Generator Operation with Speed and Voltage Regulation

Transcription

1 Exercise 3 Generator Operation with Speed and Voltage Regulation EXERCISE OBJECTIVE When you have completed this exercise, you will be familiar with the speed governor and automatic voltage regulator used to regulate the speed (and thus the frequency) and voltage, respectively, of a synchronous generator in a hydropower plant. You will know how the speed of a synchronous generator is regulated using a speed governor operating in isochronous mode, and how the voltage of a synchronous generator is regulated using an automatic voltage regulator operating in fixed voltage mode. DISCUSSION OUTLINE The Discussion of this exercise covers the following points: Operation of the speed governor Operation of the automatic voltage regulator (AVR) Operation of a synchronous generator in isochronous and fixed voltage control modes when connected to an infinite bus Synchronous generator in isochronous mode connected to an infinite bus Synchronous generator in fixed voltage mode connected to an infinite bus DISCUSSION Operation of the speed governor As discussed in Exercise 1, the speed of a synchronous generator decreases as the resistive load connected to the generator increases. Since the generator frequency is proportional to the generator speed, the generator frequency also decreases as the resistive load connected to the generator increases. With most electrical devices being rated to operate at a certain frequency, significant variations in the generator frequency are unacceptable. To prevent this, the frequency of synchronous generators is generally regulated using a speed controller. This controller is called a speed governor. The word isochronous derives from the Greek iso, which means equal, and chronos, which means time. In electrical power generation, isochronous usually designates a device which operates at a constant frequency. Different types of control modes are available for a speed governor to control the speed of a synchronous generator. The two most common control modes are the isochronous mode and the speed droop mode. The isochronous mode is covered in this exercise, while the speed droop mode is covered in Exercise 4. When a synchronous generator operates in isochronous mode, the speed governor of the generator controls the mechanical power at the generator shaft to maintain the generator speed equal to the speed command (usually the generator rotation speed required to produce voltage at the ac power network frequency) at all times, no matter the amount of active power which the synchronous generator supplies to the load. The graph in Figure 37 shows the speed versus active power curve (speed governor regulation characteristic) of a synchronous generator operating in isochronous mode. Festo Didactic

2 Exercise 3 Generator Operation with Speed and Voltage Regulation Discussion Generator speed (r/min) Generator active power (W) Figure 37. Speed versus active power curve (speed governor regulation characteristic) of a synchronous generator operating in isochronous mode. Figure 38 shows the block diagram of a turbine-driven synchronous generator whose speed is regulated using a speed governor operating in isochronous mode. Figure 39 shows the detailed block diagram of the speed governor in Figure Festo Didactic

3 Exercise 3 Generator Operation with Speed and Voltage Regulation Discussion L1 Three-Phase Load Synchronous Generator L2 Water Reservoir Shaft Encoder 1 L3 Dam Adjustable Vanes Vane Control Input 5 Vane Hydraulic Servomotor Water Outlet Vane Control Output Generator Speed Command Speed Governor Figure 38. Block diagram of a turbine-driven synchronous generator whose speed is regulated using a speed governor operating in isochronous mode. To Vane Hydraulic Servomotor 5 Vane Control Output PD Amplifier 4 Generator Speed Command ( ) 3 2 Speed measure circuit A B 1 Signals From Generator Shaft Encoder Figure 39. Detailed block diagram of the speed governor in Figure 38. Festo Didactic

4 Exercise 3 Generator Operation with Speed and Voltage Regulation Discussion As Figure 38 and Figure 39 show, the speed governor, vane hydraulic servomotor, adjustable vanes of the hydraulic turbine, and shaft encoder form a speed feedback loop. The following steps take place when the speed governor operates in isochronous mode to regulate the speed of the synchronous generator: 1. The shaft encoder installed on the shaft coupling of the hydraulic turbine to the synchronous generator produces electric signals (A and B) that can be used to determine the direction of rotation and rotation speed of the shaft. These signals are sent to the speed governor. 2. The speed measurement circuit of the speed governor determines the synchronous generator speed using the electric signals (A and B) from the shaft encoder. 3. The synchronous generator speed determined in the previous step is subtracted from the generator speed command to determine the error in the generator speed. The resulting speed error is sent to a PD amplifier. 4. The PD amplifier amplifies the speed error determined in the previous step to produce the vane control output signal of the speed governor. This signal is sent to the hydraulic servomotor controlling the opening of the adjustable vanes of the hydraulic turbine. The polarity of the vane control output signal determines whether the adjustable vanes need to be opened or closed to correct the error in the generator speed. When the vane control output signal has a positive polarity (i.e., when the generator rotates too slowly), the vane opening needs to be increased to increase the amount of water flowing through the turbine and thus the amount of mechanical power at the synchronous generator shaft. Conversely, when the vane control output signal has a negative polarity (i.e., when the generator rotates too fast), the vane opening needs to be decreased to decrease the amount of water flowing through the turbine and thus the amount of mechanical power at the synchronous generator shaft. The magnitude of the vane control output signal determines the speed at which the adjustable vanes need to open or close in order to effectively correct the error in the generator speed. The higher the magnitude of the vane control output signal, the faster the vane opening must open or close to effectively correct the error in the generator speed. 5. The hydraulic servomotor is used to change the opening of the adjustable vanes of the hydraulic turbine. The adjustable vanes open (i.e., the vane opening increases) when the hydraulic servomotor rotates in one direction, and close (i.e., the vane opening decreases) when the hydraulic servomotor rotates in the opposite direction. The speed at which the adjustable vanes open or close is proportional to the speed at which the hydraulic servomotor rotates. When the vane control output signal from the speed governor has a positive polarity (i.e., when the generator rotates too slowly), the hydraulic servomotor turns in the direction that causes the vane opening to increase, thereby increasing the amount of water flowing through the turbine. This causes the generator speed to increase, thus correcting the speed error. Conversely, when the vane control output signal has a negative polarity (i.e., when the generator rotates too fast), the hydraulic 94 Festo Didactic

5 Exercise 3 Generator Operation with Speed and Voltage Regulation Discussion servomotor turns in the direction that causes the vane opening to decrease, thereby decreasing the amount of water flowing through the turbine. This causes the generator speed to decrease, thus correcting the speed error. Figure 40. With an installed capacity of MW, the Guri dam in Venezuela is one of the largest hydropower plants in the world (photo courtesy of Fadi). Operation of the automatic voltage regulator (AVR) As discussed in Exercise 1, the voltage of a synchronous generator decreases as the load connected to the generator increases. With most electrical devices being rated to operate at a certain voltage, significant variations in the generator voltage are unacceptable. To prevent this, the voltage of synchronous generators is generally regulated using a voltage controller. This controller is called an automatic voltage regulator (AVR). Different types of control modes are available for an automatic voltage regulator to control the voltage of a synchronous generator. The two most common control modes are the fixed voltage mode and the voltage droop mode. The fixed voltage mode is covered in this exercise, while the voltage droop mode is covered in Exercise 4. When a synchronous generator operates in fixed voltage mode, the automatic voltage regulator of the generator controls the intensity of the generator field current to maintain the generator voltage equal to the voltage command (usually the nominal voltage of the ac power bus to which the generator is connected) at all times, no matter the amount of power (either active power or reactive power) which the synchronous generator supplies to the load. The graph in Figure 41 shows the voltage versus power ( or ) curve (automatic voltage regulator voltage regulation characteristic) of a synchronous generator operating in fixed voltage mode. Festo Didactic

6 Exercise 3 Generator Operation with Speed and Voltage Regulation Discussion Generator voltage (V) Generator active power or reactive power (W or var) Figure 41.Voltage versus generator power (active power or reactive power ) curve (automatic voltage regulator voltage regulation characteristic) of a synchronous generator operating in fixed voltage mode. Figure 42 shows the block diagram of a turbine-driven synchronous generator whose voltage is regulated using an automatic voltage regulator operating in fixed voltage mode. Figure 43 shows the detailed block diagram of the automatic voltage regulator in Figure Festo Didactic

7 Exercise 3 Generator Operation with Speed and Voltage Regulation Discussion L1 Three-Phase Load 1 To DC Side of Thyristor Bridge Field Winding Synchronous Generator L2 Water Reservoir L3 Dam AC Power Source Thyristor threephase bridge 7 Water Outlet To Field Winding Automatic Voltage Regulator (AVR) Generator Voltage Command ( ) Figure 42. Block diagram of a turbine-driven synchronous generator whose voltage is regulated using an automatic voltage regulator operating in fixed voltage mode. Festo Didactic

8 Exercise 3 Generator Operation with Speed and Voltage Regulation Discussion 1 To Thyristor threephase bridge 7 RMS Value Calculator Gate Driver 2 6 Filter Thyristor Firing Unit 3 4 Firing Angle 5 PI Inverting Control Limiter Amplifier Generator Voltage Command ( ) Figure 43. Detailed block diagram of the automatic voltage regulator in Figure 42. As Figure 42 and Figure 43 show, the automatic voltage regulator (AVR), thyristor three-phase bridge, and generator voltage sensor (E3) form a voltage feedback loop. The following steps take place when the automatic voltage regulator operates in fixed voltage mode to regulate the voltage of the synchronous generator: 1. The generator voltage sensor (E3) measures the line voltage produced by the synchronous generator. 2. The rms value of the generator voltage is determined from the line voltage measured in the previous step. The resulting rms value of the generator voltage is then filtered to remove any undesired fluctuations. 3. The rms value of the generator voltage obtained in the previous step is subtracted from the generator voltage command to determine the error in the generator voltage. The resulting voltage error is sent to a PI inverting amplifier. 4. The PI inverting amplifier inverts the polarity of the voltage error determined in the previous step, then amplifies its value to obtain a control signal that can be used to vary the firing angle of the thyristor three-phase bridge in a way that corrects the error in the generator voltage. When the rms value of the generator voltage is lower than the generator voltage command, the value of the firing angle control signal produced by the PI inverting amplifier decreases, thereby causing the firing angle of the thyristor three-phase bridge to decrease and the voltage at the dc side of the bridge to increase. This, in turn, causes the generator field current and thus the rms value of the generator 98 Festo Didactic

9 Exercise 3 Generator Operation with Speed and Voltage Regulation Discussion voltage, to increase, thereby correcting the voltage error. Conversely, when the rms value of the generator voltage is higher than the generator voltage command, the value of the firing angle control signal increases, thereby causing the firing angle of the thyristor three-phase bridge to increase and the voltage at the dc side of the bridge to decrease. This, in turn, causes the generator field current and thus the rms value of the generator voltage to decrease, thereby correcting the voltage error. 5. A limiter limits the firing angle control signal produced by the PI inverting amplifier to prevent the firing angle from going outside a predetermined range. This is necessary to prevent damage to the generator field winding. 6. Using line voltage measured across the ac power source connected to the thyristor three-phase bridge, the thyristor firing unit produces the firing signals for the thyristor bridge according to the firing angle control signal (limited). These firing signals are amplified by the gate driver before being routed to the thyristor three-phase bridge. 7. The thyristor three-phase bridge converts ac power into dc power to make dc current flow in the field winding of the synchronous generator. The magnitude of the generator field current depends on the value of the thyristor firing angle which, in turn, is determined by the firing angle control signal produced in the automatic voltage regulator. Figure 44. The Sir Adam Beck power stations consist of two hydropower plants located on the Niagara River in Ontario, Canada. The two power stations have a combined installed capacity of 1926 MW (photo courtesy of Ontario Power Generation). Festo Didactic

10 Exercise 3 Generator Operation with Speed and Voltage Regulation Discussion Operation of a synchronous generator in isochronous and fixed voltage control modes when connected to an infinite bus In the previous sections of this exercise discussion, it is assumed that the synchronous generator operates in isochronous mode and fixed voltage mode. It is also assumed that the synchronous generator is connected to a three-phase passive load (i.e., to a dead bus). This means that the synchronous generator imposes the magnitude, frequency, and phase angle of its voltage to the load. This makes it possible for the speed governor and automatic voltage regulator to maintain the generator speed and voltage at the values requested by the speed command and voltage command, respectively. However, when a synchronous generator is connected (i.e., synchronized) to an infinite bus such as the local ac power network, the speed governor and automatic voltage regulator can no longer maintain the generator speed and voltage at the values requested by the speed command and voltage command, respectively. This is because an infinite bus imposes the magnitude, frequency (and, consequently, imposes the generator speed), and phase angle of its voltage to the synchronous generator. This remains true even when the values of the speed command and voltage command of the synchronous generator are set to the exact values of the nominal synchronous speed (defined by the nominal frequency) and voltage of the infinite bus. This is due to the fact that even though any ac power network is rated to operate at a given frequency and voltage, the actual frequency and voltage of the ac power network do vary over time and are rarely strictly equal to the nominal value. This is illustrated in Figure 45 and Figure 46. The generator speed command is higher than the infinite bus speed Speed (r/min) The generator speed command is lower than the infinite bus speed Generator active power (W) Figure 45. Graph showing that the speed regulation characteristic of a speed governor operating in isochronous mode never intersects the infinite bus speed (defined by the infinite bus frequency ). As Figure 45 shows, the speed regulation characteristic of a speed governor is constant and parallel to the infinite bus speed (defined by the infinite bus frequency ). Consequently, the speed regulation characteristic of the speed governor never intersects the infinite bus speed. This means that there is no stable point of operation at which the speed governor can maintain the generator 100 Festo Didactic

11 Exercise 3 Generator Operation with Speed and Voltage Regulation Discussion speed, no matter the amount of active power which the generator supplies to the infinite bus. The generator voltage command is higher than the infinite bus voltage Voltage (V) The generator voltage command is lower than the infinite bus voltage Generator active power or reactive power (W or var) Figure 46. Graph showing that the voltage regulation characteristic of an automatic voltage regulator operating in fixed voltage mode never intersects the infinite bus voltage. As Figure 46 shows, the voltage regulation characteristic of an automatic voltage regulator is constant and parallel to the infinite bus voltage. Consequently, the voltage regulation characteristic of the automatic voltage regulator never intersects the infinite bus voltage. This means that no stable point of operation exists at which the automatic voltage regulator can maintain the generator voltage, no matter the amount of active power or reactive power which the generator supplies to the infinite bus. The following two subsections describe in detail what happens when operating a synchronous generator connected to an infinite bus in isochronous mode and fixed voltage mode. Synchronous generator in isochronous mode connected to an infinite bus When a synchronous generator operating in isochronous mode is connected to a dead bus, the speed governor varies the opening of the adjustable vanes determining the amount of water flowing in the turbine driving the generator to maintain the generator speed at the nominal value (i.e., equal to the generator speed command ). This also maintains the generator frequency at the nominal value. When the synchronous generator is connected to an infinite bus, the generator speed and frequency are imposed by the infinite bus. Since the actual frequency of an infinite bus such as the ac power network is rarely exactly equal to the nominal value, the generator speed also differs from the corresponding nominal speed value and thus the speed governor continually measures an error in the generator speed. To correct this error, the speed governor either increases or decreases the opening of the adjustable vanes, thereby increasing or decreasing the amount of active power produced by the generator. As the generator speed and Festo Didactic

12 Exercise 3 Generator Operation with Speed and Voltage Regulation Discussion frequency are still not corrected and, in fact, cannot be corrected because they are imposed by the infinite bus, the speed governor continues to increase or decrease the opening of the adjustable vanes until they are fully open or fully closed. When the synchronous generator speed imposed by the infinite bus is lower than the generator speed command, the speed governor measures a positive error and increases the opening of the adjustable vanes until they are fully open. This causes the amount of mechanical power at the shaft of the synchronous generator and thus the amount of active power supplied to the infinite bus by the synchronous generator to increase. Eventually, the amount of active power produced by the generator exceeds its power rating. This condition is undesirable because it could cause serious damage to the synchronous generator as well as to the electrical equipment to which it is connected. On the other hand, when the synchronous generator speed imposed by the infinite bus is higher than the generator speed command, the speed governor decreases the opening of the adjustable vanes until they are fully closed. This causes the amount of active power supplied by the synchronous generator to decrease to 0 W. At this point, the generator active power changes polarity and begins to increase again, indicating that the generator now operates as a motor and consumes active power. Eventually, the amount of active power consumed by the synchronous generator exceeds its power rating. This condition is highly undesirable as the active power consumed by the synchronous generator decreases the power capacity of the electric power generating station and could cause serious damage to the synchronous generator as well as to the electrical equipment to which it is connected. For these reasons, a synchronous generator connected to an infinite bus cannot operate in isochronous mode. This is because it either results in the generator significantly exceeding its power rating, or in the generator operating as a motor and also significantly exceeding its power rating. Synchronous generator in fixed voltage mode connected to an infinite bus A similar phenomenon is observed when a synchronous generator operating in fixed voltage mode is connected to an infinite bus. The automatic voltage regulator (AVR) can no longer control the synchronous generator voltage because its value is imposed by the infinite bus. Consequently, the AVR either increases or decreases (depending on the polarity of the error measured in the generator voltage ) the firing angle of the thyristor three-phase bridge until it reaches the upper or lower limit value (i.e., until the generator field current is either equal to 0 A or at the maximal value allowed). In both cases, this causes the amount of reactive power which the synchronous generator exchanges with the infinite bus to increase and eventually exceed the generator maximal reactive power rating. In other words, this prevents the amount of reactive power which the generator exchanges with the infinite bus from being controlled. The large amount of reactive power which the synchronous generator exchanges with the infinite bus significantly decreases its power factor, which is unacceptable in most ac power networks. Furthermore, it increases the value of the current flowing in the generator stator windings (possibly over the nominal current value), thereby increasing the copper losses and causing additional heating which can be harmful to the generator. For these reasons, a synchronous generator connected to an infinite bus cannot operate in fixed voltage mode. 102 Festo Didactic

13 Exercise 3 Generator Operation with Speed and Voltage Regulation Procedure Outline Figure 47. View of the Grand Coulee Dam on the Columbia River in the state of Washington, USA. With an installed capacity of 6800 MW, the Grand Coulee Dam is among the largest hydropower plants in the world. PROCEDURE OUTLINE The Procedure is divided into the following sections: Set up and connections Operation of a synchronous generator in isochronous and fixed voltage control modes when connected to a dead bus Log of the frequency and voltage of a synchronous generator operating in isochronous mode and fixed voltage mode Operation of a synchronous generator in isochronous and fixed voltage control modes when connected to an infinite bus 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. Festo Didactic

14 Exercise 3 Generator Operation with Speed and Voltage Regulation Procedure Set up and connections In this section, you will set up a synchronous generator driven by a hydraulic turbine and connected to a three-phase resistive-inductive load through a threephase contactor. You will then set up the measuring equipment required to study the generator operation with a speed governor and an automatic voltage regulator set to operate in isochronous mode and fixed voltage mode, respectively. 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. Before coupling rotating machines, make absolutely sure that power is turned off to prevent any machine from starting inadvertently. Mechanically couple the Synchronous Motor/Generator to the Four-Quadrant Dynamometer/Power Supply using a timing belt. 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. Make sure the main power switch on the Four-Quadrant Dynamometer/Power Supply is set to the O (off) position, then connect its Power Input to an ac power outlet. Connect the Power Input of the Data Acquisition and Control Interface to a 24 V ac power supply. Connect the Low Power Input of the Power Thyristors module to the Power Input of the Data Acquisition and Control Interface. Turn the 24 V ac power supply on. 3. Connect the USB port of the Data Acquisition and Control Interface to a USB port of the host computer. Connect the USB port of the Four-Quadrant Dynamometer/Power Supply to a USB port of the host computer. 4. Turn the Four-Quadrant Dynamometer/Power Supply on, then set the Operating Mode switch to Dynamometer. 104 Festo Didactic

15 Exercise 3 Generator Operation with Speed and Voltage Regulation Procedure 5. 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 and the Four-Quadrant Dynamometer/Power Supply are detected. Make sure the Computer-Based Instrumentation and Synchronous Generator Control functions are available for the Data Acquisition and Control Interface module. Make sure that the Turbine Emulator function is available for the Four-Quadrant Dynamometer/Power Supply. Also, select the network voltage and frequency that correspond to the voltage and frequency of the local ac power network, then click the OK button to close the LVDAC-EMS Start-Up window. 6. Connect the equipment as shown in Figure 48. Use the Four-Quadrant Dynamometer/Power Supply and the Power Supply to implement the hydraulic-turbine emulator and the three-phase ac power source, respectively. Also, use the Power Thyristors module to implement the thyristor three-phase bridge. When connecting the thyristor three-phase bridge, make sure switches S 1 and S 2 on the Power Thyristors module are set to the I (closed) position. Doing so connects thyristors Q 1 to Q 6 in a three-phase bridge configuration. a In the circuit of Figure 48, inputs E2, E3, E4, I3, and I4 are used to measure the circuit parameters necessary for controlling the synchronous generator when it is connected to a dead bus. Because of this, inputs E2, E3, E4, I3, and I4 cannot be used for circuit parameter measurement and observation in this exercise. Festo Didactic

16 Exercise 3 Generator Operation with Speed and Voltage Regulation Procedure Three-phase contactor Resistive-inductive load L1 Hydraulicturbine emulator Synchronous generator L2 L1 Thyristor threephase bridge L3 L2 L3 N Firing signals from DACI Control signal from DACI To neutral terminal of the synchronous generator Local ac power network Load resistance values (,, and ) and reactance values (,, and ) Voltage (V) Frequency (Hz) 1 st () 2 nd () 3 rd () 4 th () 5 th () 6 th () Figure 48. Turbine-driven synchronous generator connected to a three-phase resistiveinductive load (dead bus) through a three-phase contactor. 106 Festo Didactic

17 Exercise 3 Generator Operation with Speed and Voltage Regulation Procedure 7. Make the necessary switch settings on the Resistive Load and on the Inductive Load so that the resistance and reactance of the three-phase resistive-inductive load are equal to the first values indicated in the table of Figure 48 corresponding to the local ac power network voltage and frequency. 8. Make sure the Sync. switch on the Synchronizing Module/Three-Phase Contactor is set to the O position. This allows remote control of the threephase contactor by the Data Acquisition and Control Interface module. 9. Connect the Digital Outputs of the Data Acquisition and Control Interface to the Firing Control Inputs of the Power Thyristors module using the provided cable with DB9 connectors. 10. Connect Digital Output 1 (DO1) of the Data Acquisition and Control Interface to the positive (+) terminal of the Remote Control input on the Synchronizing Module/Three-Phase Contactor using a miniature banana plug lead. Connect a digital (D) common (white terminal) of the Data Acquisition and Control Interface to the negative (-) terminal of the Remote Control input on the Synchronizing Module/Three-Phase Contactor using a miniature banana plug lead. Connect Analog Output 1 (AO1) of the Data Acquisition and Control Interface to the left-hand side terminal of the Command Input of the Four-Quadrant Dynamometer/Power Supply using a miniature banana plug lead. Connect an analog (A) common (white terminal) on the Data Acquisition and Control Interface to the common (white terminal) of the Command Input on the Four- Quadrant Dynamometer/Power Supply using a miniature banana plug lead. Connect the A Shaft Encoder Output of the Four-Quadrant Dynamometer/Power Supply to the A Encoder Digital Input of the Data Acquisition and Control Interface using a miniature banana plug lead. Connect the B Shaft Encoder Output of the Four-Quadrant Dynamometer/Power Supply to the B Encoder Digital Input of the Data Acquisition and Control Interface using a miniature banana plug lead. Connect the common (white terminal) of the Shaft Encoder Outputs on the Four-Quadrant Dynamometer/Power Supply to a digital (D) common (white terminal) of the Encoder Digital Inputs on the Data Acquisition and Control Interface using a miniature banana plug lead. 11. In LVDAC-EMS, open the Synchronous Generator Control window, then make the following settings: Make sure the Function parameter is set to Hydropower Generator (Dead Bus Balanced Load). Make sure the Nominal Voltage parameter is set to the nominal value of the local ac power network voltage. Make sure the Hydropower Generator (Dead Bus Balanced Load) function is set to Stopped. Festo Didactic

18 Exercise 3 Generator Operation with Speed and Voltage Regulation Procedure Synchro-Check Relay Make sure the Live Bus Voltage Threshold parameter is set to 90% of the ac power network nominal voltage. Make sure the Relay Output parameter is set to Normal. Make sure the Dead Bus Voltage Threshold parameter is set to 10% of the ac power network nominal voltage. a Make sure the Dead Time parameter is set to 1 s. Speed Governor Make sure the Generator Speed Command parameter is set to the nominal synchronous speed of the synchronous generator. This speed command value ensures that the speed governor adjusts the vane opening of the hydraulic-turbine emulator so that the generator speed is maintained at the specified value. The nominal synchronous speed of the Synchronous Motor/Generator is 1500 r/min at a local ac power network frequency of 50 Hz and 1800 r/min at a local ac power network frequency of 60 Hz. Set the Speed Droop parameter to 0%. Setting the speed droop to 0% makes the speed governor operate in isochronous mode. Therefore, the speed governor tries to maintain the generator speed constant no matter the value of the load connected to the generator. Make sure the Generator Acceleration parameter is set to 30 r/min / s. Make sure the Proportional Gain [Kp] is set to 20. Make sure the Derivative Gain [Kd] is set to 40. Automatic Voltage Regulator Make sure the Generator Voltage Command parameter is set to the nominal value of the local ac power network line voltage. This voltage command value ensures that the automatic voltage regulator adjusts the generator field current so that the generator line voltage is maintained at the specified value. Set the Voltage Droop parameter to 0%. Setting the voltage droop to 0% makes the automatic voltage regulator operate in fixed voltage mode. Therefore, the automatic voltage regulator tries to maintain the generator voltage constant no matter the value of the load connected to the generator. Make sure the Thyristor Bridge Firing Control Mode parameter is set to Automatic. This mode allows the automatic voltage regulator to automatically control the generator voltage by varying the generator field current through the firing angle of the thyristor bridge. 108 Festo Didactic

19 Exercise 3 Generator Operation with Speed and Voltage Regulation Procedure Make sure the Minimum Firing Angle Limit parameter is set to 40. This sets the minimum firing angle limit of the thyristor threephase bridge to 40. Make sure the Maximum Firing Angle Limit parameter is set to 120. This sets the maximum firing angle limit of the thyristor three-phase bridge to 120. Make sure that the Proportional Gain [Kp] parameter is set to the value indicated in the following table that corresponds to your local ac power network voltage and frequency. Table 8. Proportional gain Kp of the automatic voltage regulator of the hydropower generator. Local ac power network Voltage (V) Frequency (Hz) Proportional gain Kp Make sure that the Integral Gain [Ki] parameter is set to the value indicated in the following table that corresponds to your local ac power network voltage and frequency. Table 9. Integral gain Ki of the automatic voltage regulator of the hydropower generator. Local ac power network Voltage (V) Frequency (Hz) Integral gain Ki In LVDAC-EMS, open the Four-Quadrant Dynamometer/Power Supply window, then make the following settings: Set the Function parameter to Hydraulic-Turbine Emulator. Set the Vane Control parameter to 8960 Command Input. This control mode allows the speed governor to automatically control the vane opening of the hydraulic-turbine emulator through the Command Input of the Four-Quadrant Dynamometer/Power Supply. Make sure the Turbine Type parameter is set to 300 W, Francis. Make sure the Vane Maximal Speed parameter is set to 10.0%/s. Make sure the Runner Inertia parameter is set to 0.3 kg m 2. Festo Didactic

20 Exercise 3 Generator Operation with Speed and Voltage Regulation Procedure Make sure the Hydraulic-Turbine Emulator function is set to Stopped. 13. In LVDAC-EMS, open the Metering window. Make the required settings in order to measure the rms value (ac) of the synchronous generator current (input I1). Set two other meters to measure the three-phase active power [metering function PQS1 (E1, I1) 3~] which the synchronous generator supplies to the load, as well as the three-phase reactive power [metering function PQS1 (E1, I1) 3~] which the synchronous generator exchanges with the load. 14. On the Synchronous Motor/Generator, set the Exciter switch to the closed position (I), then turn the Exciter knob fully clockwise (i.e., set it to the Max. position). Operation of a synchronous generator in isochronous and fixed voltage control modes when connected to a dead bus In this section, you will start the hydraulic-turbine emulator and the hydropower generator. You will vary the value of the resistive-inductive load, and observe what happens to the generator speed, frequency, and voltage when the speed governor and the automatic voltage regulator operate in isochronous mode and fixed voltage mode, respectively. For each value of the resistive-inductive load, you will record the various electrical and mechanical parameters of the synchronous generator. Finally, you will analyze the results. 15. On the Power Supply, turn the three-phase ac power source on. In the Four-Quadrant Dynamometer/Power Supply window, start the hydraulic-turbine emulator by clicking the Start/Stop button or by setting the Status parameter to Started. In the Synchronous Generator Control window, start the hydropower generator by clicking the Start/Stop button or by setting the Status parameter to Started. 110 Festo Didactic

21 Exercise 3 Generator Operation with Speed and Voltage Regulation Procedure 16. Fill in the first and second columns in Table 10 using the resistance (,, and ) and reactance (,, and ) values indicated in the table of Figure 48 corresponding to the local ac power network voltage and frequency. Table 10. Parameters of a synchronous generator whose speed and voltage are controlled using a speed governor in isochronous mode and an automatic voltage regulator in fixed voltage mode.,, (),, () (Hz) (V) (A) (W) (var) (A) ( ) (r/min) (N m) (W) Vane open. (%) 1 st 1 st 2 nd 2 nd 3 rd 3 rd 4 th 4 th 5 th 5 th 6 th 6 th 17. Record in Table 10 the generator speed, torque and mechanical power, as well as the vane opening of the hydraulic-turbine emulator (indicated in the Four-Quadrant Dynamometer/Power Supply window) in the row corresponding to the current resistance and reactance of the three-phase resistive-inductive load. Also record in Table 10 the generator frequency voltage, and field current, as well as the thyristor bridge firing angle (indicated in the Synchronous Generator Control window). Finally, record in Table 10 the generator current, as well as the generator three-phase active power, and reactive power (indicated in the Metering window). 18. Make the necessary switch settings on the Resistive Load and the Inductive Load to successively obtain the other five combinations of resistance and reactance values indicated in the first and second columns of Table 10. For each combination, wait for the generator speed and voltage to stabilize, then repeat step 17. Festo Didactic

22 Exercise 3 Generator Operation with Speed and Voltage Regulation Procedure 19. In the Synchronous Generator Control window, set the Relay Output parameter to Low to force disconnection of the synchronous generator from the load, then set the Generator Speed Command and Generator Voltage Command parameters to 0. Wait for the hydraulic turbine driving the generator to stop rotating, then stop the hydropower generator by clicking the Start/Stop button or by setting the Status parameter to Stopped. In the Four-Quadrant Dynamometer/Power Supply window, stop the hydraulic-turbine emulator 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. 20. From the results recorded in Table 10, what happens to the generator speed and thus to the generator frequency, as the generator load varies? Explain briefly. From your observations, what happens to the generator voltage as the generator load varies? Explain briefly. 21. Using the results recorded in Table 10, explain how the speed governor controls the generator speed. Explain briefly. 112 Festo Didactic

23 Exercise 3 Generator Operation with Speed and Voltage Regulation Procedure Using the results recorded in Table 10, explain how the automatic voltage regulator controls the generator voltage. Explain briefly. 22. Using the results recorded in Table 10, describe the effects that modifying the resistance of the three-phase resistive-inductive load has on the generator speed governor and automatic voltage regulator. Explain briefly. Using the results recorded in Table 10, describe the effects that modifying the reactance of the three-phase resistive-inductive load has on the generator speed governor and automatic voltage regulator. Explain briefly. Festo Didactic

24 Exercise 3 Generator Operation with Speed and Voltage Regulation Procedure 23. Considering your results, is a speed governor operating in isochronous mode an effective way to control the speed, and thus the frequency, of a synchronous generator connected to a three-phase resistive-inductive load (i.e., to a dead bus)? Yes No Considering your results, is an automatic voltage regulator operating in fixed voltage mode an effective way to control the voltage of a synchronous generator connected to a three-phase resistive-inductive load (i.e., to a dead bus)? Yes No Log of the frequency and voltage of a synchronous generator operating in isochronous mode and fixed voltage mode In this section, you will set the resistance and reactance of the three-phase resistive-inductive load to infinite. You will set the Data Table to record the generator frequency and voltage. You will then set the resistance and reactance of the three-phase resistive-inductive load to different values (the same value combinations as those used in Exercise 1), and let the generator operate for 1 minute for each load setting. You will save the data recorded in the Data Table. You will plot on separate graphs the curves of the generator frequency and voltage as a function of time obtained when the speed governor and automatic voltage regulator of the synchronous generator operate in isochronous and fixed voltage modes using the data you just recorded. You will also plot on these graphs the curves of the generator frequency and voltage as a function of time when these parameters are controlled manually (generator operation without speed governor and automatic voltage regulator) using the data recorded in Exercise Make the necessary switch settings on the Resistive Load and on the Inductive Load so that the resistance and reactance of the three-phase resistive-inductive load are infinite. 25. In the Synchronous Generator Control window, make the following settings: Synchro-Check Relay Set the Relay Output parameter to Normal. Speed Governor Set the Generator Speed Command parameter to the nominal synchronous speed of the synchronous generator. Automatic Voltage Regulator Set the Generator Voltage Command parameter to the local ac power network line voltage. 114 Festo Didactic

25 Exercise 3 Generator Operation with Speed and Voltage Regulation Procedure 26. On the Power Supply, turn the three-phase ac power source on. In the Four-Quadrant Dynamometer/Power Supply window, start the hydraulic-turbine emulator by clicking the Start/Stop button or by setting the Status parameter to Started. In the Synchronous Generator Control window, start the hydropower generator by clicking the Start/Stop button or by setting the Status parameter to Started. 27. 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 data recording period. Set the Data Table to record the synchronous generator frequency and voltage indicated in the Synchronous Generator Control window, as well as the time associated with each record. 28. Wait for the synchronous generator speed and voltage to stabilize, then, in the Data Table, start the timer to start data recording. Make the necessary switch settings on the Resistive Load and on the Inductive Load in order to successively obtain the ten combinations of load resistance and reactance values indicated in Table 11 corresponding to the local ac power network voltage and frequency. For each resistance and reactance combination, let the synchronous generator operate for 1 minute, then proceed to the next resistance and reactance 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 11. Combinations of resistance and reactance values of the three-phase resistiveinductive load to be used in the circuit of Figure 48 for different local ac power network voltages and frequencies. Local ac power network Resistances,, and and reactances,, 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 Festo Didactic

26 Exercise 3 Generator Operation with Speed and Voltage Regulation Procedure 29. In the Data Table window, stop the timer, then save the recorded data. 30. In the Synchronous Generator Control window, set the Relay Output parameter to Low to force disconnection of the synchronous generator from the load, then set the Generator Speed Command and Generator Voltage Command parameters to 0. Wait for the hydraulic turbine driving the generator to stop rotating, then stop the hydropower generator by clicking the Start/Stop button or by setting the Status parameter to Stopped. In the Four-Quadrant Dynamometer/Power Supply window, stop the hydraulic-turbine emulator 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. 31. Using the data you just recorded and the data you recorded in Exercise 1, plot (on the same graph) curves of the generator frequency as a function of time obtained when the synchronous generator operates with the speed governor in isochronous mode and without the speed governor (i.e., with the generator speed and frequency controlled manually). Compare the curves of the generator frequency as a function of time obtained when the synchronous generator operates with the speed governor in isochronous mode and without the speed governor (i.e., with the generator speed and frequency controlled manually). What do you observe? Explain briefly. Is the speed governor set to operate in isochronous mode efficient in minimizing the transients in the generator frequency caused by variations in the generator load? Yes No 32. Using the data you just recorded and the data you recorded in Exercise 1, plot (on the same graph) curves of the generator voltage as a function of time obtained when the synchronous generator operates with the automatic voltage regulator (AVR) in fixed voltage mode and without the AVR (i.e., with the generator voltage controlled manually). 116 Festo Didactic

27 Exercise 3 Generator Operation with Speed and Voltage Regulation Procedure Compare the curves of the generator voltage as a function of time obtained when the synchronous generator operates with the automatic voltage regulator (AVR) in fixed voltage mode and without the AVR (i.e., with the generator voltage controlled manually). What do you observe? Explain briefly. Is the automatic voltage regulator set to operate in fixed voltage mode efficient in minimizing the transients in the generator voltage caused by variations in the generator load? Yes No Operation of a synchronous generator in isochronous and fixed voltage control modes when connected to an infinite bus In this section, you will modify the equipment connections so that the synchronous generator can be connected to the local ac power network (infinite bus) through a three-phase contactor. You will set the generator speed command and voltage command to values slightly higher than those imposed by the local ac power network. You will synchronize the generator to the local ac power network, and observe what happens to the generator s various electrical and mechanical parameters. You will then disconnect the generator from the ac power network, and set the generator speed command and voltage command to values slightly lower than those imposed by the local ac power network. You will synchronize the generator to the local ac power network, and observe what happens to the generator s various electrical and mechanical parameters. You will analyze the results. 33. Modify the equipment connections to obtain the circuit shown in Figure 49. Note that, in the circuit, the three-phase resistive-inductive load is replaced with the three-phase ac power source of the Power Supply. Also, voltage inputs E2 and E3 change position in the circuit. All other connections remain the same. Festo Didactic

28 Exercise 3 Generator Operation with Speed and Voltage Regulation Procedure Three-phase contactor L1 Hydraulicturbine emulator Synchronous generator L2 L1 Thyristor threephase bridge L3 L2 L3 Firing signals from DACI Control signal from DACI N To neutral terminal of the synchronous generator Figure 49. Turbine-driven synchronous generator connected to the local ac power network (infinite bus) through a three-phase contactor. 34. In the Synchronous Generator Control window, make the following settings: Set the Function parameter to Hydropower Generator (Balanced Infinite Bus). Make sure the Nominal Voltage parameter is set to the nominal value of the local ac power network voltage. Make sure the Hydropower Generator (Balanced Infinite Bus) function is set to Stopped. Synchro-Check Relay Make sure the Live Bus Voltage Threshold parameter is set to 90% of the local ac power network nominal voltage. Set the Voltage Difference E parameter to 10% of the ac power network nominal voltage. 118 Festo Didactic

29 Exercise 3 Generator Operation with Speed and Voltage Regulation Procedure Set the Frequency Difference f parameter to 1.5 Hz. Make sure the Phase Difference parameter is set to 20. Make sure the Circuit-Breaker Operate Time parameter is set to 0.05 s. Make sure the Relay Output parameter is set to Low. Speed Governor Set the Generator Speed Command parameter to the generator nominal synchronous speed. Automatic Voltage Regulator Set the Generator Voltage Command parameter to the nominal value of the local ac power network voltage. Make sure that the Proportional Gain [Kp] parameter is set to the value indicated in the following table that corresponds to your local ac power network voltage and frequency. Table 12. Proportional gain Kp of the automatic voltage regulator of the hydropower generator. Local ac power network Voltage (V) Frequency (Hz) Proportional gain Kp Make sure that the Integral Gain [Ki] parameter is set to the value indicated in the following table that corresponds to your local ac power network voltage and frequency. Table 13. Integral gain Ki of the automatic voltage regulator of the hydropower generator. Local ac power network Voltage (V) Frequency (Hz) Integral gain Ki In the Metering window, make the required settings in order to measure the local ac power network voltage and frequency (both are measured via input E2). Also, set one meter to measure the power factor of the synchronous generator [metering function PF (E1, I1) 3~]. Festo Didactic

30 Exercise 3 Generator Operation with Speed and Voltage Regulation Procedure 36. On the Power Supply, turn the three-phase ac power source on. In the Four-Quadrant Dynamometer/Power Supply window, set the Vane Maximal Opening parameter to 90%. This limits the opening of the vane to 90% of the maximal opening, and thus, lowers the maximal amount of mechanical power that the hydraulic-turbine emulator can produce. Start the hydraulic-turbine emulator by clicking the Start/Stop button or by setting the Status parameter to Started. In the Synchronous Generator Control window, start the hydropower generator by clicking the Start/Stop button or by setting the Status parameter to Started. 37. Wait for the synchronous generator frequency and voltage to stabilize. In the Synchronous Generator Control window, adjust the Generator Speed Command parameter so that the generator frequency is approximately 1 Hz higher than the measured ac power network frequency (indicated in the Metering window). In the Synchronous Generator Control window, adjust the Generator Voltage Command parameter so that the generator voltage is approximately 4 V higher than the measured ac power network voltage (indicated in the Metering window). 38. In the Synchronous Generator Control window, set the Relay Output parameter to Normal. Since all synchronization conditions are met, this should synchronize the generator to the ac power network. Wait for the generator parameters to stabilize, then, in the Generator Control, Metering, and Four-Quadrant Dynamometer/Power Supply windows, click on the Single Refresh button. When this is done, proceed immediately to the next step. Do not let the synchronous generator operate in the present conditions for more than one minute, as the ratings of the Synchronous Motor/Generator can be significantly exceeded. As soon as you have completed step 38, proceed to the next step. 39. In the Synchronous Generator Control window, set the Relay Output parameter to Low to force disconnection of the synchronous generator from the local ac power network. 120 Festo Didactic

31 Exercise 3 Generator Operation with Speed and Voltage Regulation Procedure 40. In the Generator Control, Metering, and Four-Quadrant Dynamometer/Power Supply windows, observe the various electrical and mechanical parameters of the synchronous generator indicated by the meters. Record the value of all requested parameters. Generator frequency Hz Generator voltage V Generator current A Generator active power W Generator reactive power var Generator field current A Thyristor bridge firing angle Generator speed r/min Generator torque N m or lbf in Generator mechanical power W Hydraulic-turbine vane opening % 41. What happens to the generator speed, the generator frequency, the vane opening of the hydraulic-turbine emulator, and the generator active power after the generator is synchronized to the ac power network when the speed governor is set to operate in isochronous mode and the generator speed command is set so that the generator frequency is slightly higher than the measured ac power network frequency? Explain briefly. Festo Didactic

32 Exercise 3 Generator Operation with Speed and Voltage Regulation Procedure What happens to the generator voltage, the generator field current, and the generator reactive power after the generator is synchronized to the ac power network when the automatic voltage regulator is set to operate in fixed voltage mode and the generator voltage command is slightly higher than the measured ac power network voltage? Explain briefly. 42. In the Synchronous Generator Control window, make the following settings: Speed Governor Set the Generator Speed Command parameter to the generator nominal synchronous speed. Automatic Voltage Regulator Set the Generator Voltage Command parameter to the nominal value of the local ac power network voltage. Wait for the synchronous generator frequency and voltage to stabilize. 43. In the Synchronous Generator Control window, adjust the Generator Speed Command parameter so that the generator frequency is approximately 1 Hz lower than the measured ac power network frequency (indicated in the Metering window). In the Synchronous Generator Control window, adjust the Generator Voltage Command parameter so that the generator voltage is approximately 4 V lower than the measured ac power network voltage (indicated in the Metering window). 44. In the Synchronous Generator Control window, set the Relay Output parameter to Normal. Since all synchronization conditions are met, this should synchronize the generator to the ac power network. Wait for the generator parameters to stabilize, then, in the Generator Control, Metering, and Four-Quadrant Dynamometer/Power Supply windows, click on 122 Festo Didactic

33 Exercise 3 Generator Operation with Speed and Voltage Regulation Procedure the Single Refresh button. When this is done, proceed immediately to the next step. Do not let the synchronous generator operate in the present conditions for more than one minute as the ratings of the Synchronous Motor/Generator can be significantly exceeded. As soon as you have completed step 44, proceed to the next step. 45. In the Synchronous Generator Control window, set the Relay Output parameter to Low to force disconnection of the synchronous generator from the local ac power network, then set the Generator Speed Command and Generator Voltage Command parameters to 0. Wait for the hydraulic turbine driving the generator to stop rotating, then stop the hydropower generator by clicking the Start/Stop button or by setting the Status parameter to Stopped. In the Four-Quadrant Dynamometer/Power Supply window, stop the hydraulic-turbine emulator 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. 46. In the Generator Control, Metering, and Four-Quadrant Dynamometer/Power Supply windows, observe the various electrical and mechanical parameters of the synchronous generator indicated by the meters. Record the value of all requested parameters. Generator frequency Hz Generator voltage V Generator current A Generator active power W Generator reactive power var Generator field current A Thyristor bridge firing angle Generator speed r/min Generator torque N m or lbf in Generator mechanical power W Hydraulic-turbine vane opening % Festo Didactic