英国大学 电机实验报告.doc

Liverpool John Moores UniversitySchool of EngineeringENRNG 2088 Electrical EngineeringExperiment ReportAutomated Testing of Electrical MachinesAuthor: Dian GuB.Eng. in Electronic and Electrical Engineering, Year 2March 6, 2011ContentsIntroduction- 3Theory-3Result - 5 Discussion - 9Conclusion-11References- 12INTRODUCTIONThis test is called load test. The primary aim of these experiments were to investigate the various characteristics of the motor as functions of the load on the motor shaft in both shunt DC motor and The squirrel-cage three-phase induction motor.In these test, it include speed versus torque, torque versus armature current, efficiency versus torque, input and output power versus torque. Also, in the second part of shunt DC motor need to test of the motor under no-load conditions. The second part is aim to determine so-called fixed losses of the motor THEORYSTEADY-STATE OPERATION OF A SEPARATELYEXCITED DC MACHINEA separately excited DC machine can working as a motor and as a generator. It has two windings. One is called field (or excitation) winding which is wound on the stationary cylindrical structure called stator. The other one is called armature winding which is situated on the rotating part of the machine called rotor. The armature (rotor) winding is approached from the stationary is called commutator assembly. Fig. 3.2: Equivalent circuits of separately excited and shunt excited DC machines. Separately (shunt) excited DC motor have two additional equations for induced electromotive force and developed electromagnetic torque. The function in motoring is showing belong: is the excitation flux. T is the electromagnetic torque developed by the motor.K is a constant determined with the construction of the machine is the angular velocity of rotationSTEADY-STATE OPERATION OF A THREE-PHASEINDUCTION MACHINEThree-phase induction machines are fed from an AC three-phase power supply which carries a three-phase winding connected to a three phase power system.The rotor winding of Three-phase induction machines are leads to sub-division of induction machines into two groups. The first one is the called squirrel-cage induction machine. This machine rotor winding build up by many conducting bars which are cast into the rotor iron core. The bars are short-circuited at both ends with end rings. Rotor winding of a squirrel-cage induction machine can used as a three-phase and it cannot be accessed externally. RESULTSTEADY-STATE OPERATION OF A SEPARATELYEXCITED DC MACHINEDig.1 Torque vs. Armature currentDig.2 Speed vs. TorqueDig.3 Efficiency vs. TorqueDig.4 Input and Output versus TorqueSTEADY-STATE OPERATION OF A THREE-PHASEINDUCTION MACHINEDig.5 Torque versus SpeedDig.6 Torque versus SlipDig.7 Current versus TorqueDig.8 Efficiency versus TorqueDig.9 Input and Output Power versus Torque DISCUSSIONSTEADY-STATE OPERATION OF A SEPARATELYEXCITED DC MACHINELoad TestFrom Dig.1 it clearly shows that the Torque in Load Test is increase steadily with Armature Current goes higher. In Dig.2, the Speed in Load Test is decrease steadily with Torque increased.Dig.3 shows that the Efficiency is increased with Torque increased, but when Torque increased at a higher value that the Efficiency will start to decrease.In Dig.4, it shows both the Output and Input are increase with Torque goes higher. But the Output value is increased slowly and lower than Input.Form these Four Diagrams can show that the Torque in Load Test is effect by the value of armature current. And the increase values are steadily. Also, the Speed, Efficiency, output and input power are all effect by the Torques value.From this load test experiment can find out that the Torque in the separately excited DC machine is inversed with the speed, which means when the value of Torque in the machine big enough that can slowly the speed heavily.Also, the Efficiency will increase with the Torque goes up until a value and then will start to decrease. Finally, the input and output are increase with the Torque as well. but the proportion of the output and input increase values are not the same , as the torque goes higher ,and the proportion of output value will goes up slowly,NO-Load TestConstant power loss: 1- output/input*100% Input power Pin= DC2V*(DC1A+DC2A) Output power Pout=SPEED*TORQUE*0.10472 TIMEDC1ADC2VDC2ASPEEDTORQUESAVARPMNm00000010.10.051180.1500Table1, No-Load Test ResultBecause of the Torque in No-Load Test is ZERO. Thus the Constant Power Loss in No-Load Test is 100%, which means the power in No-Load Test is totally loss. When the separately excited DC machine is separated, there is no Torque income, as mentioned before that speed is effect by the torque, so the speed is ZERO as the Torque performed. When missing these two values the constant power will totally loss in the experiment because the machine separated. STEADY-STATE OPERATION OF A THREE-PHASEINDUCTION MACHINEFrom Dig.5 and 6 can find out that the Torque in a Three-Phase Induction Machine will increases steadily with the speed and slip up. And in Dig.7, the current is increase depends on if the torque goes up The Dig.8 shows the Efficiency will increase with the Torque up until a value and then goes down.Finally, the Dig.9 shows that the input and output power all increase with Torque goes up.In this Three-Phase Induction Machine, some of the result is inversed to the separately excited DC machine. For this experiment, the torque are effect by the speed and slip, when the speed of the Three-Phase Induction Machine slow down, the torque will increase with the value of the speed slowly steadily. And the slip is the inverse way with speed that controls the torque.From the Current Diagram shows the same situation as the separately excited DC machine, but in this experiment that the current was controlled by the Torque. The current and torque both increased steadily.For the Efficiency part, it appears the same situation as shows in the separately excited DC machine experiment. The efficiency will increase with the torque up and when catch a value that will decrease steadily. Finally, in the input and output part, it shows the same situation in separately excited DC machine part as well, the input and output power are both increase with the torque goes up, but the output power are increase slowly than the input power with the torque up.CONCLUSIONTo sum up, these two experiments aimed to help understand the working principle of Separately excited DC machine and Three-phase induction machine. To measurement the data for these two experimen