Exercise 4-1. Nacelle Control System EXERCISE OBJECTIVE DISCUSSION OUTLINE DISCUSSION. Control and simulation of environmental conditions

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1 Exercise 4-1 Nacelle Control System EXERCISE OBJECTIVE When you have completed this exercise, you will know more about the logic behind the control system. In particular, you will understand alarm management and see what happens when there is a loss of communication. DISCUSSION OUTLINE The Discussion of this exercise covers the following points: Control and simulation of environmental conditions Nacelle control overview Operation status (automatic mode) Trainer stopped. Automatic Stopped. Initialization in progress. Standstill. Active control in progress. Unwind in progress. Shutdown in progress. Yaw control Blade pitch control Power generation (and drive train) control How rotor braking is accomplished. Alarm monitoring Alarm management Alarm class. Alarm status. ALARMS HISTORY. System status Working condition. Interlock. Critical alarm. Control system implementation DISCUSSION Control and simulation of environmental conditions As explained in Unit 1 the nacelle trainer can be programmed to simulate wind conditions. The PLC controls the dc motors that spin the anemometer and turn the wind vane, and the motor that rotates the low-speed shaft. As a response to these conditions, the controller activates the required functions to control yaw motion, rotor and yaw brakes, and rotor blade pitch. The following parameters are also taken into account: If the gearbox and generator temperatures exceed 40ºC (104ºF), the systems start their respective cooling systems (simulated state). If the gearbox temperature falls below 5ºC (41ºF), the heating unit starts (simulated state). While the system is in operation, the FAA lights beam alternately at a rate of one 100 ms pulsation every second. Festo Didactic

2 Ex. 4-1 Nacelle Control System Discussion Nacelle control overview The nacelle trainer system PLC program is divided in different blocks that are responsible for specific functions. All these functions are called in succession during each CPU cycle from within an organization block. Organization block Operation status Yaw control Blade pitch control One CPU cycle Power generation control Alarm monitoring Figure 4-9. Organization block calling function blocks. Every function block is independent from the others and uses logic that is represented symbolically using flowcharts. Operation status (automatic mode) The operation status function block can be viewed as the conductor of a philharmonic orchestra (Figure 4-10). The other function blocks respond to the output of the operation status function block just like musicians do to a conductor baton. However, they each keep control of their own outputs ( instruments ). Figure Function blocks respond to the operation status like to the baton of a conductor. 190 Festo Didactic

3 Ex. 4-1 Nacelle Control System Discussion A simplified flowchart of the operation status function block is presented in Figure As you can see, there can only be one output status at a time. The main actions taken by the system are described below. Figure Operation status flowchart. Festo Didactic

4 Ex. 4-1 Nacelle Control System Discussion Trainer stopped Trainer Stop Mode (Figure 4-12) is the first operation status after the trainer is powered up or following a safety stop. In this mode, the system waits for the user to press the green hardware button. Figure Before the green hardware button is pressed. The next step (Figure 4-13) is to press the START TRAINER button to change to the automatic mode. Figure After the green hardware button is pressed. Automatic Stopped At this point, change is allowed between Automatic (Figure 4-14) and Manual Mode (Figure 4-15). Figure Automatic - Stopped. Figure Manual mode. When the nacelle is in manual mode, a series of buttons are enabled on the HMI, allowing manual operation of a variety of components. Initialization in progress The system enters the Initialization mode (Figure 4-16) after the START AUTOMATIC button is pressed in Automatic - Stopped mode if all the necessary conditions are fulfilled (including presence of wind). The purpose of this operation status is to verify that the actuators function correctly. Figure Initialization. 192 Festo Didactic

5 Ex. 4-1 Nacelle Control System Discussion In this operation status: Rotor soft brake is applied shortly (test) Yaw brake is released shortly (test) Hub is initialized (if connected) Standstill In Standstill mode (Figure 4-17), the system waits for favorable conditions before production mode (Active Control) is started. In this operation status: a Rotor brake is applied Figure Standstill. Pitch motion is stopped in feathered position Yaw unwinding is achieved if the number of turns is greater than one Yaw wind tracking function is active in preparation for Active Control The wind tracking function monitors wind direction and aligns the nacelle accordingly. Active control in progress When the wind conditions are right, Active Control mode (Figure 4-18) is started. This is the mode in which energy is produced. In this operation status: Figure Active control in progress. Yaw wind tracking function is active Rotor brake is released Blade pitch is controlled Connection to the grid is established when generator speed is around 1800 RPM. Connection to the grid is interrupted when generator speed falls under 1800 RPM. Festo Didactic

6 Ex. 4-1 Nacelle Control System Discussion Unwind in progress The Unwind mode (Figure 4-19) prevents potential damage to the cables that carry power down the tower by untwisting them when required. In this operation status: Yaw is returned to position 0. a Figure Unwind in progress. In standstill mode the yaw unwinds if there is more than one yaw turn. In active mode, a shutdown request is followed by yaw unwinding only if there is more than three yaw turns or if the cable twist sensor is triggered. Shutdown in progress When the system condition requires stopping the turbine, the Shutdown In Progress mode (Figure 4-20) brings the system from Active Control to Automatic - Stopped mode. If the alarm triggered is critical (e.g., hydraulic unit drive power off or emergency button pressed), the operation status goes to Automatic - Shutdown (Figure 4-21) instead. Figure Shutdown in progress. Figure Automatic - shutdown. The following conditions generate a shutdown: Operator presses the STOP button Hydraulic unit or yaw drive communication problem or fault Hub shutdown request or communication problem Yaw brake fault Rotor brake fault Yaw axis fault Anemometer problem Low- or high-speed shaft sensor problem Gearbox overheating Grid contactor or breaker fault Grid problem 194 Festo Didactic

7 Ex. 4-1 Nacelle Control System Discussion Generator temperature is out of range Yaw contactor or breaker open Hydraulic unit contactor or breaker open Wind vane sensor signal lost Cable twist detector activated Yaw exceeds maximum number of revolutions allowed Speed ratio error Rotor lock pin engaged in hub disk Vibration limit exceeded In this operation status: Alarms are triggered on the HMI ALARMS screen Yaw drive motor is stopped and the brake is applied Blades are put to the feathered position Rotor coasts to a stop until 500 RPM on the high-speed shaft, then the soft brake is applied. Parking brake is applied when speed is null. The alarm condition needs to be resolved and the green hardware and START TRAINER (HMI) buttons need to be pressed before operation status can return to automatic mode. Yaw control The nacelle trainer features an active yaw system (Figure 4-22) that relies on the wind station to know which way to point the rotor into the wind. The system uses a yaw drive to rotate the pinion moving the slewing bearing to orient the rotor in line with the wind direction. The yaw system is used during operation statuses Standstill, Active Control and Unwind, to unwind the power cables. Festo Didactic

8 Ex. 4-1 Nacelle Control System Discussion Pinion Motor Brake Slewing bearings Digital encoder assembly Figure Yaw system. Information about the nacelle position is provided by means of a digital encoder (Figure 4-23). The wind vane sensor mounted on top of the nacelle sends a signal to the turbine controller to evaluate the position of the nacelle with respect to wind direction. When the yaw error is outside the allowed range within a specified time interval, the controller activates the yaw drive to align the nacelle to face the wind direction. When not yawing, the mechanism is locked by means of the yaw brake. Digital encoder assembly Figure Digital encoder. A flowchart of the wind turbine yaw system operation that is adapted to the nacelle trainer is shown in Figure Festo Didactic

9 Ex. 4-1 Nacelle Control System Discussion Figure Yaw system flowchart. Blade pitch control A simplified pitch control flowchart is shown in Figure When the system is in Stopped or Standstill mode, the blades remain in feathered position (i.e., 90º). Otherwise, in Active Control mode, the blade pitch angle is adjusted so that the blades pick up speed and stabilize slightly over the generator nominal speed, to permit connection to the grid and power generation. Festo Didactic

10 Ex. 4-1 Nacelle Control System Discussion Figure Pitch control flowchart. Power generation (and drive train) control As you have seen previously, the nacelle remains in Standstill state if the wind is below the cut-in value of 6 m/s (13.4 mph) or over the cut-out value of 22 m/s (49.2 mph). In Active Control mode, the rotor accelerates until the generator reaches enough speed to permit connection to the grid and generate power. A simplified power generation flowchart adapted to the nacelle trainer is shown in Figure Festo Didactic

11 Ex. 4-1 Nacelle Control System Discussion Figure Power generation flowchart. How rotor braking is accomplished The nacelle rotor is stopped in three phases. First, there is an aerodynamic braking process during which the blades are feathered. When the speed has decreased somewhat, a soft brake is applied on the rotor; that is, only a fraction of the braking power is applied by the brake pads. Finally, when speed approaches zero, full braking is applied, stopping the rotor entirely. Alarm monitoring Figure 4-27 shows a flowchart used to understand the logic followed by the trainer during alarm conditions. Festo Didactic

12 Ex. 4-1 Nacelle Control System Discussion Figure Alarms flowchart. When an alarm is active, there are three main outcomes 3 : a Warning. The system continues to run but a message is displayed. System shutdown. The drive train is brought to a stop. The yaw brake is applied. The blades are maintained in feather position. The rotor parking brake is applied. Trainer safe stop. Similar to the shutdown procedure, but additionally, the following items are disabled: o o o o o o Hydraulic unit power Yaw drive power Drive train (rotor) power Grid contactor and soft starter Wind vane motor Anemometer motor Trainer safe stop state is not related to the nacelle control system. This is a state that was implemented to ensure that the safety of the student operating a machine with moving parts cannot be compromised. 3 A fourth possible outcome (during unwinding only) is Unwind abort. 200 Festo Didactic

13 Ex. 4-1 Nacelle Control System Discussion All nacelle trainer alarms can be divided into five categories: System alarms (emergency stop) Sequence alarms (initialization, unwind, or shutdown) Physical alarms Simulated alarms Hardware faults (network) Appendix E provides a detailed list of the alarms programmed in the system and identifies the result of their triggering. All these alarms are discrete errors that must be acknowledged. Alarm management Alarm class If we refer to the ALARMS screen (Figure 4-28), the first column refers to the alarm class. WinCC Flexible, the HMI software from Siemens, defines five alarm classes (symbols between parentheses refer to the display name): Errors (!). For critical errors. Require acknowledgement. Warnings (W). Indicate given state. Do not require acknowledgement. System ($). States or events occurring on the HMI device (e.g., operator error or communication fault). Diagnosis events (S7E). States or events occurring in the controller (SIMATIC or SIMOTION). STEP 7 (S7). User defined. All alarms programmed by our company in the nacelle trainer HMI are from the error class. Therefore, they show an exclamation mark (!) and require operator acknowledgement. Festo Didactic

14 Ex. 4-1 Nacelle Control System Discussion Figure ALARMS screen. Alarm status The fifth column in the ALARMS screen (Figure 4-28) is the status of the alarm. If we refer to the legend at the bottom, three letters can appear: C, A, and D. In fact, four combinations are possible: a C (activated alarm). State of new alarms that have not been acknowledged or deactivated yet. CD (activated/deactivated). Identifies alarms that were deactivated by pressing RESET ALARMS, but that have not yet been acknowledged. CA (activated/acknowledged). Identifies alarms that have been acknowledged but for which RESET ALARMS was not pressed. CDA or CAD (activated/deactivated/acknowledged). Identifies alarms that are both acknowledged and deactivated. At this point, the alarm disappears from the CURRENT ALARMS box. RESET ALARMS deactivates all current alarms at once but each alarm must be acknowledged individually. You have probably noticed by now that most alarms (critical alarms) need to be both deactivated (RESET ALARMS) and acknowledged ( ) to disappear from the CURRENT ALARMS box. a Critical alarms can be reset even though the alarm condition is still present. 202 Festo Didactic

15 Ex. 4-1 Nacelle Control System Discussion However, safe stop alarms are reset automatically when the alarm condition is removed, but they still need to be acknowledged. The safety panel (protection guards) alarms are reset by closing the panels. When an emergency stop is depressed, the pertaining alarm is deactivated only when the emergency button is reset and the green hardware button is pressed. b If you want to clear multiple alarms faster, press RESET ALARMS before acknowledging each alarm. ALARMS HISTORY Every alarm entry ends up at the bottom of the ALARMS screen. For each alarm that needs acknowledgment, three different entries can be found: one for each status it had (e.g., C, CA, and CAD). Once the alarm disappears from the CURRENT ALARMS box, it does not necessarily appear in the ALARMS HISTORY box immediately. The window is refreshed when buttons START TRAINER or START AUTOMATIC are pressed on the MAIN screen. System status Working condition System statuses provide useful information to the user about the machine state. In order to produce electricity, system status must remain as OK (Figure 4-29) or Warning (Figure 4-30). Warning status implies that a minor alarm is present, such as moderate vibration. Figure OK status. Figure Warning status. Interlock In order to be able to start the trainer active mode, some conditions must be met. If the wind simulation is not started (Figure 4-31) or if the hand lever is not in position (Figure 4-32), this information is found under System Status to help the user address the issue. Figure Auto Sequence Interlock Wind Simulation Not Active. Festo Didactic

16 Ex. 4-1 Nacelle Control System Discussion Figure Auto Sequence Interlock Rotor Lock. Critical alarm When an alarm is present, the faulty condition must be removed and the RESET ALARMS button be pressed before system status returns to OK. The alarm can be triggered by an emergency push-button or a safety panel for a trainer safe stop (Figure 4-33). Non-safety related alarm conditions such as a drive or a sensor fault generate a critical alarm shutdown (Figure 4-34). Figure Trainer Safe Stop Critical Alarm. Figure Shutdown Critical Alarm. Control system implementation The nacelle trainer uses a so-called Panel PC. The Panel PC is an industrial computer (Figure 4-35) that acts both as an interface and as a PLC to operate, monitor, and control the nacelle trainer functions. Distributed I/O rack Panel PC Figure Panel PC and distributed I/O. 204 Festo Didactic

17 Ex. 4-1 Nacelle Control System Discussion The soft PLC installed on the computer is called WinLC RTx (Figure 4-36) and is accessible from the desktop by exiting the HMI. Clicking RUN or STOP changes the PLC mode. a WinLC RTx needs some time to launch when the trainer is powered up. This causes a small delay before the trainer can be started. Figure WinLC RTx, a software acting as a PLC. The Panel PC is connected to the distributed I/O rack (Figure 4-35) in the electrical panel via PROFINET, an open industrial Ethernet standard. The three variable-frequency drives are connected to the Panel PC through PROFIBUS, a communication protocol for field devices used by Siemens and other manufacturers. Festo Didactic

18 Ex. 4-1 Nacelle Control System Discussion Figure The Panel PC is an industrial computer. Some of the important ports and power connections of the Panel PC are identified in Figure 4-37: 1. USB 2. Profinet 3. Ethernet 4. Profibus 5. Power supply The distributed I/O rack receives and transmits electrical signals in order to monitor and control various electrical devices that interact with the physical world. The distributed I/O on your training system (Figure 4-38) conveys information between the CPU and the following devices: Sensors for temperature (thermocouple), pressure (transducer), and vibration Switches (push-button, limit, proximity inductive, and safety) Actuators, such as motors (via variable frequency drives) and solenoid valves Indicators, such as FAA beacon lights Other electrical devices, such as contactors and relays 206 Festo Didactic

19 Ex. 4-1 Nacelle Control System Procedure Outline Figure Distributed I/O. PROCEDURE OUTLINE The Procedure is divided into the following sections: Accessories needed Basic safety procedure Setting up the nacelle Starting the trainer in automatic mode Starting the wind simulation Progression from cut-in to nominal wind speed Analysis. Progression from nominal to cut-out wind speed Alarm management. Vibration on the generator. Analysis. Familiarization with the distributed I/O Relay output: FAA lighting. Analog input: wind vane. Loss of communication End of the procedure PROCEDURE Accessories needed For this exercise, you will need the following accessories: Lockout device (hasp) One padlock and one tag per student Multimeter (not included) Basic safety procedure Before using the training system, complete the following checklist: You are wearing safety glasses and safety shoes. You are not wearing anything that might get caught such as a tie, jewelry, or loose clothes. If your hair is long, tie it out of the way. The working area is clean and free of oil or water. Festo Didactic

20 Ex. 4-1 Nacelle Control System Procedure Setting up the nacelle 1. Make sure the main switch is off and everything is secure inside and around the nacelle. 2. Open the safety panels. 3. Position the vibration sensor on the generator (Figure 4-39). Never let the vibration sensor cable run near moving parts as it could get stuck and become damaged. Figure Vibration sensor on the generator. 4. Close the safety panels. Starting the trainer in automatic mode 5. Notify all the people working around the nacelle that the system is about to be energized and ask your instructor for permission to power the nacelle training system. 6. Turn on the main power switch. Wait for the panel PC to boot and log into Windows. The HMI should start automatically. 7. Press the green (physical) start button under the main switch to start the system. 8. Press Start Trainer in the HMI MAIN screen. 208 Festo Didactic

21 Ex. 4-1 Nacelle Control System Procedure 9. If the ALARMS button is flashing red at this point, press it. In the opening ALARMS screen, acknowledge each current alarm. Next, press RESET ALARMS, if necessary. Starting the wind simulation 10. Program the following steps in the WIND SIMULATION screen: Table 4-2. Wind steps. Step #1 Step #2 Step #3 Step #4 Step #5 Step #6 Duration (s) Wind Direction ( ) Wind Speed [m/s (mph)] 7 (15.7) 8 (17.9) 9 (20.1) 10 (22.4) 11 (24.6) 12 (26.8) 11. Enable all six steps, start the wind simulation, but press PAUSE immediately so that the simulation remains in the first step. 12. What is the actual Operation Status? 13. Press START AUTOMATIC in the main screen. Note the three different states that the nacelle goes through. Progression from cut-in to nominal wind speed 14. Wait for the system to stabilize. 15. Go to the TREND BLADE ANGLE AND WIND SPEED screen and note the value of Blade Pitch Command RT value in Table 4-3. a You can move the vertical cursor left or right, or stop the trend to help you take measurements. 16. Go back to the MAIN screen and note the high-speed shaft speed value and generated power in Table Finally, look inside the electrical panel (Figure 4-40) and note the rotordriving mechanism (aka Drive Train) drive frequency in Table 4-3. Festo Didactic

22 Ex. 4-1 Nacelle Control System Procedure Frequency value Figure Rotor-driving mechanism drive frequency. Table 4-3. Effect of speed variation. Wind speed [m/s (mph)] Pitch angle ( ) High-speed shaft speed (RPM) Power (%) Rotor-driving mechanism (Drive Train) frequency (Hz) 7 (15.7) 8 (17.9) 9 (20.1) 10 (22.4) 11 (24.6) 12 (26.8) 18. Return to the WIND SIMULATION screen, press START so that the wind step changes, but press PAUSE immediately so that the simulation remains in the current step. 19. Repeat steps 14 through 18 until Table 4-3 is full. 20. Stop the wind simulation. The system will go back to standstill and a Wind Out of Range alarm will be generated. Analysis 21. What can you say about the pitch angle and generated power with respect to wind speed? Explain. 210 Festo Didactic

23 Ex. 4-1 Nacelle Control System Procedure 22. Does the high-speed shaft rotational speed vary between cut-in to nominal wind speed? Why is this so? 23. What does the rotor-driving mechanism drive frequency tell us? Progression from nominal to cut-out wind speed 24. Program the following steps in the WIND SIMULATION screen: Table 4-4. Wind steps. Step #1 Step #2 Step #3 Step #4 Step #5 Step #6 Duration (s) Wind Direction ( ) Wind Speed [m/s (mph)] 12 (26.8) 14 (31.3) 16 (35.8) 18 (40.3) 20 (44.7) 22 (49.2) 25. Enable all six steps, start the wind simulation, but press PAUSE immediately so that the simulation remains in the first step. Alarm management 26. Does energy production resume after wind returns? Yes No 27. Go to the ALARMS screen. What is the current System Status? 28. What is the status (C, D, and/or A) of the current alarm for out of range wind speed? 29. Press RESET ALARMS. What happens? Festo Didactic

24 Ex. 4-1 Nacelle Control System Procedure 30. Acknowledge the alarm ( ). What happens now? 31. Wait for the system to stabilize. 32. Go to the TREND BLADE ANGLE AND WIND SPEED screen and note the pitch angle (Blade Pitch Command RT) in Table Go back to the MAIN screen and note the high-speed shaft speed value and generated power in Table Finally, look inside the electrical panel and note the rotor-driving mechanism (aka Drive Train) drive frequency in Table 4-5. Table 4-5. Effect of speed variation. Wind speed [m/s (mph)] Pitch angle ( ) High-speed shaft speed (RPM) Power (%) Rotor-driving mechanism (Drive Train) frequency (Hz) 12 (26.8) 14 (31.3) 16 (35.8) 18 (40.3) 20 (44.7) 22 (49.2) 35. Return to the WIND SIMULATION screen, press START so that the wind step changes, but press PAUSE immediately so that the simulation remains in the current step. 36. Repeat steps 14 through 18 until Table 4-5 is full. Vibration on the generator 37. Go to the TRENDS ROTOR VIBRATION screen. How does the vibration level compare to what you observed when the sensor was on the gearbox in Ex. 2-2? 212 Festo Didactic

25 Ex. 4-1 Nacelle Control System Procedure Analysis 38. Stop the wind simulation. 39. What can you say about the pitch angle and generated power with respect to wind speed? Explain. 40. Does the high-speed shaft rotational speed vary between nominal and cutout wind speed? Why is this so? 41. What does the rotor drive frequency tell us? Familiarization with the distributed I/O 42. Open the electrical panel and compare the distributed I/O rack with the schematic on the inside left panel. Relay output: FAA lighting 43. Which of the 12 output relay cards is connected to the FAA lights? b Think about the frequency at which they open and close. Festo Didactic

26 Ex. 4-1 Nacelle Control System Procedure Analog input: wind vane 44. Put the trainer in MANUAL mode. Go to the SERVICE WIND STATION screen and start the DEBUG mode (Figure 4-41). Your instructor needs to enter a password in order for you to proceed. Figure Wind station DEBUG. 45. Put your multimeter in dc voltage measurement mode (voltage will be between 0 and 5 V dc) and connect the two probes to the wind vane motor feedback terminals on the analog input card, as shown in Figure Figure Connecting probes to the wind vane terminals. 214 Festo Didactic

27 Ex. 4-1 Nacelle Control System Procedure 46. On the HMI, use the JOG- and JOG+ buttons to move the vane as close as possible to 10, 90, 225 and 360 positions; measure the corresponding voltages and write down the results in Table 4-6 below. Table 4-6. Voltage according to the wind vane position. Wind direction (measured) ( ) Measured voltage (V) 47. What happens if you keep turning the vane in the same direction? Does the analog signal give an indication as to how many turns the vane is making? 48. Turn off the DEBUG mode and go to the MAIN screen. Loss of communication 49. Disconnect the communication cable linking the Panel PC and the distributed I/O rack (Figure 4-43). The communication cable is not easy to disconnect because it is deeply inserted into the port. Take your time to avoid damaging the port and/or the cable. Festo Didactic

28 Ex. 4-1 Nacelle Control System Procedure Disconnected cable a Figure Disconnecting the communication cable. The other Ethernet cable connects the Panel PC to the media converter that permits communication with a Hub trainer through an optical cable. 50. What is the current System Status, Operation Status, and Hydraulic Unit (status)? 51. Go to the ALARMS screen. Which alarms are triggered? Is there any indication of a communication problem? 52. Take a look at the distributed I/O rack. Is there any red light that can be an indication of the communication problem? If so, where is it located? 53. Reconnect the cable. Is the situation different on the distributed I/O rack now? Explain. 216 Festo Didactic

29 Ex. 4-1 Nacelle Control System Conclusion 54. Can you reset and acknowledge all the alarms you obtained at step 51? Yes No End of the procedure 55. Exit the HMI by pressing X on the top-right corner of the screen. 56. Press the Windows Start button, select Shut Down, and press OK. Wait for the system to turn off. a You may have to reset alarms before exiting the software. 57. Use the main power switch to turn all system power off. 58. Clean the area. CONCLUSION In this exercise, you analyzed what occurs in the system as wind speed increases. You learned a bit more about alarm management and saw what happens when there is a loss of communication. REVIEW QUESTIONS 1. What are the nacelle operation status and system status during energy production? 2. What happens if gearbox temperature exceeds 60ºC (140ºF)? b You can refer to Appendix E. 3. What happens if generator temperature falls under 5ºC (41ºF)? 4. Which component provides information on the yaw system position? Festo Didactic

30 Ex. 4-1 Nacelle Control System Review Questions 5. What type of communication link exists between the Panel PC and the variable-frequency drives of the electrical panel? 218 Festo Didactic