MAKAREMI, Shaw, S. (465 Greenleaf Court, Goleta, CA, 93436, US)
| C l a i m s 1. A method of detecting discontinuities in an airfoil surface, comprising steps of: a. applying a conductive paste strip (20) covering said airfoil surface at locations on said surface preferably where discontinuities are anticipated; b. connecting said conductive paste strip (20) to an alarm circuit (34), which is capable of energizing an alarm (36); and c. transmitting a signal (37) of said alarm (36) to an indicator (39) , which indicates the location of a discontinuity upon a condition that said circuit (34) is energized. 2. The method of claim 1, wherein said alarm (36) and indicator (39) are located at said airfoil surface. 3. The method of claims 1 or 2, wherein said indicator (39) is one or more of (i) an audible signal (ii) a visual signal and (iii) a digital signal. 4. The method of claim 1, wherein said indicator (39) comprises a transmitter (40) located at said airfoil surface and a receiver (42) located at a remote location. 5. The method of claims 1 or 4, wherein said indicator (39) is one or more of (i) an audible signal (ii) a visual signal, (iii) a digital signal (iv) and/or a computer display. 6. An apparatus for detecting discontinuities in an airfoil surface, comprising: a conductive paste strip or coating (20) covering said airfoil surface at locations on said surface preferably where discontinuities are anticipated; a circuit (34) connected to said conductive paste strip or coating (20), which is capable of energizing an alarm (36); and an indicator (39) connected to said alarm (36), which indicates the location of a discontinuity upon a condition that said circuit (34) is energized. 7. The apparatus of claim 6, wherein one or more of said circuit (34) and indicator (39) are located at said airfoil surface . 8. The apparatus of claims 6 or 7, wherein said indicator (39) is one or more of (i) an audible signal (ii) a visual signal and/or (iii) a digital signal. 9. The apparatus of claim 6, wherein said indicator (39) comprises a transmitter (40) located at said airfoil surface and a receiver located at a remote location (42) . 10. The apparatus of claims 6 or 9, wherein said indicator (39) is one or more of (i) an audible signal (ii) a visual signal, (iii) a digital signal and/or (iv) a computer display. 11. The apparatus of one of the claims 6 to 10, wherein the transmitter (40) transmits a digital or binary code in the form of a string of a plurality of bits indicating the damaged airfoil surface and the location of the discontinuity or crack. 12. The apparatus of one of the claims 6 to 10, wherein one or more of said circuit (34) and indicator (39) are located at a location (30) proximate said airfoil surface. |
FIELD OF THE INVENTION The present invention relates to means for detecting cracks in rotor blades of fluid-flow turbines, such as wind and water turbines.
DESCRIPTION OF THE PRIOR ART The development of practical, wind-powered generating systems creates problems, which are unique and not encountered in the development of conventional power generating systems. One such problem is the appearance of cracks in the rotor blades of an operating wind turbine. Large modern wind turbines have rotor diameters of up to or greater than 100 meters with towers at a height to accommodate them. In the US tall towers are being considered for some places, such as the American Great Plains, to take advantage of estimates that doubling tower height will increase the wind power available by 45%.
Prior methods of detecting cracks in surfaces of aircraft wings, windshields and the like are known and several examples are described below.
In Ueda, et al. US patent 4,026,660 detection of a crack in a rotary wing for aircraft is accomplished by induction or change of resonance frequency. Detection is done by comparison of stationary and moving induction elements. The rotor needs to rotate for this detection to operate.
In Koontz US patent 4,902,875, the purpose is to make sure that a heating element for a windshield functions in case of a discontinuity and to prevent arcing so the windshield being heated is not damaged. Finally a bridge circuit is used to detect an impedance imbalance. The windshield does not go through any deformation to generate cracks. An electro conductive coating is used as a leg of the bridge. In Engels US patent 5,205,710, a pressurized or evacuated spar is used in a helicopter rotor blade to detect cracks by means of differential pressure change in the hollow spar. An LED and infrared transistor are used to replace a slip ring to transmit the information.
It is an object of the invention to provide an advanced control method and system which can detect the location of a crack in the rotor blades of wind turbines at an early stage and which can communicate or transmit the location of the crack to a remote location so that the crack may be repaired while the blades remain mounted on the rotor hub.
SUMMARY OF THE INVENTION
The above mentioned object is solved by an apparatus for detecting discontinuities in an airfoil surface, comprising a conductive paste strip or coating covering said airfoil surface at locations on said surface preferably where discontinuities are anticipated; a circuit connected to said conductive paste strip or coating, which is capable of energizing an alarm; and an indicator connected to said alarm, which indicates the location of a discontinuity upon a condition that said circuit is energized.
Further, the above mentioned object is solved by a method of detecting discontinuities in an airfoil surface comprising steps of: a) applying a conductive paste strip covering said airfoil surface at locations on said surface preferably where discontinuities are anticipated; b) connecting said conductive paste strip to an alarm circuit, which is capable of energizing an alarm; and c) transmitting a signal of said alarm to an indicator, which indicates the location of a discontinuity upon a condition that said circuit is energized.
In particular, the invention relates to an apparatus and method of detecting and repairing crack in wind turbine rotor blades. A conductive paste or a conductive coating is used as a conductive strip covering at least a part of the surface of the blades at locations where it seems most susceptible or inclined to damage. The conductive paste forms a circuit with a battery and a current limiting resistor, which energizes an opto-isolator or opto-coupler . When the circuit is broken or interrupted due to a crack, the opto-isolator turns off and sets or transmits an alarm indicating the location of the crack on that blade, the blade, the turbine and the site (wind farm) .
The major advantage of the invention is its very low cost and simplicity of use. Wind turbine blades are very large about 40 to 50 meters long, hollow and not pressurized. A major advantage of the invention is the ability to detect the location or very close vicinity of the crack within a few square feet. The blade and the location of the crack on the blade are transmitted and part of a digital code.
Since modern wind turbine blades are very large it is extremely time consuming and costly to replace a damaged blade. Usually there are certain weak spots on the blades that are susceptible to cracks and damage. By covering these spots with patches of conductive paint or conductive coating, the damaged blade and the location of the crack on the blade can easily be detected at very early stages.
Another important advantage is that each patch has its own digital or binary address and can easily be located on the defective blade by, for example, five bits (two bits to designate the blade and three bits to indicate a maximum of seven patches on that blade) . Finally one bit is added to indicate the health of the patch. This means a string of 6- bits of data measured or transmitted once every hour can verify the health of a patch on a blade.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention and its mode of operation will be more fully understood from the following detailed description when taken with the appended drawings in which:
FIGURE 1 is a diagram of a wind turbine rotor blade in which the present invention is embodied; FIGURE 2 is a diagram of a single crack detection area covered by conductive paste or coating; and
FIGURE 3 is a circuit diagram of a number of crack detection areas, similar to the one shown in FIGURE 2.
DETAILED DESCRIPTION OF THE INVENTION
Refer to FIGURE 1, which is a diagram of a wind turbine three-blade rotor in which the present invention is embodied. The rotor comprises three blades 1, 2, 3, attached to a hub 9. Areas on each blade 1, 2, 3 that are susceptible or inclined to crack or damage are selected. These areas or crack detection areas may be selected in different sizes and may be about 2 x 3 feet in size (width T x length L) . A letter A, B, C, D is assigned to each crack detection area. The rotor blades are numbered blade 1, blade 2 and blade 3. The blade 1 in FIGURE 1 is assigned the address "blade 1" and the binary address (01), the blade 2 in FIGURE 1 is assigned the address "blade 2" and the binary address (10) and the blade 3 is assigned the address "blade 3" and the binary address (11) . Each area on a blade 1, 2, 3 is assigned a unique address. For example "1 A" indicates crack detection area A on blade 1 and "3 C" indicates a crack detection area C on blade 3. The addresses on blade 1 shown in FIGURE 1 are therefore "IA", "IB", "1C" and "ID". Power is supplied from the hub 9 to each blade 1, 2, 3, wherein only the blade 1 is shown in FIGURE 1. There is a junction box 10 in each blade 1, 2, 3 close to the root 11 where all the electronics are placed. Power from the hub 9 through the blade root 11 is supplied to the junction box 11 and from there distributed to the patches or crack detection areas 12, 14, 16, 18 (A, B, C, D) . The output of each patch 12, 14, 16, 18, being a zero or one level, is wired to the junction box 10. The output of the junction box 10 with the address of the patch 12, 14, 16, 18 and the blade 1, 2, 3 is transmitted to the hub 9. A control box 30 located in the hub 9, which is proximate the airfoil surface of each blade 1, 2, 3, collects all the data from each blade 1, 2, 3 and transmits the data to a Condition-Based Maintenance System (CBMS) and/or a Supervisory Control and Data Acquisition (SCADA) through a slip ring. The SCADA or CBMS based on the alarm setting will alarm the maintenance technicians. All of this is through an Ethernet connection since all wind farms are at remote locations .
Note that the blade 1 in FIGURE 1 is assigned blade-1 and is represented by the binary address (01) and each patch or crack detection area 12, 14, 16, 18 on the blade 1 is addressed accordingly as "A" represented by the binary address (001), "B" represented by the binary address (010), "C" represented by the binary address (011), and "D" represented by the binary address (100) . Further patches or crack detection areas may be embodied and would be assigned, for example, E with the binary address (101), F with the binary address (110), and G with the binary address (111) .
Example: crack detection area or patch C on blade-1 is represented by: (01 011), and crack detection area or patch B on blade-3 is (11 010) . Note that one bit is added to represent the health of the respective on of the blades 1, 2, 3 wherein (0) means healthy and (1) means broken. This means a string of 6-bits of data measured or transmitted once every hour can verify the health of a patch 12, 14, 16, 18 on a blade 1, 2, 3. Refer to FIGURE 2, which is a diagram of the single crack detection area 12 (address "IA") , which is covered by conductive paste or a conductive coating 20. The area is, for example, painted or coated with a conductive coating in strips of one inch wide and of a length to cover the area in a, for example, zigzag form, as shown in FIGURE 2. If a crack 22 appears it causes a discontinuity in the conductive coating 20.
Conductive coating 20 is applied in a zig-zag format to cover the area of the patch 12. A respective crack detection area 12, 14, 16, 18 is covered by a corresponding conductive coating 20 which follows a meandering path. The conductive coating 20 may be a conductive paste strip which covers the blade or airfoil surface at locations where discontinuities are anticipated. The zig-zag pattern of the conductive coating 20 is only an exemplary pattern. The covered area 12 is approximately 2 x 3 feet (T x L) but it can be varied according to the needs and requirements of the blades. The dimensions and shape of the patch 12 can be varied. The objective is to cover the area that is expected to fail. Further, the conductive coating may be represented by one or more layers of conductive material.
Refer to FIGURE 3, which is an exemplary circuit diagram of a number of crack detection areas 12, 14, 16, 18, 19, similar to the one shown in FIGURE 2. The circuit diagram of FIGURE 3 illustrates exemplarily how the crack detection area IA is wired together using a power source 31, for example a small 9-volt battery. A small current is passed through each area's conductive coating or element 12 (the meandering path of it), a current limiting resistor 32 and an opto-isolator or opto-coupler 34. The current energizes the opto-isolator or opto-coupler 34. The opto-isolator 34 including for example a diode 38 and a photo transistor 48 energizes a relay 36 or any other circuitry that will provide an alarm. Knowing the location of the opto-isolator 34 that is energized, the alarm 36 clearly indicates the blade (1) and the area (A) on the corresponding blade. Therefore the blade and the location on the blade can easily be located and repaired. If the discontinuity (or crack) is in area "IA" the diode 38 of the opto-coupler 34 will not emit light so that the photo transistor 48 does not receive any light and the relay 36 in area IA will change its state indicating the failure 37. This failure signal 37 will activate a transmitter 40, which is part of an indicator 39. The indicator 39 may comprise a remote monitoring station 42 with a receiver. The transmitter 40, when activated by the change of state of relay 48 will transmit, for example, a signal 44 to the receiver of the remote monitoring station 42. The signal 44 may be a code, in particular a binary code. Alternatively, the indicator 39 may be one or more of an audible signal, a visual signal or a digital signal or a computer display displaying the information of the blade state.
As described with respect to FIGURE 1, there is a junction box 10 in each blade 1, 2, 3, preferably close to the root 11 wherein some or all the electronics are placed. It should be understood that the opto-coupler 34 and relay 36 of FIGURE 3 associated with crack detection area 12 are replicated for each of the crack detection areas 14-19 and are preferably brought together in the junction box 10 of FIGURE 1.
Also, as described with respect to FIGURE 1, the output of the junction box 10 with the address of the patches 12, 14, 16, 18 and the blade 1, 2, 3 may transmitted either wired or wirelessly to the hub 9. A control box 30 located in the hub 9, which is proximate the airfoil surface of each blade 1, 2, 3, collects all the data from each blade 1, 2, 3. The control box 30 may house the transmitter 40 and the monitoring station 42 shown in FIGURE 3. Alternatively, the transmitter 40 may be located in the hub 9 and the monitoring station 42 may be located remotely from the hub 9 through, for example, an Ethernet connection.
The opto-coupler 34 is the detection mechanism. When the patch or the crack detection area is intact low current flows through the circuit and diode 38 and the detection circuit sends or transmits the code or address. In case of a crack the path is broken and the diode 38 does not transmit light, in which case the detection circuit transmitter 40 transmits the last bit as (1) indicating a failure. The circuit shown in FIGURE 3 shows exemplary the circuit of the crack detection area 12 only, wherein the circuits of the further crack detection areas 14, 16, 18 ... is similar to the circuit as described above.
Low battery or power failure will be alarmed when all patches simultaneously fail, for example:
Blade 1, patch C healthy 01 011 0 Blade 1, patch C cracked 01 011 1 Refer to TABLE 1, which is a chart of the code format use to communicate the detection of a crack. The failure can be converted to any format for communication such as an audio alarm, a light alarm or the binary codes of TABLE I and SCADA.
TABLE I
Blade-1 patches A through G 01 001 0 Patch A good 01 001 1 Patch A broken 01 010 0 Patch B good 01 010 1 Patch B broken 01 011 0 Patch C good 01 011 1 Patch C broken
01 111 0 Patch G good 01 111 1 Patch G broken
Blade-2 patches A through G 10 001 0 Patch A good 10 001 1 Patch A broken 10 010 0 Patch B good 10 010 1 Patch B broken 10 011 0 Patch C good 10 011 1 Patch C broken
10 111 0 Patch G good 10 111 1 Patch G broken
Blade-3 patches A through G 11 001 0 Patch A good 11 001 1 Patch A broken 11 010 0 Patch B good 11 010 1 Patch B broken 11 011 0 Patch C good 11 011 1 Patch C broken
11 111 0 Patch G good 11 111 1 Patch G broken
While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and detail may be made therein without departing from the scope of the invention. The present invention relates to a rotor comprised of blades 1, 2, 3 of a fluid-flow turbine, such as wind and water turbines. Each rotor blade comprises at least one crack detection area for detecting a discontinuity or crack of the rotor blade. The at least one crack detection area 12, 14, 16, 18 is equipped with a conductive coating or conductive paste strip 20 which covers at least a part of the crack detection area 12, 14, 16, 18. The conductive coating 20 being electrically conductive is connected to an energy source 31 and with an opto-coupler 34. The opto-coupler 34 generates a signal of the state of the rotor blade and transmits continuously this signal to a remote monitoring station 42. The signal may be a digital or binary code in the form of a string of a plurality of bits indicating the damaged blade and the location of the discontinuity or crack.
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