2极三相异步电机

Ansoft RMxprt Application NoteTwo-Pole Three-Phase Induction Motor ProblemThis application note describes how to set up, solve, and analyze the results of a two-pole, three-phase induction motor using RMxprt. The model created by RMxprt will then be used as an input for EMpulse as a basis for performing a more detailed analysis and for increasing the accuracy of the performance pre-dictions.RMxprt uses a combination of analytical and magnetic circuit equations to predict the performance of this motor. EMpulse is a nonlinear time-domain finite element analysis (FEA) software package that solves electromagnetic field equations, electric circuit equations, and equations of motion.You can create the project from scratch or open the pre-solved project,called3ph.pjt,located in the/ansoft/ examples/rmxprt/directory.If you are creating a project from scratch,select Three-Phase Induction Motors as the motor type in RMxprt.This project was created using version 3.0 of RMxprt and version 8.0 of Maxwell 2D.Motor CharacteristicsThe three-phase induction motor operates by producing a torque, which turns the rotor. To accomplish this, the rotating stator field is set up by out-of-phase currents in the stator windings. The magnetic field established in the stator induces an electromotive force (EMF)in the rotor bars,and a current flow is then established in these rotor bars. The rotor magnetic field created by the rotor currents is of opposite polar-ity than the stator field pole that generated it, so the rotor’s polarity is attracted to the stator’s opposite polarity. This effect produces the torque, and the rotor turns.The following table lists the characteristics of the three-phase induction motor used in this example:The figure on the previous page shows the geometry used in this example.Number of poles2Number of stator slots36Number of rotor slots28Stator outer diameter (inches)10.125Rotor outer diameter (inches)5.525Shaft diameter (inches)1.875Air gap (inches)0.046Stack length (inches)9.5General DataUse the General window to define the general data for the motor, such as the output power, number of poles, frequency and motor speed.Define the Wire Gauge➤Before generating the model, select the English units and the American wire setting:1.Choose Tools/Options ,make certain the Wire Setting is set to American (AWG),and then choose OK .2.Choose Tools/Model Units , and select English Unit .3.When you change the units before entering data, a message appears telling you that the Rated Output Power must be greater than 0. Choose Ignore , then start entering your data. Do notchoose Modify ; if you do so, RMxprt will revert to metric units.4.Choose Materials/Wire to view the wire data.5.Choose Exit to close the wire data, and do not save the settings.If you do not use this command to view the wire data, then RMxprt may fail to list values for the wire Gauge setting in the Stator2 window.Define the General Data➤Define the general data:1.Choose the General window tab.2.Enter 70.87kW in the Rated Output Power field for this two-pole motor.This is the mechanical power developed at the shaft. This value is equal to a 95 horsepower motor.3.Enter 460 kW in the driving RMS line-to-line Rated Voltage field.4.Enter 2 in the Number of Poles field.5.Enter 60 Hz in the Frequency field.6.Enter 3502 rpm in the Rated Speed field. This is the speed of the motor.7.Enter 1276 W in the Stray Loss field. If the measured stray load loss is unavailable, NEMA MG1[1],paragraph 20.52,states that this value shall be assumed to be 1.2%of the rated output for motors rated less than 2500 hp and 0.9% for motors rated 2500 hp and greater. IEEEStandard 112 [2] gives different assumed stray load loss values for motors rated less than2500hp. They are as follows:In this example, follow the IEEE guidelines, and use 1.8% or 1276 watts.8.Enter 700 W in the Friction Loss field. This value contains both the friction and wind losses at the given speed.9.Enter 9.5 inches in the Iron Core Length field. This is the length of the stator.10.Enter 0.95in the Stacking Factor field.This gives a value of 9.025inches as the net length of the steel, after taking lamination into account.11.Select D23 as the nonlinear Steel Type used in the manufacturing of the stator lamination. To examine the material BH-curve for D23, choose Materials/BH , then choose Open from the B-H Data window, and select D23.h-b . Once the data is loaded in the left window, you can plot the B-H curve for this material or the standard loss (B-P)curve.The specific weight of the material is also displayed. This information is necessary to calculate the iron core loss. Choose Exit to 1-125 hp 1.8%126-500 hp1.5%501-2499 hp 1.2%exit this window and continue the general data input.12.Select Wye as the Winding Connection.13.Select Constant Speed as the Load Type. The load type defines the load curve (torque functionof speed)for the mechanical load at the shaft.This data gives the rated load operating point for the motor. The no-load operation, break-down operation (maximum torque), and lock rotor operation are independent of the load type.14.Leave75o C as the Operating Temperature.Stator DataUse the Stator1 and Stator2 windows to define the stator.Define the Stator DimensionsUse the Stator1 window to define the stator dimensions.➤Define the stator dimensions:1.Choose the Stator1 window tab.2.Enter5.525 inches in the Inner Diameter field to specify the inner diameter of the stator.3.Enter10.125 inches in the Outer Diameter field to specify the outer diameter of the stator.4.Enter36 in the Number of Slots field. This value specifies the number of slots in the stator.5.Select2 as the Slot Type. This indicates the shape of the slot.6.Deselect Auto Design, and enter the following Slot Dimensions:Field ValueHs00.555Hs10.065Hs20.698Bs00.16Bs10.309Bs20.432Define the Stator WindingsUse the Stator2 window to define the stator windings.➤Define the windings:1.Choose the Stator2 window tab.2.Select 21 as the Winding Type . The winding is a double layer lap winding.3.Enter 0percent in both the Top Spare Space and the Bottom Spare Space fields.The spare spaces in the slot are taken to be 0% of the slot’s area.4.Enter 0.01inches in the Slot Insulation field. The slot insulation is the thickness on one side of the stator slot.5.Enter 0in the End Adjustment field.The end adjustment is taken to be the length that the stator windings extend beyond the end of the stator. For this motor, the windings do not extend beyond the stator.6.Enter 1 in the Parallel Branches field, indicating that the coils making up one phase are connected in series.7.Enter 11 in the Conductors per Slot field.8.Enter 16 in the Coil Pitch field. Had the stator used a full pitch winding, then the coil pitch would be 18 slots (36 slots/2 poles). The winding is wound 2 slots shorter, which results in a coil pitch of 16 slots.9.Enter 4.378in the Wires per Conductor field. This is not the actual number, but the equivalentnumber that gives the total wire cross-sectional area. (One conductor is made up of two 15AWG wires and of three 16 gauge wires.)10.Enter 0.01inches in the Wire Wrap field. This value represents the thickness of the wire wrap.11.Enter 0.057087inches in the Wire Diameter field. When you enter this value, the Gauge setting automatically changes to 15.12.Select 15 as the Gauge for the wire if it did not automatically appear. Wire gauge settings are given in AWG.Mean half length = Length of A + Length of B + Length of CEnd AdjustmentStack lengthRotor DataUse the Rotor1 and Rotor2 windows to define the rotor.Define the Rotor DimensionsUse the Rotor1 window to define the rotor dimensions.➤Define the rotor dimensions:1.Choose the Rotor1 window tab.2.Enter0.046inches in the Air Gap field.This value specifies the width of the air gap between therotor and the stator.3.Enter1.875inches in the Inner Diameter field.The inner diameter of the rotor is the same as theouter diameter of the shaft.4.Select Cast Rotor at the bottom of the window. In this example the rotor is cast, rather thanusing individual bars.5.Enter28 in the No.fields for both the Top slot and the Bottom slot. This defines the number ofrotor slots for both the top and the bottom.6.Select3 as the Slot Type for both the Top and Bottom slots.7.Enter the following dimensions for the Top slot:Field ValueHr00.0215Hr010.0215Hr10.01Hr20.22Br00.01Br10.15Br20.16Rr08.Enter the following dimensions for the Bottom slot:Field ValueHr00Hr10Hr20.44Br00.16Br10.3Br20.2Rr0Define the Rotor VentsUse the Rotor2 window to define the rotor vents.➤Define the rotor vents:1.Choose the Rotor2 window tab.2.Leave Axial Hole selected as the Vent Type. When you select the vent, a figure of the selectedtype appears.3.Enter0 in the Number of Vents field. There are no vents in the rotor.4.Enter0in the Skew Width field.This value defines how much the rotor bars are skewed.In thisexample, there is no skew.5.Enter0 inches in the End Length of Bar field. This value is the length of the gap between theend ring and the rotor core, for only one end of the gap, not both.6.Enter0.815 inches in the End-Ring Height field. This value is the end-ring dimension in theradius direction. The ring’s height covers at least the cross-section of the rotor conductor. The end-ring connects the bars of the rotor to one another.7.Enter1.276inches in the End-Ring Width field.This value is the end ring dimension in the axialdirection.8.Under Bar Resistivity, select Aluminum to define the resistivity. This is the material used inmanufacturing the bars.9.Under End-Ring Resistivity, select Aluminum to define the resistivity. This is the material usedin manufacturing the end ring.Process the Analytical DesignWith the motor data defined, you are ready to generate the model.➤Generate the model:1.Choose Tools/Options,make certain the Wire Setting is set to American(AWG),and choose OK.2.Choose Analysis/Analytical Design. RMxprt calculates the motor performance parameters forthis design. Choose OK when the analysis is complete.Displaying the Lamination and Winding ArrangementOnce the analysis is completed, you can display the laminations on the objects and the winding arrange-ment for the model.➤Display the laminations and the winding arrangement:1.Choose Tools/Options/Lamination, make certain all the Lamination items are checked, andchoose OK.2.Choose Post Process/View Lamination to examine the cross-section of the motor. Choose File/Exit to close the window when you are done viewing the lamination.3.Choose Post Process/View Winding Layout to see the winding arrangement. Choose File/Exitwhen you are done viewing the winding arrangement.Design OutputChoose Post Process/Design Output to examine the motor’s parameters.The Design Output window is bro-ken down into the following sections:GENERAL DATAThis information is the same as the data you entered in the General window.STATOR DATAThis information is generally the same as the data you entered in the Stator1and Stator2windows.If you selected Auto Design, RMxprt displays the optimized values for the windings.ROTOR DATAThis information is the same as the data you entered in the Rotor1 and Rotor2 windows.RATED-LOAD OPERATIONThis section displays information about the main performance parameters in the steady state: current, losses,mechanical torque,and input power,as well as the parameters of the one-phase equivalent circuit: resistance and leakage reactance for the stator winding, and magnetizing reactance for the rotor.NO-LOAD, BREAK-DOWN, AND LOCKED-ROTOR OPERATIONThese sections display information about the motor parameters at different operating conditions.DETAILED DATA AT RATED OPERATIONThis detailed data includes the slot, end-winding, differential, and skewing leakage reactance for the sta-tor winding and the rotor. The sum of these values gives the main leakage reactance as displayed in the Rated-Load Operation section. Other data listed in this area include the winding factor; the stator-teeth,rotor-teeth,stator-yoke,rotor-yoke,and air-gap flux density;and the magnetomotive force.The following table lists additional parameters that are displayed:WINDING ARRANGEMENTThis is the winding arrangement for one full A phase, B phase, and C phase winding. Only one layer arrangement is displayed; the second can be deduced rapidly from the coil pitch. For this example, the winding arrangement is:The Winding Arrangement section also displays the following values (in electrical degrees):TRANSIENT FEA INPUT DATAThis information is used when calculating the motor performance using the 2D time transient finite ele-ment field solver EMpulse.For main and auxiliary windings, this section displays:•the number of turns, as seen from the terminal.•the number of parallel branches.•the terminal resistance.•the end leakage inductance. For the rotor end ring, this section displays both the end-ring resistance and end-ring inductance between two bars at one end, as well as the skew leakage inductance.•the 2D equivalent values for the air-gap and the stacking factors. This section also displays the estimated rotor inertia, without taking into account any mechanical load attached on the shaft.When you have reviewed the output data, choose Exit to exit the Design Output window.Slot Fill Factor (%)The percentage of the available slot area (total slot area minus slot insu-lation) that is filled with the wire (copper plus insulation).Correction Factor The correction factor for the magnetic circuit length for the stator yokeand rotor yoke.Saturation Factor The saturation factor for the teeth field and for the teeth and yoke field.Stator Current Density(A/mm 2)The current density of the stator.Specific Electric Loading (A/mm)The ampere-conductors per meter of armature periphery.Stator Thermal Load (A 2/mm 3)The current density in each slot multiplied by the Specific Electric Load-ing.Half-Turn Length of Stator Winding (inch)The half-turn length of the stator windings.Top layer:AAAAAAZZZZZZBBBBBBXXXXXXCCCCCCYYYYYYBottom layer:YYAAAAAAZZZZZZBBBBBBXXXXXXCCCCCCYYYYAngle per slot 180 electrical degrees divided by the number of slots per pole.Phase-A axis The center of the A phase winding with respect to the phase first slot.First slot center The reference used to calculate phase.Plot the Performance CurvesExamine the performance curves for the model.➤Plot the performance curves:1.Choose Tools/Options, make certain the Maxwell Path points to the Ansoft folder, and chooseOK.2.Choose Post Process/Performance Curves. The PlotData window appears, with an Openwindow visible. The following plot titles are available for you to open:n_curr.dat Input Current vs Speedn_effi.dat Efficiency vs Speedn_pow2.dat Output Power vs Speedn_powf.dat Power Factor vs Speedn_torq.dat Output Torque vs Speed3.Select the name of the plot you want to view.4.Choose OK. The plot appears in the PlotData window. After you’ve opened one plot, choosePlot/Open to open a different plot.For these plots, the speed is measured per unit of the synchronous speed. The followingfigures show three of the performance plots for the sample problem:5.When you have finished viewing the performance curves, choose File/Exit to exit PlotData.Create the Maxwell 2D ProjectNow you can create the Maxwell 2D project.➤Create the Maxwell project:1.Choose Tools/Options, make certain the Periodic and Teeth-Teeth options are enabled, andchoose OK. These options allow you to take advantage of the motor symmetry.2.Choose Analysis/View Geometry. The Maxwell 2D Modeler appears, displaying the geometry.3.Choose File/Exit to exit the Maxwell 2D Modeler.4.Choose Analysis/Create Maxwell 2D Project. Enter a project name and a path for the project inthe Project Name and Path fields.5.Choose Create. A message window appears, informing you that the Maxwell 2D project hasbeen created.6.Choose OK to close the message window.7.Choose File/Save to save the setup.8.Return to the Project Manager to continue with the rest of this example.Leave RMxprt open torefer to later in the example.This completes the RMxprt design of the three-phase induction motor. You can continue the analysis of this design using the time transient FEA software program, EMpulse, to predict the operating perfor-mance of the motor.Examples of Analyzing Motor PerformanceThis section provides some useful exercises for analyzing the changes of the motor’s performance in dif-ferent situations.Y - SwitchingCreate an induction motor designed for a D-armature connection, that can be started with the armatures connected in Y. Examine the starting torque and current for the two cases of the Y-connection and the delta connection.You should obtain the following results:•For the D-connection, the torque is 461 Nm, and the phase current is 527 A.•For the Y-connection, the torque is 105 Nm, and the phase current is 252 A.Multiple Parallel CircuitsThe windings forming one phase may be connected in series or in parallel, providing multiple parallel circuits (parallel branches). Examine the changes in the winding resistance and the phase current at the rated-load operation. You should obtain the following results:•For one parallel branch, the resistance is 0.232 ohms, and the phase current is 69.9 A.•For two parallel branches, the resistance is 0.057 ohms, and the phase current is 214.4 A.Influence of Rotor Resistivity on Locked-Rotor TorqueChange the material for the rotor bars and the end ring. Use copper instead of aluminum, and examine the changes in the value of the locked-rotor torque. Keep the Y connection and two parallel paths. You should obtain the following results:•For aluminum, the locked-rotor torque is 652 Nm.•For copper, the locked-rotor torque is 512 Nm.Finite Element AnalysisNow that the Maxwell 2D project has been created, you can use the EMpulse environment to predict the operating performance of a three-phase induction motor. EMpulse is a nonlinear time-domain FEA soft-ware package that allows you to analyze the electromagnetic (plane parallel) phenomena in electromag-netic devices that are combined with electric circuits and motion.If you only want to open and inspect the finished project, the solved project is called3ph_fea.pjt. If you want to step through the project yourself,open the project you just created in RMxprt,and start from that point.If the project you previously exported from RMxprt does not appear in the projects list, you may need to refresh the list by clicking on the project directory again.Set Up the GeometryThe geometry of the model is already created by RMxprt.➤Open the project, and set up the geometry:1.From the Project Manager in the Maxwell Control Panel,open the Maxwell2D project that wascreated in the previous section. If using the pre-solved project, its name is3ph_fea.pjt. Uponopening the project, notice that the first three options on the Executive Commands menu arealready set:Transient is selected as the Solver,XY Plane is selected as the Drawing plane, andDefine Model already has a check mark next to it.2.Choose Define Model/Draw Model. The Maxwell 2D Modeler appears.3.Choose Window/Change View/Zoom In, and zoom in on the air gap. There is an additionalobject in the air gap called Band,which is used during the solution process to determine whichobjects are stationary and which rotate.4.Choose File/Save to save the file, and choose File/Exit to exit the Maxwell 2D Modeler andreturn to the Executive Commands window.5.Choose Define Model/Group Objects. The Group Objects window appears. RMxprt assignednames to all of the objects in the geometry.6.Group the objects that belong to the same winding,as follows(notice the abbreviations for thenames of the windings):Bar objects Bar0-Bar13PhA objects PhA0-PhA11PhB objects PhB0-PhB11PhReB objects PhReB10, PhReB11PhReC objects PhReC0-PhReC11The stator windings of an induction motor can be grouped into six different objects. However, since the FEA model is only half of the full model,groups PhReA and PhC are not included in the sample drawing.If you assume that the rotor turns counterclockwise (positive torque), the stator windings have to be grouped counterclockwise in the same sequence. In this example, that order is PhA (represented as A), PhReC (represented as C-), PhB (represented as B), and PhReB (represented as B-).The following figure shows the FEA model of the motor:StatorRotorShaftSlave boundary Master boundary7.Choose Exit to return to the Executive Commands menu, and save the changes as you exit.Assign Material PropertiesAfter grouping the objects,you can now assign material properties.Because this example requires materi-als not included in the material database, you must create them in the Material Manager.Add a New MaterialUse the Material Manager to add a new nonlinear material called D23 to the local material database.➤Add a new material:1.Choose Setup Materials from the Executive Commands menu.2.Choose Material/Add , and enter D23 in the name field below Material Properties .3.Select Nonlinear Material , and choose B H Curve . The B-H Curve Entry window appears.4.Choose Import . The Import Data window appears.5.Browse and select the statr_eq.bh file that was created within RMxprt.In most cases,this file is located in c:\ansoft\rmxprt\matlib .6.Make certain that bh Format is selected before importing. Choose OK to import the file.7.Choose Exit to exit the B-H Curve Entry window and return to the Material Manager.8.Choose Enter . The new material is now available in the database for this project.Derive a New MaterialDerive a new conductor material called Aluminium_115, and add it to the local material database.➤Derive the new material:1.Select aluminum from the Material list, and then choose Material/Derive .2.Enter Aluminum_115 in the name field below Material Properties .3.Enter 2.304e7S/m in the Conductivity field.4.Choose Enter to enter the new material in the local material database. This material is now available in the database for this project.Assign the MaterialsAssign the material properties to the objects in the model.➤Assign the materials:1.Assign vacuum to the AirGap and Band .2.Assign Aluminum_115 to the Bar group.3.Assign copper to groups PhA ,PhB ,PhReB , and PhReC .4.Assign D23 to the Rotor and Stator .5.Assign steel_stainless to the Shaft .6.Exclude the background from the model.7.Choose Exit when done assigning materials, and save the changes as you exit the MaterialManager.Note:The rotor bar conductivity is set up for a working temperature of 75 degrees Celsius.The conductivity of the stator windings will not be taken into account if the windings are set up as a stranded conductor.The resistances of the stator windings will be spec-ified later in the Source Setup window.Set the Boundaries and SourcesChoose Setup Boundaries/Sources from the Executive Commands menu. The 2D Boundary /S ource Man-ager appears. The first step in defining the boundary conditions is to define the Maste r/S lave boundary.You then need to define the value boundary and set up the sources.Define the Master BoundaryUse the Edit/Select/Trace command to define the master boundary.➤Define the master boundary:1.Choose Window/New , then Window/Tile to open an additional window and arrange thewindows in tile format.2.Choose Window/Change View/Zoom In , and zoom in on the air gap so that the area where the Band and the inside diameter of the stator cross the x-axis (in the positive direction) can beeasily seen.3.Choose Edit/Select/Trace .4.Starting in the window with the full model shown, click on the center axis of the motor (u=0,v=0), and then click on the Rotor Inside Diameter (u=0.9375, v=0).5.Switch to the window where the air gap is enlarged, and click on the following intersections:•Rotor Outside Diameter (u=2.7165, v=0)•Band (u=2.7395, v=0)•Stator Inside Diameter (u=2.7625, v=0)6.Switch back to the window with the full model, and double-click on the Stator OutsideDiameter (u=5.0625, v=0) to end the master boundary definition.7.Choose Assign/Boundary/Master , and then choose Assign .The master boundary is now assigned.Define the Slave Boundary Again, use the Edit/Select/Trace command to define the slave boundary.➤Define the slave boundary:1.In the window where the air gap is enlarged, use the bottom scroll bar to display the air gap where the Band and the inside diameter of the stator cross the x-axis in the NEGATIVEdirection.2.Choose Edit/Select/Trace .3.Starting in the window with the full model shown, click on the center axis of the motor (u=0,v=0), and then click on the Rotor Inside Diameter (u=-0.9375, v=0).4.Switch to the window where the air gap in enlarged, and click on the following intersections:•Rotor Outside Diameter (u=-2.7165, v=0)•Band (u=-2.7395, v=0)•Stator Inside Diameter (u=-2.7625, v=0)5.Switch back to the window with the full model, and double-click on the Stator OutsideDiameter (u=-5.0625, v=0), to end the slave boundary definition.6.Choose Assign/Boundary/Slave , and select Slave = -Master .7.Choose Assign .The slave boundary is now assigned.Note:When you are solving for an odd number of poles of an electrical machine, use theSlave =-Master symmetry.When solving for an even number of poles,use the Slave =+Master symmetry.Define the Value BoundaryDefine the remaining boundaries.➤Define the value boundary:1.To assign the outside diameter of the stator a zero value boundary, choose Edit/Select/Edge,and click on the outside diameter of the stator. Click the right mouse button when doneselecting.2.Choose Assign/Boundary/Value, and change the Name from value1 to Zero_Flux.3.Keep the Value field set to0.A zero value boundary means that all of the flux will be containedin the motor; there will be no leakage flux.4.Choose Assign.The stator edge is assigned a value boundary of zero.Source SetupWhen you are specifying the source,you have two options in EMpulse:using coils that are either current supplied or voltage supplied. In electric motors, you should generally use voltage supplied windings, in which case the resulting currents depend on the winding’s resistance and back electromotive force(emf). EMpulse can calculate the currents from the field solution and the terminal data.Phase A Winding➤Set up the Phase A winding parameters:1.Choose Edit/Select/Object/By Clicking, and select the object group PhA. Right-click the mouseto end the selection.2.Choose Assign/Source/Solid. New fields appear below the view window.3.Enter PhaseA in the Name field.4.Select Voltage, then select Strand.5.Choose Functions, and add the following three new functions, choosing Add after each:•PhaseA = 460*sqrt(2/3)*cos(360*60*T)•PhaseB = 460*sqrt(2/3)*cos(360*60*T-120)•PhaseC = 460*sqrt(2/3)*cos(360*60*T-240)6.Choose Done to close the window when you have finished entering the functions in step 5.7.Choose Options,select Function,and choose OK to indicate that the voltage will be a functionalvalue.8.Enter PhaseA in the Value field.9.Choose Winding. The Winding Setup for Boundary “Phase A”window appears.10.Assign a Positive polarity to the object group PhA.11.Under Terminal Attributes, enter the following values, which were derived using the transientFEA input data from RMxprt’s Design Output:•Enter0.231977 ohms in the Resistance field. The resistance is the total resistance of the winding at the working temperature.•Enter0.000441694henries in the Inductance field. The inductance is only the end-winding leakage inductance, which cannot be deduced from the 2D field solution.•Enter66 in the Total turns as seen from terminal field.•Enter1 in the Number of Parallel Branches field.12.Choose OK to accept the settings and return to the 2D Boundary/Source Manager.13.Choose Assign.The PhaseA winding parameters are now defined.。