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EKT 451/4 APPLIED ELECTRICAL ENGINEERING LAB 03: DC SERIES MOTOR LAB 03: DC SERIES MOTOR 3.0 OBJECTIVES 1. 2. 3.1 To operate a DC Series Motor. To study the speed characteristics of the no-load motor against current. EQUIPMENTS DC Series Motor DC Drive Contactor Selector Switch DC Voltmeter Multimeter DC Ammeter Handheld Tachometer Cable 3.2 INTRODUCTION DC machines are conveniently used when the speed of the loads need to be adjusted. The magnetizing characteristic shows the variation of the magnetic flux in the machine with the field current to be similar as the relationship between the open-circuit (OC) armature voltage and the field current, when the machine is driven at a constant speed (as a generator). This relationship is referred to as the open-circuit or magnetizing characteristic. A DC Series Motor field windings consist of a relatively few turns connected in series with the armature circuit. In a Series Motor, the armature current, field current and line current are all of the same values. The Kirchhoff’s Voltage Law equation for this motor is given in equation 1. VT = EA + IA (RA + RS) (1) Where VT is supply voltage, EA is armature voltage, RA is armature resistance, Rs is field resistance and IA the motor current. Motor on No-load condition E=N E1 N1 (2) 1 SEMESTER II (2007) EKT 451/4 APPLIED ELECTRICAL ENGINEERING LAB 03: DC SERIES MOTOR N = E (N1) ≈ V (N1) E1 E1 (3) The terminal characteristic of a DC Series Motor is different from that of the DC Shunt Motor. The basic behavior of a series dc motor is due to the fact that the flux is directly proportional to the armature current, at least until saturation is reach. As the load on the motor increases, its flux increases too. As seen earlier, an increase in flux in the motor causes a decreased in the speed. The result is that a series motor has a sharply drooping torque-speed characteristic. 3.3 PRE-LAB INTRODUCTION (BACKGROUND REVIEW) This Pre-Lab Introduction on the background review of above-mentioned laboratory title and objectives should be prepared by each student before entering this laboratory session. Marks will be given during the laboratory sessions. Students are not allowed to perform any experimental works before completing this section. 3.4 PROCEDURE Warning: 1. High voltages are used in this laboratory experiment. Do not make any connection with the Power ON. Please ask the Teaching Engineer or the Technician to check your circuits before turning on the supply for all the tests. Connect the circuit as shown in Figure 3.1 and Figure 3.2. DC Drive A + Contactor M Figure 3.1 – Circuit Diagram 2 SEMESTER II (2007) EKT 451/4 APPLIED ELECTRICAL ENGINEERING LAB 03: DC SERIES MOTOR L Selector Switch A1 240V Contactor A2 N Figure 3.2 – Control Circuit 2. Write down all the rated of the Series DC motor shown on the rating plate in a table. These ratings should not exceed at any time during the laboratory exercises. 3. Please inform to the teaching engineer or technician when need to check the connections. 4. Switch on the power supply to DC drive, firstly at the main switch and then by using the selector switch to START to engaged the contactor. 5. Slowly turn the potentiometer on the DC drive and observe the variation of the motor speed. 6. Using the handheld tachometer, measure the speed rotation of the motor and prepare for data collection. 7. Set and record the speed at different values, the corresponding voltage and current values. 8. After finish taking the measurement, please switch off all power supplies before disconnect the wiring. 9. Plot the speed against current and the speed against voltage in the graph paper. 10. Take into account the armature resistance. Calculate the speed corresponding to the different values of current. Use the rated voltage 180V and the rated speed 1500rpm under the rated load conditions as the base values for this calculation. Use an equation 2 to calculate the values of speed. 11. Plot the graph of calculated values of speed using equation 2 against current on the same graph sheet as the experimental values. 3 SEMESTER II (2007) EKT 451/4 APPLIED ELECTRICAL ENGINEERING LAB 03: DC SERIES MOTOR L1 L2 L3 A2 A1 Figure 3.3 – Wiring diagram for training kit - module REPORT Laboratory report should be prepared individually and submitted within two days. Your report contents should include the followings: 3.5. Results (Calculations, Graphs, Tables etc) 3.6. Discussions 3.7. Conclusions 3.8. References 4 SEMESTER II (2007)