Performance of dc motors experiment 2

Performance of dc motors experiment 2

• 1.
  THEORY Electrodynamometer measures torque.Electrodynamometer is an electrical break, in which the breaking force can be varied electrically. It consists of a stator and a squirrel-cage rotor. The stator is free to turn; however, its motion is restricted by a spring. A DC current is applied to the stator winding generating a magnetic field that passes through the stator and the rotor. The strength of the stator magnetic field can be increased or decreased by the front panel control. This strength determines the degree at which the revolving rotor can cause the stator to change position on its axis. As the rotor turns (being belt-coupled to the driving motor), a voltage is induced in the rotor bars, and the resulting eddy currents react with the magnetic field causing the stator to turn. The electrodynamometer is calibrated in Newton-meters (Nm). Shunt motor. The field coil and the armature windings are connected in shunt or parallel across the power source. The armature winding consists of relatively few turns of heavy gauge wire. The voltage across two windings is the same but the armature draws considerably more current than the field coil. Torque is caused by the interaction of the current caring armature winding with the magnetic field produced by the field coil. If the DC line voltage is constant, the armature voltage and the field strength will be constant. The speed regulation is quite good; the speed is a function of armature current and is not precisely constant. As the armature rotates within the magnetic field, an EMF is induced in its wining. This EMF is in the direction opposite to the source EMF and is called the counter EMF (CEMF), which varies with rotational speed. Finally, the current flow through the armature winding is a result of the difference between source EMF and CEMF. When the load increases, the motor tends to slow down and less CEMF is induced, which in turn increases the armature current providing more torque for the increased load. Motor speed is increased by inserting resistance into the field coil circuit, which weakens the magnetic field. Therefore, the speed can be increased from “basic” or full-load, full-field value to some maximum speed set by the electrical and mechanical limitations of the motor. The power difference between the motor input and the output is dissipated in form of heat and constitutes to the losses of the machine. These losses increase with load, since the motor heats up as it delivers mechanical power.
• 2.
  Series motor. Thefield coil and armature windings are connected in series to the power source. The field coil is wound with a few turns of heavy gauge wire. In this motor, the magnetic field is produced by the current flowing through the armature winding; with the result that the magnetic field is weak when the motor load is light (the armature winding draws a minimum current). The magnetic field is strong when the load is heavy (the armature winding draws a maximum current). The armature voltage is nearly equal to the PS line voltage (just as in the shunt wound motor if we neglect the small drop in the series field). Consequently, the speed of the series wound motor is entirely determined by the load current. The speed is low at heavy loads, and very high at no load. In fact, many series motors will, if operated at no load, run so fast that they destroy themselves. The high forces, associated with high speeds, cause the rotor to fly apart, often with disastrous results to people and property nearby. The torque of any DC motor depends upon the product of the armature current and the magnetic field. For the series wound motor this relationship implies that the torque will be very large for high armature currents, such as occur during start-up. The series wound motor is, therefore, well adapted to start large heavy-inertia loads, and is particularly useful as a drive motor in electric buses, trains and heavy duty traction applications. Compared to the shunt motor, the series DC motor has high starting torque and poor speed regulation
• 3.
  Cumulative compound motorcombines the operating characteristics of the series and shunt motors. The high torque capability of the series wound DC motor is some what compromised by its tendency to overspeed at light loads. This disadvantage can be overcome by adding a shunt field, connected in such a way as to aid the series field. The motor then becomes a cumulative compound machine. Again, in special applications where DC motors are used in conjunction with flywheels, the constant speed characteristic of the shunt wound motor is not entirely satisfactory since it does not permit the flywheel to give up its kinetic energy by an appropriate drop in motor speed. This kind of application (which is found in punch-press work), requires a motor with a "drooping" speed characteristic, that is, the motor speed should drop significantly with an increase in load. The cumulative compound wound DC motor is well adapted for this type of work. The series field can also be connected so that it produces a magnetic field opposing that of the shunt field. This produces a differential compound motor, which has very limited application, principally because it tends to be unstable. As the load increases, the armature current increases increasing the strength of the series field. Since it acts in opposition to the shunt winding, the total flux is reduced, with the result that the speed increases. An increase in speed will generally further increase the load, which raises the speed and could cause the motor to run away. The shunt field winding places a practical limit on maximum no-load speed and it may be operated at no load. The shunt coil also provides for better speed regulation than a series motor; while the series coil provides for greater starting torque than a shunt motor. After the motor is started, the series coil is shorted out for better speed regulation. Cumulative compound motors are used where fairly constant speed under irregular loading is needed.
• 4.
  PART A :DC SHUNT MOTOR LOAD CHARACTERISTICS OBJECTIVE 1. To construct the direct current (dc) shunt motor circuit. 2. To determine the load characteristics of dc shunt motor. 3. To interpret the load characteristics of a dc shunt motor. LIST OF REQUIREMENTS Equipment (Experimental panel system unit 1000 W) 1. Variable dc power supply 2. Brake unit 3. Control unit servo brake 4. Display panel 5. Coupling collar 6. Shaft and cover 7. DC shunt motor 8. Connection mask (3125111) 9. Voltmeter (1 unit) 10. Ammeter (2 units)
• 5.
  PROCEDURE 1) The connection was performed according to the Figure 2.3. 2) The ammeter 1 connect to 10A, ammeter2 connect to 1A and voltmeter connect to 1000V. 3) Before this experiment started, the operating elements of the control unit servo brake was adjusted as in below table 2.1 : Table 2.1 Operating switch on position M const/T Switch “Torque range” position 10Nm Switch “Speed range” position 6000 4) The power supply was switched on.The Dc voltage was adjusted to 220V.A constant voltage of 220V was maintained throught the experiment.The direction of the motor was checked and turn in clockwise direction. 5) The “store/start” button was pressed twice. The torque load was adjusted from 0Nm to 2Nm. The data was recorded in the Table2.2. 6) Then the calculation had be made and the result also recorded in Table 2.2.
• 6.
  I) Total output power,P2=(Torque X Speed)/9.55 II) Power input,P1=Voltage X Total Current III) Efficiency =P2/P1 IV) Total Current=Current A + Current E 7) N,IA,P2 and Ƞ was graphically as a function in Figure 2.4 PART B: DC SERIES MOTOR LOAD CHARACTERISTICS OBJECTIVES 1. To construct the DC series motor circuit. 2. To determine the load characteristics of a DC series motor. 3. To interpret the load characteristics of a DC series motor LIST OF REQUIREMENTS Equipment (Experimental panel system 1000W) 1. Voltage supply 2. Brake unit 3. Control unit servo brake 4. Display panel 5. Coupling collar 6. Shaft and cover 7. DC series motor 8. Connection mask(3125113)
• 7.
  9. Voltmeter(1unit) 10. Ammeter(1unit) PROCEDURES 1) Firstly, connect all the wire according to the diagram that shown in Figure 2.7 Note the maximum range: ammeter1:10A, and voltmeter:1000V 2) After that, adjust the operating elements of the control unit servo brake was adjusted as in table 2.3 and then,the control unit was switched on
• 8.
  Operating Switch onPosition M const/T const Switch “Torque range” position 10 Nm Switch “Speed range” position 6000 Table 2.3 3) The power supply was switched on.The Dc voltage was adjusted to 110V.A constant voltage of 110V was maintained throught the experiment.The direction of the motor was checked and turn in clockwise direction. 4) The “store/start” button was pressed twice. The torque load was adjusted from 0Nm to 1Nm. The data was recorded in the Table 2.4. 5) Then the calculation had be made and the result also recorded in table 2.4 i) Total output power,P2=(Torque X Speed)/9.55 ii) Power input,P1=Voltage X Current iii) Efficiency =P2/P1 6) N,IA,P2 and Ƞ was graphically as a function in Figure 2.8 PART C: DC COMPOUND MOTOR LOAD CHARACTERISTICS OBJECTIVES 1. To construct the DC series motor circuit. 2. To determine the load characteristics of a DC compound motor. 3. To interpret the load characteristics of a DC compound motor LIST OF REQUIREMENTS Equipment (Experimental panel system 1000W) 1. Voltage supply 2. Brake unit 3. Control unit servo brake
• 9.
  4. Display panel 5.Coupling collar 6. Shaft and cover 7. DC series motor 8. Connection mask(3125113) 9. Voltmeter(1unit) 10. Ammeter(1unit)
• 10.
  PROCEDURES 1) The connection was performed according to the Figure 2.11. 2) The ammeter 1 connect to 10A, ammeter2 connect to 1A and voltmeter connect to 1000V. 3) Before this experiment started, the operating elements of the control unit servo brake was adjusted as in below table 2.5 : Table 2.5 Operating switch on position M const/T Switch “Torque range” position 10Nm Switch “Speed range” position 6000 4) The power supply was switched on.The Dc voltage was adjusted to 220V.A constant voltage of 220V was maintained throught the experiment.The direction of the motor was checked and turn in clockwise direction. 5) The “store/start” button was pressed twice. The torque load was adjusted from 0Nm to 2Nm. The data was recorded in the Table2.2. 6) Then the calculation had be made and the result also recorded in Table 2.6. V) Total output power,P2=(Torque X Speed)/9.55 VI) Power input,P1=Voltage X Total Current VII) Efficiency =P2/P1
• 11.
  VIII) Total Current=Current A + Current E 7) N,IA,P2 and Ƞ was graphically as a function in Figure 2.12. RESULT Part A Table 2.2 Measured Value Torque ζ(Nm) 0.0 0.5 1.0 1.5 2.0 Current IA(A) 0.8 1.2 1.8 2.4 3.0 Current IE(A) 0.44 0.44 0.44 0.44 0.44 Speed N(rpm) 2907 2867 2815 2765 2698 Calculated Value Power P! (W) 272.8 360.8 492.8 624.8 756.8 Power P2 (W) 0.0 150.1 294.8 434.3 553.7 Efficiency η(%) 0.0 0.41 0.60 0.70 0.73 Total currentIcct(A) 1.24 1.64 2.24 2.84 3.44 Part B Measured Value Torque Nm 0.0 0.2 0.4 0.6 0.8 1.0 Current, IA (A) 2.4 2.7 3.0 3.4 3.7 3.9 Speed, N (rpm) 4100 3670 3050 2660 2290 2110 Calculated Value Power,P1 (W) 264 297 330 374 407 429 Power,P2 (W) 0.0 76.86 63.87 55.71 47.96 44.19 Efficiency (%) 0.0 0.26 0.20 0.15 0.12 0.10 Part C Measured Value Torque ζ(Nm) 0.0 0.5 1.0 1.5 2.0 Current IA(A) 0.7 1.2 1.7 2.3 2.8 Current IE(A) 0.43 0.43 0.43 0.43 0.42 Speed N(rpm) 2810 2750 2660 2570 2478 Calculated Value Power P! (W) 268.6 358.6 468.6 600.6 710.6 Power P2 (W) 0.0 144.0 278.5 403.7 519.0
• 12.
  Efficiency η(%) 0.0 0.40 0.59 0.67 0.73
• 13.
  REFERENCES Matthew N.O sadiku,Charles K. Alexander(2009), Fundamental Of Electric Circuit 4(ed), Singapore:Mc Graw Hill. Rusnani Ariffin, Mohd Aminuddin Murad(2009), Laboratory Manual : Electrical Engineering Laboratory 1 EEE230, Shah Alam: University Publication Centre (UPENA) Universiti Teknologi Mara. http://www.engineersedge.com/motors/dc http://www.micromotcontrols.com/htmls/Motor%20characteristics.html http://electriciantraining.tpub.com/14177/css/14177_59.htm
• 14.
  FACULTY OF ELETRICALENGINEERING UNIVERSITY TEKNOLOGI MARA ELECTRICAL ENGINEERING LABORATORY 1 (EEE230) EXPERIMENT 2 PERFORMANCE OF DC MOTORS
• 15.
  TABLE OF CONTENT CONTENT PAGE ABSTRACT Theory OBJECTIVES LIST OF REQUIREMENTS EXPERIMENT PROCEDURE EXPERIMENT RESULT DISCUSSION CONCLUSION REFERENCE APPENDICES