ME 269 Laboratory Session #5

Transcription

1 ME 269 Laboratory Session #5 Group # Station # First Name Last Name Arrive on time at room CPH Only call x if you have an emergency. No Entry if late for safety demonstration. NOTE: All the students must strictly follow all of the safety precautions. In case of any question or concern, please contact LAB INSTRUCTOR or TA. Safety: No loose or dangling jewellery. No long hair below shoulder, tie long hair up. No loose clothes: Neck ties, sleeves. No cell phone use. No water or liquids at the station. During Experiment: Power off prior to making any wiring changes. Lab Instructor/TA must check and initial all connections for all parts prior to your turning the power on. Do not touch any wiring while the power is on. All lab partners must be at the workstation at all times before the power is turned on. Members of your group are not to disturb or go near the other groups at the workstations. Ask the staff for help. EMERGENCY: Clear all centre areas immediately. Turn the power off at your workstation without hesitation. Stand still and quiet and ready to receive instructions. The phone is in the office. Dial 911 and keep the phone off the hood if you are designated to call 911. Listen to the instructions and stay at the phone. First Aid persons maybe asked to assist. 1

2 Wiring Hints: In this session you will be wiring most of the circuits yourselves. You need to follow definite wiring formats. Use RED colour wires starting from live/hot terminal of the source to one end of the element/device (i.e. resistor/inductor/capacitor/coil/transformer winding). Use BLACK colour wires starting from neutral/return terminal of the source to the other end of the element/device (i.e. resistor/inductor/capacitor/coil/transformer winding). Ammeter and current coil connections must be in series with the element/device. Voltmeter and voltage coil connections must be in parallel with the element/device. Make all series connections first and then parallel connections. Pre-lab calculations: Take to the laboratory Note the nameplate details of the transformer in Table #1. The nameplate details of the transformer are given in to calculate I 1 (A) (i.e. row #2 in Table #3) and I 2 (A) (i.e. row #2 in Table #4). Note that I 1 and I 2 are to be calculated on the high voltage side. Show the TA/Lab instructor to get approval in the laboratory. Table #1 Nameplate Details of the Transformer Parameter Hammond Model 25-F Rated Output Voltage of HV winding Voltage of LV winding Frequency Type of Transformer Value 1000 VA 208 volts 120 volts 60 Hz Shell No. of Phases 1 2

3 Part 1: Single Phase Transformers Pictures: Picture #1 Equipment set up Picture #2 Auto-transformer Single phase VARIAC -- two models 3

4 Picture #3 Digital Multi-meter Fluke model 8050 The current jack has been taped over. Picture #4 Transformer unit under test Picture #5 Load Side Circuit Breaker Box 4

5 Test#1: Open circuit test Preparing experiment: 1. Note that on top of the transformer in Picture #4, H 1 and H 2 stand for High-Voltage winding terminals and X 1 and X 2 stand for Low-Voltage winding terminals. 2. Make connections as per the circuit diagram of Figure #1. Picture #1 3. The single phase auto-transformer (VARIAC) is shown in Picture #2. Ensure that the VARIAC dial is set to zero before turning the power on or off. 4. The digital multi-meter shown in Picture #3 is to be used as a voltmeter. It has a current jack, which has been covered to prevent damage due to an incorrect connection. The voltage function AC and 200-volt range must be selected. 5. Watt-meter settings: Voltage range above 200V, Current range above 1A 6. Find the Multiplication Factor as given below MF = (Voltage range X Current range)/fsd of the scale you read = Procedure: Conducting experiment 7. Make sure the 1-Ø circuit breaker on the power panel for the autotransformer receptacle. 8. Make sure that the 1-Ф variable autotransformer is kept in ZERO position initially. 9. Ask the Lab Instructor/TA to check your Figure #1 and to check the connections before you turn the power on. 10. Turn the power on after getting clearance from Lab Instructor/TA. 11. Adjust the autotransformer to the values specified in the Table#2 and record I 1, V 2 and P core for each voltage step. 12. Set the autotransformer to zero position. Turn the power off. Remove the connections. Input Terminals I1 Transformer X1 H1 120 V 60 Hz V1 vc W1 cc V2 Varible Autotransformer Figure#1: Circuit diagram for conducting open circuit test. X2 H2 5

6 Open Circuit Test Report --Test Results: 1. Plot the input voltage, V 1, versus the no load input current, I 1. Use I 1 as the horizontal coordinate. Attach the plot to this report with full annotation. Use Excel or GNUplot. 2. Plot the core loss, P core, versus the input voltage, V 1. Use V 1 as the horizontal coordinate. Attach the plot to this report with full annotation. Use Excel or GNUplot. 3. Calculate the equivalent circuit parameters from this test. 4. What are the power losses that occur in the open circuit test? How can they be reduced? Do you think these losses will change from no-load to full-load? Explain. 5. Which losses are negligible in this test and why? 6. What will happen to the transformer if double the rated voltage is applied to the winding? Hint: Think about saturation of the core and current in the windings. Think about the effect of the power to be dissipated internally. 6

7 Test#2: Short circuit test Preparing experiment: 1. Make connections as per the circuit diagram in Figure# The values for current (I 1 ) at different percentages of the rated current (I 1 ) have been calculated on the High Voltage side and entered in Table#3. The rated value of I 1 has been calculated based on the nameplate details. 3. Watt-meter settings: Voltage range below 60V, Current range above 5A 4. Find the Multiplication Factor as given below MF = (Voltage range X Current range)/fsd of the scale you read = Procedure -- Conducting experiment: 5. Make sure that the 1-Ф variable autotransformer (VARIAC) is kept in ZERO position initially. 6. Ask the Lab Instructor/TA to check your Figure #2 and the connections. 7. Turn the power on after getting clearance from Lab Instructor/TA. 8. Caution! Do not move the Variac knob fast. 9. Slowly vary the 1-Ф autotransformer (VARIAC) to obtain the current close enough to the calculated values in the Table #3. Large current variations should be avoided. 10. Record V 1, I 1 and P copper for each % of rated I 1 current calculated. 11. Set the autotransformer to zero position. Turn the power off. 12. Remove the connections. Input Terminals I1 Transformer H1 X1 120 V 60 Hz V1 vc W1 cc Varible Autotransformer Figure#2: Circuit diagram for conducting short circuit test. 7 H2 X2

8 Short Circuit Test Report -- Test Results: 1. Calculate the equivalent circuit parameters from this test. 2. Draw the approximate equivalent circuit of a 1-Ф transformer referred to Low Voltage side and indicate the model values obtained from open circuit (OC) test and short circuit (SC) test. 3. What are the power losses that occur in the short circuit test? How can they be reduced? Do you think these losses will change from no-load to full-load? Explain. 4. Which losses are negligible in this test and why? 5. What will happen to the transformer if the rated voltage is applied to the winding during short circuit test? 6. What will happen to the transformer, if a DC voltage is applied to the primary winding? 8

9 Test#3: Load test. Preparing experiment: 1. Make connections as per the circuit diagram in Figure #3. Picture #5 shows the circuit breaker box for the load. 2. The values for current (I 2 ) at different percentages of the rated current (I 2 ) have been calculated on the High Voltage side and entered in Table#4. The rated value of I 2 has been calculated based on the nameplate details. 3. Watt-meter settings: For primary: Voltage range above 200V, Current range above 10A For secondary: Voltage range above 200V, Current range above 5A 4. Find the Multiplication Factors as given below MF1 = (Voltage range X Current range)/fsd of the scale you read = MF2 = (Voltage range X Current range)/fsd of the scale you read = Procedure -- Conducting experiment: 5. The 1-Ф variable autotransformer used is shown in Picture #2. 6. Make sure that the 1-Ф variable autotransformer is kept in ZERO position initially. Make sure all the switches in the load bank are in OFF position. 7. Ask the Lab Instructor/TA to check the connections. 8. Turn the power on after getting clearance from Lab Instructor/TA. 9. Vary the VARIAC SLOWLY until V 2 reads 208V at no load. 10. Make no further voltage adjustments. 11. Apply the load in steps to cause I 2 to obtain the current close enough to the calculated values in the Table # Record the measured values for I 2, V 2, I 1, V 1 and P in in each step in Table# Adjust the I 2 and V 2 to their rated values by operating switches on the load bank and the autotransformer. No need to worry about the other values. 14. Record I 2, V 2, P out, I 1, V 1 and P in in Table# Remove the load at once by turning-off the load side circuit breaker. 16. Record I 2, V 2, P out, I 1, V 1 and P in in Table#5. 9

10 17. Turn off all the switches on the load bank. Set the autotransformer to the zero position. Turn the power off. Calculate the efficiency and regulation in Table#5A & Table#5B and show them to LI/TA. 18. Remove the connections, tidy up the workstation and sign out with the Lab Instructor. Input Terminals I1 Transformer X1 H1 I2 Load 120 V 60 Hz V1 vc W1 cc V2 vc W2 cc Varible Autotransformer X2 H2 CB Load Terminals Load Test Report -- Test Results: Figure 3 Load Testing Schematic 1. Calculate and complete Table#6. Show sample calculations for P out and %Efficiency. 2. Plot the load current I 2, versus the % efficiency. Use load current I 2 as the horizontal coordinate. Attach the plot to this report with full annotation. Use Excel or GNUplot. 3. Plot the load current I 2, versus the V 2. Use load current I 2 as the horizontal coordinate. Attach the plot to this report with full annotation. Use Excel or GNUplot. 4. What are the performance parameters used to judge a transformer (to see whether it is a good or a bad transformer)? 5. Explain why the secondary terminal voltage is decreased with an increase in the load current. 6. What is the purpose of transformer in long-distance power transmission? 7. What do you understand from the term Electrical Isolation? What is the advantage of electrical isolation? 10

11 Tables: Note: 1. * represents rated value. 2. In the example given below, the slanted entry is for the V/I ranges of the watt-meter. Example: V/I range 240 The 240 volt range and the 10 amp range are indicated. 10 Table#2 Open circuit test V 1 (V) * I 1 (A) LI/TA Initial V 2 (V) P core (W) V/I range Table#3 Short circuit test % of rated I * I 1 (A) -- (Expected) LI/TA Initial I 1 (A) -- (Measured) V 1 (V) P copper (W) # V/I range Table#4: Load test: R load is varied by using the load bank connected in single phase. % of rated I I 2 (A) (Expected) I 2 (A) (Measured) H1-H2 I 1 (A) X1-X2 LI/TA Initial V 1 (V) V 2 (V) P in (W) V/I range 11

12 Table #5: To find experimental value of % efficiency and % regulation. Parameter I 1 (A) V 1 (V) I 2 (A) set rated current V 2 (V) set rated voltage P in (W) P out (W) At rated load 12 When load is thrown-off Record core rated voltage from Table #2 (P core ) Record copper rated current from Table #3 (P copper ) Total loss = P in - P out Total loss = P core + P copper Note: Compare the losses calculated in the two cells marked by. Table#5A: Calculating experimental value of percentage efficiency. P in rated load current & voltage P out rated load current & voltage % Efficiency P out (W) % = P in (W) Table#5B: Calculating experimental value of percentage regulation. Rated voltage V 2 the rated load current No load voltage V 2 (V) when load is thrown-off % Regulation 208 volts No load V 2 (V) - Rated load V 2 (V) % = Rated load V 2 (V) Table#6: Calculate after experimentation (do at home). % of rated I I 2 (A) (Measured) Copper loss (W) P out (W) % Efficiency #

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