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[music] Good day and welcome to Big Bad Tech. I'm your instructor, Jim Pitel, and today's topic of discussion is wind turbine yaw systems. Our objective is to examine the yaw system found on a modern industrial wind turbine.
Comprehensive lecture on wind turbine yaw systems, covering hardware, motor control, and operational principles for efficient wind power conversion.
Key Takeaways
- Yaw systems are critical for aligning the turbine rotor with wind direction to maximize power output.
- Yaw motors use three-phase AC power to rotate the nacelle clockwise or counterclockwise.
- Basic motor control components ensure safe and efficient yaw motor operation.
- Proper yaw control reduces mechanical stress and prolongs turbine component life.
- Understanding general yaw system principles aids in troubleshooting and maintenance but specific manuals are essential.
Summary
- Overview of yaw systems in modern industrial wind turbines and their role in maximizing rotor exposure to wind.
- Discussion of yaw system hardware including yaw motors, sloping bearings, and yaw brakes.
- Explanation of yaw motor operation, including clockwise and counterclockwise rotation controlled by three-phase AC motors.
- Introduction to basic motor control elements such as switches, sensors, rotary encoders, circuit breakers, contactors, and overloads.
- Emphasis on the importance of yaw systems for minimizing mechanical loads and extending turbine lifespan.
- Clarification that the lecture uses simplified schematics and general principles rather than manufacturer-specific implementations.
- Description of pilot level and primary level power in motor control systems.
- Explanation of closed-loop control and the use of rotary encoders for precise yaw positioning.
- Details on squirrel cage induction motors, including inrush current and rated operating conditions.
- Reminder to consult specific turbine operation manuals for exact yaw system programming and control.
Full Transcript — Download SRT & Markdown
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the hardware found in yaw systems and discuss the general operational principle. The section presumes the viewers watch the introduction to industrial wind turbines and wind turbine hydraulic systems yawn rotor break lectures both available at the big bad tech channel. The same housekeeping
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We will identify the hardware found in yaw systems and discuss the general operational principle. The section presumes the viewers watch the introduction to industrial wind turbines and wind turbine hydraulic systems, yaw, rotor brake lectures, both available at the Big Bad Tech channel. The same housekeeping
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a yaw system schematic and will not explore manufacturer specific implementations for every turbine that ever has or ever will be constructed.
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rules cited in the aforementioned lectures apply to this same lecture. Notably, it is presumed the viewer brings with them a necessary foundational electromechanical technology and an understanding that this lecture must necessarily limit itself to a simplified representation of
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between the simplified yaw system as presented in this lecture and most modern industrial wind turbines. Let us begin.
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a yaw system schematic and will not explore manufacturer-specific implementations for every turbine that ever has or ever will be constructed. Related to this qualification, we'll explore only general representations of the decisions made by the controller rather than real-world programmed instructions. Long story short, always consult the operations manual for the specific turbine of interest. This being said, you should find some commonalities
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The wind turbine NL sits on top of the tower on an externally or internally to sloing bearing allowing the NL and tower to mechanically rotate relative to one another. Yaw motors affixed to the Niss bed plate mesh with the sloowing bearing
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between the simplified yaw system as presented in this lecture and most modern industrial wind turbines. Let us begin. Viewers will recall that the act of yawing a wind turbine rotates the NL relative to the tower, thus maximizing the rotor swept area exposed to incoming wind, thereby contributing to the efficient conversion of wind power to electrical power.
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Once in position, as we'll soon learn how this is determined, the yaw motors are deenergized, the yaw brakes applied, the rotor brake released, the blades are pitched to an appropriate angle, and the turbine is free to get busy making
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The wind turbine NL sits on top of the tower on an externally or internally to sloping bearing allowing the NL and tower to mechanically rotate relative to one another. Yaw motors affixed to the Niss bed plate mesh with the sloping bearing
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wind turbine would be extremely inefficient in converting wind power to electrical power if it worked at all and might fail prematurely due to excess wear. Necessary components of a basic yaw system include inputs, actuators that produce some output and a control
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via gearbox intermediary. When energized in one direction, the yaw motors turn the NL clockwise. When energized in the other direction, the yaw motors turn the NL counterclockwise.
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our understanding of basic motor theory, reacquaint ourselves with some basic motor control elements, notably switches, sensors or transducers, rotary encoders, circuit breakers, motor starters, contacttors, and overloads.
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Once in position, as we'll soon learn how this is determined, the yaw motors are de-energized, the yaw brakes applied, the rotor brake released, the blades are pitched to an appropriate angle, and the turbine is free to get busy making
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directly proportional accitation frequency and inversely proportional to the number of pole pairs per phase.
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power. Beyond maximizing electrical power output by pointing the rotor into the wind, the yaw system also minimizes off-axis mechanical loads and contributes to the long lifespan of the drive components. Lacking a yaw system or employing one that worked poorly, a
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For example, if L1 L2 L3 establishes clockwise rotation, L2L1 L3 establishes counterclockwise rotation. More on interlocks and reversing circuits in a moment. Lastly, a squirrel cage induction motor is a common industrial three-phase AC motor that requires no connections to the
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wind turbine would be extremely inefficient in converting wind power to electrical power if it worked at all and might fail prematurely due to excess wear. Necessary components of a basic yaw system include inputs, actuators that produce some output, and a control
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overload. Temporary overloads are permissible, but only become a problem if they're sustained for any length of time. Additionally, a squirrel cage induction motor can experience a large but temporary surge of current known as inrush when energized from a dead stop.
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system which manages output based on input conditions. Since this particular lecture places a special emphasis on motor control and control theory, before we look at a yaw system schematic, it's perhaps worth a moment of our time to quickly refresh
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basic motor control hardware. Motor control. One of the most basic principles of motor control is the division between pilot and primary level power. Pilot level power is low voltage, low current, low power used to direct control the function of the system.
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our understanding of basic motor theory, reacquaint ourselves with some basic motor control elements, notably switches, sensors or transducers, rotary encoders, circuit breakers, motor starters, contactors, and overloads.
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Pilot level. You will recall switches are digital devices that can exist in one of two mutually exclusive states, deactivated or activated.
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And lastly, quickly introduce closed-loop control. Motor theory. Viewers will recall that three-phase AC creates a rotating magnetic field when applied to the stator of a three-phase AC motor, with the speed of the rotating magnetic field, the synchronous speed, is
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If however the rocker arm, roller switch or wobble stick, yes, this is a true term attached to the limit switch is struck by some physical object, the normally open limit switch closes and sends a 24volt signal to the control
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directly proportional to excitation frequency and inversely proportional to the number of pole pairs per phase. Additionally, viewers will recall that the rotational direction of the stator rotating magnetic field can be reversed by swapping any two applied phase sequences.
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to the measured quantity. Consider a 0 to 10 volt rotational position sensor capable of measuring 0 to 360°.
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For example, if L1 L2 L3 establishes clockwise rotation, L2 L1 L3 establishes counterclockwise rotation. More on interlocks and reversing circuits in a moment. Lastly, a squirrel cage induction motor is a common industrial three-phase AC motor that requires no connections to the
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certain actions at certain input conditions and be displayed or recorded. A special class of rotational position sensor is known as a rotary encoder of which there are two main types incremental and absolute.
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rotor. When operating at the rated condition, a squirrel cage induction motor exerts a rated torque, rotates at rated speed, and draws a rated amount of current. When subject to conditions above the rated condition, current draw increases, which constitutes an
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sensors receive B then A, it means it's going counterclockwise. Beyond rotational direction, AB encoders also include a third signal Z. You'd think it' be C, but it isn't. It's Z. The Z or index signal happens once per revolution
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overload. Temporary overloads are permissible, but only become a problem if they're sustained for any length of time. Additionally, a squirrel cage induction motor can experience a large but temporary surge of current known as inrush when energized from a dead stop.
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encoders on industrial wind turbines might take the form of a tooth gear that meshes with the yaw ring and rotates the specified number of turns per full turn of the yaw ring or a pair of offset magnetic proximity switches that count
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Thus concludes your review of motor theory. That was like what, 10 lectures compressed into three sentences. Like I said, this lecture necessitates you show up with a background in electromechanical technology. Presuming you're still with me, let us now review
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More on yaw errors in a moment. An absolute encoder, in contrast, produces a unique digital code for each distinct angle of the shaft. Where absolute encoders with more bit positions allow for finer and finer angular resolution. Absolute encoders
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basic motor control hardware. Motor control. One of the most basic principles of motor control is the division between pilot and primary level power. Pilot level power is low voltage, low current, low power used to directly control the function of the system.
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Primary power. Let's now discuss motor control elements that interact with primary power. You'll note some of these devices only make or break connection to primary power at the request of a low power pilot signal.
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Whereas primary power is high voltage, high current, high power actually used to do work. At a basic level, high power primary devices only function at the request of low power pilot level signals.
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In this capacity, they are a means of protecting the load and electrical distribution system from damage in the event of a short circuit or other undesirable fault. Fuses are nonreusable protection elements.
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Pilot level. You will recall switches are digital devices that can exist in one of two mutually exclusive states, deactivated or activated.
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circuit or other undesirable fault. Circuit breakers, in contrast, are reusable protection elements. A contactor is a means of making and breaking connection to primary voltage.
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For example, consider a normally open limit switch that when unperturbed and not struck by some physical object sends a 0-volt signal to the control system.
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Contacttors may also include one or more auxiliary contacts rated for pilot level voltage. In this case, a normally open auxiliary contact from 13 to 14, which can be used as indicators about a particular contact or status, form electrical interlocks, or other
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If, however, the rocker arm, roller switch, or wobble stick, yes, this is a true term attached to the limit switch, is struck by some physical object, the normally open limit switch closes and sends a 24-volt signal to the control
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specified value for a specified length of time, the overload does not open, but rather the overload tells the controller an overload is occurring and the controller deenergizes the contacttor coil which opens the contactor and stops the motor. Again, contactors have the
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system. In this capacity, the limit switch offers a clear and defined transition from one state to another. Is something there or is something not there? A sensor or transducer, in contrast, measures something and outputs a voltage or current signal proportional
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open that can be used to determine the status of the overload element. Contacttors and overloads working in combination are known as motor starters.
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to the measured quantity. Consider a 0 to 10-volt rotational position sensor capable of measuring 0 to 360°.
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A commonly available motor control element known as a manual motor starter combines the function of a circuit breaker contactor overload and manual shut off. You know the schematic symbol for a manual motor starter includes contacts could be opened manually as
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At 180°, or halfway there, the position sensor would output 5 volts. At 270 degrees, or 3/4 of the way there, the position sensor outputs 7.5 volts and so on. These analog signals can be used by the control system to perform
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branch of a circuit. Lastly, since some yaw systems do not warrant the inclusion of hydraulic brakes, I should mention that there exists spring applied electric friction brakes that are sometimes mounted right on the motor or ultimately on the N cell frame. You
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certain actions at certain input conditions and be displayed or recorded. A special class of rotational position sensor is known as a rotary encoder, of which there are two main types: incremental and absolute.
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hydraulic brakes. control theory. Lastly, automated systems often rely on closed loop control to ensure the output of the system meets expectations. Here is a very very quick summary of closed loop control. There are numerous terms associated with closed loop control
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One type of incremental rotor encoder is known as an AB encoder that uses two tags or two sensors, A and B, slightly offset from one another such that when the sensors receive A then B, it means it's revolving clockwise. If, however, the
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what you've got is equal to what you want, don't mess with it. If what you've got is less than what you want, go get some more. Finally, if what you got is more than what you want, get rid of
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sensors receive B then A, it means it's going counterclockwise. Beyond rotational direction, AB encoders also include a third signal, Z. You'd think it'd be C, but it isn't. It's Z. The Z or index signal happens once per revolution
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you've got with what you want. Notice the polarity of the signs for the comparator.
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and serves as a way of determining an absolute position from the last full revolution. The number of AB pulses since the last index signal can be used to determine rotational position with a desired degree of accuracy. Common implementations of incremental rotary
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the gas pedal where it's at. By comparing what we've got, 55, to what we want, also 55, the comparator subtracts what we've got from what we want, and generates a third signal, error. In this case, what we've got equals what we
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encoders on industrial wind turbines might take the form of a tooth gear that meshes with the yaw ring and rotates the specified number of turns per full turn of the yaw ring or a pair of offset magnetic proximity switches that count
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If, however, the car starts climbing a hill, the present throttle position might not be sufficient to keep the car going at 55.
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the teeth of the yaw ring directly. Some turbine manufacturers use more than one incremental encoder method; one is primary and one is backup and can signal a yaw error if the two systems disagree.
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controller is telling the controller to get 2 mph more. The controller adjusts the throttle sufficient to accelerate the car and speed stabilizes at 55 mph such that we're back to a condition where we've got is equal to what we want
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More on yaw errors in a moment. An absolute encoder, in contrast, produces a unique digital code for each distinct angle of the shaft. Where absolute encoders with more bit position
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error signal is minus 3 mph. Again, note the sign. What we've got is 3 miles per hour over what we want. And the error signal transmitted to the controller is telling the controller, get rid of 3 miles hour. The controller backs off the
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throttle sufficient to decelerate the car and speed eventually stabilizes at 55 such that we're back to a condition where what we've got is equal to what we want with zero error.
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Now realize this automated adjustment does not happen instantaneously and there is some rise, fall and settling time and over and undershoot that can be accounted for with some not so trivial math. We'll explore closed loop control in greater detail in later lectures. For
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now, this should be sufficient for the purposes of this lecture. All right, now that we've done a quick review of motor theory, common pilot and primary hardware devices, and discuss closed loop control at an introductory level, let's take a look at a simplified
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representation of the primary schematic for a yaw system. Again, primary is the high power portion of a system that actually does the work. Often, yaw systems use more than one motor, where the number of motors are reflective of a
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given turbine's mass and the size of the motors employed. You might expect anywhere from four to eight yaw motors on a modern industrial wind turbine. The primary schematic shows one manual motor starter feeding four separate circuits, one for each motor that are essentially
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duplicates of one another. Each individual motor shows another manual motor starter in series with pair of contacttors and an overload relay.
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You'll note the branching arrangement. If a technician was to manually open the furthest upstream manual motor starter labeled yaw system, all motors in the yaw system would be disabled. This would be helpful if one need to perform some
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service or repair on the entire yaw system. If however the upstream yaw system manual motor starter was closed, a technician could selectively disable individual yaw motors in the system by opening that particular manual motor starter. For example, if a technician
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needed to work on yaw motor 2 and motor 2 only, they would open up yaw motor 2 manual motor starter and disable yaw motor 2 only, thus allowing the remaining three yaw motors to continue to function as intended.
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While we're on the topic of selectively deenergizing smaller subsystems of a larger system, can three yaw motors do the task originally intended for four?
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Maybe yes, maybe no. Depending upon the design philosophy of a particular wind turbine manufacturer, there's often a significant safety factor built into the sizing components that comprise it. This being said, with three motors left to perform a task originally intended for
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four, you would expect the remaining three motors to draw more current and exert more power than normal. If this unequal work sharing arrangement was to continue for any length of time, you might expect the three remaining motors to not last as long.
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Continuing downstream from each individual manual motor starter, we see a pair of contacttors that make or break connection to primary voltage. Since each individual yaw system is identical, let's just zoom in on the primary schematic for yaw motor one. Yaw motors
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2, 3, and four, and for that matter 5, 6, 7, and 8 will repeat the same connection. You will note that when the clockwise contacttor closes, it applies phase sequence L1, L2, L3 to the squirrel cage induction motor such that
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it turns clockwise. Whereas when the counterclockwise contacttor closes, it applies phase sequence L2, L1, L3 to the squirrel cage induction motor such that it turns counterclockwise.
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This is obviously a paired reversing contacttor arrangement and most likely the system includes mechanical and electrical interlocks to prevent simultaneous closure both the clockwise and counterclockwise contacttors.
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You recall we examined reversing motor starters extensively in the reversing motor starters with interlocks lecture available at the big bad tack channel.
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In this lecture, we learned that simultaneous closure of both the clockwise and counterclockwise contacttors allows phase L1 and L2 to smash headfirst into each other with no current controlling element between and can yield an arc flash hotter than the
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sun. This is to be prevented at all costs. For this reason, a mechanical interlock prevents the simultaneous physical closure of the clockwise and counterclockwise contacttors. Often times paired reversing contacttors will be mounted side by side inside an electrical enclosure and the mechanical
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interlock takes the form of an accessory device mounted in between or on top of the paired reversing contacttors such that it sticks a wedge or some other physical obstruction to one contacttor assembly should the other close and vice
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versa. An electrical interlock in contrast appears inside the pilot system and prevents the coils of the opposite contacttor from being energized when the first is energized and vice versa. For example, when the clockwise coil is energized in rung one, the associated
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normally closed clockwise one contact in rung three opens and prevents the counterclockwise coil from being energized.
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Using this double layer of protection, mechanical and electrical, ensures that neither a faulty control system nor any manual override would ever inadvertently simultaneously close both the clockwise and counterclockwise contacttors. The yaw motor primary schematic additionally features an overload element in series
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with the motor. You recall an overload is a sensory device that protects the motor from sustained highcurren conditions. At the rated conditions and less, the overload does nothing. If however there's some issue with the yaw system, perhaps lack of lubrication,
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shaft misalignment, there's a loss of a single phase or perhaps the brakes are still on. We'll talk about this possibility in a bit or some other issue. Current will rise above the rated value and the overload will begin a
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countdown. Once the countdown expires, the overload says shut it down and sends a signal to the controller. The controller opens the contacttor and the motor stops. As we'll soon learn, some controllers can take additional steps during overloads and other errors.
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Before we take a look at the pilot level, you'll note the larger primary circuit necessitates each individual motor circuit handle the current for that individual motor. Whereas the furthest upstream Yaw system manual motor starter must handle all power for
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all of the yaw system. Presuming each motor draws a rated current of let's say 4 amps. The upstream Yaw system manual motor starter must handle four plus 4 + 4 + 4 or 16 amps. Long story short, each
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manual motor starter contact or an overload needs to be appropriately sized and set for the conditions it is intended to handle. And any mistake in sizing or setting can result in failure or nuisance tripping.
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So, while we've got this primary schematic up here, now I said at the beginning of this lecture I wasn't going to go down the rabbit hole of discussing manufacturer specific implementations, but when have I ever been consistent and
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prone to telling the truth? So, if you will follow me down the rabbit hole of manufacturer specific implementations for one moment, there exists an extremely common wind turbine platform that is a slightly different primary schematic than the representation I've
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illustrated in this lecture. You might run across it one day. Actually, you will run across it someday. So, I feel obligated to flash it up here real quick. This being said, it kind of does the same thing as we previously
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discussed, only in a slightly different manner. You know, rather than including a paired reversing contacttor arrangement for every single motor, this particular implementation uses a single paired reversing contactor that makes and breaks connection all yaw motors simultaneously. Makes sense because when
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you want the turbine yaw clockwise, you want all motors going clockwise and vice versa. In this implementation, you could still deenergize the complete yaw circuit using the upstream manual motor starter, and you can still selectively deenergize individual motors using their
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particular manual motor starter. What you gain is a simplified control circuit because there'll be only a single pair of contacttor coils, one clockwise, one counterclockwise. But what you lose is the ability for the control system to selectively energize individual motors,
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which again isn't ordinarily done on a regular basis. Be on the lookout for different manufacturer implementations that kind of do the same thing as discussed in this lecture. Moving on.
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All right. Now, let's take a look at the pilot level schematic. This is low power control voltage. As I stated at the beginning of this lecture, this is by necessity a simplification. Includes the bare minimum necessary to run the yaw
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system. Maybe not even that much. We'll see. Here, I've illustrated a PLC with inputs on the left and outputs on the right. As previously, let's concern ourselves with just the pilot level devices necessary to control yaw motor one. Yaw motors 2, three, and four, and
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for that matter, five, six, seven, and eight would essentially be repeats of this same setup. The most essential outputs of the interest for the yaw motor one are the coils for the clockwise and counterclockwise contacttors and outputs Q1 and Q2.
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These coils are in series with the normally closed overload contact associated with yaw motor one.
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When Q1 is energized, yaw motor one clockwise contacttor closes and the yaw motor one turns clockwise.
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Presuming the rest of the motors follow the same pattern. All the motors energize and the turbine turns clockwise.
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Conversely, when Q2 is energized, yaw motor one counterclockwise contacttor closes and yaw motor one turns counterclockwise.
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Presuming the rest of the motors follow the same pattern, all the motors energize and the turbine turns counterclockwise.
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You'll note the dashed mechanical interlock between the clockwise and counterclockwise coils. As we discussed previously, the simultaneous closure of both the clockwise and counterclockwise contacttors is the worst of worst ideas.
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and the mechanical interlock physically forces one contacttor open when the other is closed and vice versa.
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You will additionally note if the yaw motor experiences an overload in either clockwise or counterclockwise mode, the normally closed overload contact in series opens, it prevents either coil from being energized. This hardwired connection between a coil and normally
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closed overload contact ensures the overload has the last say about whether a particular motor is energized or not.
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You may or may not see this level of redundancy in a real world implementation, but in my personal experience is most wise to include it.
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Additionally, since the YA system also needs to interact with yaw brakes, there's outputs for soul one and soul 2 on Q3 and Q4. You recall we discussed the operation of the yaw brakes and the aforementioned wind turbine hydraulic
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systems. Yan rotor brakes lecture available at the big bad tech channel. Here's the primary hydraulic schematic for the business end of the yaw brakes utilizing a pair of hydraulically extended spring retracted single- acting cylinders connected in parallel inside a
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fixed caliper. On the input side, looks like the yaw controller has a couple digital and analog inputs.
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On the digital side, it looks like there's a limit switch labeled twist, a normally open pressure switch, PSY, measuring pressure at the yaw brake, a normally open auxiliary contact associated with a clockwise contacttor, and a normally open auxiliary contact
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associated with a counterclockwise contacttor. On the analog side, looks like there's inputs for the wind vein, the animometer, and the rotary encoder measuring the position of the NL.
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Internal to the PLC stored in memory would be a software generated twist count showing the number of full revolutions from the cumulative rotary encoder data. We'll discuss how this software generated twist count value is used later on.
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A more robust industrial scale system might include additional temperature sensors, current sensors, and other accessory safety and performance monitoring inputs and outputs that might trigger other systems in the turbine or react to error conditions.
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Let's now discuss how the controller uses this hardware setup to implement automatic yaw control of the turbine without need of human supervision. Often times the programmed instructions utilized by a turbine controller are written in some programming language recognizable by a PLC normally relay
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ladder logic or if you're in a country with a functional democracy and healthcare system structured text sequential function charts and/or function block diagrams. To further complicate matters you may find certain subsystems or sub routines within a larger controller program implemented in
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one style and other systems or sub routines implemented another. Additionally, you may find older wind turbine controllers implemented entirely in hardwire or relaybased diode logic.
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It is not my intention in this lecture to examine program specific implementations of yaw control, but rather keep this discussion limited to a general description of the decisions made by the controller when tasked with yawing from one location to the next. On
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a basic level, while in automatic mode, the yaw system necessitates a wind turbine know where the wind is coming from, where it is pointed at, and a means of effectively closing the distance between the two. Additionally, it needs to make basic decisions about
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when to start tracking the wind, when to stop tracking the wind, and what to do in the event of an emergency or error condition. Let's first discuss how the yaw system determines in which direction to rotate and by how much.
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One of the most fundamental inputs to a yaw system is the wind vein, which if you recall is an instrument that measures the direction from which the wind is blowing. The wind catches the rudder blade of the wind vein and makes
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it rotate from some preigned home position such that an encoder at the base quantizes this rotational angle from the home position and sends the state to the control system. In summary, a wind vein lets a turbine know if it's
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pointed straight into the wind like you want or if the wind is hitting from the side, back or some other suboptimal angle. Consider the mounting location of a wind vein ordinarily at the top of the NL and consider several NL orientations
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in wind direction scenarios. See if you notice any commonalities. So we're on the same page. Let's consider clockwise rotation positive and counterclockwise rotation negative. Scenario one. The turbine is facing west 270° and the wind is coming from the west 270°.
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The wind vein flags straight back from its home position. Scenario two, the wind turbine is facing west again and the wind is coming from the north. The wind vein flags north to south, effectively displaced positive 90° from its home position.
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Scenario three, the turbine is still facing west, only this time the wind is coming from the east. The wind vein flags east to west, effectively displaced 180° from its home position.
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You could easily consider this positive or negative 180°. Finally, the turbine is still facing west and the wind's coming from the south. The wind van flags south to north effectively displaced 90° from its home position. Notice anything? One more set
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of force scenarios to make sure you're seeing the same thing I'm seeing. For the heck of it, let's say the turbine is pointing southeast this time. The turbine is facing southeast 135° and the wind is coming from the southeast 135°.
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Wind van flag straight back from its home position. Next one, the turbine still facing southeast, only this time the wind is coming from the southwest. The wind vein is displaced positive 90° from its home position. Next, the turbine still facing
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southeast and the wind's coming from the northwest. The wind vein is displaced 180° from its home position. Finally, the turbine is still pointing southeast, only this time the wind is coming from the northeast. Wind vein is effectively displaced 90° from its home position.
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You note in all of these scenarios, regardless of turbine orientation or wind direction, the wind vein directly generates the error necessary for closed loop control. I say again, the wind vein directly generates error.
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Do we need to know the turbine's orientation? Not really. Do we need to know the wind's direction? Not really. the wind vein directly generates the difference between them. This being said, both properties can be measured and or calculated and they might be nice to
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know as we'll see in a bit. However, for the purposes of determining in which direction to yaw and by how much, the wind vein alone is sufficient for this task. For example, with a turbine pointed west and the wind coming from
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the west, the wind vein flag straight back from the home position with 0° deviation.
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Similarly, with a turbine pointed southeast and the wind coming from the southeast, the wind vein flags straight back from the home position with zero degree deviation. In these scenarios, the wind vein demonstrates the turbine is properly oriented into the wind and
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there's no need to yaw because the error is zero. For the second scenarios with the wind turbine pointed west and the wind coming from the north, the wind vein is displaced positive 90° from the home position. Similar with a turbine
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pointed southeast and the wind coming from the southwest, the wind vein is displaced positive 90°.
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In both these scenarios, the wind vein demonstrates the turbine is 90° to the left of the wind and it needs to turn 90° to the right, i.e. positive 90° clockwise.
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Sticking with these two scenarios, if the system were to energize the yaw motors clockwise, then the cell would begin a slow crawl clockwise. When the turbine initially pointing west reach northwest, the wind vein would be displaced 45° from its home position, indicating
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there's still an error of 45°. So, keep turning clockwise. Similarly, when the turbine initially pointing southeast reached south, the wind vein would flag 45° back from its home position, indicating there's 45° yet to go. So, continue turning clockwise.
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Eventually, both these systems in different initial orientations continue turning clockwise until the error signal directly generated by the wind vein gets less and less and less and eventually reaches zero. At this point, the wind vein indicates the turbine points into
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the wind. the first scenario north and the second southwest at which point the yaw motors are deenergized and the brakes applied without belaboring the point you find similar behavior for the remaining scenarios larger point being the wind vein directly generates the error signal
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necessary for closed loop control without the turbine needed to know orientation calculate wind direction and then compare the two. This being said, it still might be nice to know where a turbine is pointed and how many turns in
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one direction it's made since getting there. Inside a wind turbine tower, a large bundle of cables transfers power from the generator in the NL to the power conditioning equipment transformer at the base. As wind shifts direction throughout the day, there may be
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occasions where turbine follows it in a complete circle north to east to south to west and then another circle north to east to south to west and then another circle north to east to south to west in the same direction. For every full turn
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in one direction, the output cables of the generator get twisted together and a sufficient number of turns in the same direction may tighten the cable bundle to a degree they suffer damage.
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For this reason, the rotary encoder is an essential input to the system. From a designated home position established upon installation, the turbine uses the rotary encoder to keep track of the nal present angular position. In addition to present angular position, the controller
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also keeps a running tally of how many full revolutions in one direction have been accomplished.
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At a certain point, maybe three or four full twists in one direction, the controller is like, "Enough is enough. Let's unwind." And momentarily halts production to unwind an equal number of full turns backwards in the opposite direction, resetting the cable
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bundle to a slack position and the turn count to zero. Additionally, the turbine takes advantage of extended periods of low or no wind conditions when production ceases to take time to unwind to a slack condition.
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The obvious problem with this arrangement is this. What if the controller forgets how many full turns it's made in one direction? I mean, it happens, right? Industrial systems sometimes experience unexpected shut offs or errors that wipe out data.
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There's really no direct means of measuring the number of full turns. And this is a piece of stored data generated by the controller continually monitoring the rotary encoder.
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What happens if you lose this? Well, for this reason, turbines also include a backup electromechanical twist switch, which is essentially a limit switch tied to the cable bundle. the turbine ever forgets the number of turns it's made and the cables keep getting twisted up,
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keep getting twisted up, they eventually pull so hard the twist switch is triggered and it's like, "Hey dummy, are you lost?" The controller is like, "Oh yeah, I should probably unwind." In this sense, the hardwired electromechanical twist switch acts like a backup to the
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incremental rotary encoder and softwarebased positional data in case the controller ever loses its mind, which is always a possibility.
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Now that we've got an idea how a turbine detects in which direction to yaw and by how much, as well as handle cable twist, let's discuss how the turbine determines when it is appropriate to yaw. For obvious reasons, a turbine doesn't chase
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every gust of wind that comes along, but only does so when the wind is above a certain predetermined value and sustained for a certain duration.
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Long story short, the wind has got to be strong enough and there long enough for the turbine to yaw in that direction.
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You recall the animometer measures wind speed. This is a critical input for this particular decision.
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You recall a wind turbine possesses something known as a power curve with several notable points. Principally the cutting speed and the rated speed. The cutting speed is the wind speed at which a turbine is first capable of generating
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power. Whereas the rated speed is the wind speed at which turbine produces its rated output.
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Consider a turbine in the middle of a field on a totally calm day struck by the weakest of weak wind gusts. well below the cutin speed. Is the turbine going to yaw or not? Chances are no. Why bother? Any wind less than the cutin
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speed isn't worth chasing since it can't be used to make power. So why bother? If however the animometer detects a gust of wind above the cutin speed, the controller rather than yawning instantly in that direction begins a countdown to
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see if the gust is sustained long enough to make it worth its time to yaw in that direction.
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If a gust above the cutin speed isn't sustained for a specified period of time, the turbine returns to the idle site and waits to see if something worthwhile shows up. If however the gust is both above the cutin speed and
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sustained for a specified period of time, the turbine checks the wind vein and determines in which direction it needs to yaw or if it needs to yaw at all. Presuming twist count in that direction is below the unwind value, the
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turbine needs to yaw in the direction indicated by the wind vein. Now that we've discussed how the turbine controller utilizes the data provided by the wind vein to determine which direction yawn by how much, the rotary encoder, cumulative twist count and
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twist switch to manage cable tension and an animometer data to determine if wind speed and duration is sufficient to warrant reposition in the cell. Let's walk through a simulated yaw sequence.
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Let's see if we've got enough space to see what the PLC inputs and outputs, the primary electrical and the primary hydraulic systems do during a yaw. Got a feeling this is going to get pretty busy.
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For demonstration purposes, let's say the turbine has decided it needs to yaw clockwise. Again, to simplify the simulation, we're going to concern ourselves only with yaw motor one with the understanding that yaw motors 2 through 4 and for that
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matter 5 through 8 are all doing the same thing. Prior to energizing the yaw motors, the turbine first needs to remove the yaw brakes.
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Presuming we begin this scenario with yaw brakes applied in a pressurized standby condition with soul one energized to the closed position. and soul 2 deenergized in the closed state.
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To release the yaw brakes, the system energizes soul 2 to the open state, which jumps pressure in the yaw brake cylinders to tank. The springs in the rod end retract the cylinders and release the brakes.
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It's a simple matter of verifying if the yaw brakes are released. When pressure at pressure switch PSY falls.
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Once the status of the brakes have been verified, the controller then energizes output Q1, the coil for the clockwise contacttor.
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The clockwise contacttor closes as do the clockwise contacttors for the remaining motors. The motors energize in the clockwise direction and the N cell starts doing a slow crawl clockwise.
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You note auxiliary contact CW1 associated with clockwise contacttor also closes confirming that the yaw clockwise action is proceeding as intended.
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As the NL continues to yaw clockwise, not only does the displacement error indicated by the wind vein slowly decrease, the rotary encoder also indicates clockwise travel. We'll discuss what happens if the rotary encoder doesn't change or worse yet
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indicates counterclockwise travel in a moment. Once the wind vein indicates the cell is pointed into the wind with zero error, the system deenergizes output Q1.
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The coil for the clockwise contacttor deenergizes. The clockwise contacttor opens as do the clockwise contacttors for the remaining motors. The motors deenergize and then the cell stops.
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You know auxiliary contact CW1 associated with the clockwise contacttor also opens confirming that the yaw clockwise action is ceased as intended.
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Now the system needs to apply the brakes from the release state. First it enters a depressurized standby by deenergizing soul 2 which returns to the closed position.
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Then the system deenergizes soul one which shifts to the open position. The pump is energized and pressurized flow enters the cap end of the yaw brake cylinders. The yaw brake cylinders extend and apply the yaw brakes.
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Eventually pressure switch PSY closes indicating the yaw brakes have a good grip at which point the system can move back to the pressurized standby state by energizing soul one which shifts to the closed position. The cell is pointed in
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the right direction and parked in place. Now it's just a matter of releasing the rotor brake, pitching the blades to appropriate angle, and making power.
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You'll note during the illustrated yaw sequence, at all times, the twist count stored in memory generated by the cumulative monitoring of the rotary encoder serves to interrupt the yaw process should yawing in a particular direction ever cross a certain
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threshold. Additionally, you know, behind this software generated data stored in memory, there exists a real world electromechanical twist switch that can equally call off a yaw in action if the controller ever loses track and cable strain becomes too much.
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In summary, by coordinating the sequence removal and application of the all brakes, the selective energizing and deenergizing of a paired reversing contacttor, and monitoring the wind vein status, a turbine can readjust its position such that it faces into the
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wind. Now, realize this sequence of action doesn't happen as smoothly as I indicated at all times, and there is plenty of chances for it to go wrong.
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For this reason, modern industrial wind turbine controllers often include automated error checks along the way and a means of notifying technicians of conditions that led up to these errors.
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Some of these checks are quite simple and others quite advanced. On a basic level, when tasked with the yawn clockwise, the rotary encoder should indicate travel in the clockwise direction. If the rotary encoder doesn't move, or worse yet, goes in the opposite
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direction, something is wrong and the system might generate an error. Similar statements can be made about the rotary encoder confirming counterclockwise rotation when supposedly yawing counterclockwise.
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Consider the act of removing and reapplying the yaw bra. You note that pressure switch PSY serves as confirmation of the status of the yaw brakes. If this system released the yaw bra and pressure at psy failed to fall
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as anticipated, the system might generate an error categorized as failure to release yaw break. Conversely, when the turbine arrived at the designated position and tried to reapply the brakes, if pressure at PSY failed to rise as anticipated, the system might
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generate an error characterized as a failure to apply yaw bra. Other opportunities for error detection exist. Consider a simple overload. As does pressure switch PSY indicate the status of the yaw brake to the system, so too do the normally open auxiliary
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contacts associated with the clockwise and counterclockwise contacttor. When a contactctor coil is energized, these auxiliary contacts should also close.
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This acts as confirmation of the controller's action. Beyond confirmation, the status of the auxiliary contacts can also indicate interruption of an action already in the works. Let's say during the course of clockwise yaw, one of the yaw gearboxes
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experienced an alignment or lubrication issue, or perhaps that motor is being singlephased. current in the affected yaw motor would rise above the rated value and at a certain point the normally closed overload contact in series with this contacttor coil would open and
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deenergize the affected contacttor coil. In addition to opening the affected contacttor and deenergizing the affected motor, the normally open auxiliary contact would also open. The loss of input at this location during a yaw would tell the yaw system that a
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particular motor's contacttor unexpectedly open during operation, most likely because of an overload. The system might generate a motor protection error indicating a potential overload at that particular motor. Les do you think errors are associated to events in which
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the turbine is actively yawing considering a cell properly oriented into the wind and parked in place.
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In this presumably stable state, the rotary encoder should in no way ever send data indicating that the NL is turning. If however the rotary encoder starts sending data in a supposedly stopped state, the system will recognize a contradiction and might generate an
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error categorized as yaw drift. Depending on a particular wind turbine manufacturer's hardware setup and software configuration, the controller may or may not offer additional error detection abilities as well as performance monitoring systems. For example, some controllers, in addition
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to simply detecting an overload, may also continuously monitor current and can flag times in which the current approaches or exceeds predetermined limits and record these events.
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Beyond automatic control, wind turbines ordinarily offer a means of manually controlling the yaw system. As implied by the title, a manual override of the yaw system allows a technician to direct when and where to position the NEL relative to the tower. Manual operation.
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The yaw might occur during repair or service operations to force them to sell into a desired orientation or perhaps be used to position load handling equipment like cranes or hoist above a load to be lifted. Depending upon manufacturer and
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model, manual mode might be as simple as a pair of buttons that say yaw clockwise and yaw counterclockwise or as sophisticated as touchscreen human machine interface or HMI with the ability to yaw turbine to a specified orientation.
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Be aware certain safety systems can be bypassed in manual mode and a technician must be aware of the perhaps undesirable consequences of their every action. For example, in normal automatic operation, the turbine controller releases the brakes, confirms they're released, then
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energizes the yaw motors. Manual mode might necessitate a technician perform these actions independently. And a technician that fails to release the brakes prior to yawning. And everyone else in a two-mile radius would hear a sound that's been described as
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everything from a fog horn to the mating call of a diplo duckosaurus where the dragging brake pads use the resonant chamber of the tower as a 300t tall tuba. There is no pretending this mistake didn't happen. For this reason
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and more, be sure of your every action when taking manual control of any aspect of a wind turbine.
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All right, we are just about to close out this lecture, but before we do, let me answer a question that a lot of people have when asked in reference to the yaw system. Notably, how fast does an industrial turbine yaw? The answer is
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not very fast. I mean, think about it. Even a midsize turbine cell and rotor might weigh 80 tons or 160,000 lb or roughly 72,000 kg. That's a lot of weight. Let's pretend the system employs four 4 kW motors. So that's 16 kW or
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roughly 21 horsepower. How fast could 21 horses drag 80 tons? Not very. The thing is it doesn't need to be fast. In ideal power making conditions, wind ordinarily doesn't bounce from north to south back to north again, but rather blows
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steadily from a relatively constant direction with only minor shifts throughout the day. What allows the yaw system to move this weight efficiently, steadily, and slowly is the step down gear boxes, which convert the high-speed, low torque input of the yaw
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motors to high torque, low- speed rotation of the pinion gears that match with the yaw ring. In ordinary circumstances, you might expect a turbine to yaw a snail's pace of maybe half a degree per second. 360 degrees per circle. Half a degree per second
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means 720 seconds. Roughly 12 minutes for a full turn. Plenty of time to get out of the way. But woe unto those that do not get out of the way. Step ladder, I'm looking at you. At such a slow
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speed, 16 kW of mechanical power exerts massive torque and will cut anything and absolutely everything in half that gets pinched between the yaw deck and the necell. For this reason, modern industrial wind turbines often include a yaw disable switch in the yaw deck,
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which is the last tower platform just below the NEL. Prior to entering the NEL, a technician would disable the yaw system, thus ensuring the orientation of the NEL and tower remain fixed during their stay. It is incumbent upon any
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technician that has disabled the yaw system for repair and maintenance task. Remember to reenable it prior to climbing down the tower and returning it to service. on this. They're looking to climb the turbine again so they can reset it. All right, that's all I got
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for you today. In conclusion, this lecture examined the yaw system found on modern industrial wind turbines. We conducted a brief review of motor theory, reacquainted ourselves with primary and pilot electromechanical components commonly found in yaw systems, and introduced closed loop
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control. We additionally examined how a turbine determines in which direction to yaw and by how much. Wind vein, I'm looking at you. how it handles too many turns in one direction. That's the responsibility of the software generated twist count and the electromechanical
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twist switch and discuss the strength and duration of wind necessary to make a turbine yaw. That's the animometer's job. Finally, we took a look at a simulated yaw sequence and examined the checks performed during automatic yaw control and identified a couple
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scenarios that might yield a yaw error. Remember to review these concepts as often as you need to really drive it home. Imagine how well lab will go if you know what you're doing. Thank you very much for your attention and
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interest. We'll see you again during the next lecture of our series. Remember to tell your lazy lab partner about this resource. Be sure to check out the Big Bad Tech channel for additional resources and updates.
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[music]
Topics:wind turbineyaw systemyaw motormotor controlrotary encodersquirrel cage induction motorwind powerindustrial wind turbineclosed-loop controlyaw brake
