Dynamic Power Factor Correction Using a STATCOM

Transcription

1 Exercise 2 Dynamic Power Factor Correction Using a STATCOM EXERCISE OBJECTIVE When you have completed this exercise, you will be familiar with the reasoning behind the usage of power factor correction in industrial applications that absorb large amounts of reactive power from the ac power network. You will learn the operating principles of STATCOMs when they are used for dynamic power factor correction (i.e., for dynamic reactive power compensation) in arc furnace applications and other industrial applications operating with large random peaks of reactive power demand. You will also learn how a STATCOM achieves automatic control of the reactive power exchanged between an industrial application and the ac power network. DISCUSSION OUTLINE The Discussion of this exercise covers the following points: Power factor correction in industrial applications Using STATCOMs for dynamic power factor correction Automatic reactive power control DISCUSSION Power factor correction in industrial applications In Exercise 1, you learned that STATCOMs are commonly used for voltage compensation in ac transmission lines since they allow tight, fast, and effective control of the voltage at the receiver end of the line (and along the line when used in transmission substations). STATCOMs achieve this by supplying the exact amount of reactive power required to maintain the voltage at the receiver end (or at any substation) of the transmission line at the desired value. Just like ac transmission lines, various industrial applications absorb large amounts of reactive power during normal operation. Nowadays, most electrical power providers charge extra costs to industrial customers that have a low power factor (i.e., industrial applications that have a high reactive power requirement in comparison to their active power requirement). This is because reactive power, even though it does not produce any work, still needs to flow in the wires of the ac power network and thus reduces the amount of active power that can be supplied by the network. Because of this, most large industrial customers, in order to lower energy costs, use certain means to minimize their reactive power demand. The more an industrial application can supply its own reactive power (through the use of capacitors, for example), the less reactive power the ac power network has to supply and, therefore, the higher the power factor of the application. This can lead to important savings in energy costs. Correcting (increasing) the power factor of an industrial application in such a way is called power factor correction. In large industrial applications with a reactive power demand that varies little or varies slowly over time, power factor correction is achieved using banks of capacitors that can be switched in or out as required. This allows the amount of reactive power supplied by the capacitors to be increased or decreased in order Festo Didactic

2 Exercise 2 Dynamic Power Factor Correction Using a STATCOM Discussion to meet the exact reactive power requirement of the application and keep the power factor as close to unity as possible. On the other hand, the reactive power demand in certain large industrial applications varies greatly and suddenly over time. This is the case with arc furnace applications, as well as with several other industrial applications as diverse as rolling mills, traction systems (e.g., railroad networks), large resistance welders, and harbor cranes. These fluctuations in the reactive power demand of an industrial application can be significant and can greatly increase the amount of reactive power that the ac power network must supply since they cannot be rapidly and effectively compensated using capacitor banks. This, in turn, lowers the power factor of the application and increases the energy cost (because of the extra costs charged by the electricity provider). Arc furnace in operation. Another important effect of the large random peaks of reactive power demand produced in arc furnace applications and other similar industrial applications is that the voltage at the ac power input of the application fluctuates greatly with the reactive power demand. The higher the reactive power demand of the industrial application, the more important the voltage drop at the ac power input. These voltage fluctuations, in turn, cause a number of undesirable effects in the application, most notably light flicker (quick, repeated change in light intensity). In industrial applications requiring a particularly high amount of reactive power, these undesirable effects (voltage fluctuations, light flicker) are not only limited to the industrial application site, but can affect surrounding electrical power consumers in the ac power network. In most modern ac power networks, this cannot be tolerated. Figure 26. STATCOMs can be installed nearby large harbor cranes for dynamic power factor correction of the crane power system. Finally, in some industrial applications that stay in constant or near-constant operation (such as arc furnace applications) the voltage drops caused by the 42 Festo Didactic

3 Exercise 2 Dynamic Power Factor Correction Using a STATCOM Discussion peaks of reactive power demand lead to a significant decrease in the average value of the voltage at the ac power input of the application and thus in the amount of active power that the ac power network supplies to the application. This reduces the productivity and, therefore decreases revenues. Figure 27. STATCOMs can be used in railroad networks for dynamic power factor correction of the railroad power system. Using STATCOMs for dynamic power factor correction The undesirable effects caused by the random peaks of reactive power demand generated in arc furnace applications and other similar industrial applications can be eliminated or minimized by the installation of a STATCOM at the ac power input of the application. When used in such a way, a STATCOM greatly reduces the reactive power demand of the industrial application as well as the fluctuations in this reactive power demand. The STATCOM achieves this by continually monitoring the reactive power demand of the industrial application and compensating for it by supplying the required amount of reactive power to the application, thereby maintaining the power factor of the application as close as possible to unity. This process is called dynamic power factor correction (or dynamic reactive power compensation). Correcting the power factor in an arc furnace application or any other similar industrial application using a STATCOM minimizes the amount of reactive power that the ac power network must supply to the application and, consequently, minimizes the energy costs. It also ensures that the voltage at the ac power input of the application is maintained as close as possible to the nominal value of the ac power network voltage, and that no undesirable effect (voltage drops, light flicker) is experienced by surrounding electrical power consumers in the ac power network. Because of these effects, the installation costs of a STATCOM, although significant, can generally be recouped within a few years of the STATCOM installation. Festo Didactic

4 Exercise 2 Dynamic Power Factor Correction Using a STATCOM Discussion Figure 28 illustrates the effects of adding a STATCOM to an arc furnace application on the voltage measured at the ac power input of the application. Voltage at the ac power input of the arc furnace application (V) Without a STATCOM Gain due to the STATCOM With a STATCOM Time (min) Figure 28. Typical voltage fluctuations observed at the ac power input of an arc furnace application, with and without a STATCOM. As Figure 28 shows, the voltage measured at the ac power input of the arc furnace application fluctuates greatly over time when it operates without a STATCOM due to the peaks in reactive power demand. When a STATCOM is added to the application for dynamic power factor correction, the voltage measured at the ac power input of the application still fluctuates slightly, but does not present any large variation as when the application operates without a STATCOM. The graph also shows that the average voltage at the ac power input of the application is higher when the application operates with a STATCOM than when it operates without. As a result, the active power supplied to the industrial application is also higher when the application operates with a STATCOM. Since arc furnace applications stay in constant or near-constant operation, such an increase in the average voltage at the ac power input of the application results in a higher amount of active power supplied to the application and, consequently, higher productivity and higher revenues. 44 Festo Didactic

5 Exercise 2 Dynamic Power Factor Correction Using a STATCOM Discussion Figure 29. STATCOMs are often used for reactive power compensation of the large random peaks of reactive power demand generated by electric arc furnace industries. Automatic reactive power control When a STATCOM is used for dynamic power factor correction (i.e., for automatic reactive power compensation) in an industrial application operating with large random peaks of reactive power demand, the reactive power which the application exchanges with the ac power network is controlled so that it remains equal to 0 var (see Figure 30). The STATCOM achieves this by monitoring the reactive component ( ) of the line currents flowing between the ac power network and the ac power input of the application to which the STATCOM is connected. The STATCOM uses the reactive component of the measured line currents to determine the switching signals to be applied to the three-phase bridge in order to fully compensate the reactive power demand of the application (i.e., to zero the reactive power exchanged between the ac power network and the application). The STATCOM also monitors the voltage at its dc side and adjusts the switching signals applied to the three-phase bridge so as to maintain this voltage equal to the dc bus voltage command. The block diagram of a STATCOM designed for dynamic power factor correction (i.e., automatic reactive power control) is shown in Figure 30. The industrial application is represented in the block diagram by a resistive-inductive load. Festo Didactic

6 Exercise 2 Dynamic Power Factor Correction Using a STATCOM Discussion AC Transmission Line Line Capacitors Line Inductors Three-Phase Bridge Load STATCOM Controller (Automatic Reactive Power Control) DC Bus Voltage Command ( ) Industry Reactive Current Command ( ) Figure 30. Block diagram of a STATCOM designed for dynamic power factor correction (i.e., automatic reactive power control). As Figure 30 shows, two current sensors measure line currents and flowing between the ac power network and the industrial application, three voltage sensors measure line voltages,, and across the STATCOM side of the step-down transformer, two current sensors measure the currents and flowing through the STATCOM side of the step-down transformer, and a voltage sensor measures voltage across the dc aide of the STATCOM. These voltage and current values are sent to the STATCOM controller. The STATCOM controller determines the reactive component of the measured line currents and. It compares the reactive component of the measured line currents to the reactive current command (0 A) of the STATCOM to determine the error in the reactive component of the line currents flowing between the ac power network and the industrial application. Also, the STATCOM controller compares the measured dc voltage to the dc bus voltage command to determine the error in the measured dc voltage across the dc side of the STATCOM. Using these calculated error values and the other measured voltage and current values, the STATCOM controller determines the switching signals to be applied to the three-phase bridge so that the amount of reactive power that the STATCOM exchanges with the application zeroes the reactive component in the line currents flowing between the ac power network and the application, and that the amount of active power flowing through the STATCOM makes the voltage measured across the dc side of the STATCOM equal to the dc bus voltage command. This ensures that the amount of reactive power which the industrial application exchanges with the ac power network is maintained as close as possible to 0 var. Note that line voltage is also used to provide the phase angle ( ) information required to perform mathematical 46 Festo Didactic

7 Outline calculations in the controller. The operation of a STATCOM controller designed for automatic reactive power control is covered in further detail in Appendix D. Figure 31. STATCOM substation located near Austin, Texas, USA. This STATCOM substation was installed with the primary purpose of rapidly compensating the ac power network voltage during low voltage operation (photo courtesy of ABB). PROCEDURE OUTLINE The Procedure is divided into the following sections: Set up and connections Industry operation without dynamic power factor correction Industry operation with dynamic power factor correction PROCEDURE High voltages are present in this laboratory exercise. Do not make or modify any banana jack connections with the power on unless otherwise specified. Set up and connections In this section, you will set up a circuit representing a three-phase ac transmission line supplying power to an industrial application operating with large random peaks of reactive power demand (such as an arc furnace) that is equipped with a STATCOM. You will then set up the measuring equipment required to study the operation of the STATCOM when it is used for dynamic reactive power compensation. 1. Refer to the Equipment Utilization Chart in Appendix A to obtain the list of equipment required to perform this exercise. Install the required equipment in the Workstation. Festo Didactic

8 2. Make sure the ac and dc power switches on the Power Supply are set to the O (off) position, then connect the Power Supply to a three-phase ac power outlet. 3. Connect the Power Input of a Data Acquisition and Control Interface to the 24 V ac power supply. Turn the 24 V ac power supply on. Connect the Power Input of both Data Acquisition and Control Interfaces together. Connect the Low Power Input of the IGBT Chopper/Inverter to the Power Input of any of the Data Acquisition and Control Interface modules. 4. Connect the USB port of each Data Acquisition and Control Interface to a USB port of the host computer. 5. Turn the host computer on, then start the LVDAC-EMS software. In the LVDAC-EMS Start-Up window, make sure that both Data Acquisition and Control Interface modules are detected. Make sure the STATCOM Control and Computer-Based Instrumentation functions are available for either or both of the Data Acquisition and Control Interface modules. Also, select the network voltage and frequency that correspond to the voltage and frequency of your local ac power network, then click the OK button to close the LVDAC-EMS Start-Up window. 6. Before you begin connecting the equipment, record in the space below the serial number of the Data Acquisition and Control Interface (DACI) you will use to control the STATCOM and the serial number of the DACI you will use for data acquisition. Serial number of the DACI controlling the STATCOM : Serial number of the DACI used for data acquisition : Connect the equipment as shown in Figure 32 and Figure 33. Use the Power Supply to implement the three-phase ac power source. Use the capacitors in the Capacitive Load module to implement the line capacitors. Note that points A1, A2, A3, and A4 in Figure 32 are connected to the corresponding points in Figure 33. a In Figure 32 and Figure 33, voltage and current inputs shown in blue represent inputs from the Data Acquisition and Control Interface used to control the STATCOM while voltage and current inputs shown in red represent inputs from the Data Acquisition and Control Interface used for data acquisition. Note that the inputs used for control cannot be used for data acquisition, and vice versa. This circuit represents an ac transmission line supplying power to an industrial application operating with large random peaks of reactive power demand. The industrial application is represented by the resistive and inductive loads. By adjusting the resistance of the resistive load and the 48 Festo Didactic

9 reactance of the inductive load, it is possible to vary the active power and reactive power demand of the application. A STATCOM is shunt-connected between the receiver end of the ac transmission line and the industrial application (resistive and inductive load) for dynamic power factor correction (i.e., for dynamic reactive power compensation). In the circuit of Figure 32 and Figure 33, line capacitors are connected in parallel at the receiver end of the ac transmission line to partially compensate for the voltage drop occurring across the line. This reduces the amount of reactive power the STATCOM must supply in order to achieve dynamic power factor correction. Festo Didactic

10 AC power network, transmission line, line capacitors, and resistive and inductive loads Three-Phase Transmission Line module L1 L2 Resistive load L3 Inductive load N A1 A2 A3 To STATCOM substation A4 Line capacitors Local ac power network Voltage (V) Frequency (Hz) Line inductive reactance ( ) Line capacitors ( ) Load resistors,, ( ) Load inductors,, ( ) Figure 32. Circuit for studying the operation of a STATCOM used for dynamic power factor correction (i.e., for dynamic reactive power compensation) in an industrial application operating with large random peaks of reactive power demand. 50 Festo Didactic

11 Three-Phase Transformer Bank module Static synchronous compensator A To ac power network A A A4 Line Inductors module IGBT Chopper/Inverter module Switching control signals from the control DACI Figure 33. Circuit for studying the operation of a STATCOM used for dynamic power factor correction (i.e., for dynamic reactive power compensation) in an industrial application operating with large random peaks of reactive power demand. Festo Didactic

12 7. Connect the Digital Outputs of the Data Acquisition and Control Interface used for controlling the STATCOM to the Switching Control Inputs of the IGBT Chopper/Inverter using a DB9 connector cable. Make sure the Dumping switch on the IGBT Chopper/Inverter is set to the I position. This allows power to be dissipated in a dump resistor inside the IGBT Chopper/Inverter in the event of an overvoltage across the IGBT Chopper/Inverter. This additional protection has no effect on the STATCOM operation. 8. Make sure the I/O toggle switch on the Three-Phase Transmission Line is set to the I position. On the Three-Phase Transmission Line, set the inductive reactance selector to the value indicated in the table of Figure 32 corresponding to your local ac power network voltage and frequency. Make the necessary switch settings on the Capacitive Load to obtain the reactance of the line capacitors indicated in the table of Figure 32 corresponding to your local ac power network voltage and frequency. Make the necessary switch settings on the Resistive Load and on the Inductive Load so that the resistance of the three-phase resistive load and the reactance of the three-phase inductive load are infinite. 9. In LVDAC-EMS, open the Metering window. A dialog box appears. Select the serial number of the Data Acquisition and Control Interface used for data acquisition (recorded in step 6) then click the OK button to close the dialog box and open the Metering window. In the Metering window, open the Acquisition Settings dialog box, set the Sampling Window to 8 cycles, then click OK to close the dialog box. This enables better accuracy when measuring the different parameters (e.g., reactive power) of the STATCOM and is necessary to measure harmonic contents. Make the required settings in order to measure the rms values (ac) of the voltage (input E1) at the sender end of the ac transmission line, and the voltage (input E2) at the industrial application. Set two other meters to measure the three-phase active power and reactive power used by the industrial application [metering function PQS2 (E2, I2) 3~]. Set another meter to measure the amount of energy supplied to the industrial application [metering function W (E2, I2) 3~]. Also, set a meter to measure the numerical integral of the reactive power used by the industrial application [metering function Q (E2, I2) 3~]. Finally, set two meters to measure the three-phase power factor of the industrial application [PF (E2, I2) 3~]. On one of these two meters, modify the type of measured power factor from True to Disp in order to measure the displacement power factor of the industrial application. These meter settings are explained in more detail below. The three-phase reactive power represents the amount of reactive power that the industrial application absorbs from the ac transmission line. 52 Festo Didactic

13 This value should remain as close as possible to 0 var when the STATCOM is operating properly. The reactive power does not represent the reactive power demand of the industrial application, which will be set to a value other than zero and made to vary randomly in this exercise (just as in real-life industrial applications such as arc furnaces). The energy supplied to the industrial application represents the total amount of watt-hours (i.e., the active power integral) supplied to the application, while the numerical integral of the reactive power represents the total amount of var hours exchanged between the ac power network and the industrial application. In other words, the numerical integral of the reactive power is the equivalent of the energy related to the active power. Modifying the setting of one of the two power factor meters from True to Disp causes this meter to measure the displacement power factor of the industrial application instead of the power factor. The displacement power factor, as opposed to the power factor, only takes into account the fundamental component of the measured parameters (all harmonic components are discarded). Industry operation without dynamic power factor correction In this section, you will study the operation of the industrial application without dynamic power factor correction (i.e., without dynamic reactive power compensation by the STATCOM). You will vary the resistance of the resistive load, as well as the reactance of the inductive load representing the industrial application, and let the application operate for 1 minute at each load setting. While doing so, you will record the sender voltage, the voltage at the industrial application, the active power supplied to the application, the reactive power absorbed by the application, the power factor of the application, and the displacement power factor of the application. Finally, you will record the amount of energy supplied to the industrial application (expressed in watt-hours), as well as the numerical integral of the reactive power absorbed by the industrial application (expressed in var hours) when operating without power factor correction. 10. In LVDAC-EMS, open the Data Table window. Set the timer to make 900 records with an interval of 1 second between each record. This corresponds to a 15 minute period. Set the Data Table to record the sender voltage, the voltage at the industrial application, the active power supplied to the application, the reactive power absorbed by the application, the power factor of the application, and the displacement power factor of the application. Also, set the Data Table to record the time associated with each record. 11. On the Power Supply, turn the three-phase ac power source on. In the Data Table window, start the timer to begin recording data. Festo Didactic

14 12. Make the necessary switch settings on the Resistive Load and on the Inductive Load in order to obtain the combinations of resistance values (for resistors,, and ) and reactance values (for inductors,, and ) indicated in Table 4 (1 st to 10 th values) corresponding to your local ac power network voltage and frequency. For each resistance and reactance combination, wait for 1 minute, then proceed to the next combination. a For optimal results, modify the switch settings simultaneously on the three legs of the Resistive Load and Inductive Load in order to avoid operation with an unbalanced load as much as possible. Table 4. Resistance values of resistors,, and and reactance values of inductors,, and to be used in the circuit of Figure 32 and Figure 33 for different local ac power network voltages and frequencies. Local ac power network Resistance values of,, and, and reactance values of,, and Voltage (V) Frequency (Hz) 1 st 2 nd 3 rd 4 th 5 th 6 th 7 th 8 th 9 th 10 th On the Power Supply, turn the three-phase ac power source off. 14. In the Data Table window, stop the timer, then save the recorded data. Clear all recorded data without modifying the record and timer settings. 15. In the Metering window, measure the amount of energy supplied to the industrial application, as well as the value of the numerical integral of the reactive power used by the industrial application that are obtained without dynamic power factor correction. Record both values below. Energy W h Numerical integral var h When the values are recorded, reset both meters (i.e., the meter measuring the energy and the meter measuring the numerical integral of the reactive power). 54 Festo Didactic

15 Industry operation with dynamic power factor correction In this section, you will study the operation of the industrial application with dynamic power factor correction (i.e., with dynamic reactive power compensation by the STATCOM). You will set the STATCOM for automatic reactive power compensation. You will then vary the resistance of the resistive load, as well as the reactance of the inductive load representing the industrial application, and let the application operate for 1 minute at each load setting. While doing so, you will record the sender voltage, the voltage at the industrial application, the active power supplied to the application, the reactive power absorbed by the application, the power factor of the application, and the displacement power factor of the application. You will plot on a graph the different parameters of the industrial application as a function of time, compare the curves obtained with dynamic power factor correction to those obtained without dynamic power factor correction, and analyze the results. Finally, you will record the amount of energy supplied to the industrial application (in watt-hours) as well as the numerical integral of the reactive power used by the industrial application (in var hours) when operating with dynamic power factor correction. You will compare the values obtained with power factor correction to those obtained without dynamic power factor correction, and analyze the results. 16. Make the necessary switch settings on the Resistive Load and on the Inductive Load so that the resistance of the three-phase resistive load and the reactance of the three-phase inductive load are infinite. 17. In LVDAC-EMS, open the STATCOM Control window. A dialog box appears. Select the serial number of the Data Acquisition and Control Interface that is used to control the STATCOM (recorded in step 6), then click the OK button to close the dialog box and open the STATCOM Control window. In the STATCOM Control window, make the following settings: Set the Control Mode parameter to Automatic Reactive Power Control. This control mode allows the amount of reactive power used by the application connected to the STATCOM to be automatically controlled and maintained as close as possible to 0 var, ensuring that the power factor of the application connected to the STATCOM is maintained at unity. In order to implement this control mode, the Data Acquisition and Control Interface used for controlling the STATCOM requires voltage inputs E1, E2, E3, and E4, as well as current inputs I1, I2, I3, and I4, to be connected as shown in the circuit of Figure 32 and Figure 33. Make sure the DC Bus Voltage Command parameter is set to 200 V. Make sure the Active Current Controller Prop. Gain (Kp1) is set to 0.1. Make sure the Active Current Controller Int. Gain (Ki1) is set to 4. Make sure the Reactive Current Controller Prop. Gain (Kp2) is set to 0.3. Make sure the Reactive Current Controller Int. Gain (Ki2) is set to 10. Festo Didactic

16 Make sure the DC Bus Voltage Controller Prop. Gain (Kp3) is set to 5. Make sure the DC Bus Voltage Controller Int. Gain (Ki3) is set to 10. Start the Static Synchronous Compensator function by clicking the Start/Stop button or by setting the Status parameter to Started. 18. On the Power Supply, turn the three-phase ac power source on. In the Data Table window, start the timer to begin recording data. 19. Make the necessary switch settings on the Resistive Load and on the Inductive Load in order to obtain the combinations of resistance values (for resistors,, and ) and reactance values (for inductors,, and ) indicated in Table 4 (1 st to 10 th values) corresponding to your local ac power network voltage and frequency. For each resistance and reactance combination, wait for 1 minute, then proceed to the next combination. a For optimal results, modify the switch settings simultaneously on the three legs of the Resistive Load and Inductive Load in order to avoid operation with an unbalanced load as much as possible. 20. On the Power Supply, turn the three-phase ac power source off. In the STATCOM Control window, stop the static synchronous compensator by clicking the Start/Stop button or by setting the Status parameter to Stopped. 21. In the Data Table window, stop the timer, then save the recorded data. 22. Using the data you recorded, plot on the same graph the reactive power used by the industrial application, with and without dynamic power factor correction, as a function of the recording time. 56 Festo Didactic

17 Compare the curves of the reactive power used by the industrial application obtained with and without dynamic power factor correction. What do you observe? Explain briefly. 23. Using the data you recorded, plot on the same graph the power factor and the displacement power factor of the industrial application, obtained with and without dynamic power factor correction, as a function of the recording time. Compare the curves of the power factor of the industrial application obtained with and without dynamic power factor correction. What do you observe? Explain briefly. Festo Didactic

18 Compare the curve of the power factor of the industrial application to that of the displacement power factor of the application, obtained with dynamic power factor correction. What can you conclude? Explain briefly. 24. Using the data you recorded, plot on the same graph the sender voltage and the voltage at the industrial application, obtained with and without dynamic power factor correction, as a function of the recording time. Is the sender voltage obtained with dynamic power factor correction approximately equal to the sender voltage obtained without dynamic power factor correction, thus indicating that power factor correction has no effect on the sender voltage (i.e., on the ac power network line voltage)? Yes No Compare the curves of the voltage at the industrial application obtained with and without dynamic power factor correction. What do you observe? Explain briefly. 25. Using the data you recorded, plot on the same graph the active power supplied to the industrial application, obtained with and without dynamic power factor correction, as a function of the recording time. 58 Festo Didactic

19 Compare the curves of the active power supplied to the industrial application obtained with and without dynamic power factor correction. What do you observe? Explain briefly. 26. In the Metering window, measure the amount of energy supplied to the industrial application, as well as the value of the numerical integral of the reactive power used by the industrial application that are obtained with dynamic power factor correction. Record both values below. Energy W h Numerical integral var h 27. Compare the amount of energy and the value of the numerical integral of the reactive power you measured in the previous step when the industrial application operates with dynamic power factor correction to those you measured in step 15 when the industrial application operates without dynamic power factor correction. What can you conclude? Explain briefly how these values affect the productivity and energy costs of the industrial application. 28. Do your observations in this exercise confirm that a STATCOM can be used to effectively correct the power factor (through reactive power compensation) Festo Didactic

20 Exercise 2 Dynamic Power Factor Correction Using a STATCOM Conclusion of an industrial application operating with large random peaks of reactive power demand? Yes No 29. Close LVDAC-EMS, then turn off all the equipment. Disconnect all leads and return them to their storage location. CONCLUSION In this exercise, you familiarized yourself with the reasoning behind the usage of power factor correction in industrial applications that absorb large amounts of reactive power from the ac power network. You learned the operating principles of STATCOMs when they are used for dynamic power factor correction (i.e., dynamic reactive power compensation) in arc furnace applications and other industrial applications operating with large random peaks of reactive power demand. You also learned how a STATCOM controller designed for automatic reactive power control compensates the reactive power requirement of the industrial application to which it is connected. REVIEW QUESTIONS 1. What is the primary reason for large industrial consumers to use certain means to compensate for their reactive power demand? Explain briefly. 2. Why is it impossible to correct the power factor in industrial applications operating with large random peaks of reactive power demand using the same means as those used in industrial applications operating with a reactive power demand that does not vary or varies slowly over time? Explain briefly. 60 Festo Didactic

21 Exercise 2 Dynamic Power Factor Correction Using a STATCOM Review Questions 3. What is the effect of the large random peaks of reactive power demand generated in arc furnace applications and other similar industrial applications on the voltage at the ac power input of the application and the voltage supplied to surrounding electrical power consumers? Explain briefly. 4. Explain briefly how STATCOMs can be used to minimize the undesirable effects caused by the large random peaks of reactive power demand in arc furnace applications and other similar industrial applications. 5. Explain briefly why the installation costs of a STATCOM used for dynamic power factor correction in an arc furnace application or any similar industrial application can generally be recouped within a few years of the installation of the STATCOM. Festo Didactic