FACULTY OF ENGINEERING LAB SHEET EET2046 ENERGY CONBVERSION II TRIMESTER 2, 2012/2013

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FCULTY OF ENGINEERING LB SHEET EET2046 ENERGY CONBERSION II TRIMESTER 2, 2012/2013 EC1 - LOD CHRCTERISTICS OF DC GENERTORS EC2 - LOD CHRCTERISTICS OF DC MOTORS *Note: On-the-spot evaluation may be

1 FCULTY OF ENGINEERING LB SHEET EET2046 ENERGY CONBERSION II TRIMESTER 2, 2012/2013 EC1 - LOD CHRCTERISTICS OF DC GENERTORS EC2 - LOD CHRCTERISTICS OF DC MOTORS *Note: On-the-spot evaluation may be carried out during or at the end of the experiment. Students are advised to read through this lab sheet before doing experiment. Your performance, teamwork effort, and learning attitude will count towards the marks. Marking scheme is given at the end.

2 EET 2046 Energy Conversion II Experiment # 1 LOD CHRCTERISTICS OF DC GENERTORS OBJECTIES To construct the load characteristics of a separately excited DC generator and a self-excited shuntwound DC generator To evaluate the performance characteristics of the generators INTRODUCTION dc generator has two distinct electric circuits, a field circuit and an armature circuit. The mmf s produced by these two circuits are at quadrature the field mmf is along the direct axis and the armature mmf is along the quadrature axis. The armature of the dc generator is rotated by means of an external machine known as the prime mover. q-axis d-axis Field rmature Field circuit rmature circuit (a) Fig. 1 (a) separately excited DC generator, (b) Shunt generator (b) The field circuit and the armature circuit can be interconnected in various ways to provide a wide variety of performance characteristics. DC machines are classified on the basis of the interconnections as follows: Separately excited generator Self excited generator Shunt generator Series generator Compound generator Figure 1(a) shows a separately excited dc machine wherein the field winding is excited from a separate source. In the self-excited DC machine, the field winding can be connected in three different ways. The field winding may be connected in series with the armature resulting in a series dc machine. It may be connected across the armature (i.e., in shunt), resulting in a shunt machine (Fig. 1a). Both shunt and series windings may be used resulting in a compound machine. In this experiment we will be conducting load tests on two types of generators namely, separately excited generator and shunt excited generator. In the separately excited dc generators, as the load current increases, the terminal voltage decreases almost linearly because of the voltage drop across the armature resistance. This voltage drop is small, because the resistance of the armature circuit is small. t high values of the armature current, a further

3 voltage drop occurs in the terminal voltage; that is known as armature reaction. separately excited DC generator maintains an essentially constant terminal voltage. The terminal voltage of a shunt excited DC generator will change as the load draws current from the machine. This change in the terminal voltage with current is due to the armature voltage drop and the change in the generated voltage caused by armature reaction. It is apparent that the terminal voltage drops faster with the armature current in the shunt excited generator. The reason is that, as the terminal voltage decreases with load in the shunt generator, the field current also decreases, resulting in less generating voltage, whereas in the separately excited generator, the field current and hence the generated voltage remain unaffected. PROCEDURE 1. rrange the instruments as shown in Fig. 2. I I E Load Generato Motor r Pendulu m Brake Contro l Unit Fig. 2 rrangement of instruments 2. The prime mover of the direct-current generator is a pendulum machine. djust the operating elements of the control unit as follows. Type of power 300 W Operating switch on position : Off Switch n const., M const.. position: M const. Switch Torque range position: 10 Nm Switch Speed range position: 6000 I. DC separately excited generator 3. Connect as per the circuit diagram shown in Fig Turn-on the control unit by using the master switch. Push the reset-button, the red glowing LED must not light anymore, otherwise you did a mistake during the setup, (e.g. -missing coupling bow-wing skid, -missing bow-wing skid of the shaft cover, -the plug switch for the thermal supervision of the motor is not plugged) or the motor is too hot. Start the pendulum machine. Turn the operating switch from off to n const., M const.. The corresponding LED glows green. Set the rated speed of the generator by pressing the up button. Set the current through the excitation winding (I E ) to the rated value. Measure the voltage output () when the machine is not loaded. Enter I E and in the table. Increase the load and measure the armature-current (I ) and the terminal voltage () for different loads. Record the values in the table below.

4 L+ C 1 F 1 Load F 2 L- B 2 Fig. 3 DC separately excited generator I Measured I E Calculated P 2 5. Calculate the power output P2 =. I. Enter the calculated values in the table. 6. Plot and P2 as functions of I in a graph sheet. II. DC shunt-wound generator 7. Modify the circuit according to the circuit diagram shown in Fig. 4 for obtaining the load characteristic of the self-excited shunt-wound generator. 8. Start the pendulum machine as described in step 2 above. Measure the armature voltage () and the load current (I L ) with the shunt-wound generator unloaded. Enter the measured values in the table below. Increase the load in steps and measure the load current and the terminal voltage for different loads. Record the values in the table.

5 C 1 L+ E 1 Load E 2 B 2 L- Fig. 4 DC shunt-wound generator Measured I L Calculate P 2 9. Calculate the power output P 2 =.I L. Enter the values in the table. 10. Plot, P2 as functions of I L in a graph sheet. EXERCISE (a) How does the voltage output change as a function of load (armature current) in case of the DC separately excited generator? Explain the reasons for the curve shape.

6 (b) Devise a method to compensate the decrease of the terminal voltage in case of the DC separately excited generator? (c) Discuss the power output change as a function of load (armature current) in case of the DC separately excited generator? (d) Compare the load characteristics of the DC self-excited shunt-wound generator and the DC separately excited generator. Distinguish the significant variations. (e) How does the power output change as a function of load current of the shunt-wound generator? (g) Explain briefly what you have learned from this experiment.

7 EET 2046 Energy Conversion II Experiment # 2 LOD CHRCTERISTICS OF DC MOTORS OBJECTIE To construct the load characteristics of a direct-current shunt-wound motor and a direct-current series-wound motor. Examine the performance characteristics of the motors I. Load Characteristics of a DC Shunt-wound Motor PROCEDURE: 1. rrange the instruments as shown in Fig. 1. I I E Power Control Supply Motor Pendulum Unit Brake Fig. 1 rrangement of instruments 2. Connect as per the circuit diagram shown in Fig. 2. L + L - PE C1 E2 B2 E1 M Fig. 2 Circuit diagram for load test

8 3. The motor is loaded by means of a pendulum machine. djust the operating elements of the control unit connected to the pendulum machine as follows Type of power 300 W Operating switch on position : Off Switch n const., M const.. position: M const. Switch Torque range position: 3 Nm Switch Speed range position: 3000 Turn-on the control unit by using the master switch. Push the reset-button, the red glowing LED must not light anymore, otherwise there may a mistake during the setup, (e.g.- missing coupling bow-wing skid, - missing bow-wing skid of the shaft cover, - the plug switch for the thermal supervision of the motor is not plugged) or the motor is too hot. Correct the mistake. 4. Start the motor by increasing the DC supply voltage to the motor gradually to 220 by making sure that the starting armature current does not exceed the rated current. Check the direction of the motor by using the display. The motor must run clockwise. Measure speed n, armature current I, and field current IE at no-load. Enter the measured values. Turn the operating switch in the control unit from off to n const., M const.. The corresponding LED glows green. (The speed of the pendulum machine is adjusted automatically to the motor speed). Increase the load on the motor by means of the control unit by pressing the down button and measure the values of load torque M, speed n, armature current I, and field current IE. Enter the measured values in the table. 5. Calculate the following. The total current I tot = I + IE The power output P 2 = The power input P 1 =.I tot The efficiency η = Enter the calculated values in the table. P2 P 1 M.n 9.55 Measured Calculated M in Nm n in rpm I in I E in I tot in P i in W P o in W η 6. Plot n, I, P2, and η as functions of M in a graph sheet.

9 QUESTIONS (a) Discuss the variation of the armature current and the power output of the motor as a function of motor load? (b) Explain the reason for the small decrease in speed of the motor when loaded? (c) Evaluate the performance of the dc shunt motor based on the load characteristic obtained. II. Load Characteristics of DC Series-Wound Motor PROCEDURE 1. Connect as per the circuit diagram shown in Fig Before starting the unit, switch the speed range in the control unit to Take all the precaution as explained in step 2 above and turn on the control unit. 3. Start the motor by increasing the DC supply voltage to the motor gradually to 60 by making sure that the starting armature current does not exceed the rated current. Check the direction of the motor by using the display. The motor must run clockwise. Turn the operating switch in the control unit from off to n const., M const.. The corresponding LED glows green. (The speed of the pendulum machine is adjusted automatically to the motor speed). Increase the supply voltage to the motor gradually to 220. If the motor current exceeds the rated current adjust the load so the current reduces. Measure speed n, armature current I at no-load. Enter the measured values. djust the load on the motor by means of the control unit by pressing the down or up button and measure the values of load torque M, speed n, armature current I. Enter the measured values in the table.

10 L + L - PE C1 D2 B2 D1 M Fig. 3 Circuit diagram 4. Calculate the following. M.n The total current I = I The power output P 2 = 9.55 The power input P 1 =.I where is the supply voltage. P2 The efficiency η = P1 Enter the calculated values in the table. Measured Calculated M in Nm n in rpm I in P i in W P o in W η 5. Plot n, I, P2, and η as functions of M in a graph sheet. Mark the rated torque on the graph

11 QUESTIONS a. Discuss the shape of the load characteristics obtained in step 5. b. Describe how the speed of the series-wound motor varies as a function of load. c. Explain the term series characteristic as applied to dc motor. d. Enumerate the reasons for the series characteristic of the direct-current series-wound motor. e. State briefly what you have learned from this experiment. Marking Scheme Lab (10%) ssessment Components Hands-On & Efforts (2.5%) On the Spot Evaluation (2.5%) Lab Report (5%) Details The hands-on capability of the students and their efforts during the lab sessions will be assessed. The students will be evaluated on the spot based on the theory concerned with the lab experiments and the observations. Each student will have to submit his/her lab discussion sheet and recorded experimental data on the same day of performing the lab experiments.

Module 9. DC Machines. Version 2 EE IIT, Kharagpur

Module 9. DC Machines. Version 2 EE IIT, Kharagpur Module 9 DC Machines Lesson 38 D.C Generators Contents 38 D.C Generators (Lesson-38) 4 38.1 Goals of the lesson.. 4 38.2 Generator types & characteristics.... 4 38.2.1 Characteristics of a separately excited