Sensing in an Offshore Electrical Architecture in a Wind Power Plant

Abstract

A system is provided for monitoring characteristics within a subsea electrical architecture of an offshore wind farm having one or more wind turbines. **Solution**: The system includes a first passive optical sensor within a subsea unit for monitoring electrical or environmental characteristics within the subsea unit, a first optical fiber bundle extending integrally within a power cable, a first optical interconnect unit within the subsea unit for optically coupling one or more optical fibers of the optical fiber bundle to the passive optical sensor, a monitoring unit installed at an onshore grid connection point, and a second optical interconnect unit for optically coupling one or more optical fibers of the optical fiber bundle to the monitoring unit. The monitoring unit is configured to transmit a monitoring optical signal along one or more optical fibers of the first optical fiber bundle to the first optical interconnect unit and to identify the location of a fault and / or operate a circuit breaker based on the optical signal transmitted from the first passive optical sensor via the first optical fiber bundle.

Description

Technical Field

[0001] The present invention relates to sensing within a subsea electrical architecture in a wind farm, and more particularly, although not necessarily so, to subsea sensing of current, voltage, power, and temperature, and subsea sensing for facilitating fault location within such an architecture.

Background Art

[0002] Offshore wind farms are playing an increasingly important role in supplying electrical energy. This is driven by the increasing capacity of wind turbines 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 expected to have a generating capacity of 3.6 GW generated by approximately 600 individual turbines.

[0003] Within a particular wind farm, individual turbines or a subset of those turbines can be connected to a substation that supplies power to an onshore grid connection point via a main power or "export" cable. The power can be transferred from the substation to the onshore grid connection point by alternating current power transmission or high voltage direct current (HVDC) power transmission. The turbine itself generates alternating current power, which is transferred from the turbine to the substation for conversion to direct current and / or for boosting or reducing the voltage. The substation uses transformers and / or DC-AC converters before transferring the power via the export cable. The export cable is a subsea power cable, but the substation can be installed above the water surface or subsea, usually on the seabed.

[0004] FIG. 1 shows an exemplary electrical connection architecture of a wind power plant 1. In this architecture, a group of four wind turbines 2 are connected in a "star" configuration, i.e., in parallel, to respective connection boxes 3 via respective local cables 4. A single cable 5 (sometimes called a "collector" cable) connects each connection box 3 to an offshore substation 6 and, via that substation, to an export cable 7. Currently, an architecture with a bottom-fixed substation on the topside is being deployed. An alternative architecture possible when the wind power plant is located relatively close to the coast allows the collector cable to extend directly to the coast and avoids the need for a topside substation.

[0005] Of course, it is also conceivable to install both the connection box and the substation underwater. In this case, assuming the star configuration shown, cables 4, 5 can be connected to connection box 3 using wet mate connectors (not shown in the figure). Wet mate connectors allow the connection and disconnection of components and cables underwater, avoiding the need to bring these components and cables to the water surface for connection and making the process cheaper and faster. Wet mate connectors can be connected and disconnected underwater using a remotely operated vehicle (ROV) or other means. It may be possible to insert a blind plug / cap in place of one half of the cable connector and thus pass power through the underwater connection box with one or more cables cut. Some connectors can also have a voltage applied without a protective cap (since they have built-in protection / barriers). Cables 5, 7 can be similarly connected to substation 6 using wet mate connectors.

[0006] Other connection architectures are of course possible. As an example, FIG. 2 shows a "daisy chain" arrangement, i.e., a series of wind turbines connected in series, and FIG. 3 shows two pairs of wind turbines where each pair of turbines is connected in parallel to a subsea junction box, and the junction boxes are connected in series to a collector cable. In a modified embodiment of the architecture of FIG. 3, the wind turbines are connected in series and each wind turbine is connected to the collector cable via a T-shaped junction.

[0007] The subsea junction box 3 and the substation 6 can have built-in electrical disconnectors or circuit breakers and can have control functions for the operation of these mechanical devices. They can have sensing means for monitoring the flow of current and power, or other aspects of the plant, and can have functions for fault identification and location.

[0008] The subsea substation 6 can also have control and monitoring functions for the substation itself, the connected subsea power cables 5, 7, and the wind turbines 2. The monitoring function can be used to identify faults in the subsea electrical network including the cables, connectors, subsea junction boxes, and subsea substation and to locate the faults. The control and monitoring system can cooperate with the control and protection systems of the wind turbines and the control and protection systems at the receiving end of the export cable to ensure selectivity.

[0009] Conventional electrical sensors used for protection and monitoring, such as current transformers and voltage transformers, Rogowski coils and voltage dividers, require a nearby protection relay or similar interface unit. These devices require a low-voltage power supply and power connection and are expected to be less reliable than the sensors themselves. Of course, transferring low-voltage power over long distances is often not feasible. Circuit breakers, protection relays can be installed on land and are actually installed, but the absence of these in subsea components makes it difficult to identify faults in the electrical network, locate the faults, and remove / isolate the faults.

[0010] In the case of a subsea junction box and a substation without an incorporated circuit breaker, the circuit breaker needs to be installed on land. However, when attempting to implement sensors using conventional current transformers and voltage transformers, the absence of local subsea circuit breakers and their associated protection relays is a problem.

Summary of the Invention

Problems to be Solved by the Invention

[0011] The object of the present invention is to reduce, preferably eliminate, the need for subsea units, such as active components within subsea junction boxes and substations, i.e., components that are powered. This is achieved by introducing passive optical sensors into the unit. Local low-voltage power supplies and associated power connections are no longer required, reducing cost and complexity. Switching devices, including circuit breakers and protection relays, can be installed on land.

Means for Solving the Problems

[0012] According to a first aspect of the present invention, there is provided a system for monitoring characteristics in a subsea electrical architecture of an offshore wind farm, comprising one or more wind turbines electrically coupled to at least one subsea unit, and the subsea unit coupled via a power cable for transmitting power generated by the wind turbine or each wind turbine to a bottom-fixed unit of an offshore topside or to an onshore grid connection point. The system includes one or more first passive optical sensors within the subsea unit for monitoring electrical or environmental characteristics within the subsea unit; a first optical fiber bundle integrally within or extending proximate to the power cable; a first optical interconnect unit within the subsea unit for optically coupling one or more optical fibers of the optical fiber bundle to the first passive optical sensor or each first passive optical sensor; a monitoring unit installed at or proximate to the bottom-fixed unit of the offshore topside or the onshore grid connection point; and a second optical interconnect unit for optically coupling one or more optical fibers of the optical fiber bundle to the monitoring unit. The monitoring unit is configured to transmit a monitoring optical signal along one or more optical fibers of the first optical fiber bundle to the first optical interconnect unit, and to identify the location of a fault and / or operate a circuit breaker based on an optical signal transmitted from the first passive optical sensor or each first passive optical sensor via the first optical fiber bundle.

[0013] The subsea unit can be either a junction box or a substation. When the subsea unit is a subsea substation and the power cable is a main export power cable connected to the grid connection point, the monitoring unit and the second optical interconnect unit can be installed at or proximate to the grid connection point.

[0014] The system can comprise at least one second subsea unit, the second subsea unit being a junction box connected to a wind turbine by a local cable and to the subsea transformer station by a collector cable, the system further comprising one or more second passive optical sensors in the junction box for monitoring electrical or environmental characteristics therein, a second optical fiber bundle extending integrally within or in proximity to the collector cable, and a second optical interconnect unit in the junction box for optically coupling one or more optical fibers of the second optical fiber bundle to the second passive optical sensors or respective second passive optical sensors. The first optical interconnect unit in the subsea transformer station optically couples the fibers of the first and second optical fiber bundles, and the monitoring unit is further configured to transmit a monitoring optical signal along one or more optical fibers of the second optical fiber bundle to the second passive optical sensors and to identify the location of a fault and / or operate a circuit breaker based on an optical signal transmitted from the second passive optical sensors or respective second passive optical sensors via the second optical fiber bundle.

[0015] When the first subsea unit is a subsea junction box coupled to a bottom-fixed unit of an offshore topside by a collector power cable, the bottom-fixed unit of the offshore topside is a transformer station and can have a low-voltage power supply for the monitoring unit.

[0016] The first and / or second passive optical sensors or respective first and / or second passive optical sensors may be configured to detect one of current, voltage, power, and temperature, and the monitoring unit may be configured to identify the location of a fault and / or operate a circuit breaker when an optical signal transmitted from the first or second passive optical sensors or respective first or second passive optical sensors indicates a current, voltage, power, or temperature outside a predetermined operating range, e.g., exceeding a predetermined threshold.

[0017] The subsea unit or respective subsea units can be filled with pressurized oil.

[0018] The power cable or each power cable can be either a three-phase alternating current (AC) submarine power cable or a high-voltage direct current (HVDC) submarine power cable.

[0019] The passive optical sensor or each passive optical sensor can be an individual optical sensor or a distributed optical sensor.

[0020] The passive optical sensor or each passive optical sensor can be configured to monitor electrical characteristics or environmental characteristics within a subsea unit associated with corresponding electrical components having dynamic electrical ratings.

[0021] According to a second aspect of the present invention, there is provided a method for monitoring characteristics within a subsea electrical architecture of an offshore wind farm, comprising one or more wind turbines electrically coupled to at least one subsea unit and a subsea unit coupled to the bottom-fixed unit at the offshore topside or to a grid connection point on land via a power cable for transmitting the power generated by the wind turbine or each wind turbine. The method includes transmitting a monitoring optical signal from a monitoring unit along one or more optical fibers of a first optical fiber bundle integrally disposed within or proximate to the power cable, receiving the monitoring optical signal at a first optical interconnection unit within the subsea unit, optically coupling the signal to one or more first passive optical sensors within the subsea unit configured to monitor electrical characteristics or environmental characteristics within the subsea unit, returning an optical signal from the sensor or each sensor to the monitoring unit via the first optical interconnection unit and one or more optical fibers of the first optical fiber bundle, and analyzing the returned optical signal to identify the location of a fault and / or operate a circuit breaker.

Brief Description of the Drawings

[0022]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6A

Figure 6B

Figure 6C

DETAILED DESCRIPTION OF THE INVENTION

[0023] It will be understood that it is desirable to operate various sensors at locations in the sea within the electrical architecture of an offshore wind farm. However, if these sensors require (low voltage) power, it can be difficult and costly to supply that power, especially over long distances, for example from an onshore location or an offshore topside location. Therefore, sensors for monitoring current, voltage, power (by current and voltage measurement), temperature, and sensors for fault location are proposed to be implemented within a subsea unit as passive optical sensors that communicate directly via optical fiber communication, eliminating the need for active sensors and associated auxiliary / control power supplies. Optical fiber cables can be laid over long distances, for example up to several hundred kilometers, without the need for repeaters. Thus, such passive sensors can be operated from an onshore location or an offshore topside without the need for any offshore power or other locally generated offshore power. Multiple optical fiber cables can be laid as a single bundle from an onshore location or an offshore topside location. Components of the electrical architecture, such as a subsea substation or a subsea junction box, can include optical fiber cable wiring means for routing individual optical fiber cables into a bundle within the component and / or laying them on additional cables. Circuit breakers associated with the wind farm and the subsea cables can be installed at an onshore or an offshore topside location.

[0024] Problems can occur when laying optical fiber cables over a significant distance, but these can be mitigated by using undersea cables incorporating AC cables and optical fiber cable bundles, or in the case of HVDC, by using optical fiber cable bundles laid near HVDC power cables. Such undersea AC cables have conventionally been used to supply power to offshore facilities such as oil and gas production platforms, but can also be used for the main purpose of transferring power within the electrical architecture of a wind farm to an onshore grid connection point. Figure 4 schematically shows an exemplary three-phase alternating current undersea power cable including three main power lines 8 with associated insulation layer 9 and an outer protective layer 10. The cable includes an optical fiber cable bundle 11 containing a plurality of optical fibers 12. Accordingly, it is proposed to use such an optical fiber bundle as a means of operating and responding passive sensors within the electrical architecture of a wind farm.

[0025] Figure 5 shows an exemplary electrical architecture of a wind farm based on the architecture of Figure 1, but using optical fiber bundles incorporated in the main export cable 7 and the collector cable 5 connecting the undersea junction box 3 to the undersea substation 6. The collector cable and the main export cable can have the same or different structures, but both incorporate an optical fiber bundle 11.

[0026] Both the subsea junction box 3 and the subsea substation 6 incorporate an optical interconnect 13, which facilitates the passive routing of optical signals from the individual optical fibers 12 of each bundle to other optical components (e.g., optical sensors) within the junction box or substation or to the optical fibers of the output fiber bundle beyond the junction box or substation. In the latter case, this may be to facilitate the routing of optical signals between the fibers of the export cable and the fibers of the collector cable at the subsea substation. As an example, the optical fiber bundle within the export cable can comprise 48 fibers enclosed within one common metal tube. The 48 fibers are then distributed to the respective collector cables. For example, in the case of 4 collector cables, 12 fibers are routed to each collector cable. Note: A single optical fiber can be connected to multiple passive optical sensors. In the case of temperature sensing, the temperature is sensed directly from the fiber and a temperature profile along the length of the fiber can be read.

[0027] Considering now the passive optical sensors 14, 15 installed within the subsea junction box or subsea substation, the proposed architecture enables a direct connection, substantially, to the onshore substation 16. At the onshore substation 16, signals are connected to the protection relay such that a subsea fault can trigger the opening of the onshore circuit breaker 17 via some monitoring unit 18. Alternatively or in addition, measurements are used to locate the fault so that a ship can be mobilized to visit the site, conduct inspections and, if necessary, "repair" by disconnecting defective components or units, e.g., by means of wet-mate connectors, so that the wind farm can continue to operate (possibly at reduced capacity). The proposed architecture avoids the need for circuit breakers within the subsea substation or subsea junction box and thus the need for power at these locations.

[0028] Passive optical sensors suitable for monitoring current and voltage include, for example, those supplied by Synaptec® of Glasgow, UK. However, as far as the inventors are aware, the use of such sensors in an undersea location has not been proposed heretofore. Although it is not necessary to describe the optical sensors in detail herein, these generally operate in the immediate vicinity of a power cable and are, for example, wound around the power cable as a series of turns, where the electromagnetic field surrounding the power cable affects the light transmitted along an optical component, such as a fiber, and measurements of voltage and / or current are made so as to typically modulate the intensity or frequency of the light. For example, the light returned to an onshore monitoring station along the same fiber or a different fiber used to transmit the light to the sensor is demodulated to identify the modulation signal and thereby identify the current and / or voltage of the power cable. By examining in detail the measured current, voltage or temperature, faults can be detected, their location identified and countermeasures taken. Passive optical sensors can also be used to measure the temperature of cables within an undersea junction box or substation, or the temperature at other locations within the junction box or undersea substation. The use of such passive temperature sensors can be used for the “dynamic rating” of components, such as undersea transformers within an undersea substation, and the components can be operated above their rated power for a limited period of time.

[0029] It will be understood that various changes may be made to the above-described embodiments without departing from the scope of the present invention. In particular, although FIG. 5 shows a relatively complex scheme, other schemes using passive optical sensors incorporated in the subsea unit and long- or short-distance optical fiber bundles are possible. For example, FIG. 6A shows a scheme in which a plurality of wind turbines 20 are each connected to a respective subsea junction box 21 and via the junction box to a collector cable 22. The collector cable includes an incorporated optical fiber bundle 23, or an optical fiber bundle laid together with or in proximity to the collector cable. The optical fiber bundle 23 is connected to passive sensors within the junction box 21 and terminates at a topside bottom-fixed substation 24. The topside bottom-fixed substation 24 comprises means for transmitting and monitoring optical signals along the fiber bundle for the purpose of identifying the location of a fault and / or operating a circuit breaker. The topside substation 24 is connected to a grid connection point 26 by a main export cable 25. Since the substation is a topside substation, low-voltage power is available at the substation.

[0030] FIG. 6B shows a scheme similar to FIG. 5 in which the optical fiber bundle 23 extends from an onshore grid connection point through a subsea substation to the subsea junction box and passive sensors are installed within the subsea junction box and the substation. In this case, the optical fiber bundle 23 is incorporated in both the collector cable 22 and the main export cable 25, or laid together with or in proximity to both the collector cable 22 and the main export cable 25.

[0031] FIG. 6C shows yet another scheme in which the substation is in this case also a subsea substation 24 including passive optical sensors, and the passive optical sensors are coupled to the optical fibers of a fiber bundle 23 extending from an onshore grid connection point 26.

Claims

1. A system for monitoring characteristics within the underwater electrical architecture of an offshore wind farm, comprising one or more wind turbines electrically coupled to at least one first underwater unit, and the first underwater unit coupled to a bottom fixed unit on the offshore topside or to an onshore grid connection point for transmitting the wind turbines or the power generated by each wind turbine via power cables, The aforementioned system, One or more first passive optical sensors within the first underwater unit for monitoring electrical or environmental characteristics within the first underwater unit, A first optical fiber bundle extending integrally within the power cable or adjacent to the power cable, A first optical interconnection unit located within the first underwater unit, which optically couples one or more optical fibers of the first optical fiber bundle to the first passive optical sensor or each of the first passive optical sensors, A monitoring unit installed at the bottom fixed unit of the offshore topside or at the onshore grid connection point, or in close proximity to the bottom fixed unit of the offshore topside or the onshore grid connection point, A second optical interconnection unit that optically couples one or more optical fibers of the first optical fiber bundle to the monitoring unit, Equipped with, The monitoring unit is configured to transmit a monitoring optical signal along one or more optical fibers of the first optical fiber bundle to the first optical interconnect unit, and to locate a fault and / or activate a circuit breaker based on the optical signals transmitted from the first passive optical sensor or each of the first passive optical sensors via the first optical fiber bundle.

2. The system according to claim 1, wherein the first underwater unit is either a junction box or a substation.

3. The system according to claim 1, wherein the first underwater unit is an underwater substation, the power cable is a main export power cable connected to the grid connection point, and the monitoring unit and the second optical interconnection unit are installed at or near the grid connection point.

4. The system comprises at least one second underwater unit, the second underwater unit being a junction box connected to a wind turbine by a local cable and to the underwater substation by a collector cable. The aforementioned system further, One or more second passive optical sensors located within the junction box for monitoring the electrical or environmental characteristics within the junction box, A second optical fiber bundle extending integrally within the collector cable or adjacent to the collector cable, A second optical interconnection unit located within the connection box optically couples one or more optical fibers of the second optical fiber bundle to the second passive optical sensor or each of the second passive optical sensors. Equipped with, The system according to claim 3, wherein the first optical interconnection unit in the underwater substation optically couples the fibers of the first and second optical fiber bundles, and the monitoring unit is further configured to transmit monitoring optical signals along one or more optical fibers of the second optical fiber bundle to the second passive optical sensor, and to locate a fault and / or activate a circuit breaker based on optical signals transmitted from the second passive optical sensor or each of the second passive optical sensors via the second optical fiber bundle.

5. The system according to claim 1, wherein the first underwater unit is an underwater connection box connected by a collector power cable to a bottom-fixed unit on the offshore topside, the bottom-fixed unit on the offshore topside is a substation and has a low-voltage power supply for the monitoring unit.

6. The system according to claim 4, wherein the first passive optical sensor and / or the second passive optical sensor, or each of the first passive optical sensors and / or each of the second passive optical sensors, is configured to detect one of current, voltage, power, and temperature, and the monitoring unit is configured to locate a fault and / or operate a circuit breaker when the optical signal transmitted from the first passive optical sensor or the second passive optical sensor, or each of the first passive optical sensors, or each of the second passive optical sensors indicates a current, voltage, power, or temperature outside a predetermined operating range, for example, exceeding a predetermined threshold.

7. The system according to any one of claims 1 to 5, wherein the first underwater unit or each of the first underwater units is filled with pressurized oil.

8. The system according to any one of claims 1 to 5, wherein the power cable or each power cable is either a three-phase AC underwater power cable or a high-voltage direct current (HVDC) underwater power cable.

9. The system according to any one of claims 1 to 5, wherein the first passive optical sensor or each of the first passive optical sensors is an individual optical sensor or a dispersed optical sensor.

10. The system according to any one of claims 1 to 5, wherein the first passive optical sensor or each of the first passive optical sensors monitors electrical or environmental characteristics within the first submersible unit related to a corresponding electrical component having a dynamic electrical rating.

11. A method for monitoring characteristics within the underwater electrical architecture of an offshore wind farm, comprising one or more wind turbines electrically coupled to at least one underwater unit, and the underwater unit coupled to a bottom fixed unit on the offshore topside or to an onshore grid connection point for transmitting the wind turbines or the power generated by each wind turbine via power cables, The aforementioned method, The monitoring unit transmits a monitoring optical signal along one or more optical fibers of a first optical fiber bundle that extends integrally within the power cable or adjacent to the power cable. The monitoring optical signal is optically coupled to one or more first passive optical sensors within the underwater unit, which are configured to receive the monitoring optical signal in a first optical interconnection unit within the underwater unit and to monitor the electrical or environmental characteristics within the underwater unit. The optical signals from the first passive optical sensor or each of the first passive optical sensors are returned to the monitoring unit via the first optical interconnection unit and one or more optical fibers of the first optical fiber bundle. The returned optical signal is analyzed to locate the fault and / or activate the circuit breaker. Methods that include...

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