The present invention relates to a lightning protection of a wind turbine.
Generally, countermeasures against lightning are implemented for blades of a wind turbine.
By the wind force received by the blades 105, the rotor head 104 rotates, and then the main axis supported by the main bearing 108 is rotated. The rotation of the main axis is accelerated by a step-up gear arranged inside the nacelle 103 and drives a generator to generate an electric power.
For the lightning protection, a plurality of receptors (metallic lightning receiving parts) for receiving the lightning discharge are mounted on the surface of each blade 105. The receptor 110 is connected to the down conductor 111 (pull-down wire) which is arranged through the inside of the blade. The lightning current conducted to the root of the blade by the down conductor 111 is electrically connected to the earth line. The earth line is grounded through a route of the lightning current provided in the rotor head 104, the nacelle 103, and the tower 102.
In such a lightning protection structure of the wind turbine 101, the route of the lightning current is required to be grounded through rotatable parts such as the blade bearing 107, the main bearing 108, the yaw bearing 109 or the like by some kind of means. By utilizing these bearings as a part of the conducting line of the lightning current, it is possible for the down conductor 111 to be grounded and to let the lightning current from the receptor 110 of the blade 105 off.
For further enhancing the safety or the durability, a structure of conducting the lightning current by bypassing the bearing parts may be considered. Specifically, by utilizing the earth brash or the sliding contact as the bypassing means, it is possible for a part of the lightning current flowing through bearings to bypass the bearings.
In the above-mentioned bypassing means, since consumable supplies which are subjected to the sliding or abrasion by the rotation of the bearings are used, it is required to maintenance them periodically. Then, a lightning protection technique which can ease the maintenance is desired.
A means of utilizing a spark gap can also be adopted. In the spark gap, a current route between a bearing is formed via a gap, and the current flows via the gap by a spark. However, in this means, some countermeasures for overcoming the following problems are required.
Considering the above problems, a lightning protection technique using a current route which does not require the spark gap and being able to ease the maintenance is desired.
According to an aspect of the present invention, the lightning current received by a receptor of a blade is conducted to an earth line in the blade. The earth line is conducted to the internal space of the rotor head via the internal side space of the bearing for changing the pitch angle of the blade. It is possible to conduct the lightning current to the rotor head side without using the bearing as the current route and without using a sliding or wearing member such as a brash or the like.
According to an aspect of the present invention, a wind turbine includes: a rotor head; a blade on which a receptor for receiving a lightning discharge is mounted; a bearing configured to connect the blade to the rotor head such that a pitch angle of the blade is variable; and an earth line configured to conduct the lightning discharge to a side of the rotor head via the blade and a space of an internal side of the bearing.
According to another aspect of the present invention, the wind turbine further includes: a blade attachment plate fixed to at least one of: an edge surface of a blade root of the blade; an inner surface of the blade root; and a step formed in the inner surface of the blade root, by a connecting means; and the blade attachment plate has a through hole through which the earth line passes.
According to further another aspect of the present invention, the wind turbine further includes: an electrically insulating member formed on an inner side of the through hole.
According to further another aspect of the present invention, the wind turbine further includes: a plate member attached on the bearing in an opposite side of the blade attachment plate. The earth line which is drawn via the through hole into an opposite side of the blade is routed along a surface of the blade attachment plate in a side of the bearing, and further routed along a surface of the plate member in an opposite side of the blade.
According to further another aspect of the present invention, the wind turbine further includes: a plate member attached on the bearing in an opposite side of the blade attachment plate. A first part of the earth line is attached to the blade attachment plate on a surface of a side of the blade, and a second part of the earth line is attached to the plate member in an opposite side of the blade, and an angle between an extending direction of the first part of the earth line and an extending direction of the second part of the earth line is 90 degree or less.
According to further another aspect of the present invention, the angle between the extending direction of the first part of the earth line and the extending direction of the second part of the earth line is 30 degree or less when the blade is a feather position.
According to further another aspect of the present invention, the earth line has a slack portion at a part in the bearing.
According to further another aspect of the present invention, the wind turbine further includes a shield member fixed in the rotor head and configured to cover the earth line and made of a conductive material.
According to the present invention, it is possible to ease the maintenance for lightning protection equipment of a wind turbine.
The above objects, other objects, effects, and characteristics of the present invention will become clearer by the description of embodiments with the accompany drawings, in which:
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Some embodiments of the present invention will be explained below. The total structure of the wind turbine according to a first embodiment of the present invention is the same as that of the wind turbine explained with reference to
The blade bearing 3 is a circular-shaped bearing which supports the blade 2 such that the blade 2 is rotatable to the rotor head 1 in the pitch angle direction. The blade attachment plate 4 is attached to the surface of the blade bearing 3 on the blade 2 side. The blade attachment plate 4 has a through hole. The hole is formed in, for example, the center part of the blade attachment plate 4. The blade attachment plate 4 has a shape corresponding to the root of the blade 2. In the root part of the blade 2, a flange is formed. The flange is fixed to the blade attachment plate 4 by bolts so that the blade 2 is fixed to the blade attachment plate 4.
The means for fixing the blade attachment plate 4 to the blade 2 is not limited to the above-explained case.
On the surface of the blade bearing 3 opposing to the blade 2, a connection shaft attachment plate 5 being a plate-shaped member is attached. The connection shaft attachment plate 5 has a hole. The hole is formed at the center portion of the connection shaft attachment plate 5, for example. A connection shaft 11 is attached to the connection shaft attachment plate 5. The connection shaft 11 is attached to the pitch angle driving means 12. The pitch angle driving means 12 drives the blade 2 to the pitch angle instructed by a control signal by pushing or pulling the connection shaft 11 by an actuator.
In the internal space of the blade 2, a down conductor 7 being a conducting wire for conducting a lightning current is arranged. An end portion of the down conductor 7 is connected to a receptor corresponding to the receptor 110 in
The earth 7a is preferably an insulated cable covered by an electrically insulating member. From the viewpoint of suppressing the shape deformation caused by a continuous applying of a lightning current, EPR (Ethylene Propylene Rubber) or XLPE (Cross-Linked Polyethylene) is preferable used as the insulation covering. These members are preferable for the earth line 7a of the present embodiment in the characteristics of the electrical insulating performance, the weathering resistance, the flame resistance, and the twist resistance (robustness to torsion or bending). Further, the oil resistance characteristic is also required for the earth line 7a since lubrication oil is used around the bearings. The above members are also preferable from this viewpoint because they have high oil resistance.
The blade 2 rotates relatively to the rotor head 1. As a result, accompanying to the blade rotation, torsion of the earth line 7a occurs. For permitting this torsion, the earth line 7a is fixed to have a slack (in the state being longer than the strain state) in the part of the blade bearing 3. Alternatively, as the earth line 7a, a wiring formed by connecting the earth line in the blade 2 and the earth line in the rotor head 1 to be rotatable to each other by a slip ring, a rotatable connector device, and the like.
In the example of
When lightning strikes the wind turbine having the above structure, the lightning current irrupted from a receptor is conducted in the blade 2 along the down conductor 7 to the direction of the blade root, and is passed to the earth line 7a. The lightning current flowing through the earth line 7a is conducted via the hole 6 to the route inside the rotor head 1. The lightning current is further conducted via a route not shown in the drawings being a wiring in the nacelle and the tower to the ground electrode. In such a structure, the lightning current of the lightning received by the receptor of the blade 2 can be conducted to the internal space of the rotor head 1 without flowing the lightning current through the blade bearing 3.
When a lightning current is passing, a large potential difference is generated between the earth line 7a and the metal members supporting the earth line 7a. In a case where the tolerance width of the dielectric strength in the insulation covering of the earth line 7a is not enough, for further enhancing the safety, it is preferable to cover the surface of the metal member on the side of the earth line 7a by an electrically insulating member. In the example shown in
Next, the third embodiment of the present invention is explained. Only the portions different from the first and second embodiments will be explained.
When lightning strikes the wind turbine having the above structure, the lightning current 21 flows through the earth line 7a. The route of the earth line 7a on the blade attachment plate 4a and the route thereof in the rotor head 1 are parallel to each other. As a result, the earth line 7a on the blade attachment plate 4a is pushed onto the blade attachment plate 4a by the Lorentz force. The blade attachment plate 4a has a high strength for fixing the blades 2, and is fixed to the blade bearing 3 with high strength. Therefore, the blade attachment plate 4a can receive the Lorentz force applied to the earth line 7a with high strength. Since the force applied to the mounting bracket 22 is reduced, the strength required for the mounting bracket 22 is permitted to be smaller than the example shown in
From the vertical (the direction normal to the connection shaft attachment plate 5) viewpoint, namely, in the planar arrangement viewed from the rotational axis of the blade bearing 3, the route of the earth line 7a on the blade attachment plate 4 and the route of the earth line 7a on the connection shaft attachment plate 5 are on a single straight line. In such a structure, when a lightning current 21 flows through the earth line 7a, since the earth line 7a on the blade attachment plate 4 side and the earth line 7a on the connection shaft attachment plate 5 side are not overlapped and separated to each other from the vertical view, the Lorentz force applied between each other is small. Therefore, the force applied to the fixing brackets can be reduced.
It is not required for the earth line 7a of the side of the blade attachment plate 4 and the earth line 7a of the side of the connection shaft attachment plate 5 to be accurately on a single straight line. It is enough for the earth line 7a on the side of the connection shaft attachment plate 5 to be arranged to be in the direction of extending (the direction of the flowing current therein) whose angle with at least a part of the earth line on the side of the blade attachment plate 4 is less than 90 degree. Further, it is possible for the earth line 7a to arrange such that the earth line 7a has a planar arrangement shown in
Referring to
When the weather is in the condition that the lightning strike may occur, the normal operation of the wind turbine is stopped. The pitch angle driving means 12 drives the connection shaft 11 for controlling the pitch angle of the blade 2 to the feather state. In this state, for suppressing the Lorentz force applied to the earth line 7a, it is preferable for the angle between the route of the earth line 7b and the route of the earth line 7c to be 90 degree or less, and more preferably, it is approximately parallel (their planar arrangement forms approximately a single straight line). Even though the whole earth line 7a satisfies the above angle condition, when the angle condition is satisfied for the earth line 7a in the range within a predetermined length from the hole 6a and the hole 6b, the Lorentz force operated between the earth line 7b and the earth line 7c can be suppressed. Specifically, the angle between the earth line 7b and the earth line 7c is preferably in the range of ±30 degree or less which is the level where the influence of the electromagnetic force generated in the passing of the lightning current becomes ignorable level.
In the normal operation of the wind turbine, the pitch angle driving means 12 rotates the blade 2 (the blade attachment plate 4) relatively to the rotor head 1 (the connection shaft attachment plate 5) so that the blades 2 become fine. In this state, the earth line 7b passing a route predetermined to the blade attachment plate 4 rotates relatively to the earth line 7c in the rotor head 1 as shown in
In the above, some embodiments are explained. Those embodiments can be applied to the yaw bearing 109 between the tower 102 and the nacelle 103 of the wind turbine shown in
In the above, the present invention is explained with reference to some embodiments. However, the present invention is not limited to those above embodiments. The above embodiments can be variously modified. For example, any combination of the above embodiments, if there is no contradiction, can be another embodiment of the present invention.
The present application claims a priority based on Japanese Patent Application No. 2011-105629, which was filed on May 10, 2011, and the disclosure of which is hereby incorporated into the present application by this reference.
Number | Date | Country | Kind |
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2011-105629 | May 2011 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2012/061704 | 5/8/2012 | WO | 00 | 1/10/2014 |