Submarine AC Transmission Using Pipeline Heating for Overvoltage Control
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Solution Overview
Problem
High-voltage AC transmission systems experience significant overvoltage issues during sudden load drops in offshore plants due to the Ferranti effect and capacitive charging currents, which existing reactive compensation methods, such as SVCs, struggle to mitigate effectively, especially in longer transmission cables, and are hindered by weight and space constraints at offshore locations.
Innovation Solution
The implementation of an AC transmission system that includes an onshore power station, an offshore plant, and a submarine cable, where an electrical heating system or a wind power plant with a variable frequency drive is used to connect and control the power factor, compensating for reactive currents and reducing overvoltage by using inductive components to counteract capacitive effects in the transmission system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If SVC (Static Var Compensator) is used for reactive compensation at onshore power station, then overvoltage can be reduced in some cases, but for longer transmission cables and high load drops, the voltage rise becomes too large for SVC to reduce sufficiently, and installing more compensating components increases cost
Solution Approach 1:
The patent moves the compensation function from onshore (SVC at power station) to offshore by utilizing the pipeline heating system. This spatial dimensionality change allows compensation at the point where overvoltage occurs, bypassing the limitation of distance-dependent SVC effectiveness.
Solution Approach 2:
The pipeline heating system, which normally serves only for thermal maintenance, is made multi-functional by enabling it to provide reactive power compensation during overvoltage events. This eliminates the need for dedicated compensating components.
2Object-affected harmful factors
If higher number of compensating components are installed at onshore power station, then overvoltage reduction capability is improved, but cost of the power station increases
Solution Approach 1:
The pipeline heating system is repurposed to provide dual functionality: thermal maintenance and reactive power compensation. This eliminates the need for additional dedicated compensating components and reduces overall system cost.
Solution Approach 2:
The pipeline heating system serves itself by using its own inductive characteristics to provide compensation. The system utilizes its inherent electrical properties rather than requiring separate compensation equipment.
3Object-affected harmful factors
If reactors are installed on topside of offshore platform, then overvoltage compensation can be provided, but reactors must be shut down in case of gas leak or hazardous situations
Solution Approach 1:
The compensation function is moved from topside (above water) to subsea (below water). The heating system is relocated to the seabed, allowing it to operate independently of platform safety shutdowns while providing the same compensation function.
Solution Approach 2:
The compensation capability is extracted from the platform structure and placed in the subsea environment. The heating system is separated from the platform's hazardous zone dependencies.
4Productivity
If longer transmission cables are used to reach remote offshore plants, then power transmission capability is improved, but Ferranti effect and capacitive charging currents increase, causing more severe overvoltage during load drops
Solution Approach 1:
The inductive heating system provides preliminary counter-action to the capacitive charging currents by generating opposing inductive currents. This preemptive compensation mitigates the Ferranti effect before overvoltage becomes severe.
Solution Approach 2:
The heating system acts as an intermediary element that introduces inductive characteristics into the predominantly capacitive transmission system. This intermediary inductive component balances the capacitive effects of the long cable.
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 solution effectively reduces overvoltage at offshore plants, preventing damage from transient surges and increasing voltage stability, while also reducing the need for additional SVC equipment and allowing continuous operation during hazardous situations by utilizing subsea reactors or wind turbine VFDs, which can lower transmission losses and maintain system efficiency.
Implementation Method 1
at least one pipeline which comprises an electrical heating system which is configured to be connected to the onshore power station through the submarine cable
Implementation Method 2
This effect is further increased by the Ferranti effect due to high voltage and capacitive charging currents in the transmission cable
Data Source
AI summary
An AC transmission system for a power transmission to an offshore plant. The AC transmission system includes an onshore power station which transmits an electric power, an offshore plant which receives the electric power, a submarine cable which connects the onshore power station to the offshore plant, and at least one pipeline with an electrical heating system which is connected to the onshore power station through the submarine cable.