Note: 1. All the students must strictly follow all the safety precautions. 2. In case of any question or concern, please contact LAB INSTRUCTOR or TA.

Transcription

1 UNIVERSITY OF WATERLOO ELECTRICAL & COMPUTER ENGINEERING DEPARTMENT FALL 2006 E&CE 261: Energy Systems and Components EXPERIMENT 1: THREE-PHASE SYSTEMS Contents covered in this laboratory exercise: 1. Relationship between the line voltages and phase voltages for wye-delta connected complex load. 2. Relationship between the line currents and phase currents for wye-delta connected complex load. 3. Three phase power measurement for balanced and unbalanced loads 4. Three phase power measurement using two-wattmeter method 5. Three phase power measurement using three-wattmeter method Note: 1. All the students must strictly follow all the safety precautions. 2. In case of any question or concern, please contact LAB INSTRUCTOR or TA. Safety precautions: 1. Do not touch any exposed terminals when wall panel 3- Ø breaker is ON. 2. Do not change the connections or settings without informing the lab instructor or TA. Ensure the wall panel 3- Ø breaker is OFF while changing the connections. 3. Do not operate the wye-delta switch when load is applied. 4. Current should not exceed 5A with Y-connected load. 5. Observe the ammeter reading while operating the load switches. Definitions: 1. 3-Ø Three phase. 2. Y wye connected configuration. 3. delta connected configuration. 4. Source-load-interfacing-box It is a box used to facilitate (a) To configure the load either in Y or in and (b) To have a 3-Ø three wire or a 3-Ø four wire supply system. 5. Load bank Selectable resistive load consisting of light bulbs and resistive heating elements. 6. Capacitor bank Selectable capacitive load consisting of capacitors of different values. 7. Watt-meter It is an instrument used to measure real power by sensing current passing through the load and voltage applied across the load. 8. Balanced load All three phases have the same current by having the same load impedance per phase. 9. Unbalanced load All three phases have the different current by having the different load impedance per phase. 10. V ab, V bc, V ca Line voltages

2 V a, V b, V c Phase voltages 12. I 1, I 2, I 3 Line currents 13. I 5, I 6,I 7 Phase currents 14. Neutral switch the switch used in the neutral wire to select three wire or four wire supply. 15. Y- switch the switch used to select either Y or connected load.

3 - 3 - Watt-meter Tutorial The Watt-meter is an instrument used to measure the real power by sensing current passing through the load and voltage applied across the load. An analog watt-meter deflects according to the average value of the product of voltage and current. The formula for the real power is V X A = (Vrms ) * (Arms) cos(ø). Figure (a) shows the picture of watt-meter depicting the terminals, selectors and scales. Figure (a) shows the picture of watt-meter The current is sensed by a current coil; designated by A on the watt-meter. The voltage is sensed by a voltage coil; designated by V on the face of the watt-meter. There are two selector knobs; 1. Current selector - to select the current range depending on the current flowing through the circuit. 2. Voltage selector - to select the voltage range based on the voltage applied to the load. Do not make the wrong selection which may result in damaging the instrument. The meter display does not show actual power. The power is to be calculated based upon the reading. It can be calculated in two ways. Method#1: There will be multiple scales based on the voltage ranges. For example; if there are 120, 240 and 480 voltage selections, there will be three scales for each voltage selection. Take the reading from the appropriate scale and then multiply with the current range (selected by current selector) to get the power in watts.

4 - 4 - Power = Reading X Current range Example: Suppose the voltage selection is made 240 and Current selection is made 10. If the meter reading is 50 in 240-scale, then Power = 50X10 = 500 W. Method#2: Take the reading from smallest scale irrespective of the voltage selection and calculate the multiplication factor (MF) as follows. MF = (Voltage selection X Current selection) / Full scale deflection of the smallest scale. Power = Reading X MF. Example: Suppose the voltage selection is made 240 and Current selection is made 10. There are three scales 120-scale, 240-scale and 480-scale. If the meter reading is 25 in 120-scale MF = (240X10)/120 = 20, then Power = 25X20 = 500 W. Advantage; The second method has a better accuracy and reading can be taken easily. This method is also helpful, if there is only one scale on the meter with multiple voltage ranges. Figure (b) shows the connecting diagram of watt-meter in a simple circuit. Figure (b): watt-meter connections.

5 - 5 - Procedure: The 3-Ø source, source-load interfacing box, 3-Ø load bank and necessary instruments have been connected. Review the schematics to identify all the components connected in the lab set-up. Also identify the scales and multiplication factors of all the instruments. Record the switch configuration in the load mapping tables after applying the load in each case. 3-Ø Power measurement using Two-Wattmeter-Method Part 1: 3-Ø three wire supply system with a Y-connected load. 1.1 (a) A balanced resistive load. Refer to the circuit as shown in Figure #1 to understand the configuration. Select the neutral switch to the open position, select the Y- switch to the Y position on the source-load-interfacing-box and select the voltage coil of the watt-meters at 240 position. Connect a balanced resistive load. Record the line-to-line voltages, the phase voltages, the line currents, the phase currents, the neutral current and the wattmeter readings in Table #1. Table #1: 3-Ø three wire supply system with a balanced Y-connected Resistive load. V ab = I 1 = W 1 = Load Mapping Row # Red Yellow Blue V bc = I 2 = W 2 = Zero 1 V ca = I 3 = W 3 = 2 V a = I 4 = Zero MF 1 = 3 V b = I 5 = MF 2 = Zero 4 V c = I 6 = MF 3 = 5 I 7 = (b) Report: Find out the relationship between the measured line and phase voltages. Compare to theoretical values. Find out the relationship between the measured line and phase currents. Compare to theoretical values. Calculate the total power dissipated in the Y connected resistors from the wattmeter measurements. Calculate the total power supplied to the Y connected load from the phase current and phase voltage measurements and power factor of each phase. Compare the two powers and comment on it.

6 - 6 - Draw the phasor diagram of the power system. Include the line voltages, the phase voltages and the line and phase currents. Indicate numerical values of all quantities. 1.2 (a) A balanced resistive and capacitive load. Connect a balanced RC load. Record the line-to-line voltages, the phase voltages, the line currents, the phase currents, the neutral current and the wattmeter readings in Table #2. Table #2: 3-Ø three wire supply system with a balanced Y-connected Resistive and Capacitive load. V ab = I 1 = W 1 = Load Mapping Row # Red Yellow Blue V bc = I 2 = W 2 = Zero 1 V ca = I 3 = W 3 = 2 V a = I 4 = Zero MF 1 = 3 V b = I 5 = MF 2 = Zero 4 V c = I 6 = MF 3 = 5 I 7 = C = µf/ph (b) Report: Define and calculate the system measured power factor. Draw the phasor diagram of the power system. Include the line voltages, the phase voltages and the line and phase currents. Indicate numerical values of all quantities.

7 (a) An unbalanced resistive load. Connect an unbalanced resistive load. Record the line-to-line voltages, the phase voltages, the line currents, phase currents, the neutral current and the total power supplied to the load in Table #3. Remove the load. Table #3: 3-Ø three wire supply system with an unbalanced Y-connected Resistive load. V ab = I 1 = W 1 = Load Mapping Row # Red Yellow Blue V bc = I 2 = W 2 = Zero 1 V ca = I 3 = W 3 = 2 V a = I 4 = Zero MF 1 = 3 V b = I 5 = MF 2 = Zero 4 V c = I 6 = MF 3 = 5 I 7 = (b) Report: Calculate the total power dissipated in the Y connected unbalanced resistors from the wattmeter measurements. Calculate the total power supplied to the Y connected load from the phase current and phase voltage measurements and power factor of each phase. Compare the two powers and comment on it. Would it be possible to determine the system power factor? Explain. Can one calculate the power supplied to an unbalanced Y connected resistive-inductive load from a measurement of line voltages and line currents in the case of a) a three wire system, b) a four wire system? Assume the power factor of each phase is known. Explain the answers. 7 What is the advantage of the system neutral wire connected to the common point of the Y-connected load?

8 - 8 - Part 2: 3-Ø three wire supply system with a - connected load. Refer to the circuit as shown in Figure #2 to understand the configuration. Select Y- switch to position and neutral switch to open position. Select the voltage range of the watt-meters at 240V position. (Note: There is a chance of exceeding the readings of A 1, A 2, and A 3. If it is so, remove the load using switches and turn-off the power using the 3- Ø circuit breaker and change the meter connections to the next higher current range for ammeters and select next higher current setting for watt-meters.) 2.1 (a) A balanced resistive load. Connect the same balanced resistive load as in Part 1.1 a). Record the line-to-line voltages, the phase voltages, the line currents, the phase currents, the neutral current and the wattmeter readings in Table #4. Table #4: 3-Ø three wire supply system with a balanced -connected Resistive load. V ab = I 1 = W 1 = Load Mapping Row # Red Yellow Blue V bc = I 2 = W 2 = Zero 1 V ca = I 3 = W 3 = 2 V a = I 4 = Zero MF 1 = 3 V b = I 5 = MF 2 = Zero 4 V c = I 6 = MF 3 = (b) Report. I 7 = 6 Find out the relationship between the measured line and phase voltages. Compare to theoretical values. Find out the relationship between the measured line and phase currents. Compare to theoretical values. What is the difference between the relationship of voltages and currents compared to part1.1 (a)? Calculate the total power dissipated in the connected resistors from the wattmeter measurements. Calculate the total power supplied to the Y connected load from the phase current and the phase voltage measurements and the power factor of each phase. Compare the two powers and comment on it. What is the difference in the powers in part1.1 (a) and part 2.1 (a). Comment. Draw the phasor diagram of the power system. Include the line voltages, the phase voltages and the line and phase currents. Indicate numerical values of all quantities. 7 The intensity of light bulb is high in this case compared to the earlier cases in part1. Explain the reason.

9 (a) A balanced RC load. Connect the same balanced RC load as in Part 1.2 a). Record the line-to-line voltages, the phase voltages, the line currents, the phase currents, the neutral current and the wattmeter readings in Table #5. Table #5: 3-Ø three wire supply system with a balanced -connected Resistive and Capacitive load. V ab = I 1 = W 1 = Load Mapping Row # Red Yellow Blue V bc = I 2 = W 2 = Zero 1 V ca = I 3 = W 3 = 2 V a = I 4 = Zero MF 1 = 3 V b = I 5 = MF 2 = Zero 4 V c = I 6 = MF 3 = (b) Report. I 7 = 6 Determine the power factor (PF) of the load and compare it with the PF calculated in Part 1.2 (a). Explain the reason(s) for any differences between the power factors of Part 1.2 (a) and 2.2 (a). 7

10 (a) An unbalanced resistive load. (Note: If you have changed the meter connections in 2.1(a), do not forget to revert back the connections while the circuit breaker is OFF.) Connect the same unbalanced resistive load as in Part 1.3 (a). Record the line-to-line voltages, the phase voltages, the line currents, the phase currents, the neutral current and the wattmeter readings in Table #6. Table #6: 3-Ø three wire supply system with an unbalanced -connected Resistive load. V ab = I 1 = W 1 = Load Mapping Row # Red Yellow Blue V bc = I 2 = W 2 = Zero 1 V ca = I 3 = W 3 = 2 V a = I 4 = Zero MF 1 = 3 V b = I 5 = MF 2 = Zero 4 V c = I 6 = MF 3 = (b) Report. I 7 = 6 7 Find out the relationship between the measured line and phase voltages. Find out the relationship between the measured line and phase currents. Calculate the total power dissipated in the connected resistors from the wattmeter measurements. Calculate the total power supplied to the Y connected load from the phase current and phase voltage measurements and power factor of each phase. Compare the two powers and comment. Draw the phasor diagram of the power system. Include the line voltages, the phase voltages and the line and phase currents. Indicate numerical values of all quantities.

11 Part 3: 3-Ø four wire supply system with a Y connected load. Refer to the circuit as shown in Figure#1 to understand the configuration. Select the neutral switch to the close position and select the Y- switch to the Y position on the source-load-interfacing-box. Select the voltage coil of the watt-meters at 120V position. 3.1 (a) A balanced resistive load. Connect the same balanced resistive load that was used for Part 1.1 (a). Record the line-to-line voltages, the phase voltages, the line currents, the phase currents, the neutral current and the wattmeter readings in Table #7. Table #7: 3-Ø four wire supply system with a balanced Y-connected Resistive load. V ab = I 1 = W 1 = Load Mapping Row # Red Yellow Blue V bc = I 2 = W 2 = Zero 1 V ca = I 3 = W 3 = 2 V a = I 4 = MF 1 = 3 V b = I 5 = MF 2 = Zero 4 V c = I 6 = MF 3 = 5 I 7 = (a) Report. Compare the values of measured voltages, current and power with those recorded in Part 1.1 (a).

12 (a) An unbalanced resistive load. Connect the same unbalanced resistive load that was used for Part 1 c). Record the line-to-line voltages, the phase voltages, the line currents, the phase currents, the neutral current and the wattmeter readings in Table #8. Remove the load. Table #8: 3-Ø four wire supply system with an unbalanced Y-connected Resistive load. V ab = I 1 = W 1 = Load Mapping Row # Red Yellow Blue V bc = I 2 = W 2 = Zero 1 V ca = I 3 = W 3 = 2 V a = I 4 = MF 1 = 3 V b = I 5 = MF 2 = Zero 4 V c = I 6 = MF 3 = (b) Report. I 7 = 6 Compare the values of the voltages, currents and power with those measured in Part 1.3(a). Draw a current phasor diagram of this power system and indicate the value and show why Kirchhoff s current law for the phasors is obeyed. 7

13 Ø Power measurement using Three-Wattmeter-Method Refer to the circuit as shown in Figure#3 to understand the configuration. To change from two-watt-meter method to three-watt-meter method, the common point (i.e the common point of all the pressure coils of the watt-meters) should be shifted from Y-phase to neutral point. Ask the lab instructor or TA to verify it. Select the neutral switch to the close position, select the Y- switch to the Y position and select the voltage coil of the watt-meters at 120 position. 3.3 (a) A balanced resistive load. Connect the same balanced resistive load that was used for Part 3.1 (a). Record the line-to-line voltages, the phase voltages, the line currents, the phase currents, the neutral current and the wattmeter readings in Table #9. Table #9: 3-Ø four wire supply system with a balanced Y-connected Resistive load. V ab = I 1 = W 1 = Load Mapping Row # Red Yellow Blue V bc = I 2 = W 2 = 1 V ca = I 3 = W 3 = 2 V a = I 4 = MF 1 = 3 V b = I 5 = MF 2 = 4 V c = I 6 = MF 3 = 5 I 7 = (b) Report. Calculate the total power dissipated in the load from the wattmeter measurements. Compare the total power obtained from 3.3(a) to the total power obtained from 3.1 (a) and comment. Compare the total power obtained from 3.3(a) to the total power obtained from 1.1 (a) and comment.

14 (a) An unbalanced resistive load. Connect the same unbalanced resistive load that was used for Part 3.2 (a). Record the line-to-line voltages, the phase voltages, the line currents, the phase currents, the neutral current and the wattmeter readings in Table #10. Table #10: 3-Ø four wire supply system with an unbalanced Y-connected Resistive load. V ab = I 1 = W 1 = Load Mapping Row # Red Yellow Blue V bc = I 2 = W 2 = 1 V ca = I 3 = W 3 = 2 V a = I 4 = MF 1 = 3 V b = I 5 = MF 2 = 4 V c = I 6 = MF 3 = (b) Report. I 7 = 6 7 The sum of the wattmeter readings of Part 3.2 (a) is different than the sum of the wattmeter readings for Part 3.4 (a) while the values of load current remained unchanged. In which case are the wattmeter readings correct? Use the experimental data to prove your answer. Remove the load and de-energize the circuit. Congratulations! You have now completed the experimental part of the lab. Prepare a report based on the above test results and submit on or before the due date i.e. Friday, October 20 by 8:30am in hardcopy or Monday, October 23 by 8:30am in softcopy. REPORT due dates are posted on the ece261 web page. Submit all pre-lab and post-lab reports via Course Books. Ece261-LS1-pre.pdf is the filename.file_type format. Revisions up until the due time should hve a letter added i.e. ece261-ls1-pre-a.pdf. One revision allowed for each exercise type (pre-lab or post-lab)

15 Figures: A A1 W1 A6 C R A5 3f 208V 60Hz B C A2 C R R C A3 W3 A7 N 3f Variable Autotransformer A4 SW Fig.#1: Wye Connected Load 1. Balanced Resistive, neutral switch open. 2. Balanced Resistive and Capacitive, neutral switch open. 3. Unbalanced Resistive, neutral switch open. 4. Balanced Resistive, neutral switch closed. 5. Unbalanced Resistive, neutral switch closed. A A1 W1 B 3-phase 208V 60Hz C A2 A6 A5 A7 N A3 W3 3-phase Variable Autotransformer Figure#2: Delta-connected Fig.#2: Delta Connected Load 1. Balanced Resistive. 2. Balanced Resistive and Capacitive. 3. Unbalanced Resistive.

16 A A1 W1 A6 A5 3-phase 208V 60Hz B C A2 W2 A3 W3 A7 N 3-phase A4 SW Autotransformer Variable Figure#3: Wye-connected R Load Fig.#3: Wye Connected Load for 1. Balanced Resistive, neutral switch closed. 2. Unbalanced Resistive, neutral switch closed.

17 A picture of the overall workstation is shown below. Wall panel circuit breaker Meters Wye - Delta source-load interfacing box Resistive load bank

18 Wye-Delta and Neutral switches on the patch panel. Remember to take the load off and to turn the power off before changing the circuit. Wye - Delta switch Neutral switch

19 The meter arrangement is shown below. A single voltmeter is also available at each workstation to measure the appropriate voltages. Phase current meters Line current meters & watt-meters

20 capacitor boxes