EET-216 LAB # 3 - RLC circuits Three phase Power Correction PDF

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Lab #3 for EET-216, for the school centennial college. It is done every single week and must be done and not late....

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Electrical Engineering Electrical Engineering Technician AMAT/ SETAS Course: EET-216 DRAWINGS & INSTALLATION 3 Out of 66 Name: 1. _________________________________________________________ Name: 2. _________________________________________________________

Lab # 3 Lab 3 - Three phase LRC circuit, pf correction (Lab Volt)

Title: Three phase RLC Circuit power Factor Correction Discussion: Correcting the power factor of an industrial application. An industrial application with a low power factor has detrimental effects on the power transmission and distribution system of the electricity provider, as well as on the industrial application itself. The main detrimental effects are listed below: -

The intensity of the current flowing in the distribution lines supplying power to the industrial application increases.

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The amount of copper losses (IR2 losses) in the distribution lines, as well as in the equipment (transmission lines, transformers, etc.) upstream in the AC power network, also increases.

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The Voltage at the main power bus of the industrial application decreases.

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The amount of active power supplied to the industrial application decreases.

To illustrate these effects consider the circuit below, representing one phase of a distribution system in an industrial application. The Load in this case is purely resistive. Here you can see that where 49kVA of power is supplied to the load, there is a IR2 loss of 998W in the distribution system. The circuit also shows that the voltage delivered to the load is slightly less than the distribution voltage (Es = 510V, Eind = 499.4V).

Now consider the cirucit below, representing the same distribution system as before, but this time supplying power to an industrial applicaton that draws as much reactive power as active power (represented by a resister and inductor connected in parallel). Here the reactive power Qind (45401var) which the industrial application draws from the distribution system causes the apparent power Sind supplied to the application to increase significantly (from 49880VA to 64213VA). This, in turn, makes the intensity of the current flowing in the distrubution lines supplying power to the industrial application to pass from 99.88A to 134.76A (an increase of 34.9%). The increased current I ind also causes the voltage Eind to decrease by 4.5% (from 499.4V to 476.5V) which, in turn, makes the active power Pind decrease slightly from (49880W to 45401W). Finally, this results in a significant decrease in the industrial applications power factor (from 1 to 0.707). These values and various parameters in the above example show all the detrimental effects listed at the beginning of the lab causes by an industrial application with a low power factor. These effects can be negated by implementing power facotr correction (PFC). Done by adding a source of reactive power at the main bus of the industrial application in order to supply the reactive power required by the inductive loads in the application. See below. Here the reactive power needed for the inductive loads is supplied by the PFC capacitor. Here the application does not draw any reactive power form the distrubution system. The net power factor is 1 ( as when it was purley resistive) The principles behind PFC in three-phase circuits are identical to those behind PFC in single-phase circuits. The only difference is that any capacitor used for power factor correction in one phase must be replicated in the othe two phases to ensure equal (i.e. ballanced) PFC in all three phases. Each group of three capacitors in the switched-capacitor bank is connected in the delta configuration. This is because the DELTA configuration presents advantages over capacitors connected in the WYE configuration.

The First advantage of using the delta-connected capacitors instead of wye-connected capacitors is that the power factor correction is less uballanced when one of the capacitors in a group fails and becomes open. Consequently, this limits the ammount of voltage imbalance resulting from unbalanced power factor correction due to failure. Another advantage of the delta configuration over the wye configuration is that it helps reduce the amount of harmonics in the power lines feeding the industrial applicatoin, thereby makining the application friendlier to the power distrubution system. When using plant-wide power factor correction, the switched-capacitor bank needs to be sized so that it can supply enough reactive power to meet the maximal reacive power demand occouring when all resistive-inductive loads in the industrial application are switched on. Furthermore, the capacitance values of the various banks need to be selected so as to allow different intermediate value of reactive power demand to be met closley. Since plant wide inductive load can vary often and rapidly, plant-wide power factor correctio nis generally achieved using a power factor correction controller (switching the various capacitor banks in and out so as to supply the proper ammount of reactive power.

Introduction: Power factor correction for a three-phase industrial motor application. In this Lab, you will setup a circuit consisting of a three-phase ac power source supplying power to a three-phase resistive load and an induction motor coupled to a constant-torque brake. You will connect a three-phase capacitor in parallel with the induction motor to implement distributed power factor correction. You will vary the mechanical load applied to the motor and observe the effect on the power factor correction. You will measure the different parameters of the industrial application. You will then analyze the results by compairing the parameters measured when the power factor of the application is compensated to those measured when the power factor of the application is not compensated.

Procedure Outline:

The procedure is divided into the following sections: -

Setup and connections

-

Poser factor correction

High voltages are present in this laboratory exercise. Do not make or modify any banana jack connections with the power on unless otherwise specified. Before coupling rotating machines, make absolutely sure that power is turned off to prevent any machine from starting inadvertently.

Procedure: 1. Make sure that the AC and DC power switches on the Power Supply are set to the O (off) position, then connect the Power Supply to the three-phase AC power outlet. Make sure the main power switch on the Dynamometer is set to the O (off) position, then connect its Power Input to an AC power outlet. /1

Connect the Power Input of the Data Acquisition and Control Interface to a 24V AC power supply. Turn the 24V ac power supply on. 2. Connect the USB port of the Data Acquisition and Control interface to a USB port of the host computer. 3. Turn the Dynamometer/Power Supply on, then set the Operating Mode switch to Dynamometer. 4. Turn the host computer on, then start the LVDAC-EMS software. In the LVDAC-EMS Start-Up window, make sure the Data Acquisition and Control Interface is detected. Select the network voltage and frequency (60Hz, 120V) then click the OK button to close the LVDAC-EMS Start-Up window. 5. Connect the equipmnet as shown in the figure Below. Use the Resistive Load as the three-phase resistor bank and the Capacitive Load as the three phase capacitor bank (i.e. Set of red capacitors for XC1 , Set of black capacitors for XC2 , Set of blue capacitors for XC3). Connect the three phase motor in WYE configuration. The three-phase resistor represents purely resistive loads in the application, such as heating and lighting systems, while the three-phase capacitor is used for power factor correction (i.e. to correct the power factor of a three-phase induction motor in the industrial application).

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6. Connect the Analog inputs 7, 8 and Common from the Dynamometer to the Data Acquisition and Control Interface. 7. Have your instructor verify your connections. _____GOOD__ (initial) /5 8. Make the necessary switch settings on the Resistive Load so that the resistance of the threephase resistor is equal to 400Ω - Per phase. Make the necessary switch settings on the Capacitive Load so that he reactance of the threephase capacitor is infinite (no power factor correction, all switches in the off (0) postion). 9. In the Metering window, make the required settings to measure the following items:

E1 supply voltage I1 supply current E3 Motor voltage I3 Motor current PQS(E1,I1)3 Three phase supply Power S in Watts PQS(E1,I1)3 Three phase supply Reactive power Q in VARs PQS(E1,I1)3 Three phase supply Apparent power S in VA pf(E1,I1)3 Three phase supply power factor pf(E3,I3)3 Three phase motor/capacitor bank power factor τMot (AI7,T) counter torque applied to the motor by the break (Dynamometer) Pm (AI-7,8) Mechanical power exerted by the motor on the break (Dynamometer) 10. Set the LVDAC-EMS the Data Table window to record items above. 11. Power up the Dynamometer and configure the following settings: -

Make sure the Status parameter is set to Stopped

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Make sure the Control parameter is set to Manual

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Set the Function parameter to 2Q CT Brake (Use the function button)

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Set the Torque parameter to 0.00 N∙m (Using the command Knob) Please note this will change to aprox. 0.266 N∙m when the Dynamometer is started

12. Have your instructor verify your settings _______ (initial)

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13. On the Power Supply, turn the three-phase AC power source on to supply power to Motor, Resistors and Capacitors. 14. On the Dynamometer change the status parameter to Started by pressing the Start/Stop button. 15. In the Data Table window, click the Record Data button to record the initial parameters. 16. Using the Dynamometer vary the Torque parameter from 0.266N∙m to 1.266N∙m in steps of aproximatly 0.10N∙m. At each step, wait for the induction motor speed to stabalize, then click the Record Data button in the Data Table to record the data. 17. Change the Dynamometer status parameter to Stopped and turn of the motor.

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18. Observe the data you just recorded in the data table. a. Describe what happens to the ammount of reactive power absorbed by the three-phase induction motor (it corrasponds to the value of Q) as the mechanical is increased. ____As the mechanical increased the reative power increases as well.______________________________________________. /2

b. Consider your answer to the question above, would it be possible to correct the power factor for an industrial application using destributed power factor correction (i.e. connectiong a fixed size capacitior in parallel with the motor)? Briefly explain. ______Yes, it ________________________________________________________. /2 19. On the Capacitive Load, make the necessary switch settings to correct the power factor of the three-phase induction motor. (make switch settings so that the power factor of the industrial applicatoin indicated in the Metering window is as close as possible to unity.) Record the reactance (XC1, XC2, and XC3) of the capacitors you used to correct the power facor of the three-phase induction motor. Reactances XC1, XC2, and XC3 = _______Ω

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*** Note: Capacitors connected in DELTA configuration, therefore Phase and Line values of XC are same.

20. Using the measured Line Voltage E1 and the Line Capacitive reactance (X C1) calculate the amount of reactive power QC that the three phase capacitors will apply to the system. Three-phase capacitor reactive power Qc = _________ var

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Is the calculated value relatively close (within 75 var) to the ammount of reactive power which the three-phase induction motor absorbs? (see data recorded above) □ Yes

□ No

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21. In the Dynamometer, reset the Torque to the minimum parameter 0.00 N∙m 22. Turn on the motor. 23. Change the Dynamometer status parameter to Started. 24. In the Data Table window, add a blank line below the previously recorded data and then click the Record Data button to record the post pf correction initial parameters. 25. Using the Dynamometer vary the Torque parameter from 0.266N∙m to 1.266N∙m in steps of aproximatly 0.10N∙m. At each step, wait for the induction motor speed to stabalize, then click the Record Data button in the Data Table to record the data. 26. Save the recorded data from the Data Table and attach to lab report.

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27. Change the Dynamometer status parameter to Stopped and turn of the Dynamometer. Also turn of the motor. /3 28. Uaing the data you just recorded, plot a graph showing power factor pf of the industrial application pf(E1,I1)3 as a function of the mechanical power P m (AI-7,8) produced by the three-phase induction motor, with and without power factor correction. (use both sets of data) Save and attach Graphs to lab report (be sure to label the axes and add title) /5

29. Observe the graph you plotted in the previous step. How did the addition of the capacitor bank effect the system power factor? In systems where the quantity of motors are fixed, does the size of the capacitor bank need to change as production changes? Explain briefly. /3 ___________________________________________________________________ ___________________________________________________________________ 30. Observe your data. Compare the intensity of the induction motor current I3 measured without power factor correction to that with power facotor correction. What can you conclude? /3 ____________________________________________________________________ ____________________________________________________________________ 31. Concitering your answer to the above question, what are the effects of using power factor correction on the lines and equipment (e.g. a power transformer, a conductor, a protective device) that convey power to the induction motor? Explain briefly. ____________________________________________________________________

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____________________________________________________________________ 32. Based on the results, can you conclude that power factor correction can be used to correct the power factor of an industrial application containing resistive-inductive loads with a virtually fixed reactive power demand, such as induction motors? □ Yes

□ No

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33. Be sure to attach the data table and graph to your lab report. 34. Close LDVAC-EMS, ensure all the equipment is powered off. Disconnect leads and return them to their storage locations. /5 In this exercise, you learned how to correct the power factor of an industrial application whose reactive power deand is fixed. Review Questions: 1. What is power factor correction and how is it generally achieved? Explain briefly. /2.5 _____________________________________________________________________ _____________________________________________________________________ 2. What are the four main detrimental effects which operating an industrial application with low power factor has on the distrubution system of the electricity provider and on the industrial plant itself? /2.5 ____________________________________________________________________ ____________________________________________________________________

3. Which type of configuration (Wye or Delta) is preferable for a three-phase switched-capacitor bank used to implement power factor correction? Briefly explain why. /2.5 ____________________________________________________________________ ____________________________________________________________________ 4. Considering the parameters of an industrial application, is it acceptagle to use a fixed capacitor to correct the power factor of an industrial application whose reactive power demand varies significantly (such as when a load is switched in or switched out for example)? Explain briefly. ____________________________________________________________________

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____________________________________________________________________

5. Calculation:

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Source

Motor 1

Motor 2

Capacitor Bank

ELine

ELine

480V

ELine

480V

ELine

ILine

ILine

12A

ILine

18.5A

ILine

S

S

S

Q

Q

Q

Q



P

P

P

XC

pf 

480V

95% (Corrected pf)

pf 

75%

pf 

80%

C

480V

Conclusion:

Student Name 1 2

Example graph

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LAB MARK 36

QUESTIONS 16

Conclusion 3

SAFETY 11

Total Mark 66...