Experiment o. 1 Objective: The objectives of this experiment are to find the approximate per phase equivalent circuit parameters of a -φ transformer bank using short circuit and open circuit tests and to determine the regulation and efficiency of the transformer bank through load test. The regulation and efficiency of the transformer bank determined through load test will be compared with those calculated using the transformer parameters. Apparatus: 1. 1 -φ variac 2. 2 Test tables. 4 multimeters 4. 2 wattmeters 5. 1 15 kva - φ transformer Bank 6. 1 -φ Resistive load bank with fan 7. 1 -φ Capacitive Load Bank Procedure: 1. Short Circuit Test: a) Refer to Fig.1 for Short circuit test. Connect the high voltage windings of each 1-φ transformer in parallel and then connect them in STAR configuration. Connect the low voltage windings of each 1-φ transformer in parallel and then connect them in DELTA configuration. Make sure that the transformer is connected according to nameplate specifications. b) Connect the three phases of the low voltage windings to test table 2. Connect the three phases of the high voltage windings through the test table to the output terminals of the variac. Make sure that all test table line switches are open. Connect the input terminals of the variac to the 120V power panel. Do not turn on power. Have the lab instructor check your set up. c) With the test table's line switches still open, turn on power and adjust the variac until its output voltage is zero. 1/11
d) Calculate the rated current for the input windings. Check your value with the lab instructor. Make sure that your current transformer is set up to handle this current. e) Protecting the measuring instruments, close the test table line switches. Immediately after closing the line switches check the current in lines 1,2 and. The current should be close to zero. If the current is not close to zero de-energize your circuit and recheck it. f) Increase the output voltage of the variac until the ammeter in line 1 indicates rated current. Measure and record V H12, V H2, V H1, I H1, I H2, I H, I X1, I X2, I X, P HWM1 and P HWM2. Protect your measuring instruments and de-energize the circuit. should be taken with great precaution as you may see currents as high as 100A! 2. Open Circuit Test: a) Refer to Fig.2 for Open circuit test. Connect the high voltage windings of each 1-φ transformer in parallel and then connect them in STAR configuration. Connect the low voltage windings of each 1-φ transformer in parallel and then connect them in DELTA configuration. Make sure that the transformer is connected according to nameplate specifications. b) Connect the three phases of the high voltage windings to test table 1. Make sure that the output connections are open circuited! Connect the three phases of the low voltage windings through test table 2 to the output terminals of the 120V power panel. Make sure that all test table line switches are open. Do not turn on power. Have the lab instructor check your set up. g) Measure and record V X12, V X2, V X1, I X1, I X2, I X, P XWM1, P XWM2, V H12, V H2 and V H1. should be taken with great precaution as you may see voltages as high as 420V!. Transformer with R Load: a) Set up the circuit as shown in Fig.. b) Make sure that the resistance bank is connected to rated voltage. Open circuit the secondary; i.e., resistance set to infinity. Turn O the mains and then turn the switches on the test table to O position. c) ow adjust the resistive load until I H1 = I H2 = I H = rated current. Measure and record V X12, V X2, V X1, I X1, I X2, I X, P XWM1, P XWM2, V H12, V H2, V H1, I H1, I H2, I H, P HWM1, P HWM2 and P HWM for rated current. ote that a two-wattmeter method is used on LV side and a three-wattmeter method on HV side for measurement of three-phase power. So the selection switch on HV side should be used only between positions 1- and -. 2/11
d) ow vary the load resistance such that I H1 = I H2 = I H equals ½ of rated current. Measure and record the same quantities as in step c for each value of I H. 4. Transformer with RC Load: a) Set up the circuit as shown in Fig.4. b) Make sure that the resistance and capacitive bank are connected to rated voltage. Open circuit the secondary by setting the resistance bank and capacitance bank to infinity. Turn O the mains and then turn the switches on the test table O. ow adjust the resistive and capacitive loads such that they draw equal currents and the line currents I H1 = I H2 = I H = rated current. Measure and record V X12, V X2, V X1, I X1, I X2, I X, P XWM1, P XWM2, V H12, V H2, V H1, I H1, I H2, I H, P HWM1, P HWM2 and P HWM for rated current. ote that a two-wattmeter method is used on LV side and a threewattmeter method on HV side for measurement of three-phase power. The selection switch on HV side should be used only between positions 1- and -. c) ow vary the load resistance such that I H1 = I H2 = I H equals ½ of rated current. Measure and record the same quantities as in step c for each value of I H. Report: 1. Designate the parallel connected low voltage (X) windings the primary and the parallel connected high voltage (H) windings the secondary. 2. Using the data found in the open circuit test calculate R C,X1 and X M,X1. G CX1 is given by G MX P oc V oc 2 P oc V oc 2 B M,X is given by 2 2 B MX Y oc G MX Where Y oc I oc V oc /11
I oc V oc P oc I X1 + I X2 + I X CT V X1 + V X2 + V X12 PT WMR PT CT P XWM1 + P XWM2 ( ) Where WMR is the Wattmeter ratio, CT is the current transformer ratio and PT is the Potential Transformer ratio (Treat PT = 1 for the whole experiment).. Using the data found in the short circuit test calculate R eq,h and X eq,h. R eqh is given by V sc Z eqh I sc X eq,h is given by 2 2 X eqh Z eqh R eqh Where R eqh P sc I sc 2 Draw the approximate per phase transformer equivalent circuit with all parameters referred to the primary (LV side) as shown in Fig 5. Show the calculated values of each parameter. Remember to include units. Remember the short circuit test was performed with the voltage applied to the high voltage side! Also make a note of the transformation ratio a. 4. Efficiency from input and output power measurements: The efficiency of a transformer is given by: P out %η 100 P in a) Using the data gathered in Part, Transformer with R Load, calculate the efficiency (η) of the transformer for full, ½ and no load. b) Using the data gathered in Part 4, Transformer with RC Load, calculate the efficiency (η) of the transformer for full, ½ and no load. 4/11
5. Voltage regulation from the voltage measurements: Voltage regulation of a transformer is given by: %Reg V HLLnoload V HLLload V HLLload Where V HLL = the average Line to Line voltage on HV side. a) Using the data gathered in Part, Transformer with R Load, calculate the voltage regulation of the transformer for full, ½ and no load. b) Using the data gathered in Part 4, Transformer with RC Load, calculate the voltage regulation of the transformer for full, ½ and no load. 6. Efficiency from the transformer equivalent circuit parameters: a) Using the values of V XL (LV side average line to neutral voltage), I X (LV side average current), and PF (power factor), gathered in Part, Transformer with R Load, and the equivalent circuit of your transformer, calculate the efficiency of the transformer for full, ½ and no load. b) Using the values of V XL (LV side average line to neutral voltage), I X (LV side average current), and PF (power factor), gathered in Part 4, Transformer with RC Load, and the equivalent circuit of your transformer, calculate the efficiency for the transformer for full, ½ and no load. 7. Voltage Regulation from the transformer equivalent circuit and its parameters a) Using the values of V XL (LV side average line to neutral voltage), I X (LV side average current), and PF (power factor), gathered in Part, Transformer with R Load, and the equivalent circuit of your transformer, calculate the voltage regulation of the transformer for full, ½ and no load. b) Using the values of V XL (LV side average line to neutral voltage), I X (LV side average current), and PF (power factor), gathered in Part 4, Transformer with RC Load, and the equivalent circuit of your transformer, calculate the voltage regulation for the transformer for full, ½ and no load. 8. Compare the results found in step 4 with 6 and step 5 with 7 of the report section. Calculate percent differences. What conclusions can you draw? 5/11
Table1: Short Circuit Test: Quantity Measured reading HV Side P HWM1 P HWM2 V H12 V H2 V H1 I H1 I H2 I H LV Side I X1 I X2 I X Table 2: Open Circuit Test: Quantity Measured reading LV Side P XWM1 P XWM2 V X12 V X2 V X1 I X1 I X2 I X HV Side V H1 V H2 V H 6/11
Table : R Load: Quantity Full Load ½ Full Load LV Side P XWM1 P XWM2 V X12 V X2 V X1 I X1 I X2 I X HV Side P H1 P H2 P H V H1 V H2 V H I H1 I H2 I H 7/11
Table 4: RC Load: Quantity Full Load ½ Full Load LV Side P XWM1 P XWM2 V X12 V X2 V X1 I X1 I X2 I X HV Side P H1 P H2 P H V H1 V H2 V H I H1 I H2 I H I HR1 I HR2 I HR I HC1 I HC2 I HC 8/11
A VARI 1H TEST TABLE1 HV SIDE STAR LV SIDE DELTA TEST TABLE2 H1 H X1 X 1X C B 2H H1 H X1 X 2X H H1 H X1 X X Fig.1. Short Circuit Test, Part 1 LOW VOLTAGE SIDE SHORT CIRCUITED A 1X TEST TABLE 2 LV SIDE HV SIDE TEST TABLE 1 DELTA STAR H1 H 1H X1 X C B 2X X1 X H1 H 2H X X1 X H1 H H HIGH VOLTAGE SIDE OPE CIRCUITED Fig.2. Open Circuit Test, Part 2 9/11
A 1 TEST TABLE 2 TEST TABLE 1 LV SIDE HV SIDE DELTA STAR 1 H1 H X1 X I HR1 C B 2 X1 X H1 H 2 I HR2 R R R X1 X H1 H I HR Fig.. Transformer with resistive load, Part Fig.4. Transformer with resistive and capacitive load, Part 4 10/11
R eq,x X eq,x I X I H a a = X H V XL V X G M,X B M,X av H a 2 Z LOAD Fig. 5. Per Phase Equivalent Circuit referred to LV side for the φ Transformer. 11/11