METHOD OF DETECTING A LEAK IN A HYDRAULIC PITCH SYSTEM

Abstract

Provided is a method of detecting a leak in a hydraulic cylinder of a rotor blade pitch system of a wind turbine including a plurality of rotor blades, which method includes the steps of selecting one of the pitch systems to undergo a functionality test; actuating a fluid pump to move the pistons of the hydraulic cylinders of the pitch systems to their outermost positions; monitoring the hydraulic cylinder pressure levels of the non-selected pitch systems while performing the functionality test on the selected pitch system; and analyzing the monitored hydraulic cylinder pressure levels of the pitch systems to detect a drop in pressure in a pitch cylinder of a non-selected pitch system. A leak detection arrangement of a pitch-controlled wind turbine; and a pitch-controlled wind turbine are also provided.

Claims

1. A method of detecting a leak in a hydraulic cylinder of a rotor blade pitch system of a wind turbine comprising a plurality of rotor blades, the method comprising: selecting a pitch system of the pitch systems to undergo a functionality test; actuating a fluid pump to move pistons of the hydraulic cylinders of the pitch systems to an outermost positions; monitoring hydraulic cylinder pressure levels of non-selected pitch systems while performing the functionality test on the pitch system; and analyzing the hydraulic cylinder pressure levels of the pitch systems to detect a drop in pressure in a pitch cylinder of a non-selected pitch system.

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

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

4. The method according to claim 1, further comprising reporting a cylinder fault when a drop in pressure is observed for the non-selected pitch system.

5. A pitch-controlled wind turbine comprising a plurality of rotor blades, wherein each rotor blade is turned by a dedicated pitch system, and wherein the dedicated pitch systems is part of a common hydraulic circuit, the pitch-controlled wind turbine comprising: a scheduler module configured to schedule a functionality test for a selected pitch system and to regulate a hydraulic circuit to move pistons of hydraulic cylinders of each pitch system; and a leak detection arrangement to identify a faulty pitch system during a functionality test, which leak detection arrangement comprises an evaluation unit configured to receive: a first input signal identifying a selected pitch system scheduled for a functionality test; a second input signal defining a duration of the functionality test; and pressure level readings of the hydraulic cylinders of each pitch system; wherein the evaluation unit is further configured to track a temporal progression of a pressure reading and to identify a fault-indicative reduction in pressure.

6. The pitch-controlled wind turbine according to claim 5, wherein a fault-indicative reduction in pressure is indicated when a pressure reading of a non-selected pitch system 4decreases to less than 5% of an initial value during the functionality test.

7. The pitch-controlled wind turbine according to claim 6, comprising an error reporting unit configured to issue an error report to a wind turbine controller, the error report identifying the non-selected pitch system for which the fault-indicative reduction in pressure was observed during the functionality test.

8. The pitch-controlled wind turbine according to claim 5, wherein the scheduler module is configured to schedule a functionality test for a pitch system, at intervals of at most 100-120 hours.

Description

DETAILED DESCRIPTION

[0041] For a pitch-control wind turbine with three rotor blades, there will be three pitch systems. FIG. 1 shows a simple overview of a hydraulic arrangement of three pitch systems SA, SB, SC of a wind turbine. Each pitch system SA, SB, SC may be assumed to comprise two parallel-connected hydraulic cylinders, as well as an arrangement of valves to regulate the direction of fluid flow. Each pitch system SA, SB, SC is fed from an accumulator M.sub.A, M.sub.B, M.sub.C, and drains into a common tank T.sub.ABC.

[0042] The accumulators M.sub.A, M.sub.B, M.sub.C and tank T.sub.ABC may be part of a closed circuit, and all relevant components may be arranged at a convenient location, for example inside the hub of the wind turbine. A scheduler module 300 of the wind turbine (or wind park controller) is used to schedule a functionality test for a selected pitch system, to regulate the hydraulic circuit (by driving the pump P.sub.ABC and by opening/closing valves of the pitch systems SA, SB, SC accordingly) and to inform an evaluation unit by telling it which pitch system is undergoing the functionality test, and when. Here, a first signal 301 identifies the pitch system scheduled for a functionality test, and a second signal 302 defines the duration of that functionality test.

[0043] The pressure level in the hydraulic cylinders of a pitch system SA, SB, SC is measured and output as a pressure reading A.sub.data, B.sub.data, C.sub.data. These pressure readings are evaluated in an analysis unit 10. From signals 301, 302, the scheduler 300 knows which pitch system is scheduled for a functionality test, and when. With this information, the pressure readings A.sub.data, B.sub.data, C.sub.data can be interpreted to detect an anomaly. 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 a pressure level of a non-selected pitch system drops during the functionality test, it can be assumed that the corresponding pitch cylinder is defective. After carrying out the functionality tests on all three pitch systems SA, SB, SC and simultaneously analysing the pressure readings A.sub.data, B.sub.data, C.sub.data, the analysis unit 10 can report a cylinder status signal A.sub.OK, B.sub.OK, C.sub.OK for each pitch system. If all three status signal A.sub.OK, B.sub.OK, C.sub.OK are “high” or “logic 1”, it may be assumed that all cylinders are functioning correctly. If one of these status signals A.sub.OK, B.sub.OK, C.sub.OK is “low” or “logic 0”, it may be assumed that the corresponding pitch cylinder is leaky. An error reporting unit 11 then outputs a report 110 identifying the defective pitch system, and also identifying the wind turbine if this is one of several wind turbines of a wind park. A controller 30 may then schedule a service procedure for that wind turbine and regulate the operating parameters of the wind turbine as necessary.

[0044] FIG. 2 shows a simplified hydraulic circuit diagram of a pitch system 2 of one of the rotor blades of a wind turbine, and can be any of the pitch systems SA, SB, SC of FIG. 1. The diagram shows a pair of hydraulic cylinders 20 in a parallel arrangement, i.e. both cylinders 20 fill simultaneously and drain simultaneously, so that their pistons move synchronously. A piston divides the interior volume of a cylinder 20 into a bottom chamber and a rod-side chamber. A system of valves V1, V2, V3, V4 can be regulated accordingly to achieve a desired piston position.

[0045] Here, each piston 200 is shown in its outermost “stop” position. To achieve this, hydraulic fluid (from the accumulator arrangement 2M on the lower left) is forced under pressure through a valve-regulated fluid line into the bottom chamber of the cylinder, so that the piston with its piston rod 200 is pushed towards the cylinder head end (towards the right in this diagram). The valves V1, V2, V3, V4 are then regulated to contain the pressurized fluid in the bottom chamber. The pressure is monitored by a pressure transducer 22 in the fluid line and reported as a pressure level reading 2.sub.data (i.e. any of A.sub.data, B.sub.data, C.sub.data). If a hydraulic cylinder 20 is healthy, the reported pressure reading 2.sub.data will remain essentially constant at its maximum level until the valves V1, V2, V3, V4 are regulated to allow the fluid to drain from the bottom chamber again.

[0046] 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, resulting in a drop in pressure which is registered by the manometer 22.

[0047] Embodiments of the invention are based on the insight that a cylinder leak in one pitch system can be detected as a “bonus” during a routine functionality test being performed on another pitch system. During a functionality test on a selected pitch system, its pistons must be pushed to their “stop” positions. Therefore, the pistons of the other two pitch systems will also be pushed to their “stop” positions. Embodiments of the invention make use of this fact and, instead of only evaluating the pressure reading from the pitch system that is undergoing the functionality test, pressure readings from the other two pitch systems are also recorded and evaluated. In the prior art, only the pressure reading from the pitch system currently undergoing a functionality test is collected and evaluated, and the pressure readings from the other two pitch systems not considered to be of any interest and are ignored.

[0048] An exemplary sequence of functionality tests is illustrated in FIG. 3, which shows three pressure curves A.sub.data, B.sub.data, C.sub.data for the three pitch systems SA, SB, SC of FIG. 1, respectively. A scheduled functionality test is being performed on pitch system SA from time t.sub.1 to time t.sub.2, so that this pitch system SA is also referred to as the “selected pitch system”. The other two pitch systems SB, SC are each referred to as a “non-selected pitch system”. The functionality test requires that the pistons of the selected pitch system SA are pushed to their outermost “stop” position. Because the pitch systems SA, SB, SC are controlled by a common hydraulic circuit, the pistons of the non-selected pitch systems SB, SC are therefore also pushed to their outermost “stop” position. Ideally, the pressure in the non-selected pitch systems SB, SC would remain at a high level for the duration FT of the functionality test on the selected pitch system SA.

[0049] The cylinder pressure of the selected pitch system SA drops as expected towards a low level P.sub.lo during the functionality test. The diagram illustrates the effect of a damaged seal or other fault in a pitch cylinder of one of the non-selected pitch systems, in this case pitch system SB. Instead of remaining as expected at the high level P.sub.hi during the functionality test on pitch system SA, the pressure drops towards the low level P.sub.lo, and this unexpected pressure drop can be interpreted as a sign that a pitch cylinder of this pitch system SB is “leaky”.

[0050] The scheduled functionality test for the next pitch system, in this case pitch system SB, is performed from time t.sub.3 to time t.sub.4, so that pitch system SB is now the “selected pitch system” and pitch systems SA, SC are the “non-selected pitch systems”. The cylinder pressure drops as expected during the functionality test on pitch system SB, while the cylinder pressures of pitch systems SA, SC appear healthy. This shows that a leaky cylinder in a pitch system cannot be detected during a functionality test of that pitch system. \

[0051] The scheduled functionality test for the third pitch system, in this case pitch system SC, is performed from time t.sub.5 to time t.sub.6, 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 remaining at its maximum level P.sub.hi during the functionality test on pitch system SC, the pressure reading from pitch system SB drops towards the low level P.sub.lo, giving further confirmation that it has leaky pitch cylinder.

[0052] A leak may be assumed if the pressure drops by more than 5% of the maximum value P.sub.hi, i.e. the low pressure level P.sub.lo is less than 5% of the expected pressure level P.sub.hi. For example, for an upper pressure level P.sub.hi of 170 bar, it may be assumed that there is a leak in pitch system B if, during a pitch capacity check on pitch system A, the pressure in pitch system B drops below 160 bar while the pressure in pitch system C stays above 170 bar.

[0053] The pressure level in the hydraulic cylinders of a pitch system SA, SB, SC is measured and output as a pressure reading A.sub.data, B.sub.data, C.sub.data. This can be recorded and evaluated by modules of a suitable control arrangement. This might occur locally, for example in a local wind turbine controller. Alternatively, for the wind turbines of a wind park, such data A.sub.data, B.sub.data, C.sub.data may be collected and transmitted to a remote park controller for evaluation.

[0054] FIG. 4 shows a wind park 3 implementing an embodiment of the inventive leak detection arrangement. The wind park can have any number of wind turbines WT1, WT2, . . . , WTn that are regulated by a park controller 30. The scheduler 300 is implemented at the park controller 30, and schedules functionality tests for the pitch systems of the wind turbines WT1, WT2, . . . , WTn. Relevant information 301, 302 (along with any other relevant commands) is passed to the appropriate wind turbines WT1, WT2, . . . , WTn. During the functionality tests, the wind turbines WT1, WT2, . . . , WTn return pressure readings A.sub.data, B.sub.data, C.sub.data. An evaluation unit 10 analyses these, and an error module can flag any suspected leaky cylinder so that a maintenance procedure can be planned in good time, avoiding the development of a more severe fault.

[0055] 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.

[0056] 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.