No load test of the Three phase Asynchronous Motor

Transcription

1 No load test of the Three phase Asynchronous Motor XVI. 1. Introduction. Description of the experiment This experiment studies the no load test of the three phase asynchronous motor. The test points out the iron losses, the mechanical losses and the stator copper losses through the knowledge of the resistance measured between the two terminals. Objectives Students are expected to learn about the no load test of the asynchronous motor. Running this experiment the students will face some main objectives: To understand the schematic diagram corresponding to the no load test characteristic. Based on it, to learn how to connect the laboratory modules accordingly. To configure the OpenLab software according with the semiautomatic and automatic mode. To obtain the characteristics curves related to the experiment: I 0 f U ; P f U ; cos f U M cc

2 Exercise 4.16 No load test of the Three phase Asynchronous Motor 2. Components list According to the formulated objectives, in order to run the experiment the following De Lorenzo components are needed: A. Software: PC with Windows OS; DL 8330SW processing software application. Exercise 4.16 No load test of the Three phase Asynchronous Motor; B. Hardware: DL AC Asynchronous Machine; DL Power Supply Module; DL 10065N Electrical Power Digital Measuring Unit; DL 10050N Mechanical Power Digital Measuring Unit; DL Star/Delta starter; DL 1893 Data Acquisition Module; DL Pole Changing Unit; USB RS485 Adapter;

3 3. Procedure outline Schematic diagram phase In order to obtain the no load circuit characteristic curves, follow the figure 1. The rated parameters can be measured using the ammeter A and the voltmeter V. In this schematic diagram the AC stator configuration is presented. Figure 1. General circuit diagram for no load test of the three phase asynchronous motor Characteristics curves From the diagrams, in correspondence of the current rated value, we obtain respectively: I 0, iron losses P FE, mechanical losses P M and power factor cosϕ.

4 Exercise 4.16 No load test of the Three phase Asynchronous Motor These electrical parameters are necessary for the calculation of the series parameters of the equivalent diagram: P CU Rm I0 ; P0 P CU P M P FE Figure 2. No load characteristic related to the experiment One wire connection diagram In order to perform the experiment in Y/Δ test, proceed with the following electrical diagram. Figure 3. One wire connection diagram related to the experiment (Y/Δ)

5 See section Introduction to the Experimental Section to remember the right symbols used in the Schematic diagram phase. Setup and connection diagram In figure 4 the wiring recommendations for communication and power cables connection is presented. Arrange the modules in a convenient way for accessing and wiring. Identify the relevant ports for communication, cables and connectors. Print the practical tasks sheet shown on the next page. The student is asked to write by hands the identified devices with parameters and values that are handled during the experiment regarding the No load test of the Three-phase Asynchronous Motor example.

6 Exercise 4.16 No load test of the Three phase Asynchronous Motor Follow the diagram from the next figure and connect the power cables accordingly: Figure 3. Power and comunication cables are connected by following the general powering rules (colors, connectors).

7 Before starting any wiring activity, check all power connections: all switches must be OFF. Do not miss the ground connecting terminal! As you see from the diagram, with specific symbols, all equipment are connected to the protective network by specific connector and cable. Experimental procedure and learning plan Once we understood all these preparatory aspects, we can proceed with experimenting. Perform the circuit configuration shown in the connection diagram, presented in figure 4. Switch ON the power supply connected to the experiment. Operate the network power switch that can be found at the back of the module. Then, press the green start button from the power supply module. In order to provide power, turn the key clockwise. In order to measure the speed of the machines, first connect the modules as shown in the next wiring diagram. Before connecting the K2 connector, the speed transducers must be already mounted on the machine. See again figure 4 to complete the connection regarding the speed measurement.

8 Exercise 4.16 No load test of the Three phase Asynchronous Motor Set the supply module DL 10017, for an alternating voltage of the Asynchronous motor corresponding to the rated voltage of 24V. Turn the switches of the supply module DL to position AC on. Switch the selector of the supply module DL "a0b" to position "a".

9 SEMIAUTOMATIC mode values will be acquired from the experiment and displayed using the software. The student will decide when to acquire data from the experiment. Connect all the RS485 communications cables and use the DL 8330SW software provided with the OpenLab. Switch to man the power supply DL Open the experiment ASYN/ No load test of the Three phase Asynchronous Motor. Select the Man switch for this operating mode. The next graphical interface of the software allows you to see in a table all the measured data. You can open Configuration machine parameters to view the rated data of the machine for this test. In order to select what parameter you want to see, click on the Show MB Instruments. Then, click on the Show XY graph. First, choose which windows you want and only after that start acquiring data from the motor.

10 Exercise 4.16 No load test of the Three phase Asynchronous Motor

11 Pay attention to the DL address selection - RS485 communication default parameter. By default, the correct address are 3,5 (for DC instrument) and 4,6 (for AC instrument). Opening the MB Instruments will allow you to select the measured parameter. In order to see more instruments, click multiple times on the Show single AC measure. Select for this experiment at least the following parameters: the voltage (U) and the phase current (I). Because the speed needs to be constant during the experiment, click on the Show single Mec instrument in order to see the window that allows you to select the speed parameter. Click on the Show XY graph and select the voltage and current.

12 Exercise 4.16 No load test of the Three phase Asynchronous Motor You will obtain the characteristics related to the experiment. In order to see all three characteristics, after the experiment is complete (or even during the experiment) you can select the parameter you want to see in the XY Graph. An example of how you can arrange the instruments is shown below. You can choose a different positioning of the instruments, or even different instruments, but the important thing is to have a good overview of the main parameters and the characteristic graph. Establish the measured data as in the following sequence by suitable adjusting the excitation voltage. Gradually increase the voltage with a step of 0.1*Un. The table presents the correlation between the voltages at the three parameters I, P and cosϕ.

13 U (V) I 0 (A) P (W) cosϕ 0.1*Un 0.2*Un 0.3*Un 0.4*Un 0.5*Un 0.6*Un 0.7*Un 0.8*Un 0.9*Un 1.0*Un 1.1*Un Use the knob from the DL power supply to change the voltage from 0.1Un to 1.1*Un. Press START to acquire data when the voltage reaches the first value (0.1*Un). In this way, the first row of the DL 8330SW software will show the measured data. Continue to easily rotate the knob clockwise. Press START again to acquire new data at approximately 0.2*Un. Every time you press START a new row with measured data will be added in the table.

14 Exercise 4.16 No load test of the Three phase Asynchronous Motor AUTOMATIC mode values will be acquired from the experiment using a data acquisition system. This time the parameter values will be acquired automatically from the experiment. The students need to start the experiment and it will run automatically until the no load test of the three phase asynchronous motor is complete. In order to accomplish the asynchronous no load test, connect all the communications cables to the PC via DL 1893 acquisition system. Perform the next connections between the OpenLab modules. You need to make some hardware changes (compared to the previous step 3) in order to run the experiment in automatic mode. Please follow the next indications: See that the DL has the AC switch to on, as presented in steps 2. Rotate the knob to auto.

15 Use the DL 8330SW software provided with the OpenLab and open the experiments of the Asynchronous Machine. Set the software in the 'Auto' mode. Click on the experiment No load test of the Three phase Asynchronous Motor Follow the procedure presented in the previous step (3) regarding the instruments selection and positioning of the XY graph. Because the experiment is done automatically, there is no need to adjust the voltage through the knob.

16 Exercise 4.16 No load test of the Three phase Asynchronous Motor The computer calculates the steps according to the rated data of the machine. Supply the motor and wait until the experiment is done and you obtain the no load test. You will obtain on the XY graph a relation between the voltage (U) and the phase current (I) (you can select to display on the XY graph the characteristics P f U cos f U M ; ). You can press STOP to finish the experiment at any time. cc

17 Proposed exercises: Exercise 1 Please repeat the example using the same procedure, but this time follow the diagram from figure 3. Follow the diagram from the next figure and connect the power cables accordingly: DL allows star/delta starting of three-phase motor. See the manual for a better use of this module.

18 Exercise 4.16 No load test of the Three phase Asynchronous Motor Exercise 2 Repeat the example using the same procedure, but this time follow the diagram from figure 3. Follow the diagram from the next figure and connect the power cables accordingly: DL is a pole changing unit for dual polarity. See the manual for a better use of this module.

19 Questions Answer the following questions related to the experiment regarding the no load test of the three phase asynchronous motor. 1. Are there any difference between the star/delta electrical values? Explain why. 2. What happens when you change 2 phases on the AC stator configuration? Set the DL on STAR and then on DELTA and fill the following data form: Conclusions During this experiment we have understood the importance of the no load test of the three phase asynchronous motor. The purpose of this test was to determine the mechanical losses and the iron losses of the motor.