Electrical protection systems and methods for offshore wind power plants

Abstract

An electrical protection system for an offshore wind farm comprising one or more arrays of wind turbine generators, wherein, for the array or each array, a first wind turbine generator is (a) via tower cable to the generator of the wind turbine generator, (b) via collector cables to submarine substations, and (c) Interarray cables to one or more additional wind turbine generators of the array Provides connected connection points. This allows the power generated by the array to be transmitted through the connection point of the first wind turbine generator. The system includes a circuit breaker located above the water surface on the first wind turbine generator and between the connection point and the collector cable.

Description

Technical Field

[0001] The present invention relates to an electrical protection system and method for an offshore wind farm, and more particularly to an offshore wind farm comprising a plurality of wind turbine generators connected to a subsea substation and / or a subsea junction box.

Background Art

[0002] Offshore wind farms are playing an increasingly important role in the supply of electrical energy. This is driven by the increasing capacity of wind turbine generators (WTGs) and the increasing number of turbines in individual wind farms. For example, consider the Dogger Bank Wind Farm located off the northeast coast of England, which is predicted to have a generating capacity of 3.6 GW generated by approximately 600 individual WTGs.

[0003] Figures 1 and 2 show alternative power system connection systems that can be utilized in an offshore wind farm. In the system of Figure 1, the array comprises two pairs of WTGs 1a, 1b. Each pair of WTGs is connected in parallel to a junction box 2 via respective inter-array (between arrays) power cables 3. In the system of Figure 2, the WTG 4 is coupled in a daisy chain manner by an inter-array cable 5 that connects the WTGs in series. These systems each have advantages and disadvantages.

[0004] Within a given wind farm, individual WTGs may be connected to offshore substations (OSSes). OSSes may be fixed-bottom (e.g., monopile or jacketed), floating, or submarine, and supply power to onshore grid connections via main power supply cables, or "export" cables. Power can be transmitted from the OSS to onshore grid connections by alternating current (AC) or high-voltage direct current (HVDC). The WTGs themselves generate AC power, which is transmitted from the WTGs to the OSS via collector cables for conversion to DC and / or voltage boosting or bucking. The OSS utilizes transformers and / or AC / DC converters before transmitting power through the transmission cables. While the transmission cables are submarine power cables, the OSS is typically located above the waterline.

[0005] Traditionally, OSSes are equipped with a control and protection system that includes switchgear (SWG), protective relays, and telecommunications equipment. Figure 3 shows an exemplary configuration in which multiple daisy-chained WTG arrays 7 (only one of which is shown) are connected to the OSS 6 via their respective collector cables 8. Each collector cable 8 is connected to the power lines 9 of the OSS 6 via associated circuit breakers (CBs) 10, the CBs being located within the switchgear of the OSS. These CBs are high-voltage / high-current components designed to interrupt the flow of power if a fault is detected in the system. For OSSes located above water level, the CBs are installed within the OSS, and the associated costs are considered reasonable in relation to the overall project. It will be understood that the CBs installed in the OSS are capable of operating to disconnect WTGs at the array level, i.e., all WTGs within a given daisy-chain array 7 are connected or disconnected together.

[0006] The switchgear (SWG) 11 installed in the WTG conventionally includes three circuit breakers. A commonly used configuration is shown in Figures 3 and 4, where the following symbols are used for different circuit breaker types. Circuit breaker - "x" Load switch - "o" Disconnector - "-" Those skilled in the art will be aware of the definitions of these terms, but for clarification, the following is provided.

[0007] Circuit breaker: An electrical switch designed to protect electrical circuits from damage caused by overcurrent / overload or short circuit. Its basic function is to interrupt the flow of current after a protective relay detects a fault. The flow of current can also be interrupted manually or remotely.

[0008] Load switch: A mechanical switch configured to open, energize, and interrupt current under normal conditions. This device may also energize current for a specified time under defined abnormal circuit conditions, such as those associated with short circuits. Short-circuit current may be energized but not interrupted.

[0009] Disconnectors: High-voltage disconnectors are used to allow isolation of equipment for maintenance purposes. Disconnectors are typically intended solely for safety isolation, not for normal control of the circuit. Unlike load switches and circuit breakers, disconnectors lack a mechanism to suppress the electric arc that occurs when a conductor carrying high current is mechanically disconnected. Therefore, they are no-load devices, have very low breaking capacity, and are intended to be opened only after the current has been interrupted by other control devices such as circuit breakers.

[0010] Note: So-called switch-disconnectors can combine the characteristics of both load switches and disconnectors. In the following description, when the term "load switch" is used, it is considered to include switch-disconnectors as well.

[0011] The configurations shown in Figures 3 and 4, incorporated into the WTG, include: (1) a circuit breaker CB connected between the central interconnection point CP and the tower cable connected to the generator of the WTG; (2) a load switch (LS) connected between the central interconnection point (CP) and the interarray cable connected to the preceding WTG in the same daisy-chain array (assuming that the WTG is not the terminal (last) WTG); and (3) a disconnector (D) connected between the central interconnection point CP and the subsequent WTG or (if the WTG is the first (first) WTG) the OSS. It will be understood that the central interconnection point (CP) referred to herein may be a node or other component (e.g., including a busbar).

[0012] This configuration presents a cost-effective solution that does not compromise selectivity and protection. The CB10 on the OSS6 provides primary protection for the collector cable and inter-array cable (IAC), while the CB on the WTG protects the tower cable and WTG. The LS on the WTG is useful for disconnecting the upstream WTG without shutting down the entire inter-array string. Finally, the disconnector on the WTG serves to isolate the WTG from the downstream electrical infrastructure during maintenance.

[0013] The protection function of WTG's circuit breakers is typically limited to overcurrent protection. It is not common practice to install advanced protective relays that use both current and voltage measurements. A fault path indicator (FPI) is typically used to locate a fault. The FPI records whether the fault current passed through a branch / cable and returns a binary output. This is not used to control the circuit breaker.

[0014] Depending on the circumstances, it may be beneficial to place parts of the electrical system infrastructure, in addition to cables, on the seabed. For example, submarine OSS and / or submarine junction boxes could be considered.

[0015] Figure 5 shows an alternative architecture in which a subsea substation (SSS) 115 and subsea junction box 116 include multiple WTGs connected in a star or branch configuration, with a tower CB between each WTG and the interarray cable. In such a configuration, it may be beneficial to provide a subsea switchgear within the SSS 115 in the form of one CB for each collector cable to avoid the need to remove a single fault in either the interarray cable or the collector cable, which would require removal by the circuit breaker on the onshore transmission cable and the complete shutdown of the wind farm. In the alternative architecture, the subsea switchgear may be installed in the first subsea junction box in the string. In this way, only the string is affected in the event of a cable failure.

[0016] Submarine electrical architectures require a re-examination of conventional control and protection concepts to achieve lean, cost-effective submarine electrical architectures while ensuring selectivity and protection. For example, considering the availability and cost of specific components used in the seabed, including submarine CBs, new systems and methods may be needed to realize such architectures. For instance, considering an architecture similar to the one in Figure 3, but with the OSS located on the seabed, implementing this with a submarine CB may not be commercially viable. [Overview of the project] [Means for solving the problem]

[0017] According to a first aspect of the present invention, an electrical protection system for an offshore wind farm comprising one or more arrays of wind turbine generators, wherein, for the array or each array, the first wind turbine generator is (a) via tower cable to the generator of the wind turbine generator, (b) via collector cables to submarine substations, and (c) Interarray cables to one or more additional wind turbine generators of the array An electrical protection system is provided that provides a connected connection point.

[0018] This enables the power generated by the array to be sent through the connection point of the first wind turbine generator. The system comprises a circuit breaker located above the water surface on the first wind turbine generator and between the connection point and the collector cable.

[0019] The remaining wind turbine generators of the array can be connected in a daisy chain configuration behind the first wind turbine generator via additional inter-array cables.

[0020] The inter-array cables may be connected to a junction box, and the remaining wind turbine generators of the array may be connected to a submarine junction box in a star configuration or a branched configuration via additional inter-array cables.

[0021] The circuit breaker may be the circuit breaker of the switching device of the first wind turbine generator, and the switching device further comprises a further circuit breaker between the connection point and the tower cable, and / or a circuit breaker or load switch or circuit breaker between the connection point and the inter-array cable.

[0022] According to a second aspect of the present invention, an offshore wind power plant is provided comprising one or more arrays of wind turbine generators and an electrical protection system according to the first aspect above.

[0023] According to a further aspect of the present invention, a method of operating a wind power plant according to the second aspect is provided, the method comprising energizing a power transmission cable connecting a submarine substation to an onshore location and a collector cable, while energizing the inter-array cables at a later time.

Brief Description of the Drawings

[0024] [Figure 1] Shows two pairs of wind turbine generators connected in series to a submarine junction box. [Figure 2]Shows a set of wind turbine generators connected in a daisy chain configuration. [Figure 3] Shows a plurality of daisy chain connected wind turbine generator arrays connected in parallel to an offshore substation on water. [Figure 4] Shows the opening and closing device arrangement of a wind turbine generator. [Figure 5] Shows one of a plurality of wind turbine generator arrays, where the wind turbine generators of each array are connected in a star configuration to a submarine connection box, and the plurality of arrays are connected to an offshore substation via their respective collector cables. [Figure 6] Shows a plurality of daisy chain connected wind turbine generator arrays connected in parallel to an offshore substation on the seabed. [Figure 7] Shows the opening and closing device arrangement of a wind turbine generator. [Figure 8] Shows an array of wind turbine generators where one of the generators is connected in a daisy chain configuration between an offshore substation and a submarine connection box, and the remaining wind turbine generators are connected to the connection box in a star configuration. [Figure 9] Shows a method of energizing the components of a wind farm.

Mode for Carrying Out the Invention

[0025] Figure 6 shows the power grid interconnection architecture of a wind farm having an underwater substation (SSS) 12 and daisy-chained wind turbine generators (WTGs) 13. [Note: For simplification, the architecture is generally a three-phase architecture, but multiple phases are shown in a coupled form.] To achieve a lean and cost-effective configuration, underwater circuit breakers (CBs) are not provided in the SSS 12. Rather, the configuration of the SWG 14 of the first WTG is modified so that the disconnectors supplying power to the collector cables are replaced by CBs that replace the function of CBs (see Figure 3), which are normally installed on the top surface of the OSS but are now not present in the SSS 12. This is shown in more detail in Figure 7. It should be noted that the switchgear referred to herein may be located in the lower part of the WTG, for example, within the transition piece of the WTG, i.e., between the base (e.g., jacket) and the tower. Other switchgear may be located in other parts of the WTG, for example, within the nacelle.

[0026] Therefore, the collector CB may include a protective relay and the installation of both current and voltage measuring sensors, for example, utilizing current transformers and voltage transformers. According to the proposed configuration, in the event of a fault in the inter-array cable (IAC) system, the collector cable CB of the first WTG ensures selective disconnection of only one WTG string, avoiding tripping of the entire transmission cable system for the wind farm. It will be understood that the SWGs of the second, third, etc. WTGs of the daisy-chain array remain unchanged, i.e., the configuration in Figure 4, for example, may be used.

[0027] It is worth noting that faults in collector cables must be eliminated by the circuit breakers (CBs) of the onshore transmission cables. Current monitoring may be included in the feed lines of submarine substations (SSS) to allow for the location of faults downstream of the collector CBs. By monitoring the current in the feed lines of each collector cable, it is possible to determine whether the fault is located within the SSS or within a single specific collector cable.

[0028] Figure 8 shows a further architecture in which multiple WTGs 20 of a given array are connected in a star configuration to a junction box 21 via their respective inter-array cables. However, the first WTG 22 of the array is connected to the junction box 21 in a daisy-chain configuration. The switchgear 23 of each star-connected WTG comprises a single circuit breaker (CB), while the switchgear 24 of the daisy-chained WTG 22 comprises a load switch coupled between the WTG interconnection point (CP) and the junction box 21, a first CB connected between the CP and the tower cable, and a second CB connected between the CP and the collector cable leading to the SSS. As previously mentioned, at least the second CB may include a protective relay and voltage and current measuring sensors. This configuration relates to the junction box in both star and branch configurations.

[0029] The architecture in Figure 8 allows for the use of standard switchgear in most WTG arrays. The only modification required is for the switchgear of a single daisy-chained WTG. In particular, a second CB connected between the CP and the collector cable leading to the SSS eliminates the need for subsea switchgear at the SSS. Nevertheless, in the event of a failure in the inter-array cable (IAC) system, the collector cable CB of the first WTG ensures selective disconnection of only one WTG string, avoiding a trip of the entire transmission cable system of the wind farm.

[0030] According to the architecture in Figure 8, the power supply to the system can be simplified to some extent because the power supply to the transmission cable and collector cable can be energized, and the interarray cable can be energized simultaneously at a later time. This is shown in Figure 9.

[0031] Those skilled in the art will understand that various modifications can be made to the above embodiments without departing from the scope of the present invention.

Claims

1. An electrical protection system for an offshore wind farm comprising one or more arrays of wind turbine generators, wherein, for the array or each array, the first wind turbine generator is (a) via tower cable to the generator of the wind turbine generator, (b) via collector cable to submarine substations, and (c) via an interarray cable to one or more further wind turbine generators of the array An electrical protection system that provides a connected connection point so that the power generated by the array is transmitted through the connection point to the first wind turbine generator, and the system comprises a circuit breaker located above the water surface on the first wind turbine generator and between the connection point and the collector cable.

2. The electrical protection system according to claim 1, wherein the remaining wind turbine generators of the array are connected in a daisy-chain configuration behind the first wind turbine generator via further inter-array cables.

3. The electrical protection system according to claim 1, wherein the interarray cable is connected to a junction box, and the remaining wind turbine generators of the array are connected to the submarine junction box in a star or branch configuration via further interarray cables.

4. The electrical protection system according to any one of claims 1 to 3, wherein the circuit breaker is a circuit breaker of the switchgear of the first wind turbine generator, and the switchgear further comprises a further circuit breaker between the connection point and the tower cable, and / or a disconnector, load switch, or circuit breaker between the connection point and the interarray cable.

5. An offshore wind power plant comprising one or more arrays of wind turbine generators and an electrical protection system according to any one of claims 1 to 4.

6. A method for operating a wind power plant according to claim 5, which is dependent on claim 3, comprising energizing a transmission cable and a collector cable connecting the submarine substation to a land location, while energizing the interarray cable at a later time.

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