Method for detecting leaks in hydraulic pitch systems

Abstract

The invention describes a method for detecting leakage in a hydraulic cylinder (20) of a rotor blade pitch system (2, SA, SB, SC) of a wind turbine (WT1, WT2, ... WTn), the wind turbine comprising a plurality of rotor blades, the method comprising the following steps: selecting one of the pitch systems (SA, SB, SC) to be subjected to a functional test; actuating a fluid pump (P ABC ) to move the pistons (200) of the hydraulic cylinders (20) of the pitch systems (SA, SB, SC) to their outermost positions; while performing a functional test on the selected pitch system (SA), monitoring the pressure levels (A) of the hydraulic cylinders of the unselected pitch systems (SB, SC) data , B data , C data ); and analysis of the monitored hydraulic cylinder pressure levels (A data , B data , C data ) to detect a pressure drop in a pitch cylinder (20) of an unselected pitch system (SB). The invention further describes a leakage detection arrangement (1) of a pitch-controlled wind turbine (WT1, WT2, ... WTn); and a pitch-controlled wind turbine (WT1, WT2, ... WTn).

Description

[0001] The invention describes a method of detecting leaks in a hydraulic cylinder of a pitch system of a wind turbine rotor blade and a leak detection arrangement for a pitch-controlled wind turbine.

[0002] The rotor blades of a wind turbine are usually mounted to the hub by means of a hydraulic pitch system so that the rotor blades can be pitched about their longitudinal axis. In this way, the rotor blades can be pitched into the wind to extract as much energy as possible from the wind. Likewise, the rotor blades can be pitched away from the wind to avoid excessive loads during severe wind conditions.

[0003] If a pitch system develops a serious fault, preventing the rotor blades from being pitched correctly, it may be necessary to shut down the wind turbine. Such a serious fault may be the result of an undetected minor fault, such as a gradual deterioration of a seal in a pitch cylinder. Downtime may extend to hours or even days, for example when a maintenance procedure has to be scheduled for an offshore wind turbine. Downtime is expensive and may have an adverse effect on the annual energy production (AEP) of the wind turbine. Therefore, it is important to be able to identify the presence of a fault and to locate it.

[0004] However, in complex hydraulic circuits such as rotor blade pitch systems, it may be difficult to identify faults and their locations. In some cases, unexpected behavior in the hydraulic circuit may be detected and reported to the wind turbine controller as an alarm. Hydraulic-related alarms may indicate problems with the hydraulic pump of the pitch system, unexpected changes in pressure, etc. Such alarms are very general and often fail to clearly identify the actual root cause. For example, there may be several reasons for an unexpected change in pressure in a hydraulic circuit. For these reasons, a leak in a pitch cylinder may not be detected until it develops into a serious fault that can be easily detected but will result in the wind turbine having to be shut down.

[0005] One way to identify a leak in a pitch cylinder might be to schedule a regular inspection process for the wind turbine. This inspection would involve the following steps: manually closing the valve around the pitch cylinder, applying pressure to the hydraulic cylinder through a pressure nipple, and monitoring the pressure difference across the cylinder. A drop in pressure would indicate a leak in the cylinder. To perform this inspection, two technicians and several hours (of which three hours is typical) would typically be required for each pitch system. Obviously, in the case of a wind park with dozens or even hundreds of wind turbines, the cost of such a regular inspection process would be prohibitively high.

[0006] In an alternative approach, it is possible to narrow down the number of possible fault candidates in the pitch system by analyzing an alarm stack of hydraulic-related alarms recorded over time by the turbine controller. Incoming alarms are typically recorded along with the time, alarm type, and sender (e.g., hydraulic system) so that the pattern of alarms in the alarm stack can give some clues as to the source of the fault. However, because there may be several faults in the hydraulic system at any one time, and because alarms may be issued for reasons that are not directly related to the actual fault, it may be difficult to draw informative conclusions from the analysis of the hydraulic alarm stack.

[0007] It is therefore an object of the present invention to provide an economical and accurate way of detecting leaks in a pitch cylinder of a rotor blade pitch system.

[0008] This object is achieved by the subject matter of the present invention.

[0009] According to the present invention, a method for detecting leakage in a hydraulic cylinder of a rotor blade pitch system comprises the following steps: selecting a pitch system to undergo a functional test; actuating a fluid pump of a hydraulic circuit to move the pitch cylinder pistons of the selected pitch system to their outermost or "parked" positions, and thereby also moving the pitch cylinder pistons of unselected pitch systems to their outermost or "parked" positions; monitoring the hydraulic cylinder pressure levels of the selected pitch system and the unselected pitch systems while performing the functional test on the selected pitch system; and analyzing the monitored hydraulic cylinder pressure levels to detect a pressure drop in the pitch cylinder of the unselected pitch system.

[0010] In the context of the present invention, it is assumed that the wind turbine is a pitch-controlled wind turbine with a plurality of rotor blades, typically three. Each rotor blade has a pitch system, so that the number of pitch systems is the same as the number of rotor blades. The pitch angles of the rotor blades are usually adjusted simultaneously in order to avoid uneven load effects. Therefore, in the following, it can be assumed that the wind turbine implements the pitch system in a hydraulic circuit with a common pump and tank, as well as an accumulator for each pitch system. It can be assumed that the pitch systems are implemented identically with the same valve configuration, fluid line diameters, etc.

[0011] The step of actuating the hydraulic circuit to move the pistons of the pitch system to their "parked" position may be understood to include actuating the pump to force pressurized fluid into the end chamber of the cylinder until the piston is completely out, and then adjusting the relevant valves to maintain this state. In the context of this document, the terms "hydraulic cylinder" and "cylinder" may be used interchangeably and should be understood to have the same meaning.

[0012] An advantage of the method of the invention is that a defective cylinder can be identified quickly, since a pressure drop observed in an unselected pitch system will indicate the presence of a leak in the hydraulic cylinder of that pitch system. In this way, it is possible to quickly identify such a defect, so that a maintenance procedure can be scheduled in a timely manner, thereby avoiding unnecessary downtime.

[0013] The present invention is based on the insight that, during a customary functional test performed on another pitch system, an erroneous pitch may be detected as a "bonus effect". The inventors have realized that when a functional test is initiated for a selected pitch system, the pistons of all pitch systems will be pushed to their "stop" positions. Instead of evaluating only the pressure readings from the pitch system that is undergoing the functional test, the inventors have realized that the pressure readings from the other two pitch systems may reveal valuable information about the health of their pitch cylinders. In the prior art, only the pressure readings from the pitch system that is currently undergoing the functional test are collected and evaluated, while the pressure readings from the other two pitch systems are considered to be of no interest.

[0014] According to the present invention, a leakage detection arrangement for a pitch-controlled wind turbine comprises: an evaluation unit configured to receive at least a first input signal identifying a selected pitch system scheduled for a functional test and a second input signal defining the duration of the functional test. The evaluation unit is further configured to receive pressure readings from the pitch system and to track the time course of the pressure readings. By monitoring the pressure readings in this way, the evaluation unit can identify a fault-indicative pressure reduction.

[0015] The pressure reading from the pitch system can be understood as a signal reporting the instantaneous pressure in the end chamber of the pitch cylinder(s) of the pitch system. The pressure reading can be an analog or digital signal and can be reported continuously or at regular intervals, depending on the equipment used to measure the pitch cylinder pressure.

[0016] According to the present invention, a pitch-controlled wind turbine of the above-mentioned type comprises: a scheduler module, which is configured to schedule functional tests for selected pitch systems and adjust the hydraulic circuits to move the pistons of all pitch systems to their outermost positions; and an embodiment of the leakage detection arrangement of the present invention, for identifying faulty pitch systems during functional tests.

[0017] It will be appreciated that the wind turbine may be one of many wind turbines in a wind park, and that the wind turbines may all be controlled by a common wind park controller. The leakage detection arrangement may be implemented partially or completely in the wind park controller, for example by transmitting pressure readings of the pitch system of each wind turbine to the wind park controller over a suitable communication interface. These may be evaluated in real time, or stored in a memory for evaluation at a later date. The wind park controller may comprise several instances of the evaluation unit, so that it can evaluate pressure readings from several wind turbines simultaneously.

[0018] The evaluation unit of the leakage detection arrangement can be fully or partially implemented as a software module running on a processor of the wind turbine control unit. A mostly software module implementation can have the advantage that applications already installed on existing systems can be updated with relatively little effort to perform the steps of the inventive method.

[0019] In the following, the expression "functional test" may be understood to mean a test routine performed on the pitch system and may include measures for testing one or more aspects of the pitch system, for example a functional test may monitor the capacity of an accumulator of the pitch system, etc. In the context of the present invention, the expression "functional test" should be understood as a test routine that returns data on the functionality of the pitch system, i.e. an assessment of its ability to perform its function.

[0020] Preferably, the scheduler module is configured to schedule functional tests for the pitch system at regular intervals (e.g., at 120 hour intervals). Functional tests are performed sequentially for the pitch system. During functional tests, the pitch system is subjected to various checks. An exemplary test sequence may include the following: activating the pitch mechanism or actuating the pitch mechanism (and other hydraulic components); checking the functionality of the aerodynamic and mechanical brake systems; calibrating the proportional valve; checking the pitch pressure sensor and pitch pressure valve; checking the hydraulic valve. The functional test may take several minutes to complete.

[0021] In a preferred embodiment of the invention, the cylinder pressure level is reported by a pressure sensor of the corresponding pitch system. For example, the pitch system may have a manometer, a pressure transducer, etc., which are arranged to measure the pressure in a fluid intake line to the pitch system. Preferably, the pressure sensor is implemented to provide the measured pressure as a digital signal.

[0022] A suitable evaluation unit can receive the pressure readings and process them to detect any anomalies. Normally, the pressure in the hydraulic cylinder is at its maximum value when the hydraulic cylinder is in its outermost "rest" position. In a "healthy" cylinder, this pressure will be maintained until the appropriate valves are opened to release the pressure, allowing the fluid to drain towards the tank. In a "leaky" cylinder (e.g. a cylinder with a defective seal), the pressure will drop even if those valves remain closed, since pressurized fluid can pass from the end chamber to the piston rod chamber.

[0023] To illustrate the inventive technique when applied to three pitch systems labeled "SA," "SB," and "SC," a method of detecting a leaking pitch cylinder, for example in pitch system SB, may be formulated as a logical statement:

[0024] If, during lubrication of the pitch system SA:

[0025] The pressure of the pitch cylinder of the pitch system SB drops

[0026] and

[0027] The pitch cylinder pressure of the pitch system SC is kept high

[0028] Then a leaking cylinder is indicated in the pitch system SB.

[0029] A method of verifying a leaky pitch cylinder in a pitch system SB may be formulated as follows:

[0030] If, during lubrication of the pitch system SA:

[0031] The pressure of the pitch cylinder of the pitch system SB drops

[0032] and

[0033] The pitch cylinder pressure of the pitch system SC is kept high

[0034] And if, during lubrication of the pitch system SC:

[0035] The pressure of the pitch cylinder of the pitch system SB drops

[0036] and

[0037] The pitch cylinder pressure of the pitch system SA is kept high

[0038] So

[0039] Confirm that there is a leaking cylinder in the pitch system SB.

[0040] In a preferred embodiment of the invention, the method comprises the step of reporting the occurrence of a fault-indicative pressure reduction for a non-selected pitch system. The fault may be reported to a control unit, which may then respond by notifying service personnel and / or by scheduling a service routine for the pitch system of the wind turbine.

[0041] Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed only for the purpose of illustration and not as a definition of the limits of the present invention.

[0042] Figure 1 The hydraulic arrangement of the three pitch systems of a wind turbine is shown;

[0043] Figure 2 Shows Figure 1 Hydraulic circuit diagram of the pitch system;

[0044] Figure 3 Shows Figure 1 A graph of the cylinder pressure of the pitch system;

[0045] Figure 4 A wind farm implementing an embodiment of the leakage detection arrangement of the present invention is shown.

[0046] In the drawings, like numbers refer to like objects throughout. Objects in the drawings are not necessarily drawn to scale.

[0047] For a pitch controlled wind turbine with three rotor blades, there will be three pitch systems. Figure 1 A simple overview of the hydraulic arrangement of three pitch systems SA, SB, SC of a wind turbine is shown. It can be assumed that each pitch system SA, SB, SC comprises two hydraulic cylinders connected in parallel, and an arrangement of valves for adjusting the direction of fluid flow. Each pitch system SA, SB, SC draws power from an accumulator M. A 、M B 、M C is fed and discharged to a common tank T ABC middle.

[0048] Accumulator M A 、M B 、M C And tank T ABC It can be part of a closed loop and all relevant components can be arranged at a convenient location, such as inside the hub of the wind turbine. Using the scheduler module 300 of the wind turbine (or wind farm controller) to schedule a functional test for the selected pitch system, adjust the hydraulic circuit (by driving the pump P ABC and by opening / closing the valves of the pitch systems SA, SB, SC accordingly), and notifying the evaluation unit by telling it which pitch system is undergoing a functional test and when. Here, a first signal 301 identifies the pitch system scheduled for a functional test, and a second signal 302 defines the duration of the functional test.

[0049] The pressure level in the hydraulic cylinders of the pitch systems SA, SB, SC is measured and given as pressure reading A data , B data , C data These pressure readings are evaluated in the analysis unit 10. Based on the signals 301, 302, the scheduler 300 knows which pitch system is scheduled for the functional test and when it is scheduled for the functional test. With this information, the pressure readings A can be interpreted. data , B data , C data to detect anomalies. If the pressure levels of the two non-test pitch systems remain high, it can be assumed that the corresponding pitch cylinders are fully functional. If the pressure levels of the non-selected pitch systems drop during the functional test, it can be assumed that the corresponding pitch cylinders are defective. After performing the functional test on all three pitch systems SA, SB, SC and analyzing the pressure readings A simultaneouslydata , B data , C data Afterwards, the analysis unit 10 can report the cylinder status signal A of each pitch system OK , B OK , C OK If all three status signals A OK , B OK , C OK is "high" or "logic 1", it can be assumed that all cylinders are functioning normally. OK , B OK , C OK is "low" or "logic 0", it can be assumed that the corresponding pitch cylinder is leaking. The error reporting unit 11 then outputs a report 110, which identifies the defective pitch system and, if the wind turbine is one of several wind turbines in a wind park, also identifies the wind turbine. The controller 30 can then schedule a service procedure for the wind turbine and, if necessary, adjust the operating parameters of the wind turbine.

[0050] Figure 2 A simplified hydraulic circuit diagram of a pitch system 2 of one of the rotor blades of a wind turbine is shown and may be Figure 1 Any of the pitch systems SA, SB, SC. ​​The figure shows a pair of hydraulic cylinders 20 in a parallel arrangement, i.e., the two hydraulic cylinders 20 are filled (filled) and discharged simultaneously, so that their pistons move synchronously. The piston divides the internal volume of the cylinder 20 into a bottom chamber and a rod side chamber. The system of valves V1, V2, V3, V4 can be adjusted accordingly to achieve the desired piston position.

[0051] Here, each piston 200 is shown in its outermost "stop" position. To achieve this, hydraulic fluid is forced under pressure (from the accumulator arrangement 2M on the lower left) through a valve-regulated fluid line into the bottom chamber of the cylinder, so that the piston 200 with its piston rod is pushed towards the end of the cylinder head (pushed to the right in this figure). The valves V1, V2, V3, V4 are then adjusted to contain the pressurized fluid in the bottom chamber. The pressure is monitored by a pressure transducer 22 in the fluid line and is reported as a pressure level reading 2 data (i.e., A data , B data , C data If the hydraulic cylinder 20 is healthy, the reported pressure reading 2 data It will remain substantially constant at its maximum level until valves V1 , V2 , V3 , V4 are adjusted again to allow fluid to drain from the bottom chamber.

[0052] However, if the seal between the bottom chamber and the rod end chamber is damaged and no longer fully functional, fluid will pass from the bottom chamber to the rod end chamber, causing a pressure drop that is registered by the pressure gauge 22 .

[0053] The present invention is based on the insight that a cylinder leak in one pitch system might be detected as a "surprise" during a customary functional test performed on another pitch system. During the functional test of the selected pitch system, its pistons have to be pushed to their "rest" positions. Therefore, the pistons of the other two pitch systems will also be pushed to their "rest" positions. The present invention exploits this fact and, instead of evaluating only the pressure readings from the pitch system that is undergoing the functional test, also the pressure readings from the other two pitch systems are recorded and evaluated. In the prior art, only the pressure readings from the pitch system that is currently undergoing the functional test are collected and evaluated, while the pressure readings from the other two pitch systems are considered to be of no interest and are ignored.

[0054] Figure 3 An exemplary sequence of functional tests is illustrated in FIG. Figure 1 Three pressure curves A of the three pitch systems SA, SB, and SC data , B data and C data . From time t1 to time t2, the scheduled functional test is performed on the pitch system SA, so that the pitch system SA is also referred to as the "selected pitch system". The other two pitch systems SB, SC are referred to as "unselected pitch systems". The functional test requires that the pistons of the selected pitch system SA are pushed to their outermost "stop" positions. Because the pitch systems SA, SB, SC are controlled by a common hydraulic circuit, the pistons of the unselected pitch systems SB, SC are also pushed to their outermost "stop" positions. Ideally, the pressure in the unselected pitch systems SB, SC will remain at a high level during the duration FT of the functional test of the selected pitch system SA.

[0055] During the functional test, the cylinder pressure of the selected pitch system SA moves towards the low level P as expected. lo The figure illustrates the effect of a damaged seal or other fault in the pitch cylinder of one of the unselected pitch systems (in this case pitch system SB). Instead of maintaining a high level P as expected during the functional test of pitch system SA hi At this point, the pressure moves towards the lower level P lo drops, and this unexpected pressure drop can be interpreted as a sign of a “leak” in the pitch cylinder of the pitch system SB.

[0056] From time t3 to time t4, the scheduled functional test for the next pitch system (in this case pitch system SB) is performed, so that pitch system SB is now the "selected pitch system" and pitch systems SA, SC are the "unselected pitch systems". During the functional test of pitch system SB, the cylinder pressure drops as expected, while the cylinder pressures of pitch systems SA, SC appear healthy. This shows that during the functional test of a pitch system, a leaking cylinder in that pitch system could not be detected.

[0057] From time t5 to time t6, the scheduled functional test for the third pitch system (in this case pitch system SC) is performed, so that pitch system SC is now the "selected pitch system" and pitch systems SA, SB are the "non-selected pitch systems". Again, instead of maintaining the maximum level P during the functional test of pitch system SC, hi At , the pressure reading from the pitch system SB moves towards the low level P lo dropped, giving further confirmation that it had a leaking pitch cylinder.

[0058] If the pressure drops beyond the maximum value P hi 5%, i.e. low stress level P lo Than expected pressure level P hi If the pressure level is less than 5%, a leak can be assumed. For example, for an upper pressure level P of 170 bar hi If, during a pitch capability check of pitch system A, the pressure in pitch system B drops below 160 bar, while the pressure in pitch system C remains above 170 bar, it can be assumed that there is a leak in pitch system B.

[0059] The pressure level in the hydraulic cylinders of the pitch systems SA, SB, SC is measured and given as pressure reading A data , B data , C data This can be recorded and evaluated by a module of a suitable control arrangement. This may take place locally, for example in a local wind turbine controller. Alternatively, such data A may be collected for each wind turbine in a wind park. data , B data , C data , and transmit it to the remote wind farm controller for evaluation.

[0060] Figure 4A wind farm 3 implementing an embodiment of the leakage detection arrangement of the present invention is shown. The wind farm may have any number of wind turbines WT1, WT2 ... WTn, which are regulated by a wind farm controller 30. A scheduler 300 is implemented at the wind farm controller 30 and schedules a functional test for the pitch systems of the wind turbines WT1, WT2 ... WTn. The relevant information 301, 302 (together with any other relevant commands) is passed to the appropriate wind turbines WT1, WT2 ... WTn. During the functional test, the wind turbines WT1, WT2 ... WTn return a pressure reading A data , B data , C data The evaluation unit 10 analyses these readings and the error module can flag any suspected leaking cylinders so that maintenance procedures can be planned in good time, thus avoiding the development of more serious faults.

[0061] Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

[0062] For the sake of clarity, it is to be understood that the use of "a" or "an" throughout this application does not exclude a plurality, and "comprising" does not exclude other steps or elements. References to a "unit" or "module" do not exclude the use of more than one unit or module.

Claims

1. A method for detecting leakage in a hydraulic cylinder of a rotor blade pitch system of a wind turbine, the wind turbine comprising a plurality of rotor blades, the method comprising the following steps: - Select one of the pitch systems to undergo a functional test; - actuating the fluid pump to move the pistons of the hydraulic cylinders of the pitch system to their outermost positions; - monitoring the hydraulic cylinder pressure levels of the selected pitch system and the unselected pitch systems while performing a functional test on the selected pitch system; and - Analyzing the monitored hydraulic cylinder pressure levels to detect pressure drops in the hydraulic cylinders of unselected pitch systems.

2. The method of claim 1, wherein the hydraulic cylinder pressure level is reported by a pressure sensor of the corresponding pitch system.

3. The method according to claim 1 or 2, wherein the pressure sensor is arranged in a fluid supply line connecting a source of pressurized fluid to a hydraulic cylinder of the pitch system.

4. The method according to claim 1 or 2, The steps include: reporting a hydraulic cylinder fault when a pressure drop is observed for an unselected pitch system.

5. A pitch-controlled wind turbine comprising a plurality of rotor blades, wherein each rotor blade is rotated by a dedicated pitch system, and wherein the dedicated pitch system is part of a common hydraulic circuit, and wherein the pitch-controlled wind turbine comprises: - a scheduler module configured to schedule a functional test for the selected pitch systems and to regulate the hydraulic circuit to move the piston of the hydraulic cylinder of each pitch system; as well as - a leakage detection arrangement for identifying a faulty pitch system during a functional test, the leakage detection arrangement comprising an evaluation unit configured to receive: - a first input signal identifying a selected pitch system scheduled for functionality testing; - a second input signal defining the duration of said functional test; as well as - pressure level readings for each pitch system hydraulic cylinder; And wherein the evaluation unit is further configured to track a time progression of said pressure level readings to identify a fault-indicative pressure reduction in a hydraulic cylinder of a non-selected pitch system.

6. A pitch-controlled wind turbine according to claim 5, wherein a fault-indicative pressure reduction is indicated when a pressure level reading of a hydraulic cylinder of a non-selected pitch system decreases to less than 5% of its initial value during the functional test.

7. A pitch-controlled wind turbine according to claim 5 or 6, comprising an error reporting unit, which is configured to issue an error report to the wind turbine controller, the error report identifying the following unselected pitch systems: for which a fault-indicative pressure reduction was observed during the functional test.

8. A pitch controlled wind turbine according to claim 5 or 6, wherein the scheduler module is configured to schedule functional tests for the pitch system at intervals of 100-120 hours.

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