GB2528646A

GB2528646A - Generator assembly

Info

Publication number: GB2528646A
Application number: GB1412295.6A
Authority: GB
Inventors: Andreas Clemens Van Der Ham; Sebastian Ziegler
Original assignee: SKF AB
Current assignee: SKF AB
Priority date: 2014-07-10
Filing date: 2014-07-10
Publication date: 2016-02-03
Also published as: WO2016005550A1; GB201412295D0

Abstract

A roller bearing 10 wherein a predetermined equidistant angular spacing Î´2 of the rolling elements 12 is maintained by a cage 14, and at least two sensors 16, 16, for example strain gauges, attached to one of the bearing rings 10a, 10b at different predetermined angular locations, each generate a signal having one component with a frequency of the rolling elements passing by the sensor, the angular locations of the sensors being chosen such that the phase angles of said signal components are different. The angular spacing Î´1 between the sensors is preferably chosen such that said signal components have opposing phase angles. Preferably a shock load acting on the bearing is detected based on the sum of the signals. Also claimed is a wind turbine comprising the bearing and a method for monitoring a wind turbine. The invention provides a reliable way of detecting shock or transient loads on a wind turbine.

Description

Sensorized Bearing for Wind Turbines

Field of the Invention

The invention relates to a main shaft bearing for wind turbines, to a wind turbine equipped with the same and to a method for monitoring one or multiple wind turbines.

Background of the Invention

Condition monitoring of wind turbines is an important issue, in particular in the case of off-shore wind parks which are difficult to access by maintenance staff. Bearings for use in wind turbines, in particular main shaft bearings holding a rotor, have very large dimensions and have to support immense loads while reliably operating under a wide range of environmental conditions. Replacement is complicated and expensive and should be avoided as far as possible. It is therefore very important to provide reliable estimates of bearing lifetime, which is usually done using parameters measured by sensor systems on the bearing. It is known to provide temperature sensors, strain sensors, vibration-or acoustic emission sensors and accelerometers on bearing rings.

Various technologies using strain sensors targeting to measure load on the side face of a bearing have been proposed. The sensors are correlating the strain/displacement on the bearing side face with individual roller loads by means of a mathematical model. The peak-to-peak values of the sensor signal correspond to the roller load.

However, it has turned out that an important contribution to lifetime estimates of bearings and other components in wind turbines are shock/transient loads. These happen e.g. during emergency shutdown, swiveling of the wind turbine nacelle, manoeuvres, abrupt changes in wind conditions or turbulences. The frequency of the shock/transient loads is significantly higher than the roller pass frequency dominating the sensor signals corresponding to the roller load.

There is always a trade-off between signal processing performance, sensor quality and sensor quantity necessary to have the best possible performance/price ratio.

Reliable shock detection is further important to trigger emergency stops of wind turbines.

Accelerometers are used to detect shocks in many applications. However these do not allow to quantify the load on the bearing.

Another possibility would be to attach a strain gauge to a structure which is carrying the load, this could be a shaft or a surrounding component. However this is not possible with a bearing because the load is continuously changing in a macroscopic scale caused by the rollers passing by.

It is therefore an object of the invention to provide a roller bearing arrangement, in particular for main shaft bearings of wind turbines, which is suitable for reliably detecting shock loads or transient loads of the bearing.

Summary of the Invention

The invention relates to a bearing, in particular for use as main shaft bearing for wind turbines, comprising at least two rings with tapered or axial raceways. The bearing further comprises at least one row of rolling elements arranged between the raceways in a cage, wherein a predetermined equidistant angular spacing of the roUing elements is maintained by the cage. The rolling elements may be in particular be cylindrical or toroidal rollers. However, the invention is not limited to any particular type of rolling elements. The bearing further includes at least two sensors attached to one of the bearing rings on different predetermined angular locations respectively.

The sensors are configured to generate a signal having one signal component with a frequency of the rolling elements passing by the locations of the sensors.

It is proposed that the predetermined angular locations of the at least two sensors are chosen such that phase angles of said one signal component are different. Due to the different phase angles, the components corresponding to the roller pass frequency in the two signals cancel each other out at least partially when the signals of the sensors are summed, such that the weight of the other components in the signal, in particular the contributions of transient or sock loads, is increased correspondingly.

The invention is not limited to main shaft bearings of wind turbines but could be applied to any kind of bearing large elastic deformations on the whole assembly, called generally large size bearings or slewing bearings with a small ratio of ring width to bearing diameter, the ratio being preferably below 0.1.

Other applications might be slewing bearings for cranes, slewing bearings for pods in ship thruster.

In preferred embodiments including a number n of sensors, the phase angle of the ith sensor corresponds to i/n*3600. Expressed otherwise, the locations of the sensors are equidistantly distributed over the period length of the rollers. In this context, corre-sponds to" relates to an equivalence relation, wherein phase angles differing by integer multiples of 360°and angular differences between angular locations on the circumference of the rings differing by integer multiples of the pitch or spacing between adjacent rollers are considered equivalent. In cases where more than 2 sensors are used, it is possible to detect uneven deformations or higher multipole moments of the deformations of the ring.

In the most preferred embodiment of the invention, only two sensors are used and the predetermined angular locations are chosen so as to correspond to an uneven integer multiple of one half of the angular spacing between the rolling elements such that the components with the frequency of the rolling elements have opposing phase angles in the signals of the at least two sensors. In embodiments with three sensors, these could be arranged with phase angles of 120° between adjacent sensors and in embodiments with four sensors, these could be arranged with phase angles of 90° between each two of adjacent sensors. The sensor locations need not be homogene-ously distributed over the circumference of the bearing ring. What counts is the distribution over the period of the rollers within the equivalence relation defined above.

In a preferred embodiment of the invention, the bearing or a system including the bearing further comprises signal processing means configured to sum up signals of the at least two sensors and to detect a shock load acting on the wind turbine based on the sum signal. The summing may be done by software using digitalized signals or using an electronic circuit. In a preferred embodiment, the sensors are formed as strain gauges, wherein the sensors may be provided in a sensor package having a housing and optionally further sensors such as a vibration sensor, a temperature sensor, an acoustic emission sensor, an accelerometer or the like. The sensor package is preferably provided in a recess of one of the bearing rings so as to approach the strain sensor to the raceway of the ring.

A further aspect of the invention relates to a wind turbine including a roller bearing according to one of the preceding claims as a main shaft bearing.

The sensorized bearing as descried above lends itself to the implementation of a method for monitoring a wind turbine equipped with the bearing. The invention proposes that the method comprises the steps of summing the signals in order to obtain a signal sum; evaluating the signal sum so as to detect shock load; and storing or forwarding a signal indicating the shock load.

The above embodiments of the invention as well as the appended claims and figures show multiple characterizing features of the invention in specific combinations. The skilled person will easily be able to consider further combinations or sub-combinations of these features in order to adapt the invention as defined in the claims to his or her specific needs.

Brief Description of the Figures

Fig. 1 is a schematic representation of a bearing according to the invention; Fig. 2 is a series of graphs showing different types of load signals obtained by sensors of a main shaft bearing of a wind turbine; Fig. 3 is a series of graphs showing the signals obtained by sensors of the bearings according to Fig. 1 and of a sum thereof; and Fig. 4 illustrates a network of wind turbines equipped with bearings according to Fig. 1 and a control-and monitoring server.

Detailed Description of the Embodiments

Fig. 1 is a schematic representation of a bearing 10 according to the invention. The bearing lOis a double row roller bearing with two rings ba, lob with tapered raceways. The bearing 10 is designed for use as a main shaft bearing for wind turbines and has a very large diameter of up to 2-4m. At least one row of rolling elements 12 is arranged between the raceways of the rings lOa, lOb in a cage 14, wherein a predetermined equidistant angular spacing O2 of the rolling elements 12 is maintained and defined by the cage 14. The invention is not limited to any specific kind of bearing and the bearing 10 can have one or two rows of rollers and the rollers may be cylindrical and toroidal rollers.

Two sensors 16, 16' are attached to the outer one of the bearing rings 1 Ca on different predetermined angular locations respectively, wherein the sensors 16 16' are configured to generate a signal having one signal component with a frequency of the rolling elements 12 passing by the locations of the sensors 16,16'. The latter frequency is sometimes referred to as the roller pass frequency.

The predetermined angular locations of the at least two sensors 16, 16' are chosen such that phase angles of said one signal component are different. In other words, the angular spacing O1 of the sensors 16, 16' differs from an integer multiple of the angular spacing O2 between the angular locations of the rollers 12, which is equal to the 360° divided by the number of rollers 12.

In the cost-saving embodiment of Fig. 1, only two sensors 16, 16' are used. In this case, the predetermined angular locations are chosen so as to correspond to an uneven integer multiple of one half of the angular spacing O2between the rolling elements 12 such that the components with the frequency of the rolling elements 12 have opposing phase angles in the signals of the at least two sensors 16, 16'.

The sensors 16, 16' are formed as strain gauges and are embedded in pertinent recesses in the outer ring ba of the bearing 10 and are integrated in a sensor housing containing basic signal processing and energy harvesting means as well as a wireless or wired communication interface for communication the direct results or the pre-processed results to an outside monitoring unit 18. The monitoring unit 18 may be arranged in a nacelle of the wind turbine or in a remote server 20 (Fig. 4) for mainte-nance data. The monitoring unit 18 is a signal processing means configured to sum up signals of the at least two sensors 16, 16' and to detect a shock load acting on the wind turbine based on the sum signal as shown in further detail in Fig. 3.

The monitoring unit 18 implements a method for monitoring a wind turbine having a bearing 10 as shown in Fig. 1. The method comprises the steps of summing the signals in order to obtain a signal sum; evaluating the signal sum so as to detect shock load; storing information on the shock load in a storage unit of the monitoring unit 18 and forwarding a signal relating to the shock load to a remote maintenance data server 20 (Fig. 4) storing data used for calculating the expected remaining bearing lifetime. A shock load is detected once the sum signal exceeds a predeter-mined threshold value 0, which may depend on an average value of the signal in the last few minutes or second. In possible embodiments of the invention, the detection of a shock load may lead to an emergency stop of the windmill and to a swiveling of the windmill head. The threshold for the emergency stop can be set to a higher value than the threshold B used for identifying the shock events which are accounted for in the context of the lifetime calculation.

Fig. 2 is a series of graphs showing different types of load signals obtained by sensors 16, 16' of a main shaft bearing of a wind turbine. Periodic oscillating signal components as illustrated in the uppermost graph exist mainly due to the passing rollers at the roller pass frequency and at lower frequencies due to a mass imbalance of the rotor and due to the wings passing the tower. The load signal of the sensors further comprises stochastic components due to regular hydrodynamic and aerody-namic forces as illustrated in the graph in the middle and transient events caused a stop of the windmill or a swiveling of the windmill head as illustrated in the graph on the bottom of Fig. 2. The transient events result in a peak with a width of the order of several seconds. Shock loads can be caused e.g. by abrupt blasts of wind, forces from plunging breaking waves or seismic events have a shape of a very sharp peak and happen on even smaller timescales.

Fig. 3 is a series of graphs showing the signals obtained by sensors of the bearings according to Fig. 1 and of a sum thereof. The uppermost graph is a signal of the first sensor 16 and the second graph from the top is a signal of the second sensor 16'.

Both sensor signals contain a basic sinusoidal component of the signal caused by the passing rollers, wherein these components have opposing phases for the two components.

The lowermost graph is a sum of the two signals from the sensors 16, 16'. Due to the opposite phases, the basic roller-pass components of the signals cancel each other out such that the weight of the remaining components, in particular of a peak in the signal stemming from a shock event as illustrated on the right-hand side of the graphs in Fig. 3, increases such that the evaluation of the remaining components and the detection of transient or shock loads is facilitated. The threshold 0 is illustrated as well.

The visualization of sensor signals in Fig. 3 shows that the sensor signal of the sensor 16 and the sensor signal of sensor 16' can be summed up and wiU then partially cancel each other out. A shock load will lead to a peak in both sensor signals and in the sum signal, where it can then be reliably detected and quantified.

Fig. 4 illustrates a network of wind turbines 22 equipped with bearings 10 and monitoring units 18 according to Fig. 1 and a control-and monitoring server 20. Once the sum signal obtained by the monitoring unit in the nacelle of the wind turbine 22 based on the signals of the two sensors 16, 16' exceeds the threshold value 0, the monitoring unit 18 produces a signal indicating a shock event, which is then sent with accompanying information (wind turbine identifier, time, and strength of the shock) to the remote monitoring data server 20. For very strong shocks, the corresponding wind turbine 22 is stopped and swiveled out of the wind.

Claims

Claims 1. Roller bearing comprising at least two rings (ba, lOb) with tapered or axial raceways and at least one row of rolling elements (12) arranged between the raceways in a cage (14), wherein a predetermined equidistant angular spacing (O2) of the rolling elements (12) is maintained by the cage (14), and at least two sensors (16, 16') attached to one of the bearing rings (1 Oa, 1 Ub) on differ-ent predetermined angular locations respectively, wherein the sensors (16, 16') are configured to generate a signal having one signal component with a frequency of the rolling elements (12) passing by the locations of the sen-sors (16, 16'), characterized in that the predetermined angular locations of the at least two sensors (16, 16') are chosen such that phase angles of said one signal component are different.
2. Roller bearing according to claim 1, characterized by including a number n of sensors (16, 16'), wherein the phase angle of the ith sensor corresponds to i/n*3600.
3. Roller bearing bearing according to claim 1 or 2, characterized in that an angular spacing (O1) between the predetermined angular locations is cho- sen so as to correspond to an uneven integer multiple of one half of the angu-lar spacing (o2) between the rolhng elements (12) such that the components with the frequency of the rolling elements (12) have opposing phase angles in the signals of the at least two sensors (16, 16').
4. Roller bearing for wind turbines according one of claims 1-3, characterized by further comprising signal processing means (18) configured to sum up signals of the at least two sensors (16, 16') and to detect a shock load acting on the wind turbine based on the sum signal.
5. Roller bearing for wind turbines according to one of the preceding claims, characterized in that the sensors (16, 16') are formed as strain gauges.
6. Wind turbine including a roller bearing (10) according to one of the preceding claims as a main shaft bearing.
7. Method for monitoring a wind turbine according to claim 6, characterized by comprising the steps of: a. summing the signals in order to obtain a signal sum; b. of evaluating the signal sum so as to detect shock load; and c. storing or forwarding a signal relating to the shock load.