METHOD OF CONTROLLING A WIND TURBINE

Abstract

The invention describes a method of controlling a wind turbine (2), which method comprises steps of measuring one or more climate parameters (.sub.t, T.sub.air, T.sub.surface) in an interior (2.sub.int) of the wind turbine (2); estimating, on the basis of the climate parameters (.sub.t, T.sub.air, T.sub.surface), the electrical resistance (RW.sub.t) of an insulating material (210M) deployed in an electrical component (21) of the wind turbine (2); and evaluating the need for a dry-out procedure on the basis of the estimated resistance (RW.sub.t). The invention further describes a wind turbine (2) with a monitoring arrangement (1) configured to perform the inventive method.

Claims

1. A method of controlling a wind turbine (2), which method comprises steps of measuring one or more climate parameters (.sub.t, T.sub.air, T.sub.surface) in an interior (2.sub.int) of the wind turbine (2); estimating, on the basis of the climate parameters (.sub.t, T.sub.air, T.sub.surface), the electrical resistance (RW.sub.r) of an insulating material (210M) deployed in an electrical component (21) of the wind turbine (2); evaluating the need for a dry-out procedure on the basis of the estimated resistance (RW.sub.t).

2. The method according to the claim 1, wherein the step of estimating the electrical resistance (RW.sub.t) of the insulating material (210M) is based on a predetermined humidity threshold value (k.sub.1) for that material (210M).

3. The method according to claim 1, wherein the electrical resistance (RW.sub.t) of the insulating material (210M) is estimated on the basis of a previously established relationship between a climate parameter (.sub.t, T.sub.air, T.sub.surface) and electrical resistance of that material (210M).

4. The method according to claim 1, comprising a step of evaluating the progression of the estimated electrical resistance (RW.sub.t) to detect an increase or decrease in electrical resistance.

5. The method according to claim 1, comprising a step of initiating a dry-out procedure when the estimated electrical resistance (RW) of the insulating material (210M) no longer exceeds a minimum threshold value (RW.sub.min).

6. The method according to claim 1, comprising a step of concluding the dry-out procedure when the estimated electrical resistance (RW.sub.t) of the insulating material (210M) is at least as great as the minimum threshold value (RW.sub.min).

7. The method according to claim 1, comprising initial steps of activating a data-logging means (11) adapted to record climate parameters (.sub.t, T.sub.air, T.sub.surface); and recording an initial value of electrical resistance (RW.sub.0) of the insulating material (210M) deployed in the electrical machine (21); which initial steps are performed upon completion of assembly of the electrical machine (21).

8. The method according to claim 7, comprising a further initial step of clearing a dry-out flag.

9. The method according to claim 1, wherein the climate parameters (.sub.t, T.sub.air, T.sub.surface) are evaluated during any subsequent mode of operation (M.sub.ongrid, M.sub.offgrid, M.sub.dryout) of the wind turbine (2).

10. The method according to claim 1, wherein a dry-out procedure is performed during an on-grid mode of operation (M.sub.ongrid).

11. The method according to claim 1, wherein the measured climate parameters comprise relative humidity (.sub.t) and/or air temperature (T.sub.air) and/or surface temperature.

12. A wind turbine (2) comprising an electrical machine (21) in which a quantity of insulating material (210M) is deployed; and a monitoring arrangement (1) configured to perform the method according to claim 1, the monitoring arrangement (1) comprising a sensor arrangement (10) configured to measure one or more climate parameters (.sub.t, T.sub.air, T.sub.surface) in an interior (2.sub.int) of the wind turbine (2); a data analysis module (12) configured to estimate the electrical resistance (RW.sub.t) of the insulating material (210M) on the basis of climate parameters (.sub.t, T.sub.air, T.sub.surface) measured by the sensor arrangement (10); and a dry-out evaluation module (13) configured to evaluate the need for a dry-out procedure on the basis of the estimated resistance (RW.sub.t).

13. The wind turbine according to claim 12, wherein the electrical machine (21) is the generator of the wind turbine (2), and the insulating material (210M) is deployed about the generator windings (210W).

14. The wind turbine according to claim 12, comprising a data-logging means (11) adapted to record and evaluate the climate parameters (.sub.t, T.sub.air, T.sub.surface) measured by the sensor arrangement (10).

15. A computer program product comprising a computer program that is directly loadable into a memory of a monitoring arrangement (1) of a wind turbine (2), and which comprises program elements for performing steps of the method according claim 1 when the computer program is executed by the monitoring arrangement (1).

Description

[0033] Other objects and features of the present invention will become apparent from the following detailed descriptions considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for the purposes of illustration and not as a definition of the limits of the invention.

[0034] FIG. 1 shows a wind turbine equipped with an embodiment of the inventive monitoring arrangement;

[0035] FIG. 2 is block diagram to illustrate the inventive method;

[0036] FIG. 3 is a flowchart to illustrate steps of the inventive method;

[0037] FIGS. 4 and 5 illustrate exemplary situations arising during the inventive method;

[0038] FIGS. 6 and 7 illustrate situations corresponding to FIGS. 4 and 5 respectively;

[0039] FIG. 8 illustrates a prior art approach to resuming operation after an off-grid mode;

[0040] FIG. 9 shows a set of wind turbine generator windings.

[0041] In the diagrams, like numbers refer to like objects throughout. Objects in the diagrams are not necessarily drawn to scale.

[0042] FIG. 1 shows a wind turbine 2 equipped with an embodiment of the inventive monitoring arrangement 1. The diagram only indicates the relevant components of the wind turbine 2, in this case the generator 21, the monitoring arrangement 1, and the wind turbine controller 22. The generator windings are wrapped in an insulating material which is hygroscopic to some extent.

[0043] In this exemplary embodiment, the monitoring arrangement 1 comprises a sensor arrangement 10 with sensors that can measure relative humidity and temperature. The sensor arrangement 10 is configured to measure the relative humidity .sub.t and the air temperature T.sub.air in an enclosed space 2.sub.int of the wind turbine 2. The sensor arrangement 10 can also include a means of measuring the surface temperature T.sub.surface of the generator winding insulation. The monitoring arrangement 1 also comprises a data analysis module (realised for example as part of a data-logging means 11) that computes an estimate of the resistance of the hygroscopic material, using measurements provided by the sensor arrangement. The monitoring arrangement 1 also comprises a dry-out evaluation module (realised for example as part of a wind turbine controller 22) that evaluates the need for a dry-out procedure from the estimated resistance.

[0044] During an off-grid state, a climate-control arrangement of the wind turbine may be without power, for example if the auxiliaries of the wind turbine can only be powered by the grid, or if a backup power supply is depleted. As a result, the temperature of the air inside the nacelle will drop, and its relative humidity will increase. This applies also to the air inside the generator, and the hygroscopic material of the armature winding insulation will absorb moisture. Therefore, after grid power is restored, the procedure of re-starting the wind turbine 2 cannot be done until it is ascertained that the winding insulation is sufficiently dry.

[0045] The data analysis module 12 can be realised in a data-logger 11 as indicated in FIG. 2, which shows a simplified block diagram of the relevant units and modules that collectively implement the inventive method. The data analysis module 12 computes an estimate RW.sub.t of the resistance of the hygroscopic material, for example using equations (1) and (2) described above. To this end, a predetermined humidity threshold value k1 for that hygroscopic material can be input to the data-logger 11 during an assembly stage of the wind turbine 2. Similarly, a previously established relationship k2 between relative humidity and electrical resistance can be input to the data-logger 11 during an assembly stage of the wind turbine 2. The data analysis module continually updates its estimate of electrical resistance RW.sub.t and forwards this to the dry-out evaluation module 13, which in this exemplary embodiment is realised in the wind turbine controller 22. The dry-out evaluation module 13 compares the estimated electrical resistance RW.sub.t to a minimum threshold value RW.sub.min, which may be stored in a memory of the wind turbine controller 22 during an assembly stage of the wind turbine 2.

[0046] The computations performed by the monitoring arrangement 1 become relevant especially when grid power is restored after an off-grid mode of operation: as long as the estimate of electrical resistance exceeds this minimum threshold value RW.sub.min, it would be safe to restart the generator. However, when the estimated electrical resistance is below this minimum threshold value RW.sub.min, it is not safe to restart the generator.

[0047] In this exemplary embodiment, the dry-out evaluation module 13 can set the dry-out flag if the electrical resistance is estimated to be below the minimum threshold value RW.sub.min, or clear the dry-out flag if the electrical resistance is estimated to be at or above the minimum threshold value RW.sub.min.

[0048] If the electrical resistance was estimated to be at or above the minimum threshold value RW.sub.min, the wind turbine controller 22 can initiate a start-up procedure essentially immediately after reconnection to the grid.

[0049] If the electrical resistance was estimated to be below the minimum threshold value RW.sub.min and the dry-out flag is set, the wind turbine controller 22 can issue control signals 220 to a climate-control arrangement 24 (comprising heater(s) 241, fan(s) 242, dehumidifier(s) 243 etc.) to achieve a desirable environment in the nacelle interior.

[0050] FIG. 3 is a flowchart to illustrate steps in an exemplary embodiment of the inventive method. During initial stages in the manufacture of a wind turbine, the generator is assembled in step 30A, a data-logger and sensor arrangement is installed and activated in step 30B, and relevant parameters (e.g. initial value of winding resistance, threshold levels etc.) are stored in step 30C.

[0051] In a subsequent step 31, measurements such as relative humidity .sub.t, air temperature T.sub.air, surface temperature T.sub.surface are collected and input to the data-logger. Any change RW in electrical resistance of the winding material is computed in step 32. The net electrical resistance RW.sub.t at the present time is computed in step 33 by applying equations (1) to (4) as appropriate. In step 34, this electrical resistance RW.sub.t is compared to the minimum acceptable value RW.sub.min. If the electrical resistance RW.sub.t is equal to or exceeds the minimum acceptable value RW.sub.min, the dry-out flag is cleared in step 35, indicating that a dry-out procedure is not necessary and the generator can be safely started from an off-state. If the electrical resistance RW.sub.t is below the minimum acceptable value RW.sub.min, the dry-out flag is set in step 36 indicating that a dry-out procedure is necessary before starting the generator from an off-state.

[0052] The possible outcomes of step 34 are illustrated in FIGS. 4 and 5. In FIG. 4, the progression of electrical resistance RW is shown against time (in practice, the progression may be a series of individual winding resistance estimates RW.sub.t). A mode of normal operation M.sub.ongrid is followed by an offgrid mode M.sub.offgrid, Which can persist for any length of time. In the absence of power, the temperature in the nacelle decreases and the relative humidity increases. As a result, the electrical resistance RW of the generator winding insulation can deteriorate as the hygroscopic material absorbs moisture.

[0053] At time t.sub.0, grid power is restored again for a subsequent on-grid mode M.sub.ongrid. The modules of the monitoring arrangement are continually evaluating the relative humidity measurements and computing an up-to-date estimate of electrical resistance RW.

[0054] In FIG. 4, at time t.sub.0, the monitoring arrangement concludes that the electrical resistance RW of the generator winding insulation is too low to permit the generator to be re-started, and the wind turbine controller initiates a dry-out procedure. The hygroscopic material of the winding insulation can release moisture to the surrounding environment, and its resistance increases again. At time t.sub.RW_OK, the monitoring arrangement concludes that the electrical resistance RW of the generator winding insulation has reached the minimum level RW.sub.min so that the generator can be re-started.

[0055] In FIG. 5, at time to, the monitoring arrangement concludes that the electrical resistance RW of the generator winding insulation is already at a level that permits the generator to be re-started safely without any dry-out procedure.

[0056] These decisions determine the point in time at which the generator can commence exporting power P.sub.exp, as shown in FIGS. 6 and 7. FIG. 6 illustrates a situation corresponding to FIG. 4, and shows how the wind turbine controller waits until the electrical resistance RW has increased to a satisfactory level before re-starting the generator at time t.sub.RW_OK. FIG. 7 illustrates a situation corresponding to FIG. 5, and shows how the wind turbine controller re-starts the generator at time to, since the electrical resistance RW of the generator winding insulation is already at or above the minimum level, and the generator can be safely re-started to export power P.sub.exp without any dry-out procedure.

[0057] FIG. 8 illustrates a prior art approach to resuming operation after an off-grid mode. Here, following an off-grid mode M.sub.offgrid of indeterminate length, restoration of grid power occurs at time to, and power is again available to the auxiliary components of a wind turbine. A dry-out procedure is then initiated and persists until a predetermined dry-out duration D.sub.dry has elapsed at time t.sub.dry. This predetermined dry-out duration D.sub.dry is generally a conservative estimate based on empirical data, and can greatly exceed the actual length of time required to complete dry-out if environmental conditions in the nacelle remained favourable. Furthermore, depending on the conditions leading up to and during the off-grid mode, there may in fact be no need to perform a dry-out procedure, but this will nevertheless be initiated at time to and allowed to complete at time t.sub.dry. As a result, restart of a prior art wind turbine following an off-grid mode may be delayed without need, resulting in unnecessary sacrifice of revenue, since the wind turbine can only commence exporting power P.sub.exp at time t.sub.dry.

[0058] FIG. 9 shows a set of three windings 210 of the type that might be used in a wind turbine generator 21. Each winding 210 is wrapped in an insulating package 210P comprising layers of dielectric material 210M. In an electrical machine such as a large wind turbine generator 21, the insulating package 210P must fulfil several requirements, and the necessary materials 210M are generally hygroscopic. As explained in FIG. 1 above, the sensor arrangement 10 can also comprise one or more temperature probes placed to measure the surface temperature T.sub.surface of the generator winding insulation, so that estimation of the winding insulation resistance can be very accurately established by also taking into the consideration the dew point temperature.

[0059] 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.

[0060] 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. The mention of a unit or a module does not preclude the use of more than one unit or module.