2. A 50 Hz, 6 pole, 3 phase induction motor runs at 970 rpm. Find slip. Rotor Speed, N r =970 r.p.m 120f. Synchronous Speed, N s 1000

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1 1 Unit 3 - Induction Motor PAT - A 1. Why the rotor lot are lightly kewed in quirrel cage IM? (or)why are the clot on the cage rotor of induction motor uually kewed? The rotor bar are not parallel to the haft but lightly kewed for the following purpoe, i. It help to make the motor run quietly by reducing magnetic hum and ii. It avoid the tendency of magnetic locking between tator and rotor teeth. iii. It give more uniform torque in running.. A 50 Hz, 6 pole, 3 phae induction motor run at 970 rpm. Find lip. otor Speed, N r =970 r.p.m 10f Synchronou Speed, N 1000 r. p. m p 6 N N r Slip, 0. 03( or) 3% N Under what condition, the lip in an induction motor i (a) Negative (b) Greater than one. The lip of the induction motor i negative when it i operated above the rated peed (a induction generator). The lip i greater than one when the motor i operated at brake mode. 4. What are the two fundamental characteritic of a rotating magnetic field? i. The reultant flux i contant i.e, 1.5 time the maximum value of the flux due to any phae. ii. The reultant flux rotate around the tator at ynchronou peed given by, 10f N r. p. m p 5. Define lip of an induction motor. The difference between the ynchronou peed N and the actual peed N r of the rotor i known a lip. N N r % Slip 100 N 6. What are the merit and demerit of double quirrel cage induction motor? Merit (or) Advantage: i. Higher tarting torque ii. Wide range of torque-peed characteritic can be obtained Demerit (or) Diadvantage: i. Cotlier about 0-30% of ingle cage rotor ii. Effective rotor reitance i high, o rotor heating at the tarting i more. iii. Due to higher effective leakage reactance, the powerfactor i reduced. K.ajkumar, Aociate Profeor/EEE, Dhanalakhmi Srinivaan Intitute of Technology, Samayapuram.

2 7. How do change in upply voltage and frequency affect the performance of a 3 phae induction motor? The torque developed by the induction motor i proportional the voltage applied ( T α E ) The peed of the motor i inverely proportional to the upply frequency. (N α 1/f). 8. The tarting torque of a quirrel cage induction motor cannot be altered when the applied voltage i contant. Why? ke T t From the above relation, i contant and i independent of. So, T t i only depending on E. Therefore the tarting torque cannot be altered for contant upply voltage, where E αv. 9. A 3-Phae, 4 pole, induction motor operate from a upply whoe frequency i 50Hz. Calculate the frequency of the rotor current at tandtill and the peed at which the magnetic field of the tator i rotating. otorcurrent Frequency,f f. At tandtill, =1. Therefore, f =50Hz. 10f Speed of rotation of magnetic field, N 1500r.p.m p Write down the condition to get maximum torque under running condition. The condition for maximum torque of 3 phae induction motor i, 11. Define Cogging. With the equal number of tator and rotor lot, the peed of all the harmonic produced by the tator lotting coincide with the peed of rotor harmonic. Thu the machine refue to tart due to magnetic locking. Thi i known a cogging. Therefore the number of tator lot hould not be equal to the number of rotor lot. 1. Define Crawling. The tendency of the motor to run tably at peed a low a one-eventh of it ynchronou peed i called crawling. The torque produced during thi crawling i a harmonic induction torque. 13. How the lip doe vary with load? The greater the load, the greater the lip. 14. What are the advantage of double cage induction motor? i. Starting torque i high ii. Low tarting current hence uitable for direct on line tarting iii. Wide range of torque-lip characteritic can be obtained 15. What i an Induction generator? What are it limitation? When a 3-phae induction motor made to run at a peed higher than it ynchronou peed by mean of prime mover, it become 3-phae induction generator. Limitation: i. It need reactive power from the upply network. ii. It output voltage and frequency cannot be controlled. iii. It alway operate at a leading powerfactor. K.ajkumar, Aociate Profeor/EEE, Dhanalakhmi Srinivaan Intitute of Technology, Samayapuram.

3 3 PAT B 1. a. Explain the principle of operation of 3-phae induction motor and explain how the rotating magnetic field i produced by three-phae current. (10) Principle of Operation: Conider a portion of 3-phae induction motor a hown in Fig. (8.13). The operation of the motor can be explained a follow: i. When 3-phae tator winding i energized from a 3-phae upply, a rotating magnetic field i et up which rotate round the tator at ynchronou peed N (=10f/p). ii. The rotating field pae through the air gap and cut the rotor conductor, which a yet, are tationary. Due to the relative motion between the rotating flux and the tationary rotor, e.m.f are induced in the rotor conductor. Since the rotor circuit i hort-circuited, current tart flowing in the rotor conductor. iii. The current-carrying rotor conductor are placed in the magnetic field produced by the tator. Conequently, mechanical force act on the rotor conductor. The um of the mechanical force on all the rotor conductor produce a torque which tend to move the rotor in the ame direction a the rotating field. iv. The fact that rotor i urged to follow the tator field (i.e., rotor move in the direction of tator field) can be explained by Lenz law. According to thi law, the direction of rotor current will be uch that they tend to oppoe the caue producing them. Now, the caue producing the rotor current i the relative peed between the rotating field and the tationary rotor conductor. Hence to reduce thi relative peed, the rotor tart running in the ame direction a that of tator field and trie to catch it. otating Magnetic Field (MF): Figure 1 how three-phae winding diplaced in pace by 10º, are fed by three-phae current, diplaced in time by 10º, they produce a reultant magnetic flux, which rotate in pace a if actual magnetic pole were being rotated mechanically. The inuoidal flux due to three-phae winding i hown in Figure. Let the maximum value of flux due to any one of the three phae be Φ m. The reultant flux Φ r, Figure 1 Three Phae Winding in motor K.ajkumar, Aociate Profeor/EEE, Dhanalakhmi Srinivaan Intitute of Technology, Samayapuram.

4 4 at any intant, i given by the vector um of the individual fluxe, Φ 1, Φ and Φ 3 due to three phae. We will conider value of Φ r at four intant 1/6 th time-period apart correponding to point marked 0, 1, and 3 in Figure. Figure Three Phae otating Sinuoidal Fluxe and their 10 o diplaced vector eferring to Figure, a. At =0 o, , m and 3 m The flux Φ i drawn in a direction oppoite to the direction aumed poitive. Therefore, o r m co 3m m b. At =60 o and Point 1 in Figure, m m and 3 0, Therefore, o r m co 3m m It i clear that the reultant flux i again the ame and rotated in clockwie direction through an angle of 60 o. c. At =10 o and Point in Figure, m, 0 and 3 m Therefore, o r m co 3 m m It i found that the reultant flux i again the ame and rotated in clockwie direction through an angle of 60 o. d. At =180 o and Point 3 in Figure, , m and 3 m 3 The reultant flux, r m and ha rotated clockwie through an additional angle 60 o. K.ajkumar, Aociate Profeor/EEE, Dhanalakhmi Srinivaan Intitute of Technology, Samayapuram.

5 5 The important characteritic of the rotating magnetic field, 3 i. The reultant flux i of contant value r m due to any phae. ii. The reultant flux rotate around the tator at ynchronou 10f peed given by N p b. Dicu the different power tage of an induction motor with loe. (6) The electric power input given to the tator of an induction motor i converted into mechanical power output at the haft of the motor. The variou loe during the energy converion are: 1) Fixed Loe: a. Stator Iron Lo b. Friction and Windage Lo The rotor iron lo i negligible becaue the frequency of the rotor current i very mall under running condition. ) Variable Loe a. Stator Copper Lo b. otor Copper Lo The above figure how that the electric power fed to the tator uffer loe and finally converted into mechanical power. The important point to be noted from the diagram are, i. The tator input P in = Stator output (otor Input) P + Stator I Lo+Stator Iron Lo ii. otor input P = Stator Output It i becaue tator output i entirely tranferred to the rotor through the airgap by electromagnetic induction. iii. Mechanical Power Developed, P m =P g -otor Copper Lo. Thi mechanical power available i the gro rotor output and will produce a gro torque T g. iv. Mechanical haft output, P h = P m - Friction and Windage Lo. Mechanical power available at the haft produce a haft torque T h. K.ajkumar, Aociate Profeor/EEE, Dhanalakhmi Srinivaan Intitute of Technology, Samayapuram.

6 6 K.ajkumar, Aociate Profeor/EEE, Dhanalakhmi Srinivaan Intitute of Technology, Samayapuram.. a. Derive an expreion for the torque of an induction motor and obtain the condition for maximum torque. (8) The torque developed i proportional to the armature current, flux per pole and the powerfactor. co I T or co I k T where, I =otor current at tandtill ϕ = Angle between rotor e.m.f and rotor current k=contant At tandtill, the rotor e.m.f E i proportional to the flux ϕ. Therefore, co I ke T Here, E Z E I and Z co Then the torque, E ke T ke T --- (1) At the maximum torque, 0 d dt. 0 ke d d d dt 0 ke ke 0 ke 0 or or max ---- () Therefore the maximum torque i obtained by ubtituting the lip at maximum torque, max. ke E k E k T max max max ke T max ---- (3) From the equation (3), it i concluded that, The maximum torque i independent of rotor reitance

7 7 The maximum torque i obtained when the rotor reactance equal it reitance. Maximum torque varie inverely a tandtill reactance. Hence, it hould be kept a mall a poible. Maximum torque varie directly a quare of the applied voltage. b. Draw and explain the lip-torque characteritic of a typical 3-phae induction motor. Mark the tarting and maximum torque region on the diagram o drawn. (8) The motor torque under running condition i given by, T ke A curve drawn between the torque and lip, for a particular value of rotor reitance i called torque-lip characteritic. Figure hown below give a et of torque-lip characteritic for a lip-range from 0 to 1 for variou value of rotor reitance. Figure 3. Torque - Slip Characteritic From the Figure 3, the following point to be noted, i. At lip, = 0, torque, T = 0 o that torque-lip curve tart from the origin. ii. At normal peed, lip i mall o that i negligible a compared to. Then the torque will be proportional to, /. i.e, T and finally T when i contant. Hence torque lip curve i a traight line from zero lip to a lip that correpond to fullload. iii. A lip increae beyond full-load lip, the torque increae and become maximum at max = /. Thi maximum torque in an induction motor i called pull-out torque or break-down torque. It value i at leat twice the full-load value when the motor i operated at rated voltage and frequency. iv. A the lip increae further with increaed load, then become negligible compared to. Therefore, for larger value of lip, T or T 1. Hence, the torque-lip characteritic i a rectangular hyperbola. It i important to undertand that the load K.ajkumar, Aociate Profeor/EEE, Dhanalakhmi Srinivaan Intitute of Technology, Samayapuram.

8 8 increaed further decreae the torque beyond the maximum torque and eventually top at one point. v. It i alo een that the maximum torque doe not depend on, but it decide the value of lip at which the maximum torque occur. 3. a. Decribe the contruction and principle of operation of a 3-Phae induction motor with neat ketch. (10) A 3-phae induction motor ha two main part (i) tator and (ii) rotor. The rotor i eparated from the tator by a mall air-gap which range from 0.4 mm to 4 mm, depending on the power of the motor. Stator: It conit of a teel frame which encloe a hollow, cylindrical core made up of thin lamination of ilicon teel to reduce hyterei and eddy current loe. A number of evenly paced lot are provided on the inner periphery of the lamination.the inulated connected to form a balanced 3-phae tar or delta connected circuit. The 3- phae tator winding i wound for a definite number of pole a per requirement of peed. Greater the number of pole, leer i the peed of the motor and vice-vera. When 3-phae upply i given to the tator winding, a rotating magnetic field of contant magnitude i produced. Thi rotating field induce current in the rotor by electromagnetic induction. Figure 4 Stator otor: The rotor, mounted on a haft, i a hollow laminated core having lot on it outer periphery. The winding placed in thee lot (called rotor winding) may be one of the following two type: (i) Squirrel cage type (ii) Wound type i. Squirrel cage rotor: It conit of a laminated cylindrical core having parallel lot on it outer periphery. One copper or aluminum bar i placed in each lot. All thee bar are joined at each end by metal ring called end ring a Figure 5 Squirrel Cage otor hown in Figure 5. Thi form a permanently hortcircuited winding which i permanent. The entire contruction (bar and end ring) reemble a quirrel cage and hence the name. The rotor i not connected electrically to the upply but ha current induced in it by tranformer action from the tator. Thoe induction motor which employ quirrel cage rotor are called quirrel cage induction motor. Mot of 3-phae induction motor ue quirrel cage rotor Figure 6 Slip ing otor a it ha a remarkably imple and robut contruction enabling it to operate in the mot advere circumtance. However, it uffer from the diadvantage of a low tarting torque. It i becaue the rotor bar are permanently hort-circuited K.ajkumar, Aociate Profeor/EEE, Dhanalakhmi Srinivaan Intitute of Technology, Samayapuram.

9 9 and it i not poible to add any external reitance to the rotor circuit to have a large tarting torque. ii. Wound rotor: It conit of a laminated cylindrical core and carrie a 3- phae winding, imilar to the one on the tator a hown in Figure 6. The rotor winding i uniformly ditributed in the lot and i uually tar-connected. The open end of the rotor winding are brought out and joined to three inulated lip ring mounted on the rotor haft with one bruh reting on each lip ring. The three bruhe are connected to a 3-phae tar-connected rheotat. At tarting, external reitance are included in the rotor circuit to give a large tarting torque. Thee reitance are gradually reduced to zero a the motor run up to peed. b. Deduce and dicu the equivalent circuit of 3-phae induction motor.(6) The equivalent circuit of 3-phae induction motor can be developed on per phae bai by following the ame procedure a ued for the development of equivalent circuit of tranformer. Let, V 1 =Applied voltage per phae to the tator winding I 1 = Stator current per phae 1 = Stator winding reitance per phae 1 = Leakage reactance of the tator winding per phae E 1 =Induced EMF per phae in tator winding =4.44fϕT 1 K w1 =V 1 -I 1 ( 1 +j 1 ) I 0 =No-load current per phae = I w +I m I m =Magnetizing current per phae I w = Lo component of no-load current per phae E = Induced EMF per phae in rotor winding at tandtill =4.44fϕT K w =I ( +j ) I = otor current per phae = otor winding reitance per phae = Leakage reactance of the rotor winding per phae at tandtill When the motor i running at a lip, then the emf induced in the rotor i E at lip frequency. Hence the rotor ha been repreented by a reitance and a variable leakage reactance (due to lip frequency) with variable rotor voltage E. Figure 7 Per phae Equivalent Circuit of 3-phae induction motor eferring to Figure 7, the rotor current per phae i given by, E E I --- (1) j j K.ajkumar, Aociate Profeor/EEE, Dhanalakhmi Srinivaan Intitute of Technology, Samayapuram.

10 10 Baed on the equation (1), the rotor circuit modified to repreent the rotor reitance with repect to the change in lip a /. Thi modification i done o that the emf induced in the rotor i independent of lip and it become eaier to refer the rotor quantitie to tator. Figure 8 Modified Equivalent Circuit per phae Self induced e.m.f E 1 i induced in the tator winding and mutually induced e.m.f E E KE, where K i the tranformation ratio i induced in the rotor winding. The 1 econdary value may be tranferred to the primary and vice vera. A in the cae of tranformer, it hould be remembered that when hifting impedance or reitance from econdary to primary, it hould be divided by K wherea current hould be multiplied by K. ewriting the equation (1), I K 1 K E j I K K E K j K I K K E K j K I E 1 j Figure 9 Per phae equivalent circuit of 3-phae induction motor referred to tator The equivalent circuit can be further modified o that the hypothetical reitance, i plit into two component: i., the per phae rotor reitance referred to tator itelf, and K.ajkumar, Aociate Profeor/EEE, Dhanalakhmi Srinivaan Intitute of Technology, Samayapuram.

11 11 ii. 1, the electrical equivalent of the mechanical load on the motor and i generally called the load reitance L or the dynamic reitance. The load reitance L depend upon the peed of the motor. Figure 10 Modified Equivalent Circuit referred to tator repreenting rotor and the load reitance The following approximate equivalent circuit i ued a it implifie the analyi of the induction motor. Figure 11 Approximate Equivalent Circuit of 3-phae induction motor 4. a. Write a brief note on double cage rotor induction motor. (8) (or) Explain the advantage of double cage induction motor over ingle cage induction motor a double cage induction motor. (8) The main diadvantage of the quirrel cage induction motor i lower tarting torque. But the lip ring induction motor ha the ability to increae the tarting torque by inerting additional reitance in to the rotor circuit. However uch a procedure cannot be adopted for a quirrel cage motor becaue it cage i permanently hort-circuited. In order to provide high tarting torque at low tarting current, double-cage contruction i ued. Contruction Figure 1 Double Cage Induction Motor K.ajkumar, Aociate Profeor/EEE, Dhanalakhmi Srinivaan Intitute of Technology, Samayapuram.

12 1 The outer winding conit of bar of maller cro-ection hort-circuited by end ring. Therefore, the reitance of thi winding i high. Since the outer winding ha relatively open lot and a poorer flux path around it bar, it ha a low inductance. Thu the reitance of the outer quirrel-cage winding i high and it inductance i low. The inner winding conit of bar of greater cro-ection hort-circuited by end ring. Therefore, the reitance of thi winding i low. Since the bar of the inner winding are thoroughly buried in iron, it ha a high inductance. Thu the reitance of the inner quirrel cage winding i low and it inductance i high. Operating Principle: When a rotating magnetic field weep acro the two winding, equal e.m.f. are induced in each. At tarting, the rotor frequency i the ame a that of the line (i.e., 50 Hz), making the reactance of the lower winding much higher than that of the upper winding. Becaue of the high reactance of the lower winding, nearly all the rotor current flow in the high-reitance outer cage winding. Thi provide the good tarting characteritic of a high-reitance cage winding. Thu the outer winding give high tarting torque at low tarting current. A the motor accelerate, the rotor frequency decreae, thereby lowering the reactance of the inner winding, allowing it to carry a larger proportion of the total rotor current At the normal operating peed of the motor, the rotor frequency i o low ( to 3 Hz) that nearly all the rotor current flow in the low-reitance inner cage winding. Thi reult in good operating efficiency and peed regulation. The tarting torque of thi motor range from 00 to 50 percent of full-load torque with a tarting current of 4 to 6 time the full-load value. It i claed a a high-torque, low tarting current motor. b. Write a brief note on induction generator. (8) When an induction machine run at a peed greater than it ynchronou peed with the help of prime mover, then it i called an induction generator. But it cannot function a an iolated place without any upply, becaue it generate only when excitation come from the tator ide. Thee generator are ued in low capacity power tation, mot frequently in micro hydro power tation and wind power tation. Figure 13 Self Excited Induction Generator But, the external reactive ource mut remain permanently connected to the tator winding reponible for the output voltage control. In interconnected application, the ynchronou grid upplie uch reactive power. In tand-alone application, the reactive power mut be upplied by the load itelf, or by a bank of capacitor connected acro it terminal, or by an electronic K.ajkumar, Aociate Profeor/EEE, Dhanalakhmi Srinivaan Intitute of Technology, Samayapuram.

13 13 inverter. When capacitor are connected to induction generator, the ytem i uually called a SEIG (a elf-excited induction generator). Advantage: It doe not hunt or drop out of ynchronim. Simple and rugged contruction. Cheaper in cot Eay maintenance Diadvantage: Cannot be operated independently Can deliver only leading current May affect the ytem tability 5. a. Sketch and explain the torque lip characteritic of the 3-pahe cage and lip ring induction motor. Show the table region in the graph. (10) Squirrel Cage Induction Motor: When the load i applied to the haft of the quirrel cage induction motor, the following reaction will be oberved: Speed decreae Slip increae otor induced e.m.f increae conequently the rotor current increae Torque developed by the rotor increae until it i ufficient to carry the applied load The motor continue to run at that lip which will develop the required torque for that particular load. The motor may be loaded continuouly till pull-out torque developed, at which point the motor will top if more load i placed on it. Pull-out occur at a lip well beyond the normal range operation of the quirrel cage induction motor. Even under normal operation, however, a uddenly applied load may require the temporary development of thi maximum torque, after which the motor will peed up to it full load value. Thu, in a manner imilar to the hunt motor, the induction motor inherently adjut itelf to the applied external torque. Slip ring Induction motor: Figure 14 Slip-ring Induction Motor with Variable External eitance at otor Circuit Figure 14 how the lip-ring induction motor with a variable reitance at it rotor. If the reitance value i zero, then the motor will act ame a quirrel cage induction motor. Under normal running condition, if the rotor reitance i doubled, the following reaction will be oberved: The rotor current will become half of it previou condition ince the rotor peed, and hence the rotor voltage, cannot change intantaneouly. The developed torque decreae due to reduced rotor current. K.ajkumar, Aociate Profeor/EEE, Dhanalakhmi Srinivaan Intitute of Technology, Samayapuram.

14 14 The torque will increae even when there i no change in load, the motor low down. Slip increae The rotor induced voltage increae The rotor current now increae until it i ufficient to develop enough torque to again carry the load at a contant peed. The torque developed at tandtill i higher with increaed rotor reitance. Thi i explained by the fact that at tandtill the rotor frequency i equal to the line frequency and rotor reitance i maximum. The addition of rotor reitance obviouly improve the powerfactor in the circuit while reducing the rotor current. Since tandtill rotor reitance i much greater than it reitance, the powerfactor increae more rapidly than the decreae of rotor current, and hence the developed torque i greater with the added reitance. Cage Im Slip ing Im Stable egion Untable egion Figure 15 Torque Slip Characteritic of Induction Motor b. Decribe the principle of operation of ynchronou induction motor. (6) If the rotor of a lip-ring induction motor i fed from a DC power, thi motor can be run at a ynchronou peed. Such motor are called ynchronou induction motor. Conider a normal lip-ring induction motor with a conventional three phae rotor winding i energized by a fixed DC excitation. Hence the pole axe of due to DC excitation are alo fixed and do not change like the pole due to three phae AC excitation. Thee fixed rotor pole get magnetically locked Figure 16 Connection of Synchronou Induction Motor K.ajkumar, Aociate Profeor/EEE, Dhanalakhmi Srinivaan Intitute of Technology, Samayapuram.

15 15 with the rotating magnetic field of tator upplied from three phae AC upply. Therefore the motor run at a contant peed equal to ynchronou peed. Figure 15 how the connection diagram of ynchronou induction motor. The motor i tarted a normal lip ring induction motor with additional reitance inerted at the rotor through the lip ring when the witch i at the Start poition. When the reitance i completely removed from the rotor circuit, the witch i changed to un poition. Hence the exciter i connected to the rotor winding, and the machine with DC excited rotor pull into ynchronim jut like the ynchronou motor. Thi motor can be tated with load a lip ring induction motor and can be operated at contant peed and improved power factor a ynchronou motor. Advantage: 1. It tart and ynchronize itelf againt heavy load. The exciter ued can be mall due to relatively maller airgap. 3. No eparate damper winding i required. Important Formulae Synchronou Speed, 10f N p r.p.m Slip: N N r % Slip N 100 N r -otor peed in r.p.m Frequency of otor current, f f -lip and f- Supply frequency Full load Torque: Starting Torque: T f T t ke ke Maximum Torque: ke T m K.ajkumar, Aociate Profeor/EEE, Dhanalakhmi Srinivaan Intitute of Technology, Samayapuram.

16 16 Condition for maximum torque: ( or) m m atio of Full load torque to maximum torque: T f m T m atio of tarting torque to maximum torque: Tt m T 1 m m m otor Copper lo from otor Gro output and vice-vera: otor Copper Lo otor gro output 1 otor input from otor output and vice-vera: otor Output 1 otor Input otor Copper lo from otor Input and vice-vera: otor Copper Lo otor Input Equivalent Circuit Equation: 01 1 L I I I I V ph 01 L j 01 V ph m 1 I 0 I 1 V Z ph 01 P 3I otor Copper Lo Univerity Quetion Problem 3I Mechanical Power,P m 1 P 1 Gro Power Developed,Pg 3I 1 1 3I 3I Gro Torque,T g Nm. N N An induction motor ha an efficiency of 0.9 when the haft load i 45kW. At thi load, tator ohmic lo and rotor ohmic lo each i equal to the iron lo. The mechanical lo i onethird of the no-load loe. Neglect the ohmic loe at no-load. Calculate the lip. (8) K.ajkumar, Aociate Profeor/EEE, Dhanalakhmi Srinivaan Intitute of Technology, Samayapuram.

17 17. A 50 HP, 6 Pole, 50 Hz, lip ring IM run at 960 rpm on full load with a rotor current of 40 A. Allow 300 W for copper lo in S.C. and 100 W for mechanical loe, find per phae of the 3- phae rotor. (6) 3. An KW, 4 pole, 50 Hz, 3 phae induction motor ha friction and windage loe of.5% of the output. Full load lip i 4%. Find for full load (1) rotor copper lo, () rotor input, (3) haft torque and (4) the gro electromagnetic torque. (8) 4. A 6 pole, 50 Hz, 3-Phae, induction motor running on full load develop a ueful torque of 160 N-m. When the rotor emf make 10 complete cycle per minute. Calculate the haft power input. If the mechanical torque lot in friction and that for core lo i 10 N m, compute (1) The copper lo in the rotor winding. () The input the motor. (3) The efficiency. The total tator lo in given to be 800 W. (8) 5. A 746kW, 3-phae 50Hz, 16 Pole induction motor ha a rotor impedance of (0.0+j0.15) Ω at tandtill. Full load torque i obtained at 360 r.p.m. Calculate, (i) the ratio of maximum to full load torque (ii) The peed at maximum torque and (iii) The rotor reitance to be added to get maximum tarting torque. (1) 6. A 15kW, 400V, 50Hz, 3-Phae tar connected induction motor gave the following tet reult: No-load tet: 400V, 9A, 1310W Blocked otor Tet: 00V, 50A, 7100W Stator and rotor ohmic loe at tandtill are aumed equal. Draw the induction motor circle diagram and calculate, (i) Line Current (ii) Powerfactor (iii) Slip (iv) Torque and efficiency at full load. (16) 7. A 4 Pole 50Hz, 7.46kW motor ha, at rated voltage and frequency, at tarting Torque of 160% and maximum torque of 00% of full load torque. Determine, (i) Full load torque (ii) Speed at maximum torque (8) 8. A 3-phae, tar connected 400V, 50Hz, 4 Pole induction motor ha the following per phae parameter in ohm, referred to the tator. 1 =0.15, 1 =0.45, =0.1, =0.45, m =8.5 Compute the tator current and power factor when the motor i operated at rated voltage and frequency with Slip,=0.04. (8) 9. A 3-phae IM ha tarting torque 100% and a maximum torque of 00% of full load torque. Find lip at maximum torque. (6) 10. A 100kW (output), 3300V, 3-phae, tar connected induction motor ha a ynchronou peed of 1500 r.p.m. The full load lip i 1.8% and full load powerfactor Stator copper lo = 440W. Iron lo=3500w. otational loe=100w. Calculate (1) the rotor copper lo, () the line current and (3) the full load efficiency. (8) K.ajkumar, Aociate Profeor/EEE, Dhanalakhmi Srinivaan Intitute of Technology, Samayapuram.

18 Draw the circle diagram of a 15 HP, 30V, 50Hz, 3 - phae lip ring induction motor with a tar connected tator and rotor. The winding ratio i unity. The tator reitance i 0.4 Ohm per phae and the rotor reitance i 0.3 Ohm per phae. The following are the tet reading, No-load tet: 30V, 9A, p.f=0.143 Blocked otor Tet: 115V, 45A, p.f=0.454 Find, a. Starting Torque b. Maximum Torque c. Maximum Powerfactor d. Slip for Maximum Torque e. Maximum Power Output. (16) K.ajkumar, Aociate Profeor/EEE, Dhanalakhmi Srinivaan Intitute of Technology, Samayapuram.