ELECTRICAL MACHINES LAB MANUAL - IIVOLUME 2CONTENTSPg. No.I. A. GENERAL INSTRUCTIONS TO STUDENTS 2B. GRAPHICAL SYMBOLSII INDUCTION MACHINES2.1 INTRODUCTION 42.2 EXPERIMENTS ON INDUCTION MACHINES1. No Load test and Blocked Rotor test on induction motor (Squirrel cage, slip-ring) 52. Direct load test on induction motor (Squirrel cage, slip-ring and 1 Induction motor) 153. Variation of starting torque with rotor resistance in slip-ring Induction motor 234. Predetermination of characteristics of pole changing motor. 26III SYNCHRONOUS MACHINES3.1 INTRODUCTION 303.2 EXPERIMENTS ON SYNCHRONOUS MACHINES1. Regulation of alternator Direct loading 322. Regulation of alternator by EMF & MMF method 343. Regulation of alternator by Potier & ASA method 374. Slip Test on alternator 415. Synchronizing of alternator to mains by dark lamp and bright lamp method and determination of V and Inverted V curves 44IVSPECIAL MACHINES4.1- INTRODUCTION 474.2- EXPERIMENTS ON SPECIAL MACHINES1. V/f control of induction motors482. Synchronous induction motor V-curves. 513. Test on induction generator determination of rotor hysteresis loss 524. Load test on squirrel cage induction motor using eddy dynamometer. 57DEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 1ELECTRICAL MACHINES LAB MANUAL - IIGENERAL INSTRUCTIONS TO STUDENTSA. Procedure & Precautions to be followedIn conducting the experiments on electrical machines, certain preliminaries are to be followed. Oncetheexperiment anditsaimareunderstoodonehastochoosethemachineonwhichthe experiment is to be conducted. Note down the name plate details of the machine to know the rated voltage, current, r.p.m., etc. intheformofadatasheet. Thendecideupontheinstrumentsand accessories required for the conduct of the experiment and their ratings. Suitable types of measuring instruments must be selected. Care should be taken to see that the ammeter and wattmeter coils are not damaged due to excessive current. The current has to be limited to less than or equal to the rating of the instrument.Even though electrical machines can take short time over loads, as far as possible see that the current throughwindingsdoesnot exceedtheratedvalue. Toprevent burningof windings, or damage to insulation due to overheating the following precautions have to be taken.1) Provide fuses of appropriate rating in the circuit depending on the rating of the machine.2) Never apply full rated voltage suddenly to a device unless the experimental procedure requires it. Increase the voltage from zero gradually and bring it to the rated value using variacs (autotransformer) or other similar devices.

B. Special InstructionsThestudentsshouldcomewell preparedtoconduct theexperiment. Theinstructional material should be read before coming to the class. Students should bring with them a neat connection diagram, the ranges of meters, fuse rating, etc. shall be determined after noting down the name plate details of the machine on which they are going to do the experiment.The data sheet consisting of the name plate details of machines and the readings taken should be showntothestaff-member inchargebeforeleavingthelaboratory. As far as possibletheentire calculations shall be completed in the lab and the graphs plotted.C. Lab RecordThe laboratory record submitted by the students should have the following format:1. Experiment No. & Date2. Title of the experiment3. Aim of the experiment4. Machine specifications & instruments required, their range and type.5. Complete connection diagram with the range and type of instruments used, type of machine and its name plate details and the specific supply voltages used.6. Theory & Procedure :- write a brief theory & actual procedure followed with precautions taken 7. Readings observed in appropriate tabular form.8. Sample calculations :- Analysis of data, graphs etc. as required in the instructional material9. Results & inference10. Questions & AnswersD. Dress Code & Safety StandardsIt has tobenotedthat experiments intheElectrical MachineLabareconductedonrotating machines with exposed rotating parts. The operating voltages are also up to 415 V which is potentially dangerous to life. In addition all the terminals of the instruments are exposed. Therefore due diligence and DEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 2ELECTRICAL MACHINES LAB MANUAL - IIcare should be shown while doing experiments to avoid any accidents. For the safety of all personnel the following dress code has to be strictly followed:1) The students shall wear insulating foot wear which covers the whole foot and shall not have metal nails in the sole (i.e. should wear shoes).2) The students shall wear tight dress (pants & shirt / overcoat (for girls))3) The students shall not wear long neck chains.4) The students having long hair (going below the shoulders) should bundle up their hair.The following books, ISI standards may be referred to, for further studies:1) A. E. Fitzgerald, E. Kingsley and A. Kusko : Electric Machinery : Mc Graw Hill, Kogakusha (1971)2) M. G. Say : The Performance and Design of A. C. Machines : ELBS and Issac Pitman, London (1969)3) G. S. Broson and J. T. Hayden : Advanced Electrical Power and Machines; Issac Pitman (1966)4) A. F. Puchtein, T. C. LloydandA.G. Conrod: AlternatingCurrent Machines: AsiaPublishing House (1968)5) G. C. Jain : Theory, Performance and Design of Synchronous Machines : Asia Publishing House (1966)6) E. W. Kimbark : Power system stability synchronous machines : Vol 3, John Wiley (1948)7) A. S. Langsdorf : Theory of Alternating Machinery : Mc Graw Hill, 2nd edition (1955) DEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 3E M LAB MANUAL II INDUCTION MACHINESINDUCTION MOTORS2.1 IntroductionAn induction motor consists essentially of two parts a stator and a rotor. The stator is made up of a number of stampings which are slotted to receive the windings. The stator carries a 3-phase winding and is fed from a three phase supply. It is wound for a definite number of poles, the exact number of poles beingdeterminedbythe requirements of speed. The stator windings when suppliedby3phasecurrents produceamagneticflux whichisofconstant value butrotatesat synchronous speed. This revolving magnetic flux induces an e.m.f. in the rotor by mutual induction.Depending on the type of rotor used, 3 phase induction motors are classified into squirrel cage and slip ring.The frequency of the induced e.m.f. in the rotor is s times the supply frequency where s is theslip. Itsmagnitudeisproportional totherelativespeedbetweenfluxandrotorconductors. Since rotor bars or conductors form a closed circuit, rotor current is produced whose direction is given by Lenzs Law and it is such as to oppose the cause producing it and hence to reduce the relative speed. The rotor starts running in the same direction as that of the flux and tries to catch up with the rotating flux.The rotor never succeeds in catching up with the stator field and so the rotor runs at a speed which is always less than the speed of the stator field. The difference between the synchronous speed and the actual speed of the rotor is known as slip.Aninductionmotor is similar inactiontoapolyphasetransformer withashort circuited rotating secondary. Hence induction motors if switched on to line directly, it takes 5 to 7 times their full load current and develop only 1.5 to 2.5 times their full load torque. The initial inrush of current can be controlled by applying a reduced voltage to the stator during starting period, full normal voltage is applied when the motor has run up to speed. This can be done either by using an autotransformer or star-delta starter.There are different methods in which speed control on induction motor can be achieved. By changing the number of poles, speed control is possible in the case of squirrel cage motors. This is seen in pole changing motor. Speed control is also possible by operating two motors in cascade or by injecting an e.m.f. in the rotor circuit. Modern trend is to use V/f controller for speed control of induction machines.DEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 4E M LAB MANUAL II INDUCTION MACHINES- NO LOAD & BLOCKED ROTOR TEST2.2.1.1NO LOAD AND BLOCKED ROTOR TESTS ON SQUIRREL CAGEINDUCTION MOTORAim: 1) To conduct no load test and blocked rotor test on the given squirrel cage induction motor and to draw the equivalent circuit diagram. From the circle diagram and equivalent circuit, compare efficiency, pf, torque, slip, line current and output- corresponding to i) Name plate speed ii) Rated Output2) Also from circle diagram obtain maximum torque, maximum output and maximum power factor.Machine Details: Note the name plate details of the machine.Apparatus Required: Ammeter (to read no load current), Voltmeter (to read rated applied voltage) and Wattmeters (suitable for no load test and blocked rotor tests)Theory: No load and Blocked rotor tests are conducted to obtain the parameters to draw the equivalent circuit and also the circle diagram. No load test is conducted with motor running at normal voltage. Rotor speed is very near to synchronous speed. From the no load readings, the shunt circuit components Ro and Xm can be determined.In blocked rotor test, rated current is applied to the machine with the rotor blocked and corresponding power and voltage are noted. The machine impedance [(r1 + r2 ) +j(x1 + x2 )] is determined. In this case, slip is 1. This is equivalent to short circuit test on transformer.Circle diagram is one of the best graphical methods of determining the whole characteristics of a motor. From the circle diagram, the Stator power factor angle, Stator current/phase on load, Total input, Constant losses, Stator copper loss, Rotor input, Rotor copper loss, Rotor output, Torque, Slip, Efficiency, etc. can be determined.Procedure: No Load Test: Connections are done as shown in Fig 2.1. Start the motor and gradually increase the voltage to rated value with the help of a dimmerstat. Note the corresponding no load current and wattmeter readings. If one of the wattmeter reads negative, change the connections (current coil or pressure coil).Blocked Rotor Test: Connections are made as shown in Fig 2.2. The rotor is blocked and dimmerstat is adjusted to get rated current. The voltmeter reading and blocked rotor power input readings are taken.Stator winding resistance: To find the stator winding resistance/phase, connections are made as shown in Fig 2.3. DC supply is given, keeping the rheostat at the maximum position. Voltmeter and ammeter readings are recorded.Tabular Column:No Load Test:Blocked Rotor Test:Vo (V) Io (A) W1(watts)W2(watts)Wo=W1+W2 (watts)Vsc (V) Isc (A) Wsc (watts) Measurement of Ra:V (V) I (A) Ra () DEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 5E M LAB MANUAL II INDUCTION MACHINES- NO LOAD & BLOCKED ROTOR TEST'a a1 a3R =R2R= 1.2 R( Because the windings are connected in delta)(R1 : AC resistance)Fig 2.1 No- Load Test on Squirrel Cage Induction MotorFig 2.2 Blocked Rotor Test on Squirrel Cage Induction MotorDEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 6E M LAB MANUAL II INDUCTION MACHINES- NO LOAD & BLOCKED ROTOR TESTFig 2.3 Determination of stator winding resistanceCalculations:To draw equivalent circuit: From no load test:cos3 ?ooo ooWV INo load current/phase,oI3om oIIsin 3 ow oIIcos 3 oowoomVR= IVX= IFrom Blocked rotor test:so1sV phZ= I phsco1 2scphWR= 3 I2 2o1 o1 o1X=Z R 2 o1 1= R R R EQUIVALENT CIRCUIT DEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 7E M LAB MANUAL II INDUCTION MACHINES- NO LOAD & BLOCKED ROTOR TESTBased on Equivalent circuit:a) Corresponding to rated output

2out 2 2(1-s)P= 3IRs (Pout obtained from machine details)where ( )rated2 2 221 1 2VI= = IRR+X+ Xsj 1 _ + 1 , ] , thens = ?

1 o o 2 1 1 1 oL 1 L 1in L L 1I(ph) = I + I= I(lagging)I=3 I= IP=3 VIcos

outinP =100%P b) Corresponding to name plate speed

ssN Ns = N( )rated2 2 221 1 2V 0I= = IRR+X+ Xsj 1 _ + 1 , ]1 o o 2 1 1 1I(ph) = I + I= I in ph 1 1P= 3VIcos2out 2 2(1-s)P= 3IRs outinP =100%P To draw circle diagram:-1 -1 o sco so o sc scW W = cos, = cos3VI 3VI Assume the current scale (c:s) to draw the circle diagramDEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 8E M LAB MANUAL II INDUCTION MACHINES- NO LOAD & BLOCKED ROTOR TESToSN SscVI =I V = _____ / (c:s) = _____ cm2ratedsn scscVW =WV _ ,Power Scale = rated scale3V I(W/cm)(scale the necessary values according to the current scale and draw the circle diagram)Fig 2.4 Circle DiagramThe voltage phasor is taken along Y-axis, referring to Fig. 2.4, and draw OO at an angle o, from OV, representing no-load line-current Io in magnitude and direction. Line OF is drawn perpendicular to voltage phasor OV. Phasor OA is drawn at an angle sc , from phasor OV and equal to ISN in magnitude. Line OG is drawn parallel to OF, OA is joined and line BC is drawn perpendicular to line OA bisecting the line OA at point B and intersecting line OG at C. With C as centre, and OC as radius, the semi-circleOAG is drawn, which is the locus of the stator current, I1. Line AE is divided by D into two segments such that 011R AE Total copper loss=DE Stator copper loss R . Line OD is known as the Torque line or rotor input line. Line OA representsthe output line or mechanical power developed line.A tangent to the semi-circle is drawn parallel to NPF, and the vertical intercept PP between this tangent and horizontal line NPF, represents the maximum power input to the motor.The vertical line QQ drawn from the tangent at Q (parallel to torque line) till the torque line, represents the maximum torque.The vertical SS drawn from the tangent at S (parallel to the output line) till the output line, represents the maximum power output.Motor output(in scale) = motor outputATpower scale. From T, line TH is drawn parallel to output line OA cutting the circle at H. Point H is joined with origin O, and perpendicular HN is drawn, cutting the torque line and output line at L and K. DEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 9E M LAB MANUAL II INDUCTION MACHINES- NO LOAD & BLOCKED ROTOR TESTLine current at full load = OHFull load power factor, cos1 = NHOHMaximum power output = SS power scale = _________ watts.Slip = KLLHEfficiency = HKHN100%Result:Equivalent circuit and circle diagram drawn. Slip, efficiency, power factor and torque values compared for the eqvt. ckt. and circle diagram.Questions:1) Why is it considered preferable to calculate the power factor from wattmeter readings only?2) Why is the magnetizing current and stray losses greater in an induction motor in comparison with a transformer? How does it affect the p.f. of the motor?3) What are the possible errors in the approximate equivalent circuit?2.2.1.2 NO LOAD AND BLOCKED ROTOR TESTS ON SLIP RING INDUCTION MOTORAim: 1) To conduct no load test and blocked rotor test on the given slip ring induction motor and to draw theequivalent circuit diagram. Fromthecirclediagramandequivalent circuit, compareefficiency, pf, torque, slip, line current and output- corresponding to iii) Name plate speed iv) Rated Output2) Also from circle diagram obtain maximum torque, maximum output and maximum power factor.Machine Details: Note the name plate details of the machine.Apparatus Required:Ammeter (to read no load current), Voltmeter (to read rated applied voltage) and Wattmeters (suitable for no load test and blocked rotor tests)Theory: No load and Blocked rotor tests are conducted to obtain the parameters to draw equivalent circuit and hence also the circle diagram. Noloadtest isconductedwithmotor runningat normal voltage. Rotor speedisverynear to synchronous speed. From the no load readings, the shunt circuit components Ro and Xm can be determined.In blocked rotor test, rated current is applied to the machine with the rotor blocked and corresponding power and voltage are noted. The machine impedance [(r1 + r2 ) +j(x1 + x2 )] is determined. Rotor is blocked from moving. In this case, slip is 1. This is equivalent to short circuit test on transformer.Procedure: No Load Test: Connections are done as shown in Fig 2.5. Start the motor and gradually increase the voltage to rated value with the help of a dimmerstat. Note the corresponding no load current and wattmeter DEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 10E M LAB MANUAL II INDUCTION MACHINES- NO LOAD & BLOCKED ROTOR TESTreadings. If one of the wattmeter reads negative, interchange the connections of either the current coil or pressure coil.Blocked Rotor Test : Connections are made as shown in Fig 2.6. The rotor is blocked and dimmerstat is adjusted to get rated current. The voltmeter reading and blocked rotor power input readings are taken.Stator winding resistance: To find the stator winding resistance/phase, connections are made as shown in Fig2.7. DCsupplyis given, keepingtherheostat at themaximumposition. Voltmeter andammeter readings are recorded.Tabular Column:No Load Test:Blocked Rotor Test:Vo (V) Io (A) W1(watts)W2(watts)Wo=W1+W2 (watts)Vsc (V) Isc (A) Wsc (watts) Measurement of Ra:V (V) I (A) Ra () 'a a1 a3R =R2R= 1.2 RFig 2.5 No- Load Test on Slip Ring Induction MotorDEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 11E M LAB MANUAL II INDUCTION MACHINES- NO LOAD & BLOCKED ROTOR TESTFig 2.6 Blocked Rotor Test on Slip Ring Induction MotorFig 2.7 Determination of stator winding resistanceCalculations:To draw equivalent circuit: From no load test:cos, ?3 oo oo oWV I No load current/phase,oI3om oIIsin 3 ow oIIcos 3 DEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 12E M LAB MANUAL II INDUCTION MACHINES- NO LOAD & BLOCKED ROTOR TESToowoomVR= IVX= IFrom Blocked rotor test:so1sV phZ= I phsco1 2scphWR= 3 I2 2o1 o1 o1X=Z R 2 o1 1= R R R EQUIVALENT CIRCUIT Based on Equivalent circuit:c) Corresponding to rated output

2out 2 2(1-s)P= 3IRs (Pout obtained from machine details) where( )rated2 2 221 1 2VI= = IRR+X+ Xsj 1 _ + 1 , ], then s = ?

1 o o 2 1 1 1L 1 L 1in L L 1I(ph) = I + I= II=3I= IP=3VIcos

outinP =100%P d) Corresponding to name plate speed

ssN Ns = N( )rated2 2 221 1 2V 0I= = IRR+X+ Xsj 1 _ + 1 , ]1 o o 2 1 1 1I(ph) = I + I= I DEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 13E M LAB MANUAL II INDUCTION MACHINES- NO LOAD & BLOCKED ROTOR TESTin ph 1 1P= 3VIcos2out 2 2(1-s)P= 3IRs outinP =100%P To draw circle diagram:-1 -1 o sco so o sc scW W = cos ,= cos3VI 3VI Assume the current scale (c:s) to draw the circle diagramoSN SscVI =I V = _____ / (c:s) = _____ cm2ratedsn scscVW =WV _ ,Power Scale = rated scale3V I(W/cm)(scale the necessary values according to the current scale and draw the circle diagram refer Fig)Result: Equivalent circuit and circle diagram drawn. Slip, efficiency, power factor and torque values compared for the eqvt. ckt. and circle diagram.Questions:1) Ammeter in the rotor circuit oscillates very slowly when the rotor is running with rated voltage applied to the stator. Why ?2) Are the core loss and mechanical losses constant for all operating conditions? Comment.3) How does core loss vary with voltage and why?4) Does the no load current steadily decrease as the supply voltage is reduced? If not, explain why?5) The motor input under blocked rotor condition is taken approximately equal to the full load copper loss. Substantiate.6) Discuss Stable and unstable regions of the torque-speed characteristics.DEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 14E M LAB MANUAL II INDUCTION MACHINES-LOAD TEST

2.2.2.1 LOAD TEST ON SINGLE PHASE (CAPACITOR START) INDUCTION MOTORAim:To conduct a load test on single phase induction motor and to plot thefollowing characteristics.(i) Efficiency vs. output(ii) speed vs. output(iii) pf vs. output(iv) Line current vs. outputApparatus Required: Tachometer, Voltmeter, Ammeter and Wattmeter. Machine Details: Note the name plate details of the machineTheory: Constructionally a 1 induction motor is similar to a polyphase induction motor except that its stator is provided with a single phase winding and a centrifugal switch is used in some types of motor to cut off a winding used only for starting purpose. It has a distributed stator winding and a squirrel cage rotor. To make the rotor self starting it is temporarily converted into a two phase motor during the starting period. For this, the statorofasinglephasemotorisprovided withanextra windingknown as starting(auxiliary)windingin addition to main or running winding. The necessary phase difference is provided by connecting a capacitor in series with the starting winding as shown in figure. When the motor reaches 75% of full speed, the centrifugal switchS opens and cutoff both the starting winding and the capacitor from the supply thus leaving only the running winding across the lines. Procedure:Connectionsaremadeasshown in the fig 2.8. The motor is kept at no load and given 230V supply. Whenmotorattainsspeedalmost equal toratedspeed, noloadreadingsarenoted. Themotoris gradually loaded up to rated current. All meter readings including the spring balance reading are tabulated.Tabular Column:Sl. No.InputCurrent (A)Speed (r.p.m.)Input power (W) S1 (kg)S2 (kg)Torque (Nm)Power factorOutput power (W)Efficiency (%) Calculations:Spring balance readings S1 and S2 in kg. Torque can be computed using the equation, ( )1 2 (Nm) T S S rg , where ris the radius of the brake drum.DEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 15E M LAB MANUAL II INDUCTION MACHINES-LOAD TESTFIG 2.8Load Test on Single Phase Capacitor-Start Induction MotorInput power (Wattmeter reading) = Pin (watts)power (Pin)=VIcospower factor = cos= PinVIOutput Power = out2 NTP= (watts)60whereNis the speed in r.p.m.Tis the torque in Nm.% Efficiency = 100%outputinput FIG 2.9(a) Torque Slip characteristics, (b) Performance curvesResult: Load test on 1 phase capacitor-start induction motor. Characteristics curves plotted. Questions:1. How do you reverse the direction of rotation of a capacitor start-induction motor?2. What are the drawbacks of a shaded-pole single phase motor?DEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 16E M LAB MANUAL II INDUCTION MACHINES-LOAD TEST2.2.2.2 LOAD TEST ON SINGLE PHASE (CAPACITOR START-RUN) INDUCTION MOTORAim:To conduct a load test on single phase induction motor and to plot thefollowing characteristics.(v) Efficiency vs. output(vi) speed vs. output(vii) pf vs. output(viii) Line current vs. outputInstruments Required: Tachometer, Voltmeter, Ammeter and Wattmeter. Machine Details: Note the name plate details of the machineTheory:Constructionally a capacitor start-run 1 induction motor is similar to a polyphase induction motor except that it is a two-phase motor that is powered by a single-phase source. Its stator is provided with a start-winding and a run-winding displaced 90 apart. The necessary phase difference is provided by connecting a capacitor in series with the starting winding as shown in figure. Both the windings are designed for continuous duty. It has high power factor due to the capacitor being in the circuit continuously even while the motor is running. No centrifugal switch is needed in as much as the capacitor stays in the circuit. It does, however, have a low starting torque. Procedure:Connections are made as shown in the fig 2.10. The motor is kept at no load and given 230V supply. Whenmotorattainsspeedalmost equal toratedspeed, noloadreadingsarenoted. Themotoris gradually loaded up to rated current. All meter readings including the spring balance reading are tabulated.Tabular Column:Sl. No.InputCurrent (A)Speed (r.p.m.)Input power (W) S1 (kg)S2 (kg)Torque (Nm)Power factorOutput power (W)Efficiency (%) DEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 17E M LAB MANUAL II INDUCTION MACHINES-LOAD TESTFIG 2.10Load Test on Single Phase Capacitor-Start Capacitor-Run Induction MotorCalculations:Spring balance readings S1 and S2 in kg. Torque can be computed using the equation, ( )1 2 (Nm) T S S rg , where ris the radius of the brake drum.Input power (Wattmeter reading) = Pin (watts)power (Pin)=VIcospower factor = cos= PinVIOutput Power = out2 NTP= (watts)60whereNis the speed in r.p.m.Tis the torque in Nm.% Efficiency = 100%outputinputResult: Load test on 1 phase induction motor. Performance curves plotted (Fig 2.9). Questions:1) What is the purpose of capacitor in the capacitor-start motor? Explain the difference between capacitor-start and capacitor start-run 1 induction motor?2) How is capacitor motors advantageous over split-phase motors?3) What type of capacitor is used in this type motor?DEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 18E M LAB MANUAL II INDUCTION MACHINES-LOAD TEST2.2.2.3LOAD TEST ONSQUIRREL CAGE INDUCTION MOTORAim:To conduct a load test on squirrel cage induction motor and to plot thefollowing characteristics.(ix) Efficiency vs. output(x) Torque vs. output(xi) pf vs. output(xii) Line current vs. output(xiii) Slip vs. torqueInstruments Required: 3 Autotransformer, tachometer, Voltmeter, Ammeter, Wattmeter.Machine Details: note the name plate details of the machine.Theory:Stableoperationofaninduction motor lies over the linear portion of its torque-speed curve. The slope of this straight line depends mainly on the rotor resistance. Higher the resistance, sharper the slope. The linearrelationshipbetweentorqueandspeed enables to establish a very simple equation between different parametersof aninductionmotor. Theparametersunder twodifferent loadconditionsarerelatedbythe equation 22 2 12 11 1 2T R VS ST R V _ , . The only restriction in applying the above equation is that the new torque 2T must not be greater than 2211VTV _ ,. It yields an accuracy of better than 5% which is sufficient for all practical purposes.Procedure:ConnectionsaremadeasshownasinFig2.11. Initiallythedimmerstatiskept at minimum position. Supply is switched on. The motor is started by increasing the voltage (by adjusting the autotransformer) up to rated value.The motor is loaded in steps, up to the rated value by means of a brake drum. For each step, line voltage,line current, input power and balanced readings are noted and tabulated.Tabular Column:Sl. No.InputCurrent (A)Speed (r.p.m.)W1 (W)W2 (W)Input power (W) S1 (kg)S2 (kg)Torque (Nm)Output power (W)Efficiency (%) Slip (%)Power factorDEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 19E M LAB MANUAL II INDUCTION MACHINES-LOAD TESTFIG 2.11 Load Test on Squirrel-Cage Induction MotorCalculations:Input power = 1 2W W +(watts).Torque can be computed using the equation ( )1 2~ T S S rg , where 1S and 2S are the balance readings, r is the radius of the brake drum and g is acceleration due to gravity (9.81 m/s2).Output power = 260NT (watts)whereNis the speed in r.p.m.Tis the torque in Nm.% Efficiency = 100outputinputSynchronous speed, 120sfNp, where fis supply frequency and p, the no. of poles.% 100ssN NslipN ( )1 2 11 23 ~tanW WW W 1 1+ 1 ]power factor = cosResult: Load test on squirrel cage induction motor is conducted and performance characteristics plotted (Fig 2.9).Questions: 1. If oneofthephasesgoesout, whenandinductionmotor isdeliveringfull loadwill themachine continue to run? If so, what will be the effect on the motor?2. How will you prevent the above situation?3. Can an induction motor work as generator? Explain.DEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 20E M LAB MANUAL II INDUCTION MACHINES-LOAD TEST2.2.2.4LOAD TEST ONSLIP RING INDUCTION MOTORAim:To conduct a load test on 3 slip ring induction motor and to plot thefollowing characteristics.(xiv) Efficiency vs. output(xv) pf vs. output(xvi) Line current vs. output(xvii) Speed vs. outputApparatus Required: 3 Dimmerstat, tachometer, Voltmeter, Ammeter, Wattmeter.Machine Details: note the name plate details of the machineTheory: The 3 slip ring induction motor can be started using dimmerstat or rotor resistance starter. The star-connected rotor winding leads are coupled to the three slip rings. Three external leads brought out from the slip rings are then connected to the Rotor resistance starter. Procedure: Connections are made as shown as in Fig 2.12. Supply is switched on with rotor resistance starter at start position. Initially, the motor is started at maximum resistance position ( Start position ), then as the motor gains speed, its cut down to the minimum resistance position (Run position).The motor is loaded in steps, up to the rated value by means of a brake drum. For each step, line voltage, line current, input power and balanced readings are noted and tabulated.Tabular Column:Sl. No.InputCurrent (A)Speed (r.p.m.)W1 (W)W2 (W)Input power (W) S1 (kg)S2 (kg)Torque (Nm)Output power (W)Efficiency (%) Slip (%)Power factorDEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 21E M LAB MANUAL II INDUCTION MACHINES-LOAD TESTFIG 2.12Load Test on Slip-RingInduction MotorCalculations:Input power = 1 2W W +(watts).Torque can be computed using the equation,( )1 2T S S rg , where 1S and 2S are the balanced readings, r is the radius of the brake drum and g is acceleration due to gravity (9.81 m/s2).power factor = cosOutput power = 260NT (watts)whereNis the speed in r.p.m.Tis the torque in Nm.% Efficiency = 100outputinput%Synchronous speed, 120sfNp, where fis supply frequency and p, the no. of poles.% 100ssN NslipN ( )1 2 11 23 ~tanW WW W 1 1+ 1 ]Result: Load test on slip ring induction motor conducted, and performance curves (Fig 2.9) plotted.Questions: 1. Why resistances are included in the rotor circuit during starting?2. What is the effect of adding external resistances to the rotor on (a) Maximum Torque and (b) Starting Torque?DEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 22E M LAB MANUAL II INDUCTION MACHINES-VARIATIONOFTSWITH ROTOR RESISTANCE2.2.3VARIATION OF STARTING TORQUE WITH ROTOR CIRCUIT RESISTANCE FOR A SLIP RING INDUCTION MOTORAim: 1) To determine the variation of starting torque with resistance added to the rotor circuit and to draw the graph: starting torque Vs rotor resistance.2) To verify the above results by means of calculations based on the circle diagram.Machine Details: note the name plate details of the machineInstruments Required: Ammeters, Voltmeters, Wattmeters (lpf and upf)Theory: Varying the values of resistance in the rotor circuit can affect the characteristics of the motor in 3 ways: (1) variation in the starting torque and current, (2) smooth acceleration and (3) variation in operating speed.The external resistances in the rotor circuit reduces the speed at which the rotor will operate with a given load torque. If the rotor resistor is designed for continuous duty, a portion of it may be allowed to remaininthecircuit, thus obtaining reduced-speed operation. Therefore, the motor has a varying speed characteristic; i.e., any change in load results in a considerable change in speed. However, the efficiency of a wound-rotor motor, including the 2I Rlosses in the rotor resistance, is reduced in direct proportion to the speed reduction obtained.Procedure: Connections are made as shown in Fig 2.13. The slip rings are short circuited and rated voltage is applied through the auto transformer. All the meter readings are tabulated (Table 1.). Then connections are made as Fig 2.14. The rotor is blocked by applying a brake-load suitably. Initially, the rotor windings are short-circuited through the ammeters (i.e., the external resistances connected to each rotor phase are completely cut out). Now supply to the dimmerstat is switched on and voltage gradually increasedtill thecurrent ontherotor circuit doesnot exceedtheratedvalue. Thebrake-loadisnow gradually released until the rotor tends to rotate. At this instant, the readings of the spring balances (S1 and S2), stator impressed voltage Vsc, stator current Is, stator input power Wsc, rotor current Ir and voltage across theexternal resistanceconnectedtoeachrotor phaseVrarenoted(Table3). Thesameprocedureis repeated with the rotor kept in different relative positions with respect to the stator and for different values of external resistances added, keeping the rotor current always constant to some value.Tabular Column:Table 1:No Load Test:Measurement of Ra:Vo (V) Io (A) W1(watts)W2(watts)Wo=W1+W2 (watts)V (V) I (A) Ra () 'a a1 a3R =R2R= 1.2 RDEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 23E M LAB MANUAL II INDUCTION MACHINES-VARIATIONOFTSWITH ROTOR RESISTANCETable 2 (Test Data) :Sl No.Impressed Voltage Vsc (volts)Stator current Is (A)3 stator input power Wsc (watts)Rotor Current Ir (A)Voltage across External Resistance of the rotor circuit Vr (volts)Brake - Load1S(kg)2S(kg)1 2~ S S(kg)Table 3 (Test Results) :Sl. No.Starting Torque sT(kg-m)(from balanced readings)Starting Torque based on circle diagram External resistance RRVrI()01R ()'2R()SNW (watts)sT (based on circle diagram)(kg-m)Fig 2.13No- Load Test on Slip Ring Induction Motor Fig 2.14Blocked Rotor Test on Slip Ring Induction MotorDEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 24E M LAB MANUAL II INDUCTION MACHINES-VARIATIONOFTSWITH ROTOR RESISTANCECalculations:Starting torque (with normal voltage applied Vo) as calculated directly from the balance readings is given by( )201 2~sscVT S S RV _ ,kg-mwhereR = effective radius of brake drum in metres.To calculate sTbased on circle diagram:01 23scsphWRI()Stator resistance per phase, 1 aR= 1.2 R()Equivalent rotor resistance per phase referred to stator, '2 01 1R R R Blocked rotor power with normal voltage applied is 20SN scscVW WV _ ,(watts)Starting torque based on circle diagram is, ( )'0 2012 9.81SNssW W RTN R _ , kg-mFig 2.15Starting Torque vs Rotor resistanceResult: The starting torque computed directly from the balance readings and that based on circle diagram are tabulated as in Table 3. From Table 3, variation of starting torque (sT) vs. additional rotor resistance per phase (r) is plotted.Questions:1) What do you mean by critical slip (Scr) of an induction motor? Give an expression for Scr in terms of the machine parameters.?2) Sketch a family of torque-slip curves with different values of resistances inserted to the rotor circuit.DEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 25E M LAB MANUAL II INDUCTION MACHINES-POLE CHANGING MOTOR2.2.4POLE CHANGING INDUCTION MOTOR Aim: 1) To conduct no load test and blocked rotor test for the different pole (speed) configurations and to draw the circle diagrams (on same sheet) for all the cases. From the circle diagrams, compare the following for the different pole configurations:(i) Maximum output,(ii) Starting torque,(iii) Maximum torque (iv) Full load slip.Machine Details: Note the name plate details of the machine.Apparatus Required: Ammeter, Voltmeter, Wattmeters (lpf and upf)Theory:By providing an induction motor with a winding or windings developing alternative numbers of poles, it is givena numberofpossiblesynchronous (and therefore running) speeds. Since squirrel cage rotor can adjust itself to any number of poles, the cage rotor can be conveniently used with pole changing method of speed control. Procedure: No Load Test: Connections are made as shown in Fig 2.16. Supply is switched on and voltage gradually increased with the help of dimmerstat to rated voltage. The ammeter, voltmeter and wattmeter readings are taken for 4 pole operation. The same procedure is repeated for 8 pole configuration.BlockedRotorTest:ConnectionsaremadeasshowninFig2.17for4poleconfiguration. Supplyis switched on and voltage gradually increased with the help of dimmerstat till the current in the ammeter reads the rated value. The ammeter,voltmeter and wattmeter readings are taken. The same procedure is repeated for 8 pole configuration.Stator winding resistance: To find the stator winding resistance/phase, connections are made as shown in Fig 2.18. DC supply is given, keeping the rheostat at the maximum position. Voltmeter and ammeter readings are recorded.Tabular Column:Table 1:No Load Test: Blocked Rotor Test:No. of polesVo (V) Io (A) W1(watts)W2(watts)Wo=W1~W2 (watts)No. of polesVsc (V)Isc (A) Wsc (watts)

Measurement of Ra:No. of polesV (V) I (A) Ra () DEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 26E M LAB MANUAL II INDUCTION MACHINES-POLE CHANGING MOTORa a 1 1 1a a1 aR = R(in case of 4-pole, keeping U , V , W shorted)R = 4 R(in case of 8-pole)R= 1.2 R Table 2:Test Results:No. of poles Maximum power output (watts)Starting torque (N-m)Maximum torque (N-m)Full load slip (p.u.)Fig 2.16No- Load Test on Pole Changing Induction MotorDEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 27E M LAB MANUAL II INDUCTION MACHINES-POLE CHANGING MOTORFig 2.17Blocked Rotor Test on Pole Changing Induction MotorFig 2.18Circuit to determine Stator Winding ResistanceDEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 28E M LAB MANUAL II INDUCTION MACHINES-POLE CHANGING MOTORCalculations:No-load phase angle,-1 ooo oW = cos3VIShort-circuit phase angle, -1 scssc scW = cos3VIso1sV phZ= I phsco1 2scphWR= 3 I2 o1 1= R R R Draw circle diagram (refer fig 2.4):ratedSN SscVI =I V = _____ / (c:s) = _____ cm2ratedSN SCSCVW =W =______wattsV _ ,Assume the current scale (c:s) to draw the circle diagramPower Scale = rated scale3V I(W/cm)Circle diagram is drawn for both 4-pole and 8-pole connections (on the same graph sheet). Full load power factor, cos1 = NHOHSlip = KLLHEfficiency = HKHN100%Deduction from circle diagram Starting torque s scaleT =ADP(syn. watts)Maximum torque Tm = scaleQQ P(syn.watts) Maximum output Pm = scaleSS P(syn.watts) Result: The No- load test and Blocked Rotor test conducted, and various parameters compared for 4-pole and 8-pole.Questions:1) Can slip ring induction motor be used for pole changing method of speed control? If not, why?2) Mention the fields of application of pole changing.3) Explain the principle adopted in the connection of the stator coils for obtaining different speeds.DEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 29E M LAB MANUAL II SYNCHRONOUS MACHINESSYNCHRONOUS MACHINES3.1 IntroductionSynchronous machinesare rotating machines which run at synchronous speed. The synchronous speed is a function of the supply frequency and the no. of poles of the machine. There are two types of synchronous machines based on rotor construction, namely,(i)the cylindricalrotor machine and (ii) the salient pole machine.The performance characteristics of interest are voltage regulation, V-curves and power angle measurement.The terminal voltage of the alternator varies with changes in magnitude and power-factor of the consumer demand (i.e. load current and load power factor). Voltage regulation is defined as the rise of voltage expressed in percent of rated voltage when the load is reduced to zero, the field excitationandfrequencyremainingat their initial values. Thephraseriseinvoltageinthe definitionpresupposes aninductiveor noninductiveload, becauseif theloadis sufficiently capacitive, the magnetizing effect of leading current may cause voltage under load condition to be higher than that at no load. In that case, effect of reducing the load to zero is to produce a fall in voltage and the regulation must then be treated as negative instead of positive.Thefactors whichaffect alternator regulationarearmaturereaction,armatureleakage impedance and the change in field leakage with change in excitation. These are fundamentally the same as those involved in d.c. generators, the differences being due to the effect of power factor upon armature reaction and the substitution of armature impedance in place of armature resistance in case of dc machine.The regulation of an alternator can be determined by actually loading it and observing the change in terminal voltage when the load is disconnected keeping speed and excitation fixed. This method is out of question under full load condition except in the case of small machines, because of thecost of providingmotivepower andauxiliaryapparatus for absorbingtheoutput. So, predetermination methods have to be used, such as (1) EMF Method, (2) MMF Method, (3) Zero Power Factor (Potier) method and (4) ASA Method. In the case of a salient pole machine, the air gap around the field is not uniform. So, the reluctance offered to MMF wave also varies, being lowest when it is aligned with field pole axis (d-axis) and is highest when it is aligned at 90 to field pole axis (q-axis). Thus we can say that flux established by armature MMF wave is varying with special position of wave axis with respect to d-axis.So to find regulation,the methods based on cylindrical rotor theory are not accurate. The effect of saliency can be taken into account by resorting to two-reaction theory suggested by Andre Blondel. This introduces the concept of two reactances, one along the d-axis and the other along q-axis. To find out these quantities, slip test is conducted.Process of connecting an incoming generator in parallel with others already in operation is called synchronization. Before synchronization it is necessary that (1) the speed of the incoming generator corresponds exactly to the frequency of the system to which it is to be connected, (2) its voltage must be numerically equal to that of the system where the connection is made, and (3) its voltage must be in phase with that of the system. This requirement means that phase sequence of incomingmachinemust be sameas that of thesystem. Whenthe individual generators are DEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 30E M LAB MANUAL II SYNCHRONOUS MACHINESrelatively small, synchronization is done manually. In this case, the exact moment of synchronization is indicated by incandescent lamps or synchroscopes, connected properly in the circuit. But with the growth of system capacity and rating of generating units, it becomes necessary to resort to automatic devices.In a synchronous machine, the real electrical power exchanged with the bus bars is controlled by the mechanical shaft power irrespective of excitation.The excitation on the other handgovernsonlythe power factor ofthe machinewithoutaffectingthe real power flow.The operating characteristics of the machine can be studied under conditions of the variable load and variable excitation, keeping one of these quantities constant and varying the other. The variation of armature current with excitation at constant load gives the V-curves of the synchronous machine. It is seen that the magnitude of armature current exhibits a minimumwhen its excitation is continuously increased from an under excited state. This minimum corresponds to upf condition.Since the synchronous motor is not self starting, the unexcited rotor is speeded up to near synchronous speedbysomemethodandtheexcitedbythed.c. source. Thentherotor gets magnetically locked with the stator field and runs at synchronous speed.The coupling between stator and rotor is not an absolutely rigid one. As the load on the motor is increased, the rotor progressively tends to fall back in phase by some angle but still runs at synchronous speed. The machine meets the changing requirements of load torque by adjustment of this angle. This angle is known as load angle or power angle or torque angle.DEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 31E M LAB MANUAL II SYNCHRONOUS MACHINES-REGULATION BY DIRECT LOADING3.2.1 REGULATION OF ALTERNATOR BY DIRECT LOADINGAim: 1.To determine the regulation of the 3-phase alternator by direct loading, and todraw the regulation vs. load curve.Instruments Required: Ammeter, Voltmeter, tachometerMachine Details: note the name plate details of the machineTheory: Voltage regulation is defined as the change in terminal voltage expressed as a percentage of the rated voltage, when the load at a given power factor is removed, with speed and field current remaining unchanged.Voltage regulation = oE -V100%VThe voltage regulation may be positive or negative depending on whether the power-factor load is lagging (Eo increases) or leading (Eo decreases). The importance of computing the voltage regulation are:(i) Whenloadisthrownoff, voltagerisemust beknown, sincethewindinginsulation should be able to withstand this increased voltage.(ii) Voltageregulationdetermines the type ofautomatic voltagecontrol equipmentto be used.(iii) Steady-state short-circuit conditions and stability are affected by the voltage regulation.(iv) Parallel operation of one alternator, with other alternators is affected considerably by its voltage regulation.In case of small machines, the regulation may be found by direct loading.Procedure:Make connections as shown in Fig 3.1. Run the alternator at synchronous speed, adjust the terminal voltagetoratedvaluebyadjusting field currentusingrheostat, Rh.Notethe field currentand terminal voltage. Now switch on S. Adjust the load simultaneously keeping the terminal voltage at rated value. Open S and note the terminal voltage. This gives the induced emf corresponding to that field current, given by the ammeter, A2. Repeat the procedure for different values of load currents. Tabulate the results.Tabular Column:A1 A2 V (on load) Vo (Off load) % Regulation(Vo-V)/V*100Results:1. Regulation of alternator at various loads2. Graph showing variation of regulation with load currentQuestions:1. Can the regulation on lagging pf loads be obtained by this method of direct loading?2. What are the causes of changes in voltage in alternators when loaded?DEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 32E M LAB MANUAL II SYNCHRONOUS MACHINES-REGULATION BY DIRECT LOADING3. What practical steps are adopted to ensure that the voltage at the generator terminal, under varying load conditions, remains constant?DEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 33E M LAB MANUAL II SYNCHRONOUS MACHINES-REGULATION BY EMF AND MMF METHOD3.2.2 REGULATION OF ALTERNATOR BY EMF AND MMF METHODAim: 1. To plot the open circuit and short-circuit characteristics2. To predetermine the full load regulation of an alternator at different power factor(upf, 0.8 pf lag, 0.8 pf lead) using (a) EMF (Synchronous Impedance) method and (b) MMF (Ampere Turn) method. Instrument Required: Ammeters, VoltmetersMachine Details: Note machine specifications from machine name plateTheory:Inthecaseof largemachines, thecost of findingtheregulationbydirect loadingbecomes prohibitive. Hencesynchronousimpedance or EMF method and Ampere-turn or MMF method are two indirect methods used to determine voltage regulation. Both the methods require (1) Armature (or stator) resistance Ra, (2) Open circuit / No load characteristic and (3) Short circuit characteristic.EMF method: This procedure can be applied to cylindrical rotor synchronous machines only, because the resultant airgapfluxisnotaffectedbytheangularpositionoftherotor. Inthismethod, thearmature reaction is treated as an additional voltage drop by introduction of the fictitious armature reaction reactance Xa. Thesynchronousimpedanceisdetermined by conductingOC and SC test. The value of regulation usingthis valueobtainedfromactual loadingconditions. Hencethismethodisknownaspessimistic method.MMFmethod:In this method, theleakage reactance is treated as an additional armature reaction. The mmf required to overcome the demagnetizing effect of armature reaction on full load, is obtained from SC test .The field ampere turns required to produce to produce full load current on SC balances the armature reaction and impedance drop. The regulation calculated by this method is less than that in practice .Hence it is known as Optimistic method.Procedure:Open circuit and Short circuit characteristics:1) OC Test: Connections are made as shown in fig. 3.2. Keeping the switch open and rheostat in maximum position alternator is driven by the prime mover at rated speed in the appropriate. The field current is adjusted by means of rheostat for different values upto 125% of rated excitation. Each time OC voltage and corresponding field current are noted.2) SC Test: Here after the alternator is driven at rated speed. Switch is closed and stator current is adjusted to its rated value by adjusting the rheostat. Corresponding field currents are noted.To measure the stator resistance per phase keeping the rheostat in maximum position the supply is switched on. The voltmeter and ammeter reading is noted.3) Stator Resistance: To measure stator resistance per phase keeping the rheostat in maximum position and supply is switched on (Fig 3.3). The voltmeter and ammeter readings are noted.DEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 34E M LAB MANUAL II SYNCHRONOUS MACHINES-REGULATION BY EMF AND MMF METHODTabular Column:Voltage(V) Current (I) Raa dcR 1.2 r OCCEo (V) If (A)SCCIfsc (A) IL (A)Calculations:Draw the graphs 1. OC phase voltage vs. field current2. SC phase current vs. field currentEMF method (synchronous impedance method)V Rated phase voltage on open circuitIscThe short circuit current corresponding to the field current producing rated voltageZs Synchronous impedance/phase=scV OC voltageI SC current at some excitationRaThe resistance per phase of the windingXs=2 2Zs Ra At any load current, I and pf, cosscsEo=V+I ZAt 0.8 pf lag( ) ( )2 20cos sinsc a sc sE V I R V I X + + +At 0.8 pf lead( ) ( )2 20cos sinsc a sc sE V I R V I X + + At upf( ) ( )2 20 sc a sc sE V I R I X + +Then calculate,% regulation =Eo-VV100 % for the three cases.DEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 35E M LAB MANUAL II SYNCHRONOUS MACHINES-REGULATION BY EMF AND MMF METHODMMF Method (Ampere Turn Method) From graph for MMF method, find the corresponding value of E0 for the field current at 0.8 pf lag, 0.8 pf lead and upf. The find the voltage regulation from following relation:Then regulation= Eo VV100 %Results: The OCC and SCC characteristics were plotted and regulation was determined by EMF and MMF methods.Questions1. Explain the shape of OCC. Why do you get a straight line for SCC?2. What is meant by synchronous reactance?3. What is the practical application of pre-determining the regulation of an alternator?Fig 3.2. Regulation of Alternator by EMF and MMF Method Fig 3.3DEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 36E M LAB MANUAL II SYNCHRONOUS MACHINES-REGULATION BY POTIER AND ASA METHOD3.2.3 REGULATION OF ALTERNATOR BY POTIER AND ASA METHODAim:1. To plot the ZPF characteristics, armature reaction MMF, Potier reactance of a given alternator2. Predetermine the full load regulation at 0.8 pf lag, 0.8 pf lead and upf using Potier and ASA method. Theory:Potier method or ZPF method: In the Potier method, the leakage reactance drop and the mmf required for overcoming the armature reaction can be determined. This method is more accurate than the emf and the mmf methods.The experimental data required for this method are1) OCC2) SCC3) Armature resistance 4) Zero Power Factor characteristicsVoltage regulation of an alternator is defined as the rise in terminal voltage expressed as a percentage of ratedvoltage, whentheloadisreducedtozerothefieldexcitationandfrequencyremainingconstant. Synchronous impedance Zs= OC and SC current for the same excitation. (OCC is a drooping curve because of the effect of saturation. During SC condition the power factor is zero. Power factor lagging and therefore the effect of armature reaction is demagnetizing. Thus the net flux during SC condition is small and hence SCC is a straight line.Significance of potier method is that the effect of armature reaction and leakage reactance are separately accounted.Procedure:1) OC Test: Connections are made as shown in figure 3.4. Keeping the switch open and rheostat in maximum position alternator is driven by the prime mover at rated speed in the appropriate. The field current is adjusted by means of rheostat for different values upto 125% of rated excitation. Each time OC voltage and corresponding field current are noted.2) SC Test: Here after the alternator is driven at rated speed. Switch is closed and stator current is adjusted to its rated value by adjusting the rheostat. Corresponding field current is noted To measure the stator resistance per phase keeping the rheostat in maximum position, fig 3.3,the supply is switched on. The voltmeter and ammeter reading is noted.3) Potier Method: Connections are made as shown in figure 3.5. The alternator is driven at its rated speed. The load is connected to the alternator by means of a 3 pole switch. Now the field excitation is adjusted so that the alternator line current is equal to its rated value. Corresponding terminal voltage and field current are noted, ensuring armature current is maintained at its rated value and speed is also maintained at its rated value. Terminal voltage Vph and If are noted.DEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 37E M LAB MANUAL II SYNCHRONOUS MACHINES-REGULATION BY POTIER AND ASA METHODCircuit Diagram: Fig 3.4. Circuit diagram to plot OC and SC characteristicsFig 3.5. Circuit Diagram to plot ZPF CharacteristicDEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 38E M LAB MANUAL II SYNCHRONOUS MACHINES-SLIP TEST ON ALTERNATORTabular Column:Stator Winding ResistanceVoltage(V) Current (I) RaZero power factorVoltage IFIa IphSCCIfsc(A) IL (A)Calculations:The OCC is reproduced from the previous experiment. The field current required to circulate full load armature current on short circuit is also taken from previous experiment. With these datas the potier triangle and the full load zero power factor characteristics are drawn by Fischer-hinnen construction. From the potier triangle the full load leakage reactance drop and the field current required to overcome armature reaction are measured. The full load regulation is calculated at the desired power factor XL -- obtained from potier triangleRa-- obtained from resistance measurement( )a lE V I R jX + +Potier Method:Full Load Current, IFL = ?Per phase resistance, R = ?From Potier Triangle, IXL = full load leakage reactance dropAt upf( ) ( )2 2LE V IR IX + + , then 1fI =field current corresponding to E,2fI field current to overcome armature reaction 1 22 2f f fI = I +IE0 = Voltage corresponding to IfAt 0.8 pf lag( ) ( )2 2cos sinLE V IR V IX + + + , then 1fI =field current corresponding to E,2fI field current to overcome armature reaction 1 2 1 22 2f f f f fI = I +I 2I I cos(90 ) +E0 = Voltage corresponding to IfDEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 39E M LAB MANUAL II SYNCHRONOUS MACHINES-SLIP TEST ON ALTERNATORAt 0.8 pf lead( ) ( )2 2cos sinLE V IR V IX + + , then 1fI =field current corresponding to E,2fI field current to overcome armature reaction 1 2 1 22 2f f f f fI = I +I 2I I cos(90 ) E0 = Voltage corresponding to If% regulation = Eo VV100 %, corresponding to the different values of pf.ASA Method:Field current corresponding to rated current in SC test, 1fI = ?nf(length from X-axis to airgap line at V) IAt upf( ) ( )2 2LE V IR IX + +s1fI= field current from air gap line to E in OCC1 n2 2f f fI I I +s1f f fI =I I +Voltage in OCC corresponding to If, E0 = ?At 0.8 pf lag( ) ( )2 2cos sinLE V IR V IX + + +s2fI= field current from air gap line to E in OCC1 n 1 n2 2f f f f fI I I 2I I cos(90 ) + +s2f f fI =I I +Voltage in OCC corresponding to If, E0 = ?At 0.8 pf lead( ) ( )2 2cos sinLE V IR V IX + + s3fI= field current from air gap line to E in OCC1 n2 2f f fI I I +s3f f fI =I I +Voltage in OCC corresponding to If, E0 = ?% regulation= Eo VV100 %, corresponding to the different values of pf.DEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 40E M LAB MANUAL II SYNCHRONOUS MACHINES-SLIP TEST ON ALTERNATORResults: the experiment is conducted and the percentage regulation is found out by Potier and ASA methodQuestion1. Why this method is called approximate?2. What will be the reading of a three phase wattmeter introduced in the armature circuit?3. What is the effect of saliency on the above result? if the ratio of direct axis to quadrature axis is given, how is the vector diagram modified?4. How does the over-exited synchronous motor represent the behavior of an alternator delivering Z.P.F current?DEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 41E M LAB MANUAL II SYNCHRONOUS MACHINES-SLIP TEST ON ALTERNATOR3.2.4 SLIPTESTANDREGULATIONOFSALIENTPOLEALTERNATORUSINGTWO-REACTION THEORYAim:1) To find Xd and Xq of a salient-pole synchronous alternator by slip test2) Predetermine the full load and half load regulation at upf, 0.8 pf lag and 0.8 pflead.Machine Details:Apparatus Required: Ammeter, voltmeter, tachometer.Theory: The resultant armature m.m.f. of a salient pole synchronous machine is stationary with respect to field m.m.f. Thus, to determine the effect of armature m.m.f., it is resolved into two components one along direct axisandtheother alongquadrature axis. The d-axis component of armature m.m.f.can establish more flux as this has to overcome lesser reluctance, while the magnetic circuit along q-axis path has higher reluctance as such q-axis m.m.f will establish less flux.By conducting slip test, we can determine the d-axis and q-axis synchronous reactances. For this, the field is kept unexcited and rotor is driven at a speed slightly different from the synchronous speed. Since the rotor speed is slightly above or below the speed of rotating magnetic field, a slip speed is created. As a result, the rotor poles slip slowly through the consequent poles produced by the armature current. The sets of poles will be alternating in line and in phase quadrature. When they are in line, the armature m.m.f. cuts through the main magnetic circuit and at that instant the impressed voltage divided by the corresponding current will be Xd. When the sets of poles are in phase quadrature, ratio of armature voltage to armature current will be Xq.Direct axis synchronous reactance, Xd = maxminMax. value of armature voltage/phaseMin. value of armature current/phase IVQuadrature axis synchronous reactance, Xq = = minmaxIVProcedure: Connections are made as shown in Fig 3.6, keeping the field windings open, and the alternator is driven in the appropriate direction by the prime mover at a speed 1% above or below the synchronous speed. Now a positive sequence lowvoltage (about 20-25%of ratedvalue) is appliedtothe stator throughthe dimmerstat.[Thesequenceof thevoltageappliedshouldbesuchthat thedirectionof therotatingmagneticfield produced by this 3 supply and the direction of actual rotor rotation should be the same. This is verified by observing the reading of the voltmeter (V1) connected across the field winding if the phase sequence is correct the voltmeter (V1) will give almost zero reading; otherwise a large value the phase sequence can be corrected, if required, by interchanging any two leads of the supply.]DEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 42Min. value of armature voltage/phaseMax. value of armature current/phaseE M LAB MANUAL II SYNCHRONOUS MACHINES-SLIP TEST ON ALTERNATORWhen the slip is adjusted to be very small, the pointers of the ammeter (A) and the voltmeter (V) will swing slowly from a maximum to a minimum. The maximum and minimum readings of the ammeter and the voltmeter(i.e.Imax,Imin, Vmax,Vmin)are observed and tabulated.Two or three sets of readings in the vicinityofthe rated currentscan betaken by suitably adjusting the voltage and these readings are also tabulated.Stator resistance per phase (Ra ) is measured using d.c. measurements (Fig 3.3). Tabular Column:Sl. No. Vmax(volts)Vmin(volts)Imax(A)Imin(A)Xd()Xq()To find Stator winding resistanceV(volts)I (A) R

Ra = 1.2RCalculations: maxminIdVX minmaxIqVX Find mean of dX and qXFind 'aIR , dIX and qIX, whereIis the rated current of alternator.phV V % Regulation at upfE= OE (obtained from phasor diagram 1.) % Regulation =100%oE VV % Regulation at 0.8pf lagE= OE (obtained from phasor diagram 2.) DEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 43E M LAB MANUAL II SYNCHRONOUS MACHINES-SLIP TEST ON ALTERNATOR% Regulation =100%oE VV% Regulation at 0.8pf leadE= OE (obtained from phasor diagram 3.) % Regulation =100%oE VVResult: Slip test conducted to find Xd, Xq of the alternator, full load regulation at 0.8 pf lag, 0.8 pf lead and upf is determined.Questions:1) Sketch the variation of armature current and voltage as would be obtained from an oscillogram. Why is the current minimum when voltage is maximum and vice versa?2) What is the load angle when the machine is delivering full load at 0.8 pf lag.Fig 3.6 Slip TestDEPT OF ELECTRICAL & ELECTRONICS ENGINEERINGMAR BASELIOS COLLEGE OF ENGINEERING & TECHNOLOGY, NALANCHIRA, TVM-695015 44E M LAB MANUAL II SYNCHRONOUS MACHINES-SYNCHRONIZATION OF ALTERNATOR 3.2.5 SYNCHRONIZATION OF ALTERNATORS BY BRIGHT LAMP AND DARK LAMP METHOD AND CONTROL OF REACTIVE POWER Aim: i) To synchronize the 3 alternator to the mains by dark lamp and bright lamp method. ii) Control of reactive power and determination of V and inverted V curvesApparatus Required:voltmeter, ammeter, wattmeter, rheostats and tachometer.Machine Details: note the name plate details of the machine.Theory: The operation of connecting an alternator in parallel with another alternator or with common bus barisknownassynchronizing. Forproper synchronization of alternator,the following three conditions must be satisfied. (1) The terminal voltage of the incoming alternator must be the same as bus bar voltage, (2) The speed of the incoming machine must be such that its frequency equals the bus bar frequency, (3) The phase of the alternator voltage must be identical with the phase of the bus bar voltage. It means that the switchmustbeclosedattheinstant thetwovoltageshavecorrect phaserelationship. Condition(1)is indicated by voltmeter, while (2) and (3) by dark lamp or bright lamp method.If there is a mismatch in the frequency of the incoming machine with that of busbar, there will be a phase difference between their voltages (even when they are equal in magnitude, which is determined by field excitation). This phase difference will be continuously changing with the changes in their frequency. The result is that their resultant voltage will undergo changes similar to the frequency changes,Procedure: Connections are made as shown in figure 3.7 .R1 is kept in max position and R2 in minimum position. Alternator field rheostat R3 is kept at max positioned supply on motor side is switched on.R1 is cut off gradually as the machine picks up speed.R2 is adjusted to run the machine at rated speed.The 3 phase and DC supply on the alternator side is switched on. Excitation of alternator is varied by R3 to attain same value as supply voltage.Dark lamp method:if the phase sequence is correct all the lamps L1 L2 and L3go dim and bright simultaneously. Else exchange the leads of any two lamps on supply sideBright lamp method:here L2 and L3 are cross connected, fig 3.8. If the three lamps illuminate in cyclic manner, the phase sequence is the same. Else interchange the two supply leads.The flickering speed is reduces by adjusting the rheostat R2.in the case of dark lamp method, switch S is closed at the middle of the dark period of all the three lamps. While in the case of bright lamp method, switch S is closed at the instant when the cross connected lamp is at the middle of the dark period.AdjustR3tovarytheexcitationi.e. field current is varied and corresponding armature and watt meter reading are noted correspondingly V curves and inverted V curves are plotted.Tabular Column:IL(A) IF(A) W(Watt)Calculations:I min = IL cos Result: E M LAB MANUAL II SYNCHRONOUS MACHINES-SYNCHRONIZATION OF ALTERNATORQuestions:1) What are the conditions to b satisfied for synchronization? How are they satisfied in dark lamp method of synchronizing?2) What are the other methods of synchronizations?3) What are the advantages of dark lamp method over bright lamp method?Fig 3.7. Dark Lamp MethodFig 3.8. Bright Lamp MethodE M LAB MANUAL II SYNCHRONOUS MACHINES-SYNCHRONIZATION OF ALTERNATORAlternator field220V D.C SUPPLY220V D.C SUPPLYAR2FLE1 E2A1A2R3AF1 F2WUNVMVVLACL3L2L1415V,3PHASE 50HZ A.C SUPPLYL3L2L1E M LAB MANUAL II SPECIAL MACHINESSPECIAL MACHINES4.1 Introduction:Induction GeneratorAn "induction" generator is essentially a special purpose motor that is run slightly above synchronous speed by the turbine. Induction generators receive their excitation from the grid, or electric utility and they have no means of producing or generating voltage until such time the generator is connected to the grid. Induction generators are direct-drive. The frequency and voltage of the power generated with induction generators are governed by the frequency and voltage of the incoming electric utility line. Induction generators can only be run in parallel with the grid, which means when the electric grid goes down, or there is a blackout, all gensets, cogeneration and trigeneration power plants within the grid that has the blackout, also go down.V/F control of Induction Motors:An induction motor is operated by a power supply of variable voltage and variable frequency. The voltage and frequency of the variable-voltage variable-frequency power supply is changed by a control circuit to accelerate or decelerate the induction motor. For slowly controlling the speed of the induction motor, the ratio of the output voltage to the output frequency of the variable-voltage variable-frequency power supply is maintained substantially constant. The control circuit includes a voltage correcting means which, in response to a command for sudden acceleration or deceleration of the speed of the motor, corrects the output voltage of the power supply in accordance with the acceleration or deceleration rate and the prevailing magnitude of the output frequency of the variable-voltage variable-frequency power supply.Synchronous Induction Motor:Synchronous induction motor is a machine capable of running both as induction motor and synchronous motor during starting period and operates as a synchronous motor during running. Synchronous motor is made self starting by providing a special winding in the rotor poles known as damper winding. The short circuited bars are embedded in the field poles and the stator has 3 winding. AC supply given to stator winding produces a rotating magnetic field which causes the rotor to rotate.E M LAB MANUAL II SPECIAL MACHINES V/F CONTROL OF INDUCTION MOTOR4.2.1V/f CONTROL OF INDUCTION MOTORAim:(i) To run the machine at a frequency = 25Hz.(ii) To run the machine at 30 Hz in forward direction, reverse it and run it again at 30Hz and finally stop it.(iii) To run the motor at 25 Hz (1500 rpm) in forward direction, increases it to 50Hz (3000 rpm), reverse it, run it again at 50 Hz and conduct load test.Apparatus Required: V/F controller, voltmeter, ammeter, wattmeter, and tachometer.Machine Details: note the name plate details of the machine.Theory: If the flux carried by iron or steel in magnetic circuit is varied, hysterisis and eddy current losses are produced. The torque developed in a 3 motor depends on its speed. At full load the motor runs at a speed of N.Whenmechanicalload is increases,motor speed decreases until the motor torque becomes equal to the load torque. As long as the two torques are in balance, the motor will run at constant speed.The shape of the torque/ speed curve depends on the voltage and frequency applied to its stator. If frequency is fixed T is proportional to V2. Also, synchronous speed depends on supply frequency. Supply voltage and frequency are varied in the same proportion in order to maintain a constant flux in the air gap.Procedure:For Aim (i):1. Switch ON the power supply2. Press the LOCALREMOTE 1 1 ]key (REMOTE LED (SEQ,REF) is OFF)3. Set the frequency to 25 Hz using[ ] and[ ] key. Display shows 25.0 (reqF1 ]) LED ON.4. Press the[ ] ENTERkey to write the set frequency into the memory.5. Press[ ] DSPL key- LED display goes to 0.0.[ ]outF LED ON.6. Press[ ] RUN key LED display shows 25.0 in[ ]outF, while[ ] RUN LED is also ON, machine will run corresponding to a frequency of 25Hz.7. Press STOPRESET 1 1 ] button to stop the machine.For Aim (ii):1. Switch ON the power supply2. Press the LOCALREMOTE 1 1 ]key (REMOTE LED (SEQ,REF) is OFF)3. Set the frequency to 30 Hz using[ ] and[ ] key. Display shows 25.0 (reqF1 ]) LED ON.4. Press the[ ] ENTERkey to write the set frequency into the memory.5. Press[ ] DSPL key- LED display goes to 0.0.[ ]outF LED ON.6. Press[ ] RUN key LED display shows 30.0 in[ ]outF, while[ ] RUN LED is also ON, machine will run in forward direction.E M LAB MANUAL II SPECIAL MACHINES V/F CONTROL OF INDUCTION MOTOR7. Press[ ] DSPL three times,[ ] / F R LED ON, displays[ ] FOR (for forward direction).8. Set display using[ ] and[ ] keys to[ ] REV,[ ] / F R LED ON.9. Press the[ ] ENTERkey machine runs in reverse mode.10. Press[ ] DSPL four times, and display shows 30.0 in[ ]outF.11. Press STOPRESET 1 1 ] button to stop the machine.For Aim (iii)1. Switch ON the power supply2. Press the LOCALREMOTE 1 1 ]key (REMOTE LED (SEQ,REF) is OFF)3. Set the frequency to 25 Hz using[ ] and[ ] key. Display shows 25.0 (reqF1 ]) LED ON.4. Press the[ ] ENTERkey to write the set frequency into the memory.5. Press[ ] DSPL key- LED display goes to 0.0.[ ]outF LED ON.6. Press[ ] RUN key LED display shows 25.0 in[ ]outF, while[ ] RUN LED is also ON, machine will run corresponding to a frequency of 25Hz.7. Press[ ] DSPL key seven times, reqF1 ] LED ON.8. Press[ ] key to increase the frequency to 50.0, display shows 50.09. Press the[ ] ENTERkey10. Press[ ] DSPL key- LED display goes to 50.0.[ ]outF LED ON11. Press[ ] DSPL three times,[ ] / F R LED ON, displays[ ] FOR (for forward direction).12. Set display using[ ] and[ ] keys to[ ] REV,[ ] / F R LED ON.13. Press the[ ] ENTERkey machine runs in reverse mode.14. Press[ ] DSPL four times, and display shows 30.0 in[ ]outF.15. Load the machine, note the readings. Release the load and press STOPRESET 1 1 ].Result: Questions:1. What are the specific advantages of v/f method in controlling the speed of induction motors?2. How do you compare Pole changing method with v/f method?3. What is the use of cascade connection of induction motors?E M LAB MANUAL II SPECIAL MACHINES V/F CONTROL OF INDUCTION MOTORFig 4.1 V/f Control of Induction MotorE M LAB MANUAL II SPECIAL MACHINES SYNCHRONOUS INDUCTION MOTOR4.2.2 SYNCHRONOUS INDUCTION MOTORAim: To start the machine as an induction motor and also to determine V curves at no-load, constant input and constant output.Instruments Required: voltmeter, ammeter, wattmeter, rheostats and tachometer.Machine Details: 5kVA, 3, 415V, 7A,1500r.p.m synchronous induction motor.Theory:Synchronous inductionmotor is amachinecapableof runningbothasinductionmotor and synchronous motor during starting period and operates as a synchronous motor during running. Synchronous motor is made self starting by providing a special winding in the rotor poles known as damper winding. The short circuited bars are embedded in the field poles and the stator has 3 winding. AC supply given to stator winding produces a rotating magnetic field which causes the rotor to rotate.Procedure:The motor is kept at no load. Start the motor with switch initially connected across rheostat1, which is in the maximum position. When the speed becomes 95% of rated speed, cut off the resistance completely and the switch is changed to position2 so that when dc supply is given to the field, the field current varies by varying the field rheostat. Note all the meter readings for different field current values.Tabular Column: IL(A) If(A) W(watts)Circuit Diagram:E M LAB MANUAL II SPECIAL MACHINES SYNCHRONOUS INDUCTION MOTORResult: Questions:1. What methods can be applied to make a synchronous motor self starting?2. Draw the circle diagram for synchronous induction motor.3. Explain the principle of operation of synchronous induction motor.E M LAB MANUAL II SPECIAL MACHINES INDUCTION GENERATOR4.2.3 INDUCTION GENERATORAim:TofindthehysterisistorquebyLinks method and to find the variation of efficiency and power factor with slip.Instruments Required: Note the machine specifications from machine name plate.V1 -To suit the rated voltage of dc machineA1 - To suit the rated current of dc machineRh1- 1000, 1.2A rheostat(field)Rh2- 100, 5A rheostat(armature)V- To measure nearly double the ac voltageV2- To measure rated voltage of Induction motor A2-To measure rated current of Induction motorW1- To suit V2, A2, hpfW2- To suit V2, A2, hpfStroboscope or Tachometer to measure the speedMachine Details:Theory:Aninductionmotor connectedtoaconstant voltageandfrequencysupplyisabletorunonlyat sub-synchronousspeed. Supposeifthemotor is drivenbyanothermachine atsynchronous speed,then the relativespeedbetweentheair gapandmotor conductorsbecomezero, andtherotor emf andcurrent vanishes, the torque also becomes zero. Then the machine operates as an induction generator drawing its excitation or systemsupply. Determine the flux and frequency and hence the synchronous speed above which the induction generator must run to generate power. At super-synchronous speed, the condition of an inductor is similar to those at sub-synchronous speed for induction motor. The equivalent circuit and all characteristic equations for theinductionmotor alsoapplyfor inductiongenerator wherethe slipis introduced with a negative sign. An induction generator always operates with leading power factor.Procedure: Couple the Induction motor to a DC shunt machine. The direction of rotation of the two machines should be the same.Now start the set from the AC side and gradually apply rated voltage to the Induction motor. Then adjust the excitation of the DC machine and voltage is built up as a generator. When the generated DC voltage becomes equal to the DC rated voltage, parallel it to the DC mains. Then the DC machine just floats in the supply, neither giving nor consuming any electrical energy. The losses being supplied from the AC side.Increase the excitation of the DC machine. Induction machine runs as motor while DC machine works as a generator and feed DC back to the mains. Take the various meter readings for different sub synchronous speeds. Calculate the corresponding slip by a stroboscope.Under excite the DC machine. Induction machine acts as a generator as speed of the set increases. Again note the slip and various meter readings for different super synchronous speeds. Assume a suitable value (say 80 or 85%) for the efficiency of DC machine. Plot the variations of and pf with slip. Also plot AC powervariationwith% slipfor both sub synchronous, super synchronous speeds. Extend the graphs to E M LAB MANUAL II SPECIAL MACHINES INDUCTION GENERATORmeet the Y-axis. Take the intercept of the graph on the Y-axis. Then by Links method *hysterisis torque is half the Y intercept.Tabular columnMode V1A1V2A2W1W2Time forSlip%slip pf %E M LAB MANUAL II SPECIAL MACHINES INDUCTION GENERATOR10 revolutionsspeedMotorGeneratorCalculations Voltage across rotor winding, V ?Speed, N ?Line Current, I ?Wattmeter readings, W1, W2 ?Input Power, W = W1 + W2Output Power, Ws = W- 3I2RSynchronous Speed, Ns = 120 f /pSlip speed=10 60/(time for 10 rev)rpm% Slip=[(Ns-N)/Ns] 100From Graph: Find (1) rotor hysteresis loss, (2) Hysteresis TorqueResultsThe rotor hysteresis loss is determined by Links methodDraw the graph 1. AC power Vs % slip2. %, pf, current Vs %slipQuestions1. Why cannot ordinary Induction generator supply separate loads?2. What is meant by self excitation?3. Why is Induction generator not so common as Synchronous generator?4.2.4 LOAD TEST ONSQUIRREL CAGE INDUCTION MOTOR USING EDDY DYNAMOMETERE M LAB MANUAL II SPECIAL MACHINES INDUCTION GENERATORAim:To conduct a load test on squirrel cage induction motor using eddy dynamometer and to plot thefollowing characteristics.(xviii) Efficiency vs. output(xix) Torque vs. output(xx) pf vs. output(xxi) Line current vs. output(xxii) Slip vs. torqueInstruments Required: 3 Autotransformer, tachometer, Voltmeter, Ammeter, Wattmeter.Machine Details: note the name plate details of the machine.Theory: Stable operation of an induction motor lies over the linear portion of its torque-speed curve. The slope of this straight line depends mainly on the rotor resistance. Higher the resistance, sharper the slope. Loading is done using eddy dynamometer. It consists of an eddy current brake, control panel, pulley and a flexible coupling to couple the motor output shaft to the input side of the dynamometer.Procedure:Connections are made as shown as in Fig 2.11. Initially the dimmer stat is kept at minimum position. Supply is switched on. The motor is started by increasing the voltage (by adjusting the autotransformer) up to rated value.Themotor is loadedinsteps, uptotheratedvalue bymeans of turningtheknobof theeddy dynamometer. For each step, line voltage, line current, input power and balanced readings are noted and tabulated.Tabular Column:Sl. No.InputCurrent (A)Speed (r.p.m.)W1 (W)W2 (W)Input power (W)S (kg)Torque (Nm)Output power (W)Efficiency (%)Slip (%)Power factorE M LAB MANUAL II SPECIAL MACHINES INDUCTION GENERATORFIG 2.11 Load Test on Squirrel-Cage Induction Motor using eddy dynamometerCalculations:Input power = 1 2W W +(watts).Torque can be computed using the equation ( )1 2~ T S S rg , where 1S and 2S are the balance readings, r is the radius of the brake drum and g is acceleration due to gravity (9.81 m/s2).Output power = 260NT (watts)whereNis the speed in r.p.m.Tis the torque in Nm.% Efficiency = 100outputinputSynchronous speed, 120sfNp, where fis supply frequency and p, the no. of poles.% 100ssN NslipN ( )1 2 11 23 ~tanW WW W 1 1+ 1 ]power factor = cosResult: Questions: 1.Explain the working of an eddy dynamometer.2.Can an induction motor work as generator? Explain.E M LAB MANUAL II SPECIAL MACHINES INDUCTION GENERATOR3. Compare the performance characteristics of an ordinary and eddydynamometer type squirrel cage induction motor.