Method of operating an electrical heating element

Abstract

A method is for operating an electrical heating element of a wind turbine rotor blade. The method includes: applying a voltage to the heating element, measuring a current flowing through the heating element, measuring the voltage applied to the heating element, calculating a reference current by applying a normalization factor to the measured current, wherein the normalization factor corresponds to the ratio of a nominal voltage to the measured voltage, triggering an action when the reference current is outside a first predetermined reference current range.

Claims

1. A method of operating an electrical heating element of a wind turbine rotor blade, the method comprising: applying a voltage to the heating element; measuring a current flowing through the heating element; measuring the voltage applied to the heating element; calculating a reference current by applying a normalization factor to the measured current, wherein the normalization factor corresponds to the ratio of a nominal voltage to the measured voltage; and, triggering an action when the reference current is outside a first predetermined reference current range.

2. The method of claim 1, wherein the reference current is monitored over time by continuously repeating said measuring the current flowing through the heating element, said measuring the voltage applied to the heating element, and said calculating the reference current.

3. The method of claim 1, wherein at least one of no reference current is calculated and no action is triggered before the voltage has been applied to the heating element for a predetermined time.

4. The method of claim 1, wherein at least one of no reference current is calculated and no action is triggered when the measured current is below a predetermined threshold.

5. The method of claim 1, wherein at least one of no reference current is calculated and no action is triggered when the measured voltage is outside a predetermined voltage range.

6. The method of claim 1, wherein said measuring the voltage applied to the heating element includes repeated measurements and determination of an average voltage; and, wherein in said calculating the reference current, the average voltage is used as the measured voltage.

7. The method of claim 1, wherein said measuring the current flowing through the heating element includes repeated measurements and determination of an average current; and, wherein in said calculating the reference current, the average current is used as the measured current.

8. The method of claim 1, wherein the first predetermined reference current range is stored in a control system after having been determined during commissioning of a wind turbine rotor blade heating system which includes the heating element.

9. The method of claim 1, wherein the action triggered when the reference current is outside the first predetermined reference current range is at least one of: stopping applying a voltage to the heating element, stopping a wind turbine heating system which includes the heating element, stopping a wind turbine, sending a notification, and requesting a service team.

10. The method of claim 1 further comprising: triggering an action when the reference current is outside a second predetermined reference current range defined by general limitations of an electrical supply system.

11. A wind turbine comprising: a wind turbine rotor blade having an electrical heating element; a controller configured to apply a voltage to the heating element; a current meter configured to measure a current flowing through said heating element; a voltage meter configured to measure the voltage applied to said heating element; and, said controller being further configured to calculate a reference current by applying a normalization factor to the measured current, wherein the normalization factor corresponds to a ratio of a nominal voltage to the measured voltage, and to trigger an action when said reference current is outside a first predetermined reference current range.

12. The wind turbine of claim 11, wherein said controller is configured to monitor the reference current over time by repeatedly measuring the current flowing through said heating element via said current meter, measuring the voltage applied to said heating element, and calculating the reference current.

13. The wind turbine of claim 11, wherein said controller is configured to at least one of calculate no reference current and trigger no action before the voltage has been applied to said heating element for a predetermined time.

14. The wind turbine of claim 11, wherein said controller is configured to at least one of calculate no reference current and trigger no action when the measured current is below a predetermined threshold.

15. The wind turbine of claim 11, wherein said controller is configured to at least one of calculate no reference current and trigger no action when the measured voltage is outside a predetermined voltage range.

16. The wind turbine of claim 11, wherein said controller is configured to measure the voltage applied to said heating element by repeatedly measuring the voltage applied to said heating element via said voltage meter and determining an average voltage; and, wherein said controller is configured to, when calculating the reference current, use the average voltage as the measured voltage.

17. The wind turbine of claim 11, wherein said controller is configured to measure the current flowing through said heating element by repeatedly measuring the current flowing through said heating element via said current meter and determining of an average current; and, wherein in said calculating the reference current, the average current is used as the measured current.

18. The wind turbine of claim 11, wherein the first predetermined reference current range is stored in a control system after having been determined during commissioning of a wind turbine rotor blade heating system which includes said heating element.

19. The wind turbine of claim 11, wherein the action triggered when the reference current is outside the first predetermined reference current range is at least one of: stopping applying a voltage to the heating element, stopping a wind turbine heating system which includes the heating element, stopping the wind turbine, sending a notification, and requesting a service team.

20. The wind turbine of claim 11, wherein said controller is further configured to trigger an action when the reference current is outside a second predetermined reference current range defined by general limitations of an electrical supply system.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The invention will now be described with reference to the drawings wherein:

(2) FIG. 1 is a schematic illustration of a wind turbine;

(3) FIG. 2 is a flow diagram illustrating a method according to the disclosure;

(4) FIG. 3 is a diagram showing voltage and current measured over time;

(5) FIG. 4 is a diagram illustrating the long-term progression of a reference current of a typical heating element;

(6) FIG. 5 is a diagram illustrating monitoring of a reference current over time; and,

(7) FIG. 6 shows development and implementation stages of a wind turbine rotor blade heating system.

DETAILED DESCRIPTION

(8) FIG. 1 shows a wind turbine 10 having a tower 12, a nacelle 14, and a wind turbine rotor 16 with a wind turbine rotor hub 18 and three wind turbine rotor blades 20. A heating element 22 is arranged on each wind turbine rotor blade 20 such that it covers a leading edge of the respective wind turbine rotor blade 20.

(9) A controller 24 is arranged in the nacelle 14 and connected to each of the heating elements 22. The details of the electrical system are not shown. However, the controller 24, which forms a part of a wind turbine controller, is able to apply a voltage to each of the heating elements 22 (for example by closing a switch connecting the heating element 22 or a group of heating elements 22 to a power supply). This voltage and a current flowing through each of the heating elements 22 or through a group of heating elements 22 is measured by a voltage meter 23 and a current meter 25 respectively 2and the measured values are transferred to the controller 24.

(10) FIG. 2 illustrates the steps of a method, presuming a voltage has already been applied to a heating element 22. In step 100, the current I.sub.meas flowing through the heating element 22 is measured. In step 102, the voltage U.sub.meas applied to the heating element 22 is measured.

(11) In step 104, a reference current I.sub.ref is calculated by applying a normalization factor to the measured current I.sub.meas, wherein the normalization factor corresponds to the ratio of a nominal voltage U.sub.nom to the measured voltage U.sub.meas.

(12) In step 106, it is determined whether the calculated reference current I.sub.ref is outside a second predetermined reference current range 26 (see FIG. 4). If so, the controller 24 in step 108 triggers an action, for example stops the application of voltage to the heating element 22.

(13) In step 110, it is determined whether the calculated reference current I.sub.ref is outside a first predetermined reference current range 28 (see FIG. 4). If so, the controller 24 in step 112 triggers an action, for example sends a notification including a warning to a service team.

(14) FIG. 3 shows a measured current I.sub.meas and a measured voltage U.sub.meas over time. One can see the measured voltage U.sub.meas fluctuates around a nominal voltage U.sub.nom, which is mainly due to fluctuations of a supply grid. The measured current I.sub.meas reflects these fluctuations. The reference current I.sub.ref calculated as I.sub.ref=I.sub.meas*(U.sub.nom/U.sub.meas) is shown as a straight line in the diagram, because it has been corrected for voltage-induced fluctuations.

(15) FIG. 4 illustrates the long-term progression of a reference current I.sub.ref of a typical heating element 22. A first predetermined current range 28 is defined by an upper limit I.sub.ref,warn+ and a lower limit I.sub.ref,warn. A second predetermined current range 26 is defined by an upper limit I.sub.ref,max and a lower limit I.sub.ref,min.

(16) The reference current I.sub.ref at t=0 starts at a value of I.sub.ref,com, which is determined when commissioning the wind turbine heating system. The reference current I.sub.ref gradually decreases due to a slight decrease in the electrical conductivity of the heating element 22. After several years, at t=t.sub.1, the reference current I.sub.ref exceeds the lower limit I.sub.ref,warn and is thus outside the first predetermined range 28. At this point in time, an action such as a notification sent to a service team may be appropriate.

(17) Later, at t=t.sub.2, the reference current I.sub.ref exceeds the lower limit I.sub.ref,min and is thus outside the second predetermined current range 26. At this point in time, an action such as stopping to apply a voltage to the heating element 22 or even stopping of the wind turbine 10 may be appropriate.

(18) FIG. 5 illustrates monitoring of a reference current over time. At t=t.sub.3, the reference current I.sub.ref falls below the lower limit I.sub.ref,warn and is thus outside the first predetermined current range 28, indicating a potential incident. At t=t.sub.4, the reference current I.sub.ref falls below the lower limit I.sub.ref,min and is thus outside the second predetermined current range 26, indicating a potential loss of electrical connection.

(19) FIG. 6 illustrates three stages of development, implementation and use of a wind turbine rotor blade heating system. In the first stage A (system configuration), the configuration of the system is determined. At this stage, the nominal voltage U.sub.nom and general limits of the electrical system such I.sub.ref,max and I.sub.ref,min will be determined, so that the first predetermined current range 28 can be defined.

(20) In the second stage B (commissioning), the wind turbine heating system is commissioned. At this stage, an individual reference current value I.sub.ref,com is determined, in particular based on a measurement of the electrical resistance of the heating element 22 or alternatively based on a first measurement of the reference current taken by a power meter and transferred to the controller. The commissioner sets this individual reference current value I.sub.ref,com as the center of the range. The upper and lower limits I.sub.ref, warn+ and I.sub.ref,warn are calculated by adding/subtracting a fixed percentage, so that the predetermined current range 26 can be defined at this stage.

(21) In the third stage C (monitoring), the reference current I.sub.ref is being monitored with the method, using U.sub.meas and I.sub.meas to calculate I.sub.ref.

(22) It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.

LIST OF REFERENCE NUMERALS

(23) 10 wind turbine 12 tower 14 nacelle 16 wind turbine rotor 18 wind turbine rotor hub 20 wind turbine rotor blade 22 heating element 23 voltage meter 24 controller 25 current meter 26 second predetermined reference current range 28 first predetermined current range