Subsea Temporary Load Device for Voltage Stability
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Solution Overview
Problem
Subsea electrical power distribution systems face voltage stability issues due to sudden load reductions in long cables, leading to over-voltages caused by capacitive currents, which can damage equipment and limit maximum installed load or distance.
Innovation Solution
A temporary load device is introduced at the load side of the cable, using thyristors to rapidly connect and disconnect, reducing over-voltages by allowing voltage adjustments through tap-changer mechanisms, and disconnecting once the target voltage is reached, thus minimizing energy input into faults and preventing equipment damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage control is performed using tap-changing transformers, then voltage quality is improved, but response time to sudden load reductions is too slow, allowing over-voltages to damage equipment
Solution Approach 1:
The patent introduces a temporary load device as an intermediary component that acts as a buffer between the power supply and the main load. This device rapidly absorbs excess energy during sudden load reductions, preventing over-voltages from reaching equipment while the slower tap-changing transformer responds to restore normal voltage levels.
Solution Approach 2:
The temporary load device is pre-positioned and ready to activate immediately upon detecting sudden load reductions. By having this protective mechanism in place beforehand, the system can respond instantaneously to voltage spikes, eliminating the time delay inherent in tap-changing operations.
2Length of stationary object
If long cables are used to extend power distribution distance, then coverage area is improved, but capacitive effects generate harmful over-voltages during load changes
Solution Approach 1:
The patent converts the harmful capacitive energy stored in long cables during normal operation into a beneficial protective mechanism. The temporary load device captures and dissipates this stored energy during sudden load reductions, transforming what would be destructive over-voltages into controlled energy discharge that protects the system.
3Power
If maximum installed load is increased at given distance, then power capacity is improved, but voltage stability becomes more difficult to maintain during load changes
Solution Approach 1:
The temporary load device serves as a cushioning mechanism that is activated beforehand or simultaneously with sudden load reductions. It absorbs the shock of rapid load changes, preventing voltage instability that would otherwise occur when maximum installed load operates over long cables, thereby enabling higher power capacity while maintaining stability.
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
The temporary load device effectively reduces over-voltage sizes and duration, preventing damage from electrical faults and ensuring voltage stability, allowing for safer and more reliable subsea power distribution.
Implementation Method 1
A temporary load device is introduced at the load side of the cable, using thyristors to rapidly connect and disconnect
Implementation Method 2
allowing voltage adjustments through tap-changer mechanisms
Implementation Method 3
This is related to the capacitive nature of long power cables and the transmission frequency
Implementation Method 4
The self-excitation of induction motors or Ferranti effect can occur if the electrical source is suddenly disconnected while the motor is running
Data Source
Figure 1
Figure 2a
Figure 2b
AI summary
The invention discloses temporary load device (2) comprised in a subsea distribution bus (14) connecting a power load system (3) to electrical power supplied by an AC power supply (1) by means of at least one long cable (7). The subsea distribution bus (14) comprises a local control unit (4), and a temporary load device (2), which is arranged, upon receipt of a first signal from the local control unit, to close and reduce the voltage to the power load (3), and, on receipt of a second signal is arranged to open and disconnect said temporary load device (2) from the subsea distribution bus (14) having avoided or reduced an overvoltage, or a load drop, at the power load system (3). The temporary load device (2) may be used to mitigate a measured or estimated over-voltage or other voltage fault condition such as voltage oscillation caused by connecting a subsea load to the power supply. In other aspects of the invention are disclosed: a subsea distribution bus including the temporary load device; a method; and a computer program for carrying out the method.