications o f load commutated inverter fed synchronous motor drive are high speed and high power drives for compressors.C.voltages. 136 Give some application of load commutated inverter fed synchronous motor . 138 What is meant by margin angle of . as in normal synchronous motors. conveyers. Application o f this type of drive is in gas turbine starting pumped hydroturbine starting.K Dubey pg.no. The machine size is large Due to o verexciting it is c.41 ‘Fundamentals of Electric drives’ by G. [8M] Ans: First Motoring Quad rant-Forward .51 3. A cycloconverter requires large number of thyristors and ts control circuitry is complex. etc.37 ‘Fundamentals of Electric drives’ by G. underutilized. mo . b. mine heists. [8M] Ans: 1. 144 Give the application o f CSI fed synchronous .Solid State Drives 1. pump and blower drives.Kinds of enclo sures ‘Solid state drives’ by V. e.no.Requirement of a drive motor wer losses &heating of 2. Give a brief explanation on the selection of drives. low speed reversing mils requiring rapid acceleration and deceleration. motor are low cost.Thiyagarajan pg. Give a brief explanation on the rating of drives.C. Refer: 2. motor? Sometimes when the power is small an auxiliary motor can be used to run up the synchronous motor to the desired speed.g. 146 What is the use of an auxiliary . drives for reversing mills. tor? The brushless D.Kinds of Motors 3. 143 What are the applications of . BIG QUES TIONS AND ANSWE R KE Y EE1351. etc. simplicity reliability and good performance.C.Heating &cooling of a Electric motor ‘Solid state drives’ by V. motor. Typical applications are large gearless drives. 145 What are the disadvantages of machine .no.142 What are the disadvantages of cycloconverter? .Selection of Electric Motors 2.Thiyagarajan pg. Converter grade thyristors are sufficient but the cost of the converter is high.51 2. motor is in fact an inverter-fed self controlled permanent synchronous motor drive.K Dubey pg. Refer: 2.C. commutation? The disadvantages of machine commutation a. are.no.Po motors 3. The advantages of brushless D. Limitation on the speed range.Explain the four quadrant operation of electric drives. 147 What are the advantages of brushless D. [8M] Ans: 1. cycloconverter? A cycloconverter drive is attractive for law speed operation and is frequently employed in large. 151 diagram of chopper drive for Regenerative braking of DC ii) Circuit motor m a a . Ans: Circuit diagram of f fully controlled 1 rectifier Mode of operation under Motoring – Continuous conduction mode Discontinuous co nduction mode of operation under braking – Continuous conduction Mode mode Discontinuous co nduction mode2V Va = cos a m p w pk k 2 Refer: ‘Power semico nductor controlled drives’ pg. Explain the motoring op eration and braking operation of three p hase fully controlled rectifier control dc separately excited mo tor with aid of diagrams and waveforms.233 by G.103 7.R a Ta by G.K Dubey 6.R T 2 k k Refer: ‘Power semico nductor controlled drives’ by G.K Dubey 5.33 ‘Fundamentals of Electric drives’ by G.Pm. frequency Refer: ‘Power semiconductor co ntrolled drives’ pg.no. = dV .14 4.K Dubey pk k 2 Refer: ‘Power semico nductor controlled drives’ pg. waveforms and speed-torque motor curves.Explain the constant torque and constant HP operations. Also obtain the expression of for motor terminal voltage and speed. to rque and constant power • constant operation Wsl with respect to ‘a’ per unit • V.Second Quadrant-Fo rward Braking Third Quadrant-Reverse Motoring QuadrantFourth Reverse Braking T-Wm characteristics Refer: ‘Solid state drives’ by V. Ans : • V/f operation. Explain the operation of chopper for forward motoring and braking control of separately excited dc with aid of diagrams. Ans: Circuit diagram of f fully controlled 3 rectifier Mode of operation under Motoring – Continuous conduction mode Discontinuous co nduction mode of operation under braking – Continuous conduction Mode mode Discontinuous co nduction mode3V Va = cos a m p w m = 3 V m cos a .K Dubey pg.no.Is.no.R a Ta by G. 2.72 m = 2 V m cos a . Describe the operation of f fully controlled rectifier control of DC separately excited motor 1 and obtain the expression of motor speed for continuous and discontinuous modes of operations.no. Ans: i)Circuit diagram of chopp er drive for forward motoring Waveforms of motor terminal & current – Continuous conduction Discontinuous conduction a)Duty interval b)Freewheeling interval equivalent circuits Va= dV.Thiyagarajan pg.K Dubey pg.no.no.T. no.K Dubey pg. Ans: Circuit diagram of f half controlled 1 rectifier us conduction Mod e o f operation under Moto ring – Continuo mode Discontinuous mode Va = V w =V conduction (1+co a ) p s m m m (1+ cos a ). Also obtain the expression for motor terminal voltage and speed.164 diagram of chopper drive for Regenerative braking of DC ii) Circuit motor rms of motor terminal & current – Continuous Wavefo conduction Discontinuousconducti on a)Energy sto rage interval b)Energy transfer interval equivalent circuits Va= (1d)V m a a T P curves m .K Dubey pg.no. Explain the closed loop speed control of DC drives.no. Ans: Class-C Circuit diagram & operation – Mod e I. Explain the two Quadrant operation by using Class-D and Class-C chopper with aid of diagrams and waveforms . II Class-D Circuit diagram & operation – Mode I. Blo ck diagram. controlled drives’ Refer: ‘Power semico nductor pg.159 by G. IV Refer: ‘Power semiconductor contro lled drives’ by G.101 by G. Explain the Four Quadrant operation by using Class-E chopper with aid of diagrams and waveforms.K Dubey 9.K Dubey Refer: pg.184 11. Explain the operation of f half controlled rectifier control of dc separately excited motor 1 for continuous and discontinuo us modes of operations with aid of diagrams and waveforms.R a T a pk k 2 Refer: ‘Power semico nductor controlled drives’ pg. = dV .K Dubey 10.no.rg curves.R T 2 k k Refer: ‘Power semico nductor controlled drives’ by G.Waveforms of motor terminal & current – Continuous conduction Discontinuousconducti on a)Energy sto rage interval b)Energy transfer interval equivalent circuits Va= (1d)V Refer: ‘Power semico nductor controlled drives’ pg.164 m - by G.175 12.no.no.K Dubey pg. 172 .169.II.III.no.K Dubey 8.IV Refer: ‘Power semiconductor controlled drives’ by G. diagram of chopper drive for forward Ans: i)Circuit motoring Waveforms of motor terminal & current – Continuous conduction Discontinuous conduction a)Duty interval b)Freewheeling interval equivalent circuits Va= dV. Ans: Circuit diagram & operation – Mode I. operation – i)drive with current limit Ans: control with inner current loop ii)drive control ‘Power semiconductor contro lled drives’ by G. Explain the operation of cho pper controlled dc series motor for motoring and braking with circuit diagrams and waveforms. 2 0 rpm Refer: ‘Fundamentals of Electric d 9. d=0. So lution: Va = i) 3V ii) a) cos a . The 15.K Dubey pg. speed iii)Motor a =16 0 and rated for Solution: E at rated operation 0 torque. Ans : • Ac voltage controllers circuit. 1500 rpm 50 A separately excited motor with armature resistance of .139 .50 Hz. 960 rpm and 200 A separately excited dc motor has an armature resistance of 0. d=0. Explain the of operation constant V/f control of induction motor and draw the . maximum duty ratio of chopper is limited to 0. e. 875 rpm.no.274 • by G. E=V0 i) a =2 ii a =12 0 iii)N=-893.K Dubey 17.K Dubey pg. Calculate the transformer turns ratio.06 a 1 f fully controlled rectifier with an ac source voltage of 220 V.6 16 iii)N=962 rpm. A star. Solution: E at rated operation E=VIaRa=226 v i)Va = d= Va/ V . Determine the value of firing angle when motor is running at 1200 rpm & rated a) torque b) When motor is running at (-800) rpm & twice the rated torque. ii) duty cycle ratio of chopp er for braking operation at rated torque and 350 rpm.4 KW Refer: ‘Fundamentals of Electric drives’ by G.3 delta connected transformer is used to feed the armature so that motor terminal voltage eq uals rated voltageconverter firing angle is when zero.no.5 fully controlled rectifier.6 5 b) a= 104. A 2 00 V. Available ac source has a line voltage of 440 V. d= Va/ V . Discuss in brief abo ut the control of an inductio n motor by stator voltage variation 3 using phase voltage controller. Assuming m continuous conduction. Calculate i)firing angle for rated motor torque and 750 rpm ii)firing angle for rated motor torque and (– 500)rpm. t/f ratio=1.20 Refer: ‘Fundamentals of Electric drives’ pg. 50 Hz. A 230 V. Assume continuous cond uction.02 motor is fed from a chopper which p rovides both mo toring and braking operations. i)Calculate ratio of chopper for motoring operatio ns at 350 duty cycle rpm.13.no.117 IaRa=191 v 14. Calculate the maximum permissible permissible motor speed and power fed to the source. d.3 rives’ ) by G. power= VaIa= 87. 6 ii)Va = E-IaRa.star and delta quadrant ac voltage controllers circuit & o • Four peration Speed-torque curves loop speed co • Closed ntrol Refer: ‘Power semiconductor controlled drives’ pg. It is fed fro 0.559 0 f m turns 0 p a =34. 150 A separately excited motor has an armature resistance of . The source has a voltage of 230 V.K Dubey 16.no. is fed from a 0. A 220 V. Assuming continuous conduction.37 E+IaRa.129 by G.95 and iii) If maximium motor current is twice the rated. I/C. derive the expressions Also used.K Dubey pg.K Dubey pg. 3f ind i)the Evaluate motor current to rated motor current maximum ratio. 335 20.Pm.no.T. In a pump drive.S.Is. derive an expression fortorque-speed characteristics.no.2 79 23.15. Stator voltage controlled uction motor is used for driving the pump. Describe briefly the PWM inverter fed induction motor drive.no. operation – dynamic drive braking Regenerative braking Refer: ‘Power semiconductor controlled drives’ by G.no.no. : V/f operation.K Dubey pg. Ans: PWM inverter circuits Control signal generation. based on this expression.waveforms Ans . frequency Refer: ‘Power semiconductor controlled drives’ by G.sinusoidal PWM Operatio n Refer: ‘Power semiconductor controlled drives’ by G.2 98 19.316.K Dubey pg. Current source inverter Ans: circuit CSI variable frequency drives – Block diagram. 226 • 21.no. Imax Ans: = 2 1. Discuss the operation of an open-loop variable frequency voltage source inverter induction motor fed drive. Explain the operation of induction motor fed by current source inverter. to rque and constant power constant operation Wsl with respect to ‘a’ per unit • V.K Dubey pg.233 18. the fluid flow is to be varied from full down to 50 percent.325.I fed induction motor drives? Ans: VSI fed IM drive Block diagram.S. Starting from the approximate equivalent circuit. operation – dynamic braking Regenerative CSI fed IM brakingBlock diagram. If full load slip of the moto r is 0. operation Refer: ‘Power semiconductor controlled drives’ b y G.K Dubey pg.169 Irated 3 v 3 (1-s ra t e d) vs ra t e d Expression for Imax/ Irated Refer: ‘Power semiconductor controlled drives’ by G. i) when stator vo ltage is varied (keeping frequency constant) the rotor resistance is ii) when varied? Ans : • performance of f IM & equivalent 3 circuits speed-torque curves • expression for torque T Refer: ‘Power semiconductor controlled drives’ by G.206. 336 22. How does the this characteristics change. How is dynamic/ regenerative braking achieved in a variable frequency V. Ans: Block diagram Operatio n • • . Modified operation Kramer drive – diagram.6 .362. 50 Hz.2) = 1 .no.2 35 25.Refer: ‘Power semicond uctor controlled drives’ g. Discuss o n the power factor and locus scheme diagram of • • .no. (8M) ‘Power semicond uctor controlled drives’ by G.no.no. Derive an expression for the torque T for the rotor resistance control using the chopper scheme. Irs’ (a=0.K Dubey pg. 4 pole induction motor has the following parameters in ohms p er phase referred to the stator.2) = 2. Determine the fo llowing for an operating frequency of 15 Hz.no. star connected.31 5 by G. ii) The starting torque and rotor current in terms of their values at the rated frequency . Ans : • Circuit diagram • Operation.18 The motor is connected by the variable frequency control with a constant (V/f). • Modified operation Refer: ‘Power semiconductor controlled drives’ by G.K Dubey pg. Explain schematic diagram two method s of super synchronous speed control of induction motor under slip power recovery scheme. So lution: i ) Motoring Tmax (a=0. operation ii) Block d iagram. 68 Tmax (a= 1) Braking Tmax (a=0.034 0. 380 26. 35 6 27.K Dubey p 24. operation Refer: ‘Power semiconductor controlled drives’ by G. What are its applications. What are slip ring the advantages and disad vantages of slip po wer recovery scheme? Ans : Super synchronous speed control operation Scherb ius drive – diagram. A 3 f . 46 Tmax (a= 1) ii) Ts (a=0. Refer: 356 28. ii) Compare this scheme of control with the slip power recovery scheme. Explain the closed loop scheme of i) speed control of poly phase induction motor by ro tor resistance contro l. Rs =Rr’ = & Xs =Xr’ = 0. i) The breakdown torque as a ratio of its value at the rated frequency for motoring and braking.K Dubey pg.With block diagram explain the closed loop operation of slip power recovery of induction motor.K Dubey pg.2) = 0.K Dubey p g.72 Ts (a=1) Irs’ (a= 1) Refer: ‘Power semiconductor controlled drives’ by G. 3 83 29. equivalent circuits • Derivation for torque Refer: ‘Power semiconductor co ntrolled drives’ by G.no. Ans: i) Block diagram. State the merits and demerits of rotor resistance control of wound rotor induction motor.2) = 0 . Operation . . The filter inductor has a resistance of 0. controlled mode Ans: Self diagram. Ans: Block diagram Operatio n Refer: ‘Power semiconductor co ntrolled drives’ by Murphy and Turnbull 34. 9 60rpm. Explain the working of a self controlled synchronous mode fed from a three phase inverter. The filter resistance is . 6 pole . Dtermine that value of external the resistance. the break-down torque is obtained at standstill. 50 Hz.5 1. = Rs . For a duty cycle of 0. Explain with schematic diagram of sub-synchronous speed control of slip -ring Inductio n Motor under slip power recovery scheme.no.no.6 Stator the rotor resistance. i)Describ e the self control of synchronous moto r fed from VSI. Brushless Operation Refer: ‘Power semiconductor co ntrolled drives’ by G. (16) Ans : • Sub synchronous sp eed contro l operation • static Scherbius drive – diagram. 418.supply current for constant to rque operation of slip power recovery scheme.01 is chosen such a =0. The stator to rotor turns ratio is 2. 960 rpm. This motor 5 =0.no . Write short notes on Brushless Excitation system.K Dubey pg. Derive the expression for the torque. A 3 f . 400 V. Why a self controlled synchronous motor is free from hunting oscillations? Ans: Rotor position encoder operation -diagram AC & DC motor –diagram.no .7 and a speed of 600 4 rpm.01 external resistance is The . evaluate the torque developed. X1= X2= . has: Rs=0. The motor speed is controlled by 35 static =0. Refer: 407 35.angle control’ based self – controlled us motor synchrono drive. 50 Hz. ii)Compare the above two schemes. Xm= 0. block diagram factor and locus • Power diagram Refer: ‘Power semico nductor controlled drives’ by G.98 Nm ‘Power semiconductor controlled drives’ by G.1 .K Dubey pg. Discuss about separately controlled synchrono us motor fed from VSI.connected wound ro tor Ind uction Motor 32. (8M) Ans: diagram (4M) Operation (4M) ‘Power semiconductor co ntrolled drives’ by G. 365A 440 V. Ans : • Closed speed control o peration . Explain the operation of a ‘torque. Solution: T= 258 . star connected. wound rotor induction motor has the following parameters per phase referred to the stator. star.no.6 Xm=20 is controlled by a rotor-chopper scheme.37 Refer: ‘Power semiconductor controlled drives’ by G.K Dubey pg.K Dubey pg. Xr’ and .no. Refer: ‘Power semiconductor controlled drives’ by 366 31. operation • Expression for torqueG. The value of the external resistance 0. Solution: R=1. Rr’ . 423 36. 368 30.K Dubey p g.3 to rotor turns ratio is 2.K Dubey p g. Refer: 365 33. 380. K Dubey p g.no. Operation Refer: ‘Power semiconductor co ntrolled drives’ by G. Refer: 421 38. 423. Explain the operation of a ‘power factor control’ based self – controlled us motor synchrono drive. Block Ans: d iagram Operatio n Refer: ‘Power semiconductor co ntrolled drives’ by Murphy and Turnbull . 412 37.no. Ans: VSI and CSI fed Synchronous motor drives Block diagram (8M) Operation (8M) ‘Power semiconductor co ntrolled drives’ by G.True synchronous mode diagram.K Dubey p g. Explain the closed loop control scheme of adjustable speed synchronous motor drive .