Diagnosis of wind turbine systematic yaw error through nacelle anemometer measurement analysis (2023)


Wind turbines at present are the leading renewable energy technology worldwide, due to their advantageous energy density and wind kinetic energy conversion efficiency, and their exploitation is fundamental in the transition to a sustainable energy future[1], [2], [3]. The growth of wind turbines installation worldwide almost doubled from 2019 (58 GW) to 2020 (111 GW)[4] and the trend has been further accelerating, which gives immense opportunities as well as risks related to the grid management[5], [6].

Wind turbine monitoring is a far from trivial task, due to the stochastic nature of the source and to the complexity of the machine, but it is crucial in order to improve the efficiency of energy conversion and finally diminish the levelized cost of energy. The individuation of systematic errors[7], [8] affecting wind turbine operation is an overlooked topic, which should be analyzed more in depth. A systematic yaw error[9] occurs when a wind turbine is controlled to achieve a set point of rotor orientation, which is believed to be front of the wind flow but in fact it is not. This can occur due to wind vane defects, incorrect installation or maintenance, or the aging of the machine. In[10], it is estimated that over 50% of the industrial wind turbines operate with more than 6° of systematic yaw error. Aerodynamic considerations[11] indicate that, in presence of a systematic yaw error γ, the extracted power P is reduced by a factor cos3γ. By assuming for simplicity the cos3 law, a systematic yaw error of 6° causes an average production loss in the order of 2%. This leads to estimate that, by correcting the systematic yaw error of the wind turbines worldwide, the wind energy production would increase of the 1%.

Supervisory Control And Data Acquisition (SCADA) systems have been historically conceived for allowing remote control of the wind turbines, but they have been evolving into a powerful information source for condition monitoring[12], [13]. Actually, SCADA systems store and make available a vast set of environmental, operational, electrical, mechanical and thermal measurements with a typical averaging time of ten minutes. Nevertheless, extracting knowledge from this information is particularly challenging when dealing with systematic errors which regard the rotor.

In line of principle, a wind turbine systematic yaw error can be ascertained by using upwind sensor systems and by comparing the rotor orientation to the upwind wind direction. In fact, LiDARs[14], [15] or spinner[16] anemometers have been employed at this aim. By a practical point of view, the use of such sensors systems in addition to those already implemented on the wind turbine might be discouraged by their installation cost. Given this, it makes sense to employ the SCADA-collected data (which are typically available to the end user without additional cost) at least as a first advice for directing the installation of LiDARs or spinners to the wind turbines which are more suspected to be affected by the systematic yaw error. The general problem with the use of SCADA data for diagnosing systematic errors related to the rotor is that the anemometer is mounted on the nacelle behind the rotor span[17]. This means that the nacelle anemometer measures the wind perturbed by the rotor in intensity and direction and the undisturbed field is reconstructed through a nacelle transfer function.

(Video) Next generation of wind turbine testing procedures

On top of this, the literature about SCADA-based detection of wind turbine systematic yaw error has overlooked a further critical point, which is the fact that the nacelle anemometer measurements are affected by the presence of the systematic yaw error[18]. This occurs because, if a wind turbine operates subjected to a systematic yaw error, its nacelle anemometer (being behind the rotor) will be more upwind or more downwind with respect to what happens in normal operation and therefore, for a given free flow wind speed, the nacelle anemometer will respectively measure more or less wind intensity with respect to what would happen normally. The core of the present work is therefore a critical analysis of what the above statement implies and of how the SCADA-based methods for individuating and assessing the impact of the systematic yaw error should be reconsidered.

The structure of the manuscript is as follows. The related work is summarized in Section1.1, where the innovative contribution of the present study is outlined as well. In Section2, the test case is described and the method is illustrated. A real-world test case is contemplated, which is a wind farm owned by the ENGIE Italia utility company. In Section3, the results are collected and the conclusion are drawn in Section4.

The caveat which orientates most studies in the literature is that SCADA-collected direction measurements of a wind turbine affected by a systematic yaw error are very likely indistinguishable with respect to those of a wind turbine operating correctly. The nacelle wind direction and rotor orientation measurements indicate a correct alignment, while this does not occur. This implies that most studies in the literature are based on the individuation of the systematic yaw error through secondary effects and the most straightforward effect is an under-performance (recall the cos3 law).

An under-performance consists of less power extracted for a certain incoming wind speed. The most common SCADA-based approach for individuating and quantifying an under-performance is the analysis of the power curve, because it is the relation between wind speed (x-axis) and extracted power (y-axis). In this regard, a very interesting study related to the use of the power curve for systematic yaw error detection is[19]. The most noticeable aspect of that work is that a 2.5 MW utility-scale wind turbine (Eolos research station) has been fully controlled by the authors, who have forced the operation under several static yaw errors in order to characterize the different behavior with respect to the normal operation. Actually, a gap in the research is given by the lack of a clear data labeling (with error or not). In this context, the work of[19] is particularly valuable. The data-driven procedure employed in[19] is substantially a fit of the observed power curve in presence of the systematic yaw error to cos3γ times the power curve in normal operation. The systematic yaw error is diagnosed also in[20] as an under-performance detected by a data-driven method. A Gaussian Process regression for the power curve is set up, employing operation variables as blade pitch and rotor speed.

Several studies in the literature employ a mixture of analyses, which include jointly the power curve and the behavior of the wind vane measurements. The common assumption is that the best performance of the machine should occur for vanishing yaw error. If this does not occur, it is likely that there is a systematic yaw error, which is consequently estimated as the angle at which the best performance is observed. This line of reasoning is applied for example in[21], where an analysis of the binned power curve is performed upon grouping the data per yaw error intervals of 2°. A similar approach is employed in[22], [23]. The difference with respect to[21] is in the power curve model, which is Least-Square B-spline Approximation. In[24], the power curve analysis is applied upon a non-trivial data rejection algorithm that takes into account several features of the machine functioning. In[25], the data are pre-processed appropriately, so that small portions of the power curve are employed for diagnosing and individuating the yaw error.

The same kind of concept is employed in other studies where the target is the power coefficient, rather than the power curve. In[26], the systematic yaw error is individuated by looking at what value of the yaw error the maximum power coefficient occurs actually (measurements) and theoretically, where the theoretical estimate is achieved with a data-driven method that takes into account environmental variables like turbulence intensity and external temperature. In[27], the yaw angle - power coefficient curve is analyzed and the diagnosis is formulated directly from the observed data. The behavior of the yaw angle - rotor speed curve is studied in[28]. The approach employed in[29] instead stands apart somehow, because a wind-farm approach is formulated for diagnosing the systematic yaw error, which is given by the analysis of the distribution of the relative wind direction measurements.

The point of this study is that the above works overlook the fact that the nacelle wind speed measurements are affected by the presence of the yaw error. This implies that it is not completely consistent to compare the power curve of a wind turbine subjected to systematic yaw error to that of a well aligned wind turbine. In this regard, it is worth discussing the recent work in[24]. LiDAR measurements have been employed to diagnose the systematic yaw error on some target wind turbines and to assess its absence upon appropriate intervention on the wind turbines. Therefore, in[24] a clear data labeling is at disposal and the authors elaborate on the SCADA data collected by the wind turbines when operating with and without the systematic yaw error. Through a straightforward comparison of the power curves in presence and absence of the systematic yaw error, it is estimated that less than 10° of yaw error correction provides order of 15% of performance improvement, which is implausible (the cos3 law gives a 5%). The conclusion drawn in[24] is that there are data quality issues related to the wind turbine nacelle anemometer. Given the line of reasoning of this work, a more plausible interpretation is that, when operating with 10° of yaw error, the nacelle anemometer was more upwind than the normal and then overestimated the wind speed, thus amplifying the apparent difference in the power curve with respect to the case of vanishing yaw error.

At present, there is only one work in the literature dealing with the effects of the systematic yaw error on nacelle wind speed measurements. In[30], the flow equilibrium condition of two nacelle anemometers is employed for individuating the systematic yaw error. The study in[30] raises substantial issues also on the methods based on the characteristic curves of wind turbines as a function of the yaw angle as estimated by the SCADA-collected measurements. Actually, it is argued that the flow distortion induced by the nacelle is disregarded in most studies in the literature.

Based on the above line of reasoning, with this work a research gap is filled regarding the following points:

  • Detection. A systematic yaw error detection algorithm based on nacelle anemometer measurements analysis is formulated. The points of strength of this algorithm are the consistency following from first principles, the simplicity and the universality (it does not depend on the particular wind turbine model).

  • Assessment. A method for quantifying the effect of the systematic yaw error on wind turbine performance is formulated, which is the generalization of the concept of relative performance. This method does not employ nacelle wind speed measurements, because those depend on the presence or not of the systematic yaw error. In this work, it is argued that the proposed method provides more consistent results with respect to the power curve analysis.

The selected test case is a further point of strength of this work. Actually, the presence of a systematic yaw error on two wind turbines out of six from an Italian wind farm has been ascertained through an upwind sensor system (spinner anemometer). This means that the data sets are labelled. Furthermore, the systematic yaw error has been corrected and this means that data sets describing the behavior in presence or absence of a remarkable systematic yaw error are at disposal. Summarizing, therefore, the proposed method for detection and assessment of systematic yaw error is shown to be more consistent and effective with respect to the state of the art.

Section snippets

Definition of systematic yaw error

The yaw error γ is defined as the difference between the wind direction θwd and the rotor direction θrot, as indicated inEq.(1): γ=θwdθrot.The control system of the wind turbine operates for achieving the set point given by γ=0 through the actuation of yaw motors and-or by using the blade pitch control[31] of the turbine[32]. As discussed in detail for example in[32], the critical point for wind turbine yaw control is the measurement or estimation of the wind direction and several

Detection: Comparison against state of the art methods

In Fig.3, the frequency of wind vane measurements for each wind turbine during the data set D1 is reported. From this Figure, it arises that all the wind turbines orientate to a set point which the SCADA reports to be zero, but in fact it is not for wind turbines T3 and T5 (as arises from Table1). From Fig.3, it is impossible to clearly distinguish T3 and T5 with respect to the other wind turbines in the farm.

Fig.4 reports the wind vane - power coefficient curve. Also in this case, it is


The present study has dealt with the use of nacelle anemometer SCADA-collected data for the diagnosis and the assessment of the performance impact of wind turbine systematic yaw error. The starting point of this work is the fact that the presence of a systematic yaw error affects nacelle wind speed measurements and this leads to revisit the methods for diagnosis and assessment. Despite being as simple as that, this aspect has never been investigated in deep before in the literature about

CRediT authorship contribution statement

Davide Astolfi: Conceptualization, Methodology, Software, Validation, Formal analysis, Investigation, Data curation, Writing – original draft, Writing – review & editing, Visualization. Ravi Pandit: Validation, Investigation, Writing – review & editing, Visualization. Andrea Lombardi: Validation, Investigation, Supervision, Writing – review & editing. Ludovico Terzi: Supervision, Project administration, Writing – review & editing.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

© 2023 Elsevier Ltd. All rights reserved.


What is the yaw error in wind turbines? ›

Any measured difference between the wind direction and the nacelle position of the turbine is known as the yaw error. When the yaw error is at 0°, the turbine is ideally pointing directly into the wind. Any wind turbine that is not pointing directly into the wind is experiencing what is known as yaw misalignment.

What is the effect of yaw error on the reliability of wind turbine blades? ›

Specifically, yaw error significantly reduces the power capture and increases fatigue load acting on turbine blades. Besides, yaw error can also lead to inaccurate power forecasts and reduce the economy of power grid dispatching [5].

What causes the turbine to yaw mechanically? ›

The yaw mechanism is activated by the electronic controller which several times per second checks the position of the wind vane on the turbine, whenever the turbine is running. Cables carry the current from the wind turbine generator down through the tower.

What are the different controls used to regulate the power generated from Hawt Yawing pitching stalling? ›

Pitch, Yaw, and Rotational Speed Control were the main control methods used to optimize or limit the power extracted from the wind.

What are the most common wind turbine failures? ›

The most common external wind turbine failure is typically damage to the blades caused by bird strikes, lightning strikes, rainfall, blade furniture detachment, delamination, leading-edge corrosion or blade cracks.

What are the three main causes of turbine blade failures? ›

The combined mechanism of the buckling of the spar cap, the delamination of the panel and the debonding of the trailing edge leads to the catastrophic failure of the blade. Thus, the identified root causes of buckling under flapwise loading include the Brazier effect, local buckling and delamination and debonding.

What is the effect of yaw misalignment? ›

In the most basic terms, yaw misalignment occurs when your wind turbine does not face directly into the wind. Since power can only be generated by wind perpendicular to the rotor plane, any yaw misalignment will result in a power loss for a turbine.

What is reliability analysis of wind turbines? ›

Wind turbine reliability analysis. The reliability definition is the probability that subassembly will meet its required function under a stated condition for a specified period of time. For an unrepairable system, the rating scale is reliability; for a repairable system, the rating scale is availability.

What controls the yaw movement? ›

The Rudder Controls Yaw

On the vertical tail fin, the rudder swivels from side to side, pushing the tail in a left or right direction. A pilot usually uses the rudder along with the ailerons to turn the airplane.

How is the yaw controlled in wind turbine? ›

The yaw control mechanism comprises a motor and drive. The main purpose of this arrangement is to move the nacelle and blades according to the wind direction. It enables the wind turbine to capture the maximum available wind. During the nacelle movement, a fair chance of cable twisting occurs inside the tower.

How is the action of yaw controlled in biggest turbines? ›

Direct-Drive Yaw System

The yaw motors power the yaw drive, which rotates the nacelle on upwind turbines to keep them facing the wind when the wind direction changes.

What is the difference between yaw control and pitch angle control in wind turbines? ›

Currently, almost all wind turbines use pitch control systems and yaw systems. The yaw drives control the alignment of the nacelle with the wind; the pitch control system is constantly adjusting the angle of attack of the rotor blades—the pitch angle—in order to achieve the greatest possible energy yield.

Do yaw bearings teeth point outward or inward? ›

The large wheel is called the yaw bearing. On some yaw bearings the teeth point outwards, while on others they are turned inwards. It all depends on the position of the yaw motor.

What controls pitch and yaw? ›

Elevators (moving flaps on the horizontal tail) produce pitch, a rudder on the vertical tail produces yaw, and ailerons (flaps on the wings that move in opposing directions) produce roll.

What are the two major types of turbine failure? ›

Engine failures may be classified as either as "contained" or "uncontained". A contained engine failure is one in which all internal rotating components remain within or embedded in the engine's case (including any containment wrapping that is part of the engine), or exit the engine through the tail pipe or air inlet.

What are 2 negatives of wind turbines? ›

Disadvantages of Wind Energy
  • Wind turbines can be dangerous to some wildlife. Wind turbines can be fatal to wildlife. ...
  • Wind turbines can be noisy. ...
  • Wind power is limited by location.

What are the main bearing failure modes of wind turbine? ›

Among the most commonly encountered failure modes: Cracks with white etching (often called WECs, or white etching cracks) can develop in bearings at multiple wind turbine gearbox locations — especially prevalent in larger megawatt and multi-megawatt class wind turbines.

What is one problem that wind turbines can cause? ›

Birds and bats can be injured or killed if they are hit by turbine blades. These deaths may contribute to declines in the population of species also affected by other human-related impacts. The wind energy industry and the U.S. government are researching ways to reduce the effect of wind turbines on birds and bats.

What is the number one cause of failure on the wind turbine gearbox? ›

Their findings, published in the journal Tribology International , confirmed that bearing slip occurs during wind turbine operations as a result of factors including bearing design, load, speed, lubrication, and temperature.

What are the common troubles in working of a turbine? ›

One of the most common problems in the turbine section is blade damage, which can be caused by erosion, corrosion, fatigue, foreign object damage, or thermal stress. Blade damage can reduce the efficiency, power, and durability of the engine, and can also lead to blade failure and engine shutdown.

What are the four possible losses in a turbine? ›

These losses can be categorized into four main types of losses; leakage, friction, moisture, and particle.

What 3 main factors determine the efficiency of a wind turbine? ›

The three main factors that influence power output are: wind speed, air density, and blade radius. Wind turbines need to be in areas with a lot of wind on a regular basis, which is more important than having occasional high winds.

What are the four main factors which affect turbine engine performance? ›

The pressure ratio of the compressor, the engine operating temperatures (turbine inlet temperature), and the individual component efficiencies will also influence both the performance and the efficiency of the overall engine.

How do you reduce yaw? ›

Countering Adverse Yaw

In a coordinated turn, adverse yaw is countered by using the rudder (in almost all cases, stepping on the rudder into the turn). When you add rudder input, you're creating a side force on the vertical tail that opposes adverse yaw.

What are two causes of roll due to yaw? ›

For example, yaw causes a slight increase in airspeed over the outer wing of the turn and a decrease in airspeed over the inner wing. As a result, the outer wing will generate more lift than the other, introducing a rolling motion. Yaw also causes side-slip which triggers several effects.

What changes the yaw? ›

The rudder is the primary flight control that controls yaw. The rudder is located along the trailing edge of the vertical tail fin, called vertical stabilizer. As the rudder moves from side to side, the tail moves in a left or right direction.

What data are important for analyzing wind turbine performance? ›

The universal standard to assess the performance of a wind turbine is a plot of the Power Coefficient versus the Tip Speed Ratio performance curve. This curve tells you how efficiently a turbine converts the energy in the wind to electricity. Various methods were used to plot this curve.

What is fault tree analysis of wind turbine? ›

Fault tree analysis

FTA is a directed graph that reflects the fault propagation,18,19 which is used to evaluate the reliability of large and complex systems like wind turbines. FTA establishes and analyzes wind turbine event fault tree to research the fault mechanism.

What is the best wind turbine efficiency? ›

The theoretical maximum efficiency of a turbine is ~59%, also known as the Betz Limit. Most turbines extract ~50% of the energy from the wind that passes through the rotor area.

What causes yaw instability? ›

It is caused by the difference in lift and drag of each wing. The effect can be greatly minimized with ailerons deliberately designed to create drag when deflected upward and/or mechanisms which automatically apply some amount of coordinated rudder.

What affects yaw stability? ›

Directional stability (also known as weather vane stability) is what determines the airplane's response to being yawed relative to the oncoming airstream. The airplane is stable when it tends to yaw to point the nose back into the wind and unstable if the yawing moments tend to increase the yaw.

What stabilizes yaw? ›

Rudder - Yaw. At the rear of the fuselage of most aircraft one finds a vertical stabilizer and a rudder. The stabilizer is a fixed wing section whose job is to provide stability for the aircraft, to keep it flying straight. The vertical stabilizer prevents side-to-side, or yawing, motion of the aircraft nose.

What prevents the nacelle from over rotating? ›

Roller Bearing - Brake (Semi-active system): The nacelle is mounted on a roller bearing and it is free to rotate towards any direction, but when the necessary orientation is achieved an active yaw brake arrests the nacelle. This prevents the uncontrolled vibration and reduced gyroscopic and fatigue loads.

What is the effect of the turbine scale on yaw control? ›

While the power production of the downstream turbine increases because of the lateral deflection of the incoming wake, the efficiency of the upstream (yawed) turbine decreases because only the wind velocity perpendicular to the rotor disk contributes to the power production.

What does the nacelle do in a wind turbine? ›

A nacelle /nəˈsɛl/ is a cover housing that houses all of the generating components in a wind turbine, including the generator, gearbox, drive train, and brake assembly.

What is the maximum yaw angle of wind turbine? ›

The yaw angle can reach up to around 60°, depending on the wind flow characteristic on site. While the yawed flow scenario presents an important and challenging problem, the basis of understanding the wind turbine aerodynamics is the axial flow case.

What kind of turbines likely don t need the yaw mechanism? ›

There are several advantages associated with the Darrieus Wind Turbine. First of all, the Darrieus turbine is omnidirectional and does not require any special yaw mechanisms to continuously orient itself toward the wind direction.

What is the difference between azimuth and yaw? ›

Azimuth seems to be used to represent an absolute heading, while yaw is a measurement of how much a craft turns from its current orientation. Thus, if your azimuth went from 90∘ to 184∘, your yaw was 94∘, while your current azimuth is 184∘.

How does pitch angle affect wind turbines? ›

Wind turbine blades have to be streamlined so they can efficiently pass through the air. Changing the angle of the blades will change the area facing the apparent wind. This is why blade pitch angles of 10- 20 degrees tend to have much less drag than greater angles. Drag also increases with wind speed.

What are the three different types of speed control operations in windmill? ›

Pitch, Yaw, and Rotational Speed Control were the main control methods used to optimize or limit the power extracted from the wind.

What turns the nacelle? ›

The yaw motor turns the nacelle so that the rotor faces the wind. The motor has a cam wheel which fits into the large yaw bearing cam wheel. The controller tells the yaw motor when to turn the nacelle. The rotor turns the large shaft.

Which bearing is used for rotation of nacelle to wind direction? ›

Yaw bearings are used for angular realignment of the nacelle into the predominant wind direction.

What are the 12 parts of a nacelle? ›

Parts of the nacelle: 1, transformer; 2, alternator; 3, gearbox; 4, hydraulic equipment: 5, blade pitch regulation system; 6, weather sensors; 7, yaw system.

Which sensor determines yaw pitch and roll values? ›

The Quaternion method is used to calculate the pitch and roll angle of the accelerometer sensor. It is also used to calculate the yaw angle of the magnetometer sensor. Boole's rule is used to calculate the pitch, roll, and yaw angles of the sensor gyroscope.

What creates yaw? ›

A yaw motion is a side to side movement of the nose of the aircraft as shown in the animation. The yawing motion is being caused by the deflection of the rudder of this aircraft. The rudder is a hinged section at the rear of the vertical stabilizer.

Why is it called yaw? ›

In the heyday of large sailing ships, numerous nautical words appeared on the horizon. Yaw is one such word. Its origin isn't exactly known, but it began turning up in print in the 16th century, first as a noun (meaning "movement off course" or "side to side movement") and then as a verb.

What is meant by yaw control in wind power system? ›

Yaw refers to the rotation of the entire wind turbine in the horizontal axis. Yaw control ensures that the turbine is constantly facing into the wind to maximize the effective rotor area and, as a result, power.

How does the yaw drive work on a wind turbine? ›

Direct-Drive Yaw System

The yaw motors power the yaw drive, which rotates the nacelle on upwind turbines to keep them facing the wind when the wind direction changes.

What is yaw value? ›

The yaw rate or yaw velocity of a car, aircraft, projectile or other rigid body is the angular velocity of this rotation, or rate of change of the heading angle when the aircraft is horizontal. It is commonly measured in degrees per second or radians per second.

How do you control yaw? ›

Yaw is controlled with the rudder of the airplane. Modern aircraft rudders are located on the tail with hinges. The rudder is operated with pedals. Together with the airplane's ailerons, the rudder pushes the tail to the right and the left to direct the airplane along this axis.

How do yaw control and pitch control compare in wind energy system? ›

Currently, almost all wind turbines use pitch control systems and yaw systems. The yaw drives control the alignment of the nacelle with the wind; the pitch control system is constantly adjusting the angle of attack of the rotor blades—the pitch angle—in order to achieve the greatest possible energy yield.

What is nacelle anemometer transfer function? ›

The purpose of the nacelle transfer function is to assess the influence of the wind turbine's rotor and nacelle on the nacelle wind speed and to identify the relationship between the free stream wind speed and the nacelle wind speed.

What are the stages of yaw drive? ›

Yaws consists of primary, secondary, and tertiary phases. The infection may become latent at any time, with only serologic evidence of the infection.

How do you calculate yaw value? ›

Assuming you aren't moving much first find the up direction by using the accelerometers to measure gravity. Then use the gyroscopes to measure rates of turn on each axis. Scale these by the correct amount based on the orientation and that will give you a yaw rate. Integrate the yaw rate over time to give you yaw.

What causes yaw? ›

A yaw motion is a side to side movement of the nose of the aircraft as shown in the animation. The yawing motion is being caused by the deflection of the rudder of this aircraft. The rudder is a hinged section at the rear of the vertical stabilizer.

What is yaw in simple terms? ›

What does 'yaw' mean? The official definition is a twisting, or rotation of up to 360 degrees, of a moving ship or aircraft around a vertical axis. To define yaw is to describe an airplane, boat, or even a fish with the nose or front moving side-to-side through the air.

What is the slowest speed of wind necessary to spin the turbine? ›

Wind turbines require:

winds of less than 90 km/h; beyond that speed, the turbines must be stopped to avoid damage.

Why are some wind turbines not turning while others are? ›

But why else might the wind turbines you see standing still not be turning? Essentially for one of two reasons: They're being maintained, or need maintenance. It's not windy enough for them to operate at all, or too windy for them to operate.

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