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Jawaharlal Nehru Engineering College Laboratory Manual ELECTRICAL MACHINE & APPLIED ELECTRONICS. For Second Year (MECH) Students Manual made by Prof. M. S. JADHAV Author JNEC, Aurangabad. FORWARD It is my great pleasure to present this laboratory manual for second year engineering students for the subject of Electrical Machine & Applied Electronics. Keeping in view the vast coverage required for visualization of concepts of Electrical Machines & basic electronic components .With simple language. As a student, many of you may be wondering with some of the questions in your mind regarding the subject and exactly what has been tried is to answer through this manual. Faculty members are also advised that covering these aspects in initial stage itself, will greatly relived them in future as much of the load will be taken care by the enthusiasm energies of the students once they are conceptually clear. H. O. D LABORATORY MANNUAL CONTENTS This manual is intended for the second year students of Mechanical & Production Engineering branch in the subject of Electrical Machine & Applied Electronics. This manual typically contains practical/Lab Sessions related electrical machine & electronics covering various aspects related the subject to enhanced understanding. Although, as per the syllabus, only descriptive treatment is prescribed, we have made the efforts to cover various aspects of electrical machine & Electronics subject covering types of different electrical machines, their operating principals, their characteristics and different sensors, Industrial panel meters & signal conditioning will be complete in itself to make it meaningful, elaborative understandable concepts and conceptual visualization. Students are advised to thoroughly go through this manual rather than only topics mentioned in the syllabus as practical aspects are the key to understanding and conceptual visualization of theoretical aspects covered in the books. Good Luck for your Enjoyable Laboratory Sessions Prof. M. S. JADHAV SUBJECT INDEX 1. Do’s and Don’ts 2. Lab exercise 1) To perform speed control of d. c. shunt motor. 2) To perform load test on d. c. shunt motor. 3) To study operation of single-phase induction motor. 4) To study three phase Induction motor starter. 5) To perform speed control of three phase induction motor. 6) To perform load test on three phase induction motor. 7) To study different types of sensors. 8) To study power devices. 3. Quiz on the subject 4. Conduction of Viva-Voce Examination 5. Evaluation and Marking Systems Do’s and Don’ts 1. Understand the equipment to be tested and apparatus to be used. 2. Select proper type (i.e. A. c. or D. C.) and range of meters. 3. Do not touch the live terminals. 4. Use suitable wires (type and size). 5. All the connection should be tight. 1. Do not leave loose wires (i.e. wires not connected). 2. Get the connection checked before switching ‘ON’ the supply. 3. Never exceed the permissible values of current, voltage, and / or speed of any machine, apparatus, wire, load, etc. 4. Switch ON or OFF the load gradually and not suddenly. 5. Strictly observe the instructions given by the teacher/Lab Instructor Instruction for Laboratory Teachers: 1. Submission related to whatever lab work has been completed should be done during the next lab session. The immediate arrangements for printouts related to submission on the day of practical assignments. 2. Students should be taught for taking the observations /readings of different measuring instruments under the able observation of lab teacher. 3. The promptness of submission should be encouraged by way of marking and evaluation patterns that will benefit the sincere students. Exercise No1: ( 2 Hours) – 1 Practical Speed control of a d. c. shunt motor. AIM: to study the speed control of a d. c. shunt motor. a) by varying field current with armature voltage kept constant. b) By varying armature voltage with field current kept constant. APPARATUS:1) Rheostat (100Ω, 1.2 amp) --------------------- 1no 2) Rheostat (100Ω, 6.0 amp) -------------------- 1no 3) D. c. voltmeter (0-300volt) -------------------- 1no. 4) D.C. Ammeter (0-1A) --- --------------------- 1no THEORY:1. What is effect of voltage on D. C. shunt motor? 2. What are different factors which affect the speed of D. C. shunt motor? PROCEDURE: 1) Make the connections as per circuit dia. 2) Set up the field and armature rheostat to their maximum value. 3) Switch on the D.C. Supply start the motor with the help of starter. Adjust the field current to rated value. 4) Note the speed with the help of tachometer, the voltage across armature and the field current. 5) Change the speed by varying the rheostat in the armature circuit. Note the speed and armature voltage, the field current remaining constant. 6) Repeat steps 4. And 5.above, for different field currents. 7) Plot speed V/s armature voltage 8) Keep the rheostat in the armature circuit to some fixed value. Note the voltage across armature. Note the field current and speed. 9) Vary the field current. OBSERVATION TABLE:a) Armature voltage variation. 1) Field current (constant) = ____amps. Sr. no. 1. 2. 3. 4. 5. 6. Armature voltage ( Va in volts) Speed (r. p. m.) b) Variable Field current 1) Armature voltage (constant) = _____volts. Sr. no 1. 2. 3. 4. 5. 6. Field current (If in amps) Speed (r. p. m.) GRAPH : F I E L D V O L T S C U R R E N T SPEED SPEED CONSTANT FIELD CURRENT CONCLUSION:The variation of speed with armature voltage and field current has been studied. The speed of d. c. Shunt motor is directly proportional to the armature voltage and inversely proportional to the field current. Thus, to increase speed above rated speed field current should be decreased & to decrease the speed below rated speed armature voltage should decrease. Exercise No2: ( 2 Hours) – 1 Practical Load test on D.C. shunt motor. AIM- To perform load test on D.C. shunt motor APPARATUS1) Rheostat (570 ohm, l Amp) ----------------------- 1 no 2) Rheostat (300 ohm, 1.7 amps) ---------------------1no. 3) D. c. voltmeter (0-10ohm) -------------------------2no. 4) D. c. voltmeter (0-300v) --------------------------2no 5) Tachometer. THEORY: 1. What is effect of load on D. C. shunt motor? 2. What is the relation between efficiency & load of D. C. shunt motor? 3. Why current & torque increases linearly with the load? PROCEDURE 1) Make the connection as per circuit dia. 2) Set the field rheostat of motor to zero and field rheostat of generator to maximum. 3) Switch on D.C. supply and start the motor with the help of starter. 4) Adjust field rheostat for motor to obtain rated speed. For one set of readings the setting of field rheostat should not be altered. 5) Adjust D.C. shunt generator voltage to it’s rated voltage with the help of it’s field rheostat. 6) Load the generator with keeping it’s terminal voltage constant. 7) Note the reading of ammeters, voltmeters and speed. 8) Repeat (6) and (7) above to a cover the range of no load to full load of motor. 9) Plot speed vs. output, armature current Vs output, efficiency Vs output, torque vs. output curves SAMPLE CALCULATIONEfficiency of generator is assumed as 87% Generator output – Vg Ig watts. Generator input = generator output / 0.87 Generator input = motor output. Motor input – Vm Im watts. % Motor efficiency = (motor output / motor input) * 100 Motor Torque = (motor output in watts) * 60 N-M 2n OBSERVATION TABLE : Sr.No. 1 2 3 4 5 GENERATOR MOTOR Vg Ig SPEED Vm Im (rpm) MOTOR MOTOR EFFI. TORQUE I/P O/P OF (N.M) (watts) (watts) MOTOR GRAPH : M O T O R T O R Q U E C U R R E N T OUTPUT OUTPUT MOTOR CURRENT Vs OUTPUT TORQUE Vs OUTPUT E F F I C I E N C Y S P E E D OUTPUT EFFICIENCY Vs OUTPUT OUTPUT SPEED Vs OUTPUT CONCLUSIONFrom the above graphs, the motor current increases with the load, and the speed decreases slightly with increase in load. The efficiency initially increases with the load, and then reaches its maximum (at about 80 to 90 % of the full load) and then decreases. Exercise No3: ( 2 Hours) – 1 Practical Study of single phase induction motor. AIM: - To study the operation of single phase induction motor. THEORY:Types of single-phase motors: The single-phase motors are manufactured in large No. of types to perform a wide variety of services, e.g.-domestic use, industrial use etc. The motor manufacturers have developed various types of such motors: each being designed to meet specific demands, the single phase motors may be classified in following groups depending upon their construction and principles of operation. 1) 2) 3) 4) Single phase induction motors Repulsion motors. Ac series motors. Unexcited synchronous motors. SINGLE PHASE INDUCTION MOTORS:The single-phase induction motor in construction is somewhat similar to a poly phase induction motor, except that the stator winding is supplied with a single phase AC power. The single phase AC voltage of stator winding produces a alternating magnetic field, but this alternating magnetic field cannot generate induced voltage, in a standstill rotor, hence single phase Induction motor is basically not a self starting motor. To start the motor additional starting winding is required to be used which is disconnected by a centrifugal switch when the rotor gathers 70 to 80% of its rated speed. SINGLE PHASE INDUCTION MOTOR STARTING OF SINGLE PHASE INDUCTION MOTORS:The various methods of starting basically employ a starting winding and a centrifugal switch, in some cases when starting winding is required to be disconnected while normal running of the motor. The starting and sunning or main winding are spaced 90 electrically apart as shown in fig. 1 and are connected in parallel across the single phase supply. It is so arranged that the phase difference between the currents in the two-stator windings in very large (Ideal value being 90). Hence the motor behaves like a two-phase motor. These two currents produce a revolving flux and hence make the motor self-starting. There are different methods by which necessary phase difference between the two currents can be created. 1) SPLIT PHASE MOTOR:In the split phase machine as shown in fig.2 the main winding has low resistance and high resistance and low reactance. The resistance of the starting winding may be increased either by connecting a high resistance R in series with it or by using a high resistance fine copper wire for winding purposes. Hence as shows in fig.3 the current Is drawn by the starting winding logs behind the applied voltage V by a small angle whereas the current I’m taken by the main winding lags behind V by a very large angle. The phase angle between the currents I’m and Is in made a large as possible, because the starting torque of a split phase motor is proportional to sin. the function of the centrifugal switch ‘S’ is to disconnect the starting winding when the motor gather 70-80% of its normal running speed. The direction of rotation of these motors can be reversed by reversing the connection of one of the two-stator winding (not both). SPLIT PHASE INDUCTION MOTOR 2) CAPACITOR START MOTOR:In these motors the necessary phase difference between I’m and Is is produced by connecting a capacitor in series with the starting winding as shown in fig.4. The capacitor is generally of electrolytic type and is usually mounted on the outside of the motor as a separate unit. The capacitor is designed for extremely short-duty service and when the motor reaches around 79-80% of its full speed, the centrifugal switch S opens and cuts out both the starting winding and capacitor from the supply. As shown in fig.5 the current main winding draws me. Lags behind the supply voltage V by large angle whereas is leads by a certain angle. The two currents are out of phase with each other by a large angle approaching 90. Their resultant current is small and is almost in phase with V as shown in the figure. CAPACITOR START MOTOR 3) CAPACITOR START AND RUN MOTOR:In case of capacitor start and run motor there is no centrifugal switch and capacitor remains permanently in the circuit. This improves the power factor. The schematic diagram of such motor is shown in fig. The performance not only at start but in running condition also depends on the capacitor ‘C' hence its value is to be designed so as to compromise between best starting and best running conditions . Hence the starting torque available in such type of motor is about 50-100% of full load torque. The direction of rotation can be interchanging the connection of main winding or auxiliary winding. These motors are more costly than split phase type motor. The capacitor value can be selected as per the required value of starting torque. The torque can be high as 350-400% of full load torque,the torque speed characteristics is shown in fig. CAPACITOR START CAPACITOR RUN MOTOR TORQUE-SPEED CHARACTERISTICS 4) SHADED POLE MOTOR:In such motors the necessary phase shift is obtained by induction. These motors have salient poles on the stator and squirrel cage type rotor. Fig shows the four-pole motor and one pole of such motor is shows in fig. The laminated pole has a slot cut across the lamination approximately one third distance from one edge. Around the small part of the pole is placed short-circuited copper coil known as shedding coil. This part of the coil is known is shaded part and other is unshaded part. When an alternating current passed through field winding surrounding whole pole, the axis of the pole shifts from unshaded part “a” to shaded part. This shifting of magnetic axis is in effect equivalent to actual physical movement of the pole. Hence the motor starts rotating the direction of this shift i.e for un shaded part to the shaded part. SHADED POLE INDUCTION MOTOR Exercise No4: ( 2 Hours) – 1 Practical Induction Motor Starter. AIM: to study the Induction Motor Starter. THEORY: NESSCISITY OF STARTER If normal supply voltage is applied to stationary motor then the motor takes very large initial current. Induction Motor when direct switched takes 5 to 7 times their full load current & develops only 1.5 to 2.5 times their full load torque. This will produce large line drop affect the operation of other electrical equipment connected in same circuit. Starters should be used for the motors of rating above 25 KW to 40KW. TYPES OF STARTER The current of the motor can be controlled by reducing supply voltage or by increasing the rotor resistance at start. The second method is possible only in the case of slip ring induction motos. For Squirrel-cage Motors: a. b. c. d. Direct on line starter. Stator Resistance Starter. Star-Delta Starter. Auto transformer Starter. For Slip Ring Induction Motor a. Rotor Resistance Starter. 1. DIRECT ON LINE STARTER In case of small capacity motors having rating less than 5 h. p., the starting current is not very high and such motors can with stand such a starting current without any starter Thus there is a no need to reduce applied voltage to control the starting current . Such motors use a type of starter which is used to connect stator directly to the supply lines without any reduction in voltage Hence the stator is known as direct –on-line starter. Though this starter does not reduce the applied voltage it is used because it protects the motor from various several abnormal conditions, like over loading , low voltage, single phasing etc. DIRECT ONLINE STRTER 2) STATOR RESISTANCE STARTER In order to apply the reduced voltage to the stator of the inductionmotor, three resistances are added in each phase of the stator winding. Initially the resistances are kept maximum in the circuit, due to this large voltage gets dropped across the resistances. Hence a reduced voltage gets applied to the stator which reduces the high starting current. When the motor starts running the resistances are gradually cut off from the stator circuit. When the resistances are entirely removed from the stator circuit i. e. rheostats are in run position then the rated voltage gets applied to the stator. Motor runs with normal speed. The starter is simple is construction and cheap. It can be used for both star and delta connected stator, but there are large power losses due to resistances. Also the starting torque of the motor reduces due to reduced voltage applied to stator. STATOR RESISTANCE STARTER 3. STAR- DELTA STARTER This is the cheapest starter of all hence used very commonly for the induction motors .It uses triple pole double through (TPDT) switch. The switch connects the stator winding in star at start. Hence the per phase voltage gets reduced by the factor 1/√3. Due to this reduced voltage the starting current is limited. When the switch is thrown on the other side the winding gets connected in delta, across the supply so it gets normal rated voltage .The windings are connected in delta when motors gathers sufficient speed STAR-DELTA STARTER 4. AUTO TRANSFORMER STARTER A three phase star connected auto transformer can be used to reduce the voltage applied to the stator such a starter is called auto transformer starter. It consist of a suitable change over switch When the switch is in the start position the stator winding is supplied with reduced voltage. This can be controlled by tapings provided with autotransformer. When motor gathers 80% of the normal speed, the change over switch is thrown into run position ,due to this rated voltage gets applied to stator winding. Changing of switch is done automatically by using relays. The power loss is much less in this type of starting. AUTOTRANSFORMER STARTER FOR SLIP RING INDUCTION MOTORS 1. ROTOR RESISTANCE STARTER To limit the rotor current which consequently reduces the current drawn by the motor from the supply. The resistance can be inserted in the motor circuit at start. This addition of the resistance in rotor is in the form of 3 phase star connected rheostat. The external resistance is inserted in each phase of the rotor winding through slip ring and brush assembly initially maximum resistance is in the circuit. As motor gathers speed the resistance is gradually cut-off the operation may be automatic or manually. ROTOR RESISTANCE STARTER Exercise No5: ( 2 Hours) – 1 Practical Aim: To perform speed control of three phase induction motor using autotransformer by changing supply voltage. Apparatus: 1) Voltage (0-500v) 2) Ammeter (0-10A) 3) Auto-transformer 4) Connecting wire 5) Three phase induction motor 6) Wattmeter(0-150W) Theory: Three phase IM works on faradays law of electromagnetic induction. The speed of three phase IM can changed by using three phase autotransformer. The speed of three phase IM can be changed by the the supply voltage. The speed can be changed by using following factors : 1 By controlling stator parameters 2 By controlling rotor parameters The expression for actual speed of IM can be given by N=Ns(1-S) This shows that the actual speed depends on two factors mainly Synchronous speed and Slip.By changing these factors we can change the speed of IM. Another way to change the speed of three phase IM from torque equation of motor but R2 is constant and K is also constant .Hence This directly proportional to SV^2 In these type of speed control of the stator supply voltage V1 is reduced from rated voltage Hence from the above expression we can control the speed of three phase IM by varying the supply voltage. Procedure: 1. Make the connection as per circuit diagram 2. Connect the three ammeters in phase with proper rating 3. Connect autotransformer at starting of the supply to vary three phase supply voltage. 4. Voltmeter should be connect between any two phases 5. Connet the two wattmeter for measuring three phase power drawn by the motor 6. Switch on the supply and note down accurate reading . Observation Table Sr No Voltage Current (V) I1 I2 Power Power Speed W1 W2 r.p.m I3 1 2 3 4 5 Conclusion: Hence from the above experiment we have successfully observed the variation of speed of three phase IM with varying the three phase AC input supply by using three phase autotransformer. Exercise No 6: ( 2 Hours) – 1 Practical Load Test On 3-Phase Induction Motor AIM: To perform the load test on 3-Phase induction motor. APPARATUS: 1)Two-element wattmeter (10A, 500v) ---------------------1 No. 2) Ammeter (0-10A) ------------------------------------------1 No 3) Voltmeter (0-500v) ----------------------------------------1 No 4) Rheostat (500 ohm, 1.2A) ---------------------------------1 No 5) Ammeter D.C. (O-10A) ------------------------------------1 No 6) Voltmeter D.C. (0-300v) ----------------------------------1 No 7) Tachometer. THEORY: 1.What is effect of load on 3 phase Induction motor ? 2.What is the relation between speed & load of 3 phase Induction motor ? 3.Why current & torque increases linearly with the load ? 4.How power factor is affected by load ? PROCEDURE: 1) Make the connection as per the circuit diagram. 2) Put the load switches off. Set generator field rheostat to maximum start the induction motor with the help of the start & run it to it’s normal speed. 3) Excite the dc shunt generator to it’s voltage. Note power input, to motor & the speed, with the generator not loaded. 4) Put some load on generator & Note the D.C. generator output, motor input and the speed. 5) Take the more readings by increasing the load gradually till the full load is reached. 6) Calculate & plot the graphs. Output Vs speed, Output Vs Efficiency, Output Vs motor current. Output Vs slip, output Vs P.F. OBSERVATION TABLE: sr. no 1. 2. 3. 4. 5. I. M. Vm in volts. Im in Motor input Amp Power in watts Speed in rpm Ig. I. M. Input watts %n Slip p.f. GRAPH: E F F I C I E N C Y S P E E D OUTPUT SPEED Vs OUTPUT OUTPUT EFFICIENCY Vs OUTPUT P O W E R C U R R E N T F A C T O R OUTPUT POWER FACTOR Vs OUTPUT OUTPUT CURRENT Vs OUTPUT CONCLUSION: The speed falls, the power improves and the current increases, with as increase in output of motor. The efficiency increases and is maximum near full load. Exercise No 7 : ( 2 Hours) – 1 Practical To Study different sensors AIM: To Study different sensors THEORY: QUESTIONS: 1. Definition of sensor. 2. Different types of sensor. 3. Different applications of sensors. 4. Selection criteria of sensors 5. LVDT. 6. Proximity switch. 7. Piezo sensors. 8. Airflow sensor. 9. Thermocouple. 10. Load cell Exercise No8: ( 2 Hours) – 1 Practical To study power devices AIM: To study power devices THEORY: QUESTIONS: 1. Theory and working principle of transistor. 2. Different types of power devices. 3. Different applications of heating. 4. Light dimmer circuit. 5. Temperature controller. 6. Sequential timer circuit. 7. MOSFET. 8. DIAC. 9. TRIAC. 10. SCR. 3. Quiz on the subject: 1. Load characteristics of D.C. Compound Generator. a. What are the different types of D.C. compound Generator? b. What is the difference between flat compounded & over compounded generator. c. Why the terminal voltage drops when the generator is loaded? d. What happens if we connect the shunt field of compound generator in series with the armature & series field across the armature? e. What are the applications of d. c. compound generator? f. How to identify the series field & terminal at the terminal box? 2. Speed control of D.C. Shunt motor a. What are the factors on which speed of D.C. Shunt motor depends? b. Name the different speed control methods. C. What is the disadvantage of armature rheostat method? d. What is the advantage of Ward Leonard method? e. Where the D.C. Shunt motor is applicable? 3 .Load test on d.c. shunt motor. a. What is the purpose of Load test on d. c. shunt motors? b. What is the relation between Ia and Armature Cu loss? c. What are different losses in D.C. shunt motor. 4.Generators a. Why speed control methods are not needed in d. c. generators? b. What is the use of commutator & brushes in D C Generator? c. How energy conversion takes place in D C Generator. d. What is the effect of increasing load on terminal voltage in D C shunt generator. 5. Motor a. How energy conversion takes place in D C Generator. b. D C Motor is known as constant speed motor? c. Why starter is necessary for starting of D C motor? d. Explain the disadvantage of 3pt. Starter. e. How to reverse the direction of rotation of D C shunt Motor. f. What is the use of commutator & brushes in D C Motor? 4. Conduction of Viva-Voce Examinations: Teacher should oral exams of the students with full preparation. Normally, the objective questions with guess are to be avoided. To make it meaningful, the questions should be such that depth of the students in the subject is tested Oral examinations are to be conducted in co-cordial environment amongst the teachers taking the examination. Teachers taking such examinations should not have ill thoughts about each other and courtesies should be offered to each other in case of difference of opinion, which should be critically suppressed in front of the students. 5. Evaluation and marking system: Basic honesty in the evaluation and marking system is absolutely essential and in the process impartial nature of the evaluator is required in the examination system to become popular amongst the students. It is a wrong approach or concept to award the students by way of easy marking to get cheap popularity among the students to which they do not deserve. It is a primary responsibility of the teacher that right students who are really putting up lot of hard work with right kind of intelligence are correctly awarded. The marking patterns should be justifiable to the students without any ambiguity and teacher should see that students are faced with unjust circumstances.