Voltage Compensation of AC Transmission Lines Using a STATCOM

Exercise 1 Voltage Compensation of AC Transmission Lines Using a STATCOM EXERCISE OBJECTIVE When you have completed this exercise, you will be familiar with the operating principles of STATCOMs used for voltage compensation of ac transmission lines. You will learn how a STATCOM controller designed for automatic voltage control compensates the voltage across the ac power system to which the STATCOM is connected. DISCUSSION OUTLINE The Discussion of this exercise covers the following points: Voltage compensation of ac transmission lines using a STATCOM Automatic voltage control DISCUSSION Voltage compensation of ac transmission lines using a STATCOM In the Introduction to this manual, you learned that a significant voltage drop occurs at the receiver end of ac transmission lines. The magnitude of this voltage drop increases with the length of the line, as well as with the load at the receiver end of the line. Such a voltage drop cannot be tolerated in ac power networks. This is due to many electrical devices such as motors, relays, and lighting equipment working properly only under stable voltage conditions (close to the voltage for which they are rated). One way to compensate for the voltage drop occurring across an ac transmission line is to add substations containing shunt capacitors along the line. Adding shunt-capacitor substations in such a way produces the effect of dividing an ac transmission line into many segments of shorter length. Each substation serves the purpose of compensating the voltage drops across the ac transmission line (i.e., maintaining a constant voltage across each segment of the ac transmission line). Figure 18 illustrates a typical ac transmission line used to transfer large amounts of electrical power over a long distance from a power generating station to the distribution network (which, in turn, distributes the electrical power to consumers). Festo Didactic 86371-00 17

Exercise 1 Voltage Compensation of AC Transmission Lines Using a STATCOM Discussion Shunt-capacitor substations Sender end (to power generating station) Receiver end station (STATCOM) Receiver end (to distribution network) Figure 18. Typical ac transmission line used to transfer large amounts of electrical power over a long distance from a power generating station to the distribution network. As Figure 18 shows, the ac transmission line is divided into three segments of equal length by two shunt-capacitor substations used for voltage compensation. The voltage at each substation is compensated by switching shunt capacitors in and out to maintain the voltage along the ac transmission line as close as possible to the nominal value of the ac power network voltage. As mentioned in the Introduction to this manual, shunt-capacitor substations have certain drawbacks, such as the difficulty in coordinating all substations and perfectly compensating the voltage across each segment of the ac transmission line. However, since the shunt-capacitor substations are located along the ac transmission line, and thus do not directly supply power to consumers, it is not necessary for the voltage at the shunt-capacitor substations to be perfectly compensated at all times. On the other hand, the voltage at the end of the third segment (i.e., the receiver end) of the ac transmission line in Figure 18 is compensated using a STATCOM substation, instead of a shunt-capacitor substation. This is due to the numerous advantages STATCOMs offer over shunt-capacitor substations, most notably a tight and fast compensation of the voltage across the line. Since the receiver end station is located at the end of the ac transmission line, it is important for the voltage at this station to be as perfectly compensated as possible before the electrical power is distributed to consumers; hence, a STATCOM substation is used here instead of a shunt-capacitor substation. Due to its fast and precise compensation of the voltage at the receiver end of an ac transmission line, a STATCOM substation is able to compensate for the voltage fluctuations occurring across the line (generated by switching shunt capacitors in and out in substations), and then compensate for the voltage fluctuations caused by the variation of the load (i.e., the electrical power demand of the consumers). To obtain a level of precision in the voltage compensation comparable to a STATCOM while using a shunt-capacitor substation at the receiver end of an ac transmission line, a large number of capacitors of different reactance values would need to be installed in the shunt-capacitor substation. This would give the shunt-capacitor substation a large variety of possible shunt capacitor combinations and, therefore would enable the shunt-capacitor substation to precisely compensate the voltage at the receiver end of the ac transmission line. Such a shunt-capacitor substation, however, would be just as costly as a STATCOM substation (if not more so), while having a response time that is much slower than a STATCOM substation. This is why, for fast and precise voltage 18 Festo Didactic 86371-00

Exercise 1 Voltage Compensation of AC Transmission Lines Using a STATCOM Discussion compensation at the receiver end of an ac transmission line, STATCOM substations are much more efficient than shunt-capacitor substations. It would be possible to replace all the shunt-capacitor substations in the ac transmission line of Figure 18 with STATCOM substations to achieve even more effective voltage compensation. However, even though STATCOMs are more efficient than shunt-capacitor substations in every aspect, it is not common practice to systematically replace shunt-capacitor substations with STATCOM substations. This is primarily due to a STATCOM substation being much more costly (about 6 times more) than a shunt-capacitor substation possessing a comparable power rating. Since the use of shunt-capacitor substations to compensate the voltage along ac transmission lines already yields acceptable results, replacing all shunt-capacitor substations in an ac transmission line with STATCOM substations would not be cost effective. Figure 19. STATCOM substations can be used for fast-acting, precise, and adjustable voltage compensation of ac transmission lines ( Copyright 2012 Guc Kalitesi). Automatic voltage control When a STATCOM is used for compensating the voltage across an ac power system (typically ac transmission lines), the voltage across the STATCOM is regulated using a voltage control loop implemented in the STATCOM controller (see Figure 20). This controller monitors the voltage across the STATCOM side of the step-down transformer, the current flowing through the STATCOM side of the step-down transformer, and the voltage across the dc side of the STATCOM. Using these measured values, the STATCOM controller determines the switching signals to be applied to the three-phase bridge in order to ensure that the line voltages measured across the STATCOM side of the stepdown transformer are equal to the ac bus line voltage command (the value of this command being set so that the resulting voltage across the STATCOM is at the Festo Didactic 86371-00 19

Exercise 1 Voltage Compensation of AC Transmission Lines Using a STATCOM Discussion required value), and that the voltage measured across the dc side of the STATCOM is equal to the dc bus voltage command. The block diagram of a STATCOM designed for voltage compensation (i.e., automatic voltage control) is shown in Figure 20. AC Transmission Line Line Capacitors Line Inductors Three-Phase Bridge Load STATCOM Controller (Automatic Voltage Control) DC Bus Voltage Command ( ) AC Bus Line Voltage Command ( ) Figure 20. Block diagram of a STATCOM designed for voltage compensation. As Figure 20 shows, 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 dc voltage across the dc side of the STATCOM. These voltage and current values are sent to the STATCOM controller. The STATCOM controller compares the measured line voltages to the ac bus line voltage command, and determines the error in the measured line voltages across the STATCOM side of the step-down transformer. The STATCOM controller also compares the measured dc voltage to the dc bus voltage command, and determines the error in the measured voltage across the dc side of the STATCOM. Using these calculated error values and the 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 the STATCOM exchanges with the ac power system to which it is connected ensures that the line voltages measured across the STATCOM side of the step-down transformer are equal to the ac bus line voltage command, 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. Note that line voltage is also used to provide the phase angle ( ) information required to perform mathematical calculations in the 20 Festo Didactic 86371-00

Exercise 1 Voltage Compensation of AC Transmission Lines Using a STATCOM Discussion controller. The operation of a STATCOM controller designed for automatic voltage control is covered in more detail in Appendix D. Figure 21. The voltage across a STATCOM designed for automatic voltage compensation is controlled using a voltage control loop. This ensures that the voltage across the STATCOM is maintained virtually constant ( Copyright 2012 Guc Kalitesi). Festo Didactic 86371-00 21

Outline PROCEDURE OUTLINE The Procedure is divided into the following sections: Set up and connections Voltage compensation at the receiver end of an ac transmission line using a STATCOM Precision of the voltage compensation achieved by a STATCOM during load variations. Speed of the voltage compensation achieved by a STATCOM during load variations. Voltage compensation using a STATCOM at the receiver end of an ac transmission line containing a shunt-capacitor substation 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 consisting of an ac transmission line supplying power to a resistive load, with a STATCOM at the receiver end of the line for voltage compensation. You will then set up the measuring equipment required to study the operation of the STATCOM when it is used for voltage 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. 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. 22 Festo Didactic 86371-00

In the LVDAC-EMS Start-Up window, make sure that both Data Acquisition and Control Interface modules are detected. Make sure the Computer-Based Instrumentation and STATCOM Control 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 22 and Figure 23. Use the Power Supply to implement the three-phase ac power source. Use the capacitors in the Three-Phase Filter module to implement the line capacitors. Note that points A1, A2, A3, and A4 in Figure 22 are connected to the corresponding points in Figure 23. a In Figure 22 and Figure 23, 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 that is voltage compensated at the receiver end of the line using a STATCOM substation. The resistive load in the circuit represents the electrical power demand of the consumers. By adjusting the resistance of the resistive load, it is then possible to vary the intensity of the electrical power demand. In the circuit of Figure 22 and Figure 23, 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 which the STATCOM must supply in order to achieve voltage compensation at the receiver end of the ac transmission line. Festo Didactic 86371-00 23

AC power network, transmission line, line capacitors, and load Three-Phase Transmission Line module L1 Resistive load L2 L3 N A1 A2 A3 A4 To STATCOM Line capacitors Local ac power network Voltage (V) Frequency (Hz) Line inductive reactance ( ) Resistive loads,, ( ) 1 st 2 nd 3 rd 4 th 5 th 6 th 120 60 120 600 400 300 240 200 171 220 50 400 2200 1467 1100 880 733 629 240 50 400 2400 1600 1200 960 800 686 220 60 400 2200 1467 1100 880 733 629 Figure 22. Circuit for studying the operation of a STATCOM used for voltage compensation of an ac transmission line supplying power to a resistive load. 24 Festo Didactic 86371-00

Static synchronous compensator Three-Phase Transformer Bank module A1 1 2 7 12 To ac power network A2 3 4 11 8 9 A3 5 6 10 A4 Line Inductors module IGBT Chopper/Inverter module Switching control signals from the control DACI Figure 23. Circuit for studying the operation of a STATCOM used for voltage compensation of an ac transmission line supplying power to a resistive load. Festo Didactic 86371-00 25

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 22 corresponding to your local ac power network voltage and frequency. Make the necessary switch settings on the Resistive Load to obtain the 1 st resistance value indicated in the table of Figure 22 corresponding to your local ac power network voltage and frequency. a Appendix C lists the switch settings required on the Resistive Load, the Inductive Load, and the Capacitive Load in order to obtain various resistance (or reactance) values. 9. 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 Voltage Control. This control mode allows the voltage of the ac power system to which the STATCOM is connected to be automatically compensated and maintained at a specified value (e.g., at the voltage of your local ac power network). 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 I3 and I4, to be connected as shown in the circuit of Figure 22 and Figure 23. Make sure the DC Bus Voltage Command parameter is set to 200 V. This dc voltage value is high enough to allow the STATCOM to be able to exchange reactive power with the ac power system to which it is connected (i.e., is high enough for the STATCOM to be able to produce ac voltage at the required value). Make sure the AC Bus Line Voltage Command parameter is set to 83 V. With this line voltage command value, the STATCOM controller automatically adjusts the amount of reactive power supplied or absorbed by the STATCOM so that the line voltage across the STATCOM side of the three-phase transformer is 26 Festo Didactic 86371-00

maintained at 83 V. Due to the transformer voltage ratio and configuration (Y- ), the measured line voltage across the ac power system connected to the STATCOM should be close to your local ac power network line voltage. 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. 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. Make sure the AC Bus Line Voltage Controller Prop. Gain (Kp4) is set to 2.5. Make sure the AC Bus Line Voltage Controller Int. Gain (Ki4) is set to 10. Make sure the Static Synchronous Compensator function is Stopped. 10. 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. Make the required settings in order to measure the rms values (ac) of the line voltage (input E1) at the sender end of the ac transmission line, and the line voltage (input E2) at the receiver end of the ac transmission line. Also set a meter to measure the three-phase reactive power the STATCOM exchanges with the ac power system to which it is connected [metering function PQS2 (E2, I2) 3~]. Festo Didactic 86371-00 27

Voltage compensation at the receiver end of an ac transmission line using a STATCOM In this section, you will vary the resistance of the resistive load and record, for each value, the three-phase PWM rectifier/inverter active current and reactive current, the reactive power exchanged by the STATCOM, the sender voltage, and the receiver voltage. You will analyze the results and determine how precise is the voltage compensation achieved by the STATCOM during load variations. You will then use the Oscilloscope to record the transient in the receiver voltage and current when the resistive load decreases and when the resistive load increases. Using the signals recorded on the Oscilloscope, you will determine how fast the STATCOM achieves voltage compensation during load variations. Precision of the voltage compensation achieved by a STATCOM during load variations 11. On the Power Supply, turn the three-phase ac power source on. 12. In the STATCOM Control window, start the static synchronous compensator by clicking the Start/Stop button or by setting the Status parameter to Started. 13. In the STATCOM Control window, adjust the AC Bus Line Voltage Command parameter so that the receiver voltage indicated in the Metering window is as close as possible to the nominal value of your local ac power network voltage. 14. Fill in the first column in Table 2 using the resistance values indicated in the table of Figure 22 corresponding to your local ac power network voltage and frequency. Table 2. Three-phase PWM rectifier/inverter active current and reactive current, reactive power exchanged by the STATCOM, sender voltage, and receiver voltage for different resistive load values when the STATCOM compensates the voltage at the receiver end of an ac transmission line. Resistive loads,, ( ) Active current (A) Reactive current (A) Reactive power (var) Sender voltage (V) Receiver voltage (V) 1 st 2 nd 3 rd 4 th 5 th 6 th 28 Festo Didactic 86371-00

15. Record in Table 2 the three-phase PWM rectifier/inverter active current and reactive current (indicated in the STATCOM Control window) in the appropriate cells of the row corresponding to the current resistance of resistive loads,,. Also, record in Table 2 the reactive power exchanged by the STATCOM, the sender voltage, and the receiver voltage (indicated in the Metering window) in the appropriate cells of the row corresponding to the current resistance value of resistive loads,,. 16. Make the necessary switch settings on the Resistive Load to obtain successively the other resistive load values indicated in the first column of Table 2 corresponding to your local ac power network voltage and frequency. For each resistive load value, repeat step 0. 17. In the STATCOM Control window, stop the static synchronous compensator by clicking the Start/Stop button or by setting the Status parameter to Stopped. On the Power Supply, turn the three-phase ac power source off. 18. From the results recorded in Table 2, can you conclude that the STATCOM perfectly compensates the voltage across the ac power system to which it is connected (i.e., the receiver voltage )? Explain briefly. Compare the precision of the voltage compensation achieved using the STATCOM to that which can be achieved using a battery of shuntcapacitors. What can you conclude? Explain briefly. Festo Didactic 86371-00 29

19. From the results recorded in Table 2, explain how the STATCOM compensates the voltage across the ac power system to which it is connected (i.e., the receiver voltage ). Speed of the voltage compensation achieved by a STATCOM during load variations 20. Make the necessary switch settings on the Resistive Load to obtain the 1 st resistive load value indicated in Table 3 corresponding to your local ac power network voltage and frequency. Table 3. Values of resistive loads,, and to be used for observing the speed of the voltage compensation achieved by the STATCOM during load variations. Local ac power network Resistive loads,, ( ) Voltage (V) Frequency (Hz) 1 st 2 nd 120 60 200 600 220 50 733 2200 240 50 800 2400 220 60 733 2200 21. On the Power Supply, turn the three-phase ac power source on. 22. In the STATCOM Control window, start the static synchronous compensator by clicking the Start/Stop button or by setting the Status parameter to Started. 23. In LVDAC-EMS, open the Oscilloscope. Make the appropriate settings in order to observe the waveform of the voltage (input E2) and current (input I2) at the receiver end of the ac transmission line. a It is recommended to set the time base to 0.1 s/div. 30 Festo Didactic 86371-00

On the Oscilloscope, set the trigger type to Hardware, the trigger source to the channel used to observe the waveform of the receiver voltage, and the trigger level to approximately 10 V higher than the peak value of the receiver voltage. Adjust the horizontal position of the trigger point to about 4 divisions of the left-hand side of the oscilloscope screen. a These settings ensure that the Oscilloscope begins to record data only when the peak value of the receiver voltage increases above its nominal peak value (i.e., when the load at the receiver end of the line decreases). On the Oscilloscope, click the Single Refresh button. 24. Make the necessary switch settings on the Resistive Load to obtain the 2 nd resistive load value indicated in Table 3 corresponding to your local ac power network voltage and frequency. This simulates a large decrease in the power demand of the consumers. a For optimal results, modify the switch settings simultaneously on the three legs of the Resistive Load in order to avoid operation with an unbalanced load as much as possible. On the Oscilloscope, save all recorded voltage and current waveforms to the first memory. The recorded waveforms will be used for comparison later in the exercise. 25. On the Oscilloscope, set the trigger source to the channel used to observe the receiver current, and the trigger level to approximately 0.05 A higher than the peak value of the receiver current. Click the Single Refresh button. a These settings ensure that the Oscilloscope begins to record data only when the peak value of the receiver current increases above its current peak value (i.e., when the load at the receiver end of the line increases). 26. Make the necessary switch settings on the Resistive Load to obtain the 1 st resistive load value indicated in Table 3 corresponding to your local ac power network voltage and frequency. This simulates a large increase in the power demand of the consumers. a For optimal results, modify the switch settings simultaneously on the three legs of the Resistive Load in order to avoid operation with an unbalanced load as much as possible. On the Oscilloscope, save all recorded voltage and current waveforms to the second memory. The recorded waveforms will be used for comparison later in the exercise. Festo Didactic 86371-00 31

27. Using the voltage and current waveforms saved in the memories of the Oscilloscope, can you conclude that the STATCOM compensates the voltage across the ac power system to which it is connected (i.e., the receiver voltage ) almost instantaneously? Explain briefly. 28. In the Metering window, measure the line voltage at the sender end of the ac transmission line. Record the value below as it is required in the next section of this exercise. Sender line voltage V 29. In the STATCOM Control window, stop the static synchronous compensator by clicking the Start/Stop button or by setting the Status parameter to Stopped. 30. On the Power Supply, turn the three-phase ac power source off. 32 Festo Didactic 86371-00

Voltage compensation using a STATCOM at the receiver end of an ac transmission line containing a shunt-capacitor substation In this section, you will set up a circuit consisting of a long ac transmission line that supplies power to a resistive load, and is voltage compensated using a shunt-capacitor substation located at the middle of the line as well as a STATCOM located at the receiver end of the line. You will set the resistance of the resistive load and the reactance of the shunt capacitors to preliminary values. You will then use the Oscilloscope to record the transient in the receiver voltage and current when the resistive load increases and when the voltage compensation provided by the shunt capacitors increases. Using the signals recorded on the Oscilloscope, you will determine how fast the STATCOM achieves voltage compensation during voltage fluctuations. For each resistance value of the resistive load and reactance value of the shunt capacitors, you will also record the voltage at the shunt-capacitor substation and the voltage at the receiver end of the ac transmission line. Finally, you will analyze these voltage values. 31. Modify the equipment connections to obtain the circuit shown in Figure 24 and Figure 25. Note that, in this circuit, the three-phase ac transmission line consists of two segments instead of one, with a shunt-capacitor substation after the first line segment. Also, voltage input E1 is used to measure the voltage at the shunt-capacitor substation instead of the sender voltage. The connections of the various STATCOM components remain the same. Use the capacitors in the Capacitive Load module to implement the shuntcapacitor substation. a In Figure 24 and Figure 25, voltage and current inputs shown in blue represent inputs from the Data Acquisition and Control Interface used for STATCOM control 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. The circuit shown in Figure 24 and Figure 25 represents a long ac transmission line that supplies power to a resistive load and is voltage compensated using a shunt-capacitor substation (manually controlled) located at the middle of the line as well as a STATCOM located at the receiver end of the line. The resistive load in the circuit represents the electrical power demand of the electricity consumers. By adjusting the resistance of the resistive load, it is possible to vary the intensity of the electrical power demand. Festo Didactic 86371-00 33

AC Power network, transmission line with shunt-capacitor substation, line capacitors, and load Three-Phase Transmission Line module Three-Phase Transmission Line module L1 Resistive load L2 L3 N Shunt capacitor substation Line capacitors A1 A2 A3 A4 To STATCOM substation Local ac power network Voltage (V) Frequency (Hz) Line inductive reactance ( ),, ( ),, ( ) 1 st 2 nd 1 st 2 nd 120 60 120 600 400 600 220 50 400 2200 1467 2200 240 50 400 2400 1600 2400 220 60 400 2200 1467 2200 Figure 24. Circuit for studying the operation of a STATCOM used for voltage compensation of an ac transmission line containing a shunt-capacitor substation. 34 Festo Didactic 86371-00

Static synchronous compensator Three-Phase Transformer Bank module A1 1 2 7 12 To ac power network A2 3 4 11 8 9 A3 5 6 10 A4 Line Inductors module IGBT Chopper/Inverter module Switching control signals from the control DACI Figure 25. Circuit for studying the operation of a STATCOM used for voltage compensation of an ac transmission line containing a shunt-capacitor substation. Festo Didactic 86371-00 35

32. Make sure the I/O toggle switch on the second Three-Phase Transmission Line is set to the I position. On the second Three-Phase Transmission Line, set the inductive reactance selector to the value indicated in the table of Figure 24 corresponding to your local ac power network voltage and frequency. Make the necessary switch settings on the Resistive Load and on the Capacitive Load to obtain the first resistance value (for resistors,, and ) and the first reactance value (for capacitors,, and ), respectively, indicated in the table of Figure 24 corresponding to your local ac power network voltage and frequency. 33. In the Metering window, make sure that two meters are set to measure the rms values (ac) of the line voltage (input E1) at the shunt-capacitor substation and the line voltage (input E2) at the receiver end of the ac transmission line. 34. In the STATCOM Control window, make the following settings: Set the AC Bus Line Voltage Controller Prop. Gain (Kp4) to 2. Set the AC Bus Line Voltage Controller Int. Gain (Ki4) to 5. 35. On the Power Supply, turn the three-phase ac power source on. 36. In the STATCOM Control window, start the static synchronous compensator by clicking the Start/Stop button or by setting the Status parameter to Started. 37. In the STATCOM Control window, adjust the AC Bus Line Voltage Command parameter so that the receiver voltage indicated in the Metering window is approximately equal to your ac power network voltage. 38. In the Metering window, measure the line voltage at the shunt-capacitor substation and the line voltage at the receiver end of the ac transmission line. Record both values below. Line voltage V Line voltage V 36 Festo Didactic 86371-00

39. On the Oscilloscope, set the trigger source to the channel used to observe the receiver current, and the trigger level to approximately 0.05 A higher than the peak value of the receiver current. Click the Single Refresh button. a These settings ensure that the Oscilloscope begins to record data only when the peak value of the receiver current increases slightly above its nominal peak value (i.e., when the load at the receiver end of the line increases). 40. Make the necessary switch settings on the Resistive Load to obtain the second resistance value indicated in the table of Figure 24 corresponding to your local ac power network voltage and frequency. This simulates an increase in the power demand of the consumers. a For optimal results, modify the switch settings simultaneously on the three legs of the Resistive Load in order to avoid operation with an unbalanced load as much as possible. On the Oscilloscope, save all recorded voltage and current waveforms to the first memory. The recorded waveforms will be used for comparison later in the exercise. 41. In the Metering window, measure the line voltage at the shunt-capacitor substation and the line voltage at the receiver end of the ac transmission line. Record both values below. Line voltage V Line voltage V 42. On the Oscilloscope, set the trigger source to the channel used to observe the waveform of the receiver voltage, and the trigger level to approximately 10 V higher than the peak value of the receiver voltage. Click the Single Refresh button. a These settings ensure that the Oscilloscope begins to record data only when the peak value of the receiver voltage increases above its current peak value (i.e., when the voltage compensation provided by the shunt-capacitor substation increases). 43. Make the necessary switch settings on the Capacitive Load to obtain the second reactance value indicated in the table of Figure 24 corresponding to your local ac power network voltage and frequency. a For optimal results, modify the switch settings simultaneously on the three legs of the Capacitive Load in order to avoid operation with unbalanced shunt capacitors as much as possible. On the Oscilloscope, save all recorded voltage and current waveforms to the second memory. The recorded waveforms will be used for comparison later in the exercise. Festo Didactic 86371-00 37

44. In the Metering window, measure the line voltage at the shunt-capacitor substation and the line voltage at the receiver end of the ac transmission line. Record both values below. Line voltage V Line voltage V 45. Considering the values of voltages and you recorded above, does varying the load at the receiver end of the ac transmission line (i.e., varying the electrical power demand) have any significant effect on the voltage at the receiver end of the line? Yes No Considering the values of voltages and you recorded above, does adjusting the reactances,, and of the shunt capacitors in the shunt-capacitor substation have any significant effect on the voltage at the receiver end of the line? Yes No 46. Using the voltage and current waveforms stored in the memories of the Oscilloscope, can you conclude that the STATCOM perfectly and almost instantaneously compensates the voltage at the receiver end of a long ac transmission line containing a shunt-capacitor substation? Explain briefly. 47. In the STATCOM Control window, stop the static synchronous compensator by clicking the Start/Stop button or by setting the Status parameter to Stopped. 48. On the Power Supply, turn the three-phase ac power source off. 49. Close LVDAC-EMS, then turn off all the equipment. Disconnect all leads and return them to their storage location. 38 Festo Didactic 86371-00

Exercise 1 Voltage Compensation of AC Transmission Lines Using a STATCOM Conclusion CONCLUSION In this exercise, you familiarized yourself with the operating principles of STATCOMs when they are used for voltage compensation of ac transmission lines. You learned how a STATCOM controller designed for automatic voltage control compensates the voltage across the ac power system to which the STATCOM is connected. REVIEW QUESTIONS 1. What are the two primary advantages of STATCOMs over shunt-capacitor substations when they are used for voltage compensation of ac transmission lines? 2. Which component acts as the dc power source in a STATCOM? How is it possible to adjust the voltage across that component? Explain briefly. 3. What are the primary advantages of STATCOMs over SVCs? Festo Didactic 86371-00 39

Exercise 1 Voltage Compensation of AC Transmission Lines Using a STATCOM Review Questions 4. Describe how shunt-capacitor substations and STATCOM substations are distributed along a typical voltage-compensated ac transmission line. Explain briefly. 5. Is it common practice to replace all the shunt-capacitor substations along an ac transmission line with STATCOM substations? Explain briefly. 40 Festo Didactic 86371-00