EET-216 LAB # 3 - RLC circuits Three phase Power Correction (Rev1) PDF

Preview

Summary

Lab 3...

Description

Electrical Engineering Electrical Engineering Technician AMAT/ SETAS Course: EET-216 DRAWINGS & INSTALLATION 3 Out of 60 Name: 1. Deanne Aira P. Pimentel, Sec. 005 . Name: 2. _________________________________________________________ Name: 3. _________________________________________________________

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.

-

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.

-

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

-

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. Connect the 2mm T Analog Output, n Analog Output, and Analog Ground of the Dynamometer to the 2mm T Analog Input, n Analog Input, and Analog Ground of the Data Acquisition and Control Interface.

3. Turn the Dynamometer/Power Supply on. 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 Power Supply to implement the AC power source. Use the Resistive Load to implement the three-phase resistor and the Capacitive Load to implement the three-phase capacitor. The three-phase resistor represents purely resistive loads in the application, such as heating and lighting systems, while the threephase capacitor is used for power factor correction (i.e. to correct the power factor of a threephase induction motor in the industrial application).

6. Have your instructor verify your connections. _______ (initial)

/5

7. Make the necessary switch settings on the Resistive Load so that the resistance of the threephase resistor is equal to 400Ω.

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). 8. In the Metering window, make the required settings in order to measure the RMS value (AC) of the industrial application (from source) Line Voltage Eind (input E1) and Line current Iind (input I1), as well as the RMS value of the indduction motor line current IMot (input I3). Set three meters to measure the active power Pind supplied to the industrial application, the reactive power Qind which the industrial application exchanges with the distribution system (i.e. the ac power source), and the apparent power Sind delivered to the inductrial application. In all three cases, use the metering function (E1, I1) 3~. Set a meter to measure the power factor pf of the industrial application [metering function PF (E1, I1) 3~ ]. Finally, set three meters to record the the motor torque T, motor speed n, and mechanical power Pm. 9. In the LVDAC-EMS, open the Four-Quadrand Dynamometer/Power Supply window, then make the following settings: -

Set the Function parameter to 2Q CT Brake.

-

Make sure the Torque Control parameter is set to Knob.

-

Sett the Torque parameter to 0.00 N∙m

-

Make sure the Status parameter is set to Stopped.

10. On the Power Supply, turn the three-phase AC power source on to supply power to the threephase resistive load and the phree-phase induction motor. 11. In the LVDAC-EMS, open the Data Table window. Set the Data Table to record the voltage Eind., and current Iind., active power Pind., reactive power Qind., apparent power Sind., and power factor pf of the industrial application, as well as the induction motor current IMot. (indictated in the Metering window). Also set the Data Table to record the rotational speed n, the motor torque τMot., the amount of mechanical power PM produced by the induction motor. 12. In the Data Table window, click the Record Data button to record the initial parameters. 13. In the Dynamometer window, vary the Torque parameter from 0.00N∙m to -1.20N∙m in steps of 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 parameters. 14. 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 load varies. As the mechanical load is varied, the reactive power that is absorbed by the induction motor varies very little. /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. In industrial applications, by the use of distributed power factor correction, correcting the power factor would be possible. It's because, regardless of the mechanical load that is applied to the motor, the reactive power of the three-phase induction motor varies so little. Therefore, to provide the reactive power needed by the induction motor, a correctly-sized fixed capacitor may be used. /2 15. In the Data Table window save the recorded data then clear the Data Table without modifing the recorded settings.

16. 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 capacitor you used to correct the power facor of the three-phase induction motor. Reactances XC1, XC2, and XC3 = 600 Ω

/2

17. Using the measured voltage Eind, calculate the amount of reactive power QC that the three phase capacitor used for power factor correction. Three-phase capacitor reactive power Qc = 216 var

/2

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 in step 12)? □ Yes

□ No

/2

18. In the Four-Quadrand Dynamometer/Power Supply window, set the Torque paramere to 0.00 N∙m 19. In the Data Table window, click the Record Data button to record the initial parameters. 20. In the Four-Quadrant Dynamometer/Power Supply window, vary the Torque parameter from 0.00N∙m to -1.20N∙m if the in steps of 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 parameters.

21. In the Data Table window, save the recorded data.

22. In the Four-Quadrant Dynamometer/Power Supply window, stop the Negative Constant-Torque Prime Mover/Break. On the Power Supply, turn the three-phase ac power source off to stop the three-phase induction motor. /5 23. Uaing the data you just recorded, plot on the same graph the curves of the power factor p f of the indultrial application as a function of the mechanical power P M produced by the three-phase induction motor, with and without power factor correction. (use both sets of data) /2

24. Observe the graph you plotted in the previous step. Does the graph show that power factor correction to correct the power factor of a resistive-inductive load with a virtually fixed reactive power demand (succh as a three-phase induction motor) significantly improves the power factor of the industrial applicatoin? Explain briefly. /3 Indeed. The graph clearly depicted that the power factor of an industrial application is always slightly smaller than unity (or 1) without distributed power factor correction, even as the mechanical power (Pm) produced by the induction motor increases. Consequently , the power factor of the industrial application is held at unity at all times by using distributed power factor correction.

25. Observe the data you saved at steps 15 and 21 (the data obtained without and with power factor correction at the induction motor, respectively). Compare the intensity of the induction motor current IMot measured without power factor correction to that with power facotor correction. What can you conclude? The induction motor current ( I 3 ¿ is great in amount without power factor correction, but when power factor correction was introduced the current decreased gradually. I can conclude that the intensity of the motor induction current measured without the distributed power factor correction is always considerably higher than that measured with the distributed power factor correction. /4 26. 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) in the industrial application that conveys power to the induction motor? Explain briefly. In the industrial application, the use of distributed power factor correction reduces either the size and rating of power lines and equipment that is responsible for transmitting power to the induction motor or it reduces the heat generated due to power losses. 27. 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

/1

28. Attach a clear and properly labled print out of your data, and the graph from step 23 to the lab sheet /5 29. Close LDVAC-EMS, then turn off all the equipment. Disconnect all the 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. /3 The main objective of power factor correction is to increase the power factor of a certain load to a value that is as close as possible to unity. In general, this is done by connecting capacitors tthat will provide the required amount of reactive power to the load. 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? /3 1. It increases the intensity of the flow of current in the distribution lines that is providing electric power to the industrial application. 2. It decreases the amount of true power being supplied to the industrial application. 3. It increases the amount of copper losses in the distribution lines and in the upstream equipment in the system.

4. It decreases the voltage of the industrial application, specifically at the main power bus.

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. /3 Delta configuration is much preferred over wye configuration when it comes to implementing power factor correction in a three-phase switched-capacitor bank. For the reason that threephase capacitors connected in delta are more advantageous than three-phase capacitors connected in wye. Foremost, when one of the capacitors fails and becomes open, the power factor correction is less unbalanced. Hence, this reduces the chance of having a voltage imbalance cause by a power factor correction that became unbalanced due to the open capacitor. Also, the harmonics that is feeding the industrial application in the power lines are reduced, thus making it favorable to the distribution system.

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. No, the use of a fixed capacitor to correct the power factor of an industrial application whose reactive power demand differs considerably is not appropriate. Due to the fact that, as the required reactive power of the industrial application changes, the capacitor is no longer sized to provide the same amount of reactive power needed to correct the industrial application’s power /3 factor.

DATA TABLE

GRAPH (WITHOUT POWER FACTOR CORRECTION)

GRAPH (WITH POWER FACTOR CORRECTION)

Conclusion:

/3

At the end of the lab, I learned how significant power factor correction is, specifically in industrial applications. Notably, a poor power factor may result to an inefficient power distribution system and an increased energy cost. However, this can be corrected by making the value closer to unity, and this can be achieved by connecting parallel capacitance to the load. Why capacitors? It is because only capacitors can alter the effect of the inductive load, and because capacitors have their own source of reactive power. Thereby, reducing the amount of reactive power that is being supplied by the utility.

Student Name

LAB MARK 35

QUESTIONS 12

Conclusion 3

SAFETY 10

1 2 3

This Lab MUST be submitted to your instructor at end of lab class.

Total Mark 60...