Three-Core Cable DC Transmission Wind Turbine
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Solution Overview
Problem
The existing methods for transmitting power from wind turbine generators to the grid are inefficient and costly, particularly when transitioning from three-phase ac current to medium-voltage dc current, as they require significant investment in new cabling and auxiliary circuits that need both dc and ac power, which is expensive and labor-intensive.
Innovation Solution
A method utilizing a three-core cable to transmit dc current along one core, return dc current along a second core, and ac current along the third core, with the return ac current shared among all three conductive sheaths in parallel, allowing for the reuse of existing cables and reducing the need for dedicated converters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If medium-voltage DC power transmission is implemented using two cables, then the power transmission capacity is improved, but the requirement for dedicated DC cabling increases investment costs
Solution Approach 1:
The patent applies multi-functionality by enabling three-core AC cables to serve dual purposes: transmitting DC power between wind turbines and substations, and simultaneously providing AC power to auxiliary circuits. This eliminates the need for separate DC-specific cabling infrastructure, reducing investment costs while maintaining high power transmission capacity.
Solution Approach 2:
The patent changes the electrical parameters of existing AC cables by superimposing DC voltage on the cable system. By injecting DC voltage at the substation and utilizing the cable's capacitive properties, the system transforms standard AC cables into functional DC transmission medium without physical modification, thereby avoiding costly cable replacement.
2Device complexity
If AC power is transmitted back to wind turbine auxiliary circuits, then the need for dedicated DC-AC converters is eliminated, but the cabling must handle both DC and AC current transmission
Solution Approach 1:
The patent makes the three-core cable universally functional by enabling it to carry both DC power transmission and AC power delivery to auxiliary circuits. The cable system becomes adaptable to multiple electrical functions simultaneously, eliminating the need for separate converters while meeting all power requirements.
Solution Approach 2:
The patent merges DC power transmission and AC auxiliary power supply into a single integrated cable system. By combining these two previously separate functions into one cable infrastructure, the system reduces device complexity and eliminates the need for additional DC-AC converter equipment.
3Ease of manufacture
If three-core AC cables are used for DC power transmission, then existing cable infrastructure can be reused, but the cables must be adapted to handle DC voltage and current
Solution Approach 1:
The patent changes the operational parameters of existing AC cables by superimposing DC voltage on them. The system exploits the capacitive coupling between cable cores and sheaths to enable DC voltage transmission without modifying the cable's physical structure, thereby maintaining reliability while achieving parameter adaptation.
Solution Approach 2:
The patent introduces a DC voltage injection mechanism at the substation end as an intermediary to enable DC power transmission through AC cables. This intermediary device transforms the cable system's electrical characteristics without requiring cable replacement, ensuring both reuse and reliability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables efficient and cost-effective transmission of both dc and ac power using existing cables, reducing the need for new cabling and converters, thereby lowering costs and maintaining sufficient current-carrying capacity for auxiliary circuits.
Implementation Method 1
transmitting the return ac current along all three conductive sheaths in parallel
Implementation Method 2
transmitting dc current along a first core; and transmitting the return dc current along a second core
Data Source
Figure 1
Figure 2
AI summary
A conventional cable 1 comprises three conductive cores 2a, 2b, 2c, each provided with a respective conductive sheath 3a, 3b, 3c, which are together housed within an outer insulating sheath. The three-core cable 1 is used to transmit electric power in the form of dc current and single-phase ac current. A first one of the conductive cores 2a is used to transmit dc current, while a second conductive core 2b is used to transmit the return dc current. The third conductive core 2c is used to transmit the single-phase ac current. The return ac current is transmitted along all three conductive outer sheaths 3a, 3b, 3c in parallel. The cable is used to transmit dc current from a wind turbine generator to a substation where it is converted to ac before connecting to the mains electricity grid. The ac current is used to power auxiliary circuitry of the wind turbine generator 5 when the output of the turbine generator 5 falls below a give value.