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Title:
METHOD AND ARRANGEMENT TO DETECT AN OIL LEAKAGE BETWEEN SECTIONS OF A HYDRAULIC CYLINDER
Document Type and Number:
WIPO Patent Application WO/2018/153524
Kind Code:
A1
Abstract:
The invention refers to an arrangement and to a method to detect an oil leakage (LKG) between a first section (S1) of a hydraulic cylinder (HC) and a second section (S2) of the hydraulic cylinder (HC). A movable piston (MP) is arranged between the first section (S1) and the second section (S2) in a way that the piston (MP) changes its position (POS) between the sections (S1, S2). The change of the position is done in dependency of a difference between a first force (F1), which acts at the first section (S1) on a first cross sectional area (A1) of the movable piston (MP), and a second force (F2), which acts at the second section (S2) on a second cross sectional area (A2) of the movable piston (MP). The first section (S1) comprises hydraulic oil (HO) with a predefined first pressure (P1), while the first force (F1) is calculated based on this pressure (P1) and based on the first area (A1). The second section (S2) comprises hydraulic oil (HO) with a predefined second pressure (P2), while the second force (F2) is calculated based on this pressure (P2) and based on the second area (A2). The first section (S1) is connected with a remote controlled first valve (V1), which is closed for the leakage detection. A sensor (SEN) is coupled with the movable piston (MP) in a way that any change in its position (POS) is detected, while the change of the position results from the difference of forces (F1, F2) resulting from the closed valve (V1) and from the alignment of the first pressure (P1) to the second pressure (P2) due to the leakage (LKG). The sensor (SEN) is coupled with a control (CONT), which is prepared and arranged to detect the leakage of oil based on the change of the position (POS).

Inventors:
NIELSEN, Lars Holm (Rørbækvej 28, 8766 Nørre Snede, 8766, DK)
Application Number:
EP2017/080462
Publication Date:
August 30, 2018
Filing Date:
November 27, 2017
Export Citation:
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Assignee:
SIEMENS WIND POWER A/S (Borupvej 16, 7330 Brande, 7330, DK)
International Classes:
F15B20/00; F03D7/02; F03D17/00; F15B19/00
Domestic Patent References:
WO2013003150A12013-01-03
Foreign References:
EP1812718B12008-08-20
EP2270342A12011-01-05
Other References:
None
Attorney, Agent or Firm:
ASPACHER, Karl-Georg (Postfach 22 16 34, München, 80506, DE)
Download PDF:
Claims:
Arrangement to detect an oil leakage (LKG) between a first section (SI) of a hydraulic cylinder (HC) and a second section (S2) of the hydraulic cylinder (HC) ,

- wherein a movable piston (MP) is arranged between the first section (SI) and the second section (S2) in a way that the piston (MP) changes its position (POS) between the sections (SI, S2) in dependency of a difference be¬ tween a first force (Fl), which acts at the first sec¬ tion (SI) on a first cross sectional area (Al) of the movable piston (MP), and a second force (F2), which acts at the second section (S2) on a second cross sectional area (A2) of the movable piston (MP),

- wherein the first section (SI) comprises hydraulic oil (HO) with a predefined first pressure (PI), while the first force (Fl) is calculated based on this pressure (PI) and based on the first area (Al),

- wherein the second section (S2) comprises hydraulic oil (HO) with a predefined second pressure (P2), while the second force (F2) is calculated based on the this pres¬ sure (P2) and based on the second area (A2),

- wherein the first section (SI) is connected with a re¬ mote controlled first valve (VI), which is closed for the leakage detection,

- wherein a sensor (SEN) is coupled with the movable pis¬ ton (MP) in a way that any change in its position (POS) is detected, while the change of the position results from the difference of forces (Fl, F2) resulting from the closed valve (VI) and from the alignment of the first pressure (PI) to the second pressure (P2) due to the leakage (LKG) , and

- wherein the sensor (SEN) is coupled with a control

(CONT) , which is prepared and arranged to detect the leakage of oil based on the change of the position

(POS) . Arrangement according to claim 1, wherein the first valve (VI) is connected with the control (CONT) via a first con¬ trol signal (CS1), thus hydraulic oil (HO) is provided in and out of the first section (SI) in a remote controlled manner .

Arrangement according to claim 1, wherein the second valve (V2) is connected with the control (CONT) via a second control signal (CS2), thus hydraulic oil (HO) is provided in and out of the second section (S2) in a remote con¬ trolled manner.

Arrangement according to claim 1, wherein the movable pis¬ ton (MP) interacts via its position (POS) with a blade of a wind turbine, turning the blade to specific pitch an¬ gles .

Arrangement according to claim 4, wherein the pitch angel is chosen between values, which are most relevant for wear and tear of the blade, preferably the pitch angel is cho¬ sen between 0° and 15° for detecting a leakage of oil.

Arrangement according to claim 4 or 5, wherein the hydrau¬ lic cylinder is part of a hydraulic pitch drive system of a wind turbine.

Arrangement according to claim 6, wherein the control unit is the control unit of the wind turbine, providing the control signals and performing the oil leakage detection automatically . Method to detect an oil leakage (LKG) between a first sec¬ tion (SI) of a hydraulic cylinder (HC) and a second sec¬ tion (S2) of the hydraulic cylinder (HC) ,

- wherein a movable piston (MP) , which is arranged between the first section (SI) and the second section (S2), changes its position (POS) between the sections (SI, S2) in dependency of a difference between a first force (Fl), which acts at the first section (SI) on a first cross sectional area (Al) of the movable piston (MP), and a second force (F2), which acts at the second sec¬ tion (S2) on a second cross sectional area (A2) of the movable piston (MP) ,

- wherein the first force (Fl) is calculated based on a first pressure (PI), which is defined by hydraulic oil (HO) at the first section (SI), and based on the first area (Al ) ,

- wherein the second force (F2) is calculated based on a second pressure (PI), which is defined by hydraulic oil (HO) at the second section (S2), and based on the second area (Al ) ,

- wherein a first valve (VI), which is connected with the first section (SI), is closed remote controlled for the leakage detection,

- wherein the movable piston (MP) changes its position

(POS) between the first section (SI) and the second sec¬ tion (S2) due to the difference of forces (Fl, F2) re¬ sulting from the closed valve (VI) and from the alignment of the first pressure (PI) to the second pressure (P2) due to the leakage (LKG),

- wherein the change of the position (POS) is detected by a sensor, which is coupled with the movable piston (MP) ,

- wherein a control (CONT) , which is coupled with the sensor (SEN) detects the leakage of oil based on the change of the position (POS) .

Description:
Description

Method and arrangement to detect an oil leakage between sec ¬ tions of a hydraulic cylinder

The invention refers to an arrangement and to a method to de ¬ tect an oil leakage between a first section of a hydraulic cylinder and a second section of the hydraulic cylinder. The hydraulic cylinder is preferably used in a hydraulic pitch drive system of a wind turbine.

Modern wind turbines are showing a number of three rotor blades preferably, which are rotating around a horizontal ax ¬ is of rotation. The rotor blades are connected with an elec- trical generator to convert wind energy into electrical ener ¬ gy.

Each rotor blade can be aligned into the incoming wind by typically two hydraulic cylinders, being part of a hydraulic pitch drive system.

Hydraulic oil is applied by pressure to each hydraulic cylin ¬ der. The hydraulic cylinder comprises a first section and a second section, while a movable piston is arranged between the first section and the second section.

Hydraulic oil is applied to these sections, creating forces, which are acting on the respective area of the piston. In ex ¬ ample: A first force Fl is created at the first section ac- cording to this formula: Fl = PI * Al while PI is the pres ¬ sure at the first section and while Al is the respective cross sectional area of the movable piston, which is exposed to the pressure PI. A second force F2 is created at the second section according to this formula: F2 = P2 * A2 while P2 is the pressure at the second section and while A2 is the respective cross sectional area of the movable piston, which is exposed to pressure P2. Based on the difference of the forces Fl and F2 the movable piston changes its relative position - it might be moved to ¬ wards the second section for example if the situation is like this:

Fl > F2

PI * Al > P2 * A2

With A2 = Al - Arod and with Arod as those cross sectional area of a rod being part of the movable piston and reducing the respective area A2 the formula results in:

PI * Al > P2 * Al - P2 * Arod. Thus the movable piston will be pushed towards the second section if PI > P2.

Based on the respective formula Fl < F2

PI * Al < P2 * Al - P2 * Arod the movable piston might be pushed towards the first section by choosing respective values for PI and P2, taking into ac- count the known cross-sectional areas Al and Arod.

The hydraulic cylinder always comprises a high pressure sec ¬ tion and a low pressure section and a respective high pres ¬ sure side and low pressure side.

The movable piston interacts via its position change and via a root end bearing with the blade. The root end bearing is a functional part of the blade and is used to set a specific pitch angle of the blade.

In detail the rod of the movable piston is coupled with or is acting on the root end bearing. A service report revealed that most hydraulic cylinders will fail between operation year 7 and operation year 11 according to a Weibull distribution. The failure results from a leakage of hydraulic oil.

Hydraulic oil might leak externally, leaving the hydraulic cylinder and the hydraulic system itself.

H

ydraulic oil even might leak inside the hydraulic cylinder, which is known as internal leakage: i.e. if there is a leak ¬ age at the movable piston hydraulic oil might be transferred between the first and the second section in an uncontrolled manner . The internal leakage often evolves over time and results in an increased pumping and circulation of oil in the hydraulic system, which might comprises the cylinder, an oil-reservoir, oil supply connections, a pump, valves, etc. An internal leakage cannot be detected easily as the hydrau ¬ lic oil stays inside the hydraulic system and cannot be de ¬ tected by checking the level of the hydraulic oil in the oil- reservoir for example. The hydraulic system tries to compensate external oil losses by using oil, which is stored in the oil reservoir. Thus a loss of hydraulic oil can be detected easily by service per ¬ sonal, checking the oil level therein. The effects of oil leakages will increase over time and will finally result in an operational error, which is reported to a control of the wind turbine. Depending on the rank of the report signal an alarm, calling for service, might be sig ¬ naled to a control center.

Each wind turbine is checked and serviced in given time peri ¬ ods, i.e. there might be an annual inspection. Thus service personal might detect an external oil leakage visually as de- scribed above or the service personal might notice an (inter ¬ nal) oil leakage by given report signals.

Especially for offshore wind turbines, showing a guaranteed lifetime of 25 years or more, maintenance work for hydraulic components is a huge and costly problem.

It was found that such wind turbines might require in a worst case scenario two hydraulic cylinder exchanges over the life- time of the wind turbine. Due to the harsh offshore environ ¬ ment service time is restricted and limited while equipment, which is needed for the service work, might be expensive as well . It is therefore the aim of the invention to provide an im ¬ proved method and arrangement to detect a leakage of a hy ¬ draulic cylinder reducing or avoiding the problems given above . This aim is solved by the features of the independent claims. Preferred configurations are addressed by the dependent claims .

According to the invention an oil leakage between a first section of a hydraulic cylinder and a second section of the hydraulic cylinder is detected. A movable piston is arranged between the first section and the second section in a way that the piston changes its position between the sections. The change of the position is done in dependency of a differ- ence between a first force, which acts at the first section on a first cross sectional area of the movable piston, and a second force, which acts at the second section on a second cross sectional area of the movable piston. The first section comprises hydraulic oil with a predefined first pressure, while the first force is calculated based on this pressure and based on the first area. The second section comprises hy ¬ draulic oil with a predefined second pressure, while the se ¬ cond force is calculated based on this pressure and based on the second area. The first section is connected with a remote controlled first valve. This first valve is closed for the leakage detection. A sensor is coupled with the movable pis ¬ ton in a way that any change in its position is detected. The change of the position results from the difference of forces, which is in return resulting from the closed valve and from the alignment of the first pressure to the second pressure due to the leakage, which is between the first section and the second section. The sensor is coupled with a control, which is prepared and arranged to detect the leakage of oil based on the change of the position.

In a preferred configuration the piston interacts via its po ¬ sition with a blade of a wind turbine thus the blade is turned via the piston and other components to specific pitch angles .

In a preferred configuration the pitch angel is chosen between 0° and 15° for detecting a leakage of oil as these blade angles are most relevant for wear and tear of the blade .

The 0° pitch angle represents a position of the blade, where ¬ in the blade surface, facing the wind, is essentially turned in the rotor plane as seen from a chord-wise direction. Ac ¬ cordingly a 90° pitch angle refers to the "feathered posi ¬ tion" of the rotor blade, wherein the blade surface is turned out of the wind. In a preferred configuration the controller-software will test the cylinder for internal leakage several times a year. The aligned rotor blade pitch drive will be parked at a given testing time in one of these positions: 0° - 10° - 15° as de ¬ scribed above.

In a preferred configuration the hydraulic cylinder is part of a hydraulic pitch drive system of a wind turbine. In a preferred configuration the control is the controller (the central control unit) of the wind turbine, providing the control signals and initiating and performing the oil leakage detection automatically and in a remote controlled manner.

Thus all relevant surveillance signals of the whole wind tur ¬ bine are combined at the wind turbine controller.

By performing this controller based leakage detection any in- ternal cylinder defects are detected quite early. Thus faulty cylinders can be returned to the supplier for reimbursement as long as the respective warranty period has not lapsed.

A wind turbine often starts to report errors according to this sequence:

- Report: pumping time becomes prolonged,

- Report: temperature of the hydraulic oil starts to in ¬ crease, and finally an

- Report: an unwanted pitch tracking occurs during the

wind turbine operation.

In a preferred configuration this sequence is additionally taken into account to initiate the leakage control or leakage detection. Thus the leakage in the cylinder is detected quite early and before severe damages of the cylinder took place.

In a preferred configuration the controller-software will test the cylinder for internal leakage some times a year. The aligned rotor blade pitch drive will be parked at a given testing time in one of these positions: 0° - 10° - 15° as de ¬ scribed above.

The invention allows a self-diagnostic procedure of the hy ¬ draulic system (hydraulic cylinder) , which is done remote controlled.

The invention can be implemented with a cheap software pack ¬ age, programming the cylinder self-test on the wind turbine controller, taking into account limits of the piston move ¬ ment .

Thus all other relevant components are controlled easily by software and without the need for additional hardware and without implementation work for hardware.

Due to the invention operational stops, which are implemented in prior art wind turbines for security reasons, and unneces ¬ sary maintenance visits can be avoided. This results in con- siderable cost savings especially for offshore wind turbines.

Thus the wind turbines can be triggered to perform an oil leakage test on demand to avoid severe damages just in time. If a production series of cylinders is known to be burdened with troubles the respective cylinders can be checked more often than usual, leading to an increased system security.

Unplanned cylinder exchanges can be avoided by an optimized and adjusted maintenance service interval.

Additional a more constant functionality and lubrication is achieved by the invention, thus the overall lifetime of the cylinder is prolonged as well.

The cylinder wear depends on the site of the wind turbine thus turbulences might affect the lifetime negatively. Taking this into account as well the invention allows a certain pre ¬ diction of an exchange of a cylinder.

The invention is shown in more detail by help of figures. The figures show preferred configurations and do not limit the scope of the invention. FIG 1 shows the arrangement invented, and

FIG 2 shows details of a wind turbine, which is equipped with the oil leakage detection according to the invention. FIG 1 shows the arrangement invented.

A hydraulic cylinder HC comprises a first section SI, while hydraulic oil HO is provided in and out of the first section SI by a predefined first pressure PI.

The hydraulic cylinder HC even comprises a second section S2, while hydraulic oil HO is provided in and out of the second section S2 by a predefined second pressure P2.

The hydraulic cylinder HC comprises a movable piston MP, which is arranged between the first section SI and the second section S2 in a way that the movable piston MP changes its position POS between the sections SI and S2.

The hydraulic oil HO is applied to these sections SI and S2 thus respective forces Fl and F2 are created.

A first force Fl is created at the first section SI according to this formula:

Fl = PI * Al.

PI is the first pressure at the first section SI, which acts on a first cross sectional area Al of the movable piston MP.

A second force F2 is created at the second section S2 accord ¬ ing to this formula:

F2 = P2 * A2. P2 is the second pressure at the second section S2, which acts on a second cross sectional area A2 of the movable pis ¬ ton MP.

For this example the effective cross sectional areas Al and A2 show this dependency:

A2 = Al - AROD while AROD is the cross sectional area of a rod ROD, being part of the movable piston MP.

The first section SI is connected with a first valve VI, which is opened or closed remote controlled by a first con ¬ trol signal CS1.

The second section S2 is connected with a second valve V2, which is opened or closed remote controlled by a second con- trol signal CS2.

A sensor SEN is coupled with the movable piston MP in a way that any change in the position POS of the movable piston MP is detected. The Sensor SEN is coupled with a control unit CONT, which is prepared and arranged to detect a leakage of hydraulic oil HO based on the change of the position POS.

Let's assume a leakage LKG between the first section SI and the second section S2 exists, i.e. due to a faulty seal of the movable piston MP.

For the cylinder leakage test the first valve VI is closed remote controlled by the controller CONT.

Thus in case of a hydraulic cylinder HC without faults the pressure PI should be somehow "frozen" in its value.

Due to the leakage LKG the first pressure and the second pressure will adapt to each other thus finally the first pressure PI will show the same value than the second pressure P2 :

PI = P2

For the respective forces this situation results in:

Fl = PI * Al

Fl = P2 * Al

and for F2 = P2 * A2

F2 = P2 * (Al-AROD) .

By comparison of the forces Fl and F2 it is shown that for a leaking LKG in the hydraulic cylinder HC :

Fl > F2 as the second (active) area A2 is smaller in its value than the first (active) area Al .

Thus the movable piston MP will change its position into the direction of the second section S2. Summoned up - if there is a leakage LKG in the cylinder HC the pressures PI and P2 will be equate and due to the known active areas Al and A2 the movable piston MP will change its position POS . The change of the position POS will be detected by the sensor SEN, resulting in the knowledge that the hydraulic cylinder HC shows an internal leakage LKG.

FIG 2 shows details of a wind turbine WT, which is equipped with the oil leakage detection according to the invention.

The movable pistons MP (as described in FIG 1) of i.e. two hydraulic cylinders HC1, HC2 interact with the blade BL thus the blade BL is turned into specific pitch angles PA.

For the leakage detection the pitch angel PA is chosen between 0° and 15°, thus the surface of the rotor blade BL is aligned and turned in an optimum manner into the incoming wind W.

These blade pitch angles are most relevant for wear and tear of the blade. The hydraulic cylinders HCl, HC2 are part of a hydraulic pitch drive system HPS of the wind turbine WT .

The wind turbine control CONT is used to provide the control signals CS1, CS2 and to perform the oil leakage detection au ¬ tomatically.