WO2009003508A1

WO2009003508A1 - Switchgear for a wind turbine and system for arranging electrical connections in a wind farm

Info

Publication number: WO2009003508A1
Application number: PCT/EP2007/056533
Authority: WO
Inventors: Lars Liljestrand; Ambra Sannino; Lars Hultqvist
Original assignee: Abb Research Ltd
Priority date: 2007-06-29
Filing date: 2007-06-29
Publication date: 2009-01-08

Abstract

The present invention presents a switchgear for use with wind turbines, said switchgear comprises two or more switching units arranged for interrupting two or more currents the switching units are arranged above one another. The present invention also presents a wind farm system comprising at least one first wind turbine arranged with a medium or high voltage switchgear, said switchgear comprises two or more switching units arranged for interrupting two or more currents, and the wind farm system comprises a plurality of wind turbines where said switching units are arranged above one another and said first wind turbine is electrically connected to two or more other wind turbines.

Description

10270 SE/DR

Switchgβar for a wind turbine and system for arranging electrical connections in a wind farm

2007-06-28

TECHNICAL AREA

The present invention relates to a system for arranging electrical switching units e.g. breakers or switches in wind turbines. The wind turbines can be connected in installations comprising several wind turbines known as wind farms.

TECHNICAL BACKGROUND

Wind power is the conversion of wind energy into electricity using wind turbines by converting the rotation of turbine blades into electrical current by means of an electrical generator. A collection of wind turbines in the same location is usually called a wind farm or wind park.

For wind turbines placed on land, the best places are on ridgelines and coastal areas but the installation of wind turbines in these areas can be highly controversial to the public. A solution to this is to put the wind turbines out at sea, either near-shore (within 3 km from the coast) or offshore. The placements of wind turbines at sea have some advantages. A water surface offers lower friction for wind than land does and therefore the average wind speed is usually considerably higher over open water. The wind turbines are much less visible off-shore than on land therefore an installation at sea will be less controversial.

Offshore wind turbines have a number of challenges compared to land based wind turbines;

- offshore wind turbine foundations are more difficult to build - repairs and maintenance are usually much more difficult and costly on offshore wind turbines

- electrical power transmission from offshore turbines are more difficult and costly - offshore humid and possible saltwater environment raise construction and maintenance costs

Offshore wind turbines are normally installed in wind farms with many wind turbines to spread the high fixed costs involved in offshore operation. Offshore wind farms tend to be quite large.

The wind turbines in wind farms are spaced from one another at such distances that the effects of one wind turbine on another as a result of changing air flow conditions are kept as small as possible. For large wind turbines the distance between two towers can be 1000m or more making a large wind farm spread out over an extensive area and the power connection distances from one end of the wind farm to the other end substantial.

In a wind farm, the wind turbines are connected in 'strings' by sub-sea cables. The strings are then connected to the platform by one feeder cable. This cable, together with necessary switching equipment such as breakers, disconnectors, etc, forms the collection grid. In the collection grid, the feeder cables that connect one string of wind turbines to the platform (located most likely in a central position) will be quite long, especially those reaching the most peripheral string of wind turbines. On the other hand, if the transformer is in a station onshore, all feeders will be quite long.

Patent WO0146583 entitled "OFFSHORE WIND POWER INSTALLATION COMPRISING INTERCHANGEABLE CONTAINERS FOR HOUSING SUBSYSTEMS" describes an offshore wind power installation with subsystems such as a switchgear or a transformer station housed in at least one container which is attached to the exterior of the tower. Patent DE10013442 entitled "Offshore wind turbine power plant has container housing electrical operating component positioned at side of machine housing provided with helicopter landing platform" where the electrical operating components of the power plant, e.g. the switchgear and transformer, are housed in a container mounted at the side of the machine housing.

Both patents show alternative ways of arranging the switchgear on a wind turbine.

SUMMARY OF THE INVENTION An embodiment of the present invention is a wind turbine arranged with a medium or high voltage switchgear, said switchgear comprises two or more switching units arranged for interrupting two or more currents and the switching units are arranged above one another.

Another embodiment of the present invention is that the switching units can be any of the type switch, load switch, breaker.

Another embodiment of the present invention is that the switching units are all connected to an external busbar arranged vertically.

Another embodiment of the present invention is that a switching unit is directly connected to the switching unit above and below.

Another embodiment of the present invention is that said switchgear is located in the wind turbine tower and another embodiment is that the switchgear is built up of modules. The modules can comprise one switching unit or several switching units. The modules can also comprise units for sensing or measuring voltage or current. The connection between modules arranged above one another can replace the vertical busbar.

Another embodiment of the present invention is that at least one switching unit in the switchgear is arranged to break a current generated by the wind turbine and least one switching unit is arranged to break a current generated by another wind turbine .

In another embodiment of the present invention a wind farm system comprising at least one first wind turbine arranged with a medium or high voltage switchgear, said switchgear comprises two or more switching units arranged for interrupting two or more currents, and the wind farm system comprises a plurality of wind turbines where said switching units are arranged above one another and said first wind turbine is electrically connected to two or more other wind turbines .

Another embodiment of the present invention is that said wind farm system comprises at least two second wind turbines are electrically connected to a first wind turbine.

Another embodiment of the present invention is that the at least two second wind turbines are arranged without a said medium or high voltage switchgear.

Another embodiment of the present invention is that the switchgear in first wind turbine is arranged to break electrical connection to two or more electrically connected second wind turbine (s) . Another embodiment of the present invention is that all switching units are connected to a vertically arranged busbar.

Another embodiment of the present invention is that the wind farm is placed near shore or off shore or that the wind farm is placed on land.

Another embodiment of the present invention is that first wind turbine is connected to the second wind turbine in a star topology.

The advantage of arranging switching units above one another is the smaller footprint of the switchgear. Such small footprint switchgear could be placed inside the wind turbine tower. The switchgear could have several switching units e.g. more than five. This would allow for new connection configurations e.g. star configuration. A star configuration will be more robust against cable failures between wind turbines. A cable failure between wind turbines connected in a star will only disconnect the wind turbine affected by the cable failure. A star configuration therefore ensures higher availability of the wind turbines in the wind farm.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings constitute a part of this specification and include exemplary embodiments to the invention, which may be embodied in various forms .

Figure 1 shows schematically a radial connected wind farm

(prior art) .

Figure 2 shows schematically a wind turbine (prior art) .

Figure 3 shows schematically a small wind farm in star configuration. Figure 4 shows schematically a wind farm with several star configurations connected radially.

Figure 5 shows the vertical arrangement of the switchgear in the wind turbine tower at the center of a star configuration. Figure 6 shows schematically a wind farm with several star configurations connected in a star topology. Figure 7 shows schematically an embodiment of the present invention where several switches are arranged vertically inside a wind turbine tower. Figure 8 shows schematically an embodiment of the present invention where several compact switches are arranged vertically.

DETAILED DESCRIPTION OF THE DRAWINGS Detailed descriptions of the preferred embodiment are provided herein. It is to be understood, however, that the present invention may be embodied in various forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but rather as a basis for the claims and as a representative basis for teaching one skilled in the art to employ the present invention in virtually any appropriately detailed system, structure or manner.

Figure 1 shows schematically a radial electrically connected wind farm 1 (prior art) . The wind turbines 2 (each small circle symbolizes a wind turbine) are serially connected in branches or strings with sub-sea cables 3. The cross-section of the cables can increases from the outermost turbine going closer to the platform, resulting in high cable costs. The cost of the collection grid for a wind farm can be estimated in the range of about 15% of the cost of the whole wind farm, where the cost of the wind turbines is about 50%. The voltage from the generator is currently in the order of 0,7kV and in the future it could be 3.3 kV. This current is transformed to medium voltage (e.g. 33kV) in the nacelle. From the branches a feeder cable 4 transports the current to the transformer 6. The transformer 6 might be placed on a separate platform. The cable, together with necessary switching equipment such as breakers, disconnectors, etc, forms the collection grid of the wind farm. In the collection grid, the feeder cables that connect one string of wind turbines to the transformer platform (located most likely in a central position) will be quite long, especially those reaching the most peripheral string of wind turbines. On the other hand, if the transformer is in a station onshore, all feeders will be quite long.

The transformer 6 can transform the electricity from MV (e.g. 33 kV) to HV (e.g. 132 kV) . From the transformer 6 the current is carried on shore with another cable 7. The branch or string in the wind farm system also comprises a breaker 5.

Other issues with this configuration are that the turbines far out at the end of the feeder may incur voltage rise problems, and that the impact of transient over-voltages due to e.g. switching operation of the switchgear on the transformer platform (typically a vacuum circuit breaker) are different depending on the location along the feeder.

Figure 2 shows schematically a wind turbine 10. The buildup of an offshore wind turbine is known art. The rotating blades 11 collect the wind energy and the rotation energy is transformed into electrical energy by a generator placed in the nacelle 12 on top of a mast or tower 13. In a wind turbine area, the structure which houses all of the generating components, gearbox, drive train, etc. is referred to as the nacelle. Below the sea surface 15 the mast 13 is placed on a foundation 14 on the sea bed. A cable 16 transports the electric energy to a collection point. A transformer can be placed in the nacelle 12 or in the mast 13 to increase the voltage of the electrical energy generated by the wind turbine 10.

Figure 3 shows schematically a small wind farm 20 in star configuration according to an embodiment of the present invention. The wind turbines 21 (each small circle symbolizes a wind turbine) are connected in star configuration with cables 22 to a central wind turbine 23. From the central wind turbine 23 goes a cable 24 to a transformer 26 and the electric power is transported to shore by a cable 27. The star configuration refers to the electrical configuration of the wind turbines, not the actual layout of the wind farm.

On a wind farm arranged in a star configuration all 'branches' in the star only have to carry the full load current of one wind turbine, and so the cross-section, thus the cost of wind farm cabling may be lower.

A star configuration is also more robust against cable failures between wind turbines. A cable failure between wind turbines in a traditional radially connected wind farm will disconnect all wind turbines further away from the collection point. A cable failure between wind turbines connected in a star configuration will only disconnect the wind turbine affected by the cable failure. A star configuration therefore ensures higher availability of the wind turbines in the wind farm.

Furthermore, this star configuration is symmetrical, which means that

- the voltage rise will be the same at all turbines in one star;

- the stress from transient over-voltages will be the same at all turbine locations and can be more easily predicted, prevented or suppressed. A wind farm in star configuration should have less energy losses than a wind farm in radial configuration

The difficulty is in realizing the middle point of the star, including all in- and outgoing cables with corresponding switching apparatus, without having to build a separate platform or without increasing the size and weight of the equipment in the turbine. This will effectively limit the number of single wind turbine branches that can originate from one such star.

The star topology refers only to the electrical connections. The physical layout of wind turbines in a wind farm can be different from a star form but when the wind turbines in a wind farm are connected as a star it has a star topology.

Figure 4 shows schematically a wind farm 30 with several 5- star configurations connected radially according to one embodiment of the present invention. The wind turbines 31

(each small circle symbolize a wind turbine) are connected in star configuration with cables to a central wind turbine 32. From the central wind turbine in all stars goes a feeder cable 33 to a transformer 35 and the electric power is transported to shore by a cable 36.

Figure 5 shows the vertical arrangement of the switchgear in the wind turbine tower 44 at the center of a 5-star configuration according to one embodiment of the present invention. The cables 41 from the external wind turbines in the 5-star configuration are connected over switching units 42 to the vertical busbar or busriser 43. The cable 45 from the nacelle is also connected to the vertical busbar 43 over switchgear. The vertical arrangement, shown in figure 5, makes it possible to place switching units inside the turbine tower, without requiring additional space. With today's equipment the footprint of the switchgear with such vertical arrangement could be contained within about 2 m², however by using more modern apparatus such as electronic technology for the switches it is predicted that the footprint of the vertically arranged switchgear could be further decreased.

The switching units 42 or switching devices are apparatuses designed to make or break the current in one or more electric circuits. They can be mechanical switching devices that make or break the current by means of separable contacts. The mechanical switching device may have different medium between the separable contacts such as air, vacuum, oil, SF6. The switching unit can be a load switch or switch-disconnector which is capable of switching the rated current and in the open position satisfies the isolating requirements specified for a disconnector. The switching unit can be a breaker or circuit breaker which is capable of making, carrying and breaking currents under normal circuit conditions. The breaker is also capable of making, carrying and breaking currents under specified abnormal circuit conditions such as those of short circuit.

Figure 6 shows schematically a wind farm with several star configurations 50 of wind turbines connected in a star topology. The star configurations 50 are all connected to a transformer 51 and the transformer 51 is connected to the grid with a cable 52.

Figure 7 shows schematically an embodiment of the present invention where several switching units 65 are arranged vertically inside a wind turbine tower 61. The switching units can be with Standard technology or custom made for the application. The switching units can be arranged very compact for the application. Cables 62 from other wind turbines are connected to the switching units 65. The generated electricity in the wind turbine is also connected 63 to a switching unit 65. The vertical busbar or busriser 64 connects the switching units and transport away the current generated by all the wind turbines connected in star configuration. The vertical busbar is connected with a cable which leads the generated current to a collection point (not shown in the figure) .

Figure 8 shows schematically an embodiment of the present invention where several compact switching units 70, 71 are arranged vertically. The switching units can be any of the type switch, load switch or breaker and the switching units can be modularized. The switching units modules could be cast in solid insulation. The switching units 70, 71 are stacked on top of each other and the vertical busbar is arranged inside of the switching units 70, 71. The top of one switching unit 71 and the bottom of another switching unit 70 are arranged with contacts so that when they are placed on top of each other, a connection 72 is achieved. Several switching units 70, 71 can be stacked in this manner, ensuring a small footprint for example inside the wind turbine tower. Each switching unit 70, 71 is connected with a cable 74, 75 which transports the current generated by a wind turbine.

While the invention has been described in connection with a preferred embodiment, it is not intended to limit the scope of the invention to the particular form set forth, but on the contrary, it is intended to cover such alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims .

Claims

1. A wind turbine arranged with a medium or high voltage switchgear, said switchgear comprises two or more switching units arranged for interrupting two or more currents characterized in that said switching units are arranged above one another.

2. A wind turbine, according to claim 1, characterized in that said switching units can be any of the type switch, load switch, switch-disconnector, breaker, circuit breaker.

3. A wind turbine, according to any of the claims 1-2, characterized in that the switching units are all connected to an external busbar arranged vertically.

4. A wind turbine, according to any of the claims 1-2, characterized in that a switching unit is directly connected to the switching unit above and below.

5. A wind turbine, according to any of the claims 1-4, characterized in that said switchgear is located in a wind turbine tower.

6. A wind turbine, according to any of the claims 1-5, characterized in that said switchgear is built up of modules.

7. A wind turbine, according to claim 6, characterized in that said modules comprise at least one switching unit.

8. A wind turbine, according to claim 6, characterized in that said modules comprise at least one unit for sensing or measuring voltage or current .

9. A wind turbine, according to claim 6, characterized in that said modules comprise at least one fuse.

10. A wind turbine, according to any of the claims 1-9, characterized in that at least one switching unit is arranged to break a current generated by the wind turbine .

11. A wind turbine, according to any of the claims 1-10, characterized in that at least one switching unit is arranged to break a current generated by another wind turbine.

12. A wind farm system comprising at least one first wind turbine arranged with a medium or high voltage switchgear, said switchgear comprises two or more switching units arranged for interrupting two or more currents, and the wind farm system comprises a plurality of wind turbines, characterized in that said switching units are arranged above one another and said first wind turbine is electrically connected to two or more other wind turbines.

13. A wind farm system, according to claim 12, characterized in that said wind farm system comprises at least two second wind turbines are electrically connected to a first wind turbine.

14. A wind farm system, according to any of the claims 12-13, characterized in that the at least two second wind turbines are arranged without a said medium or high voltage switchgear.

15. A wind farm system, according to any of the claims 12-14, characterized in that the switchgear in first wind turbine is arranged to break electrical connection to two or more electrically connected second wind turbines.

16. A wind farm system, according to any of the claims 12-15, characterized in that all switching units are connected to a vertically arranged busbar.

17. A wind farm system, according to any of the claims 12-16, characterized in that the wind farm is placed near shore or off shore.

18. A wind farm system, according to any of the claims 12-16, characterized in that the wind farm is placed on land.

19. A wind farm system, according to any of the claims 12-18, characterized in that the first wind turbine is connected to three or more other wind turbines.

20. A wind farm system, according to any of the claims 12-19, characterized in that first wind turbine is connected to the second wind turbine in a star topology.

21. A wind farm system, according to any of the claims 12-20, characterized in that two or more first wind turbines are serially connected.

22. A wind farm system, according to any of the claims 12-21, characterized in that two or more first wind turbines are connected in a star topology.

23. A wind farm system, according to any of the claims 12-22, characterized in that two or more first wind turbines are serially connected and two or more first wind turbines are connected in a star topology.