Incorporating Non-Operating Station Into Multi-Terminal Flexible DC System
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Solution Overview
Problem
The existing methods for incorporating a non-operating station into a multi-terminal flexible DC transmission system require shutting down the entire system, leading to increased outage probability, significant losses, and reduced energy utilization, especially when connecting new energy sources like wind power plants.
Innovation Solution
A method that involves selecting a STATCOM operation mode, pre-charging through a charging resistor, controlling DC voltage differences, and switching to a DC operation mode to safely incorporate a non-operating station into the system without disrupting the operating system, using converter stations with pole-connection devices and AC incoming-line breakers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the entire multi-terminal flexible DC transmission system is shut down to incorporate a non-operating station, then the station can be connected to the system, but the outage probability of the system increases and energy utilization rate decreases
Solution Approach 1:
The system is divided into operating and non-operating stations, allowing independent operation of different segments. The charging resistor is connected to the AC line through a breaker to pre-charge the DC side of the non-operating station independently, enabling incorporation without shutting down the entire system.
Solution Approach 2:
The charging resistor pre-charges the DC side of the non-operating station before it is fully incorporated into the operating system. This preliminary charging action prevents overcurrent when the station is connected, allowing seamless integration without system shutdown.
2Reliability
If the operating system is shut down to incorporate a non-operating station, then the station can be connected safely, but significant loss occurs when the system is connected to important loads
Solution Approach 1:
The charging resistor performs preliminary charging of the non-operating station's DC side through the AC breaker before full system integration. This ensures safe connection without requiring shutdown of the operating system, maintaining continuous power supply to important loads.
3Reliability
If the operating system is shut down to incorporate a non-operating station, then the station can be integrated into the system, but the complexity of the incorporation process increases
Solution Approach 1:
The incorporation process is segmented into independent steps: AC breaker closure, charging resistor connection, DC side pre-charging, and full system integration. This segmentation simplifies the overall process by allowing controlled, incremental incorporation without system shutdown.
Solution Approach 2:
The charging resistor acts as an intermediary element between the AC line and the DC side of the non-operating station. It provides a controlled path for charging, simplifying the incorporation process by managing the transition from non-operating to operating state without requiring full system shutdown.
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 method prevents forced outages, suppresses overcurrents, and allows for seamless integration of non-operating stations into the grid, enhancing system stability and reliability while maintaining operational flexibility.
Implementation Method 1
an AC incoming-line breaker, a transformer and a charging resistor connected in series with one another, two ends of said charging resistor being further connected in parallel with a bypass switch
Data Source
AI summary
A method for incorporating a non-operating station into an operating system in a multi-terminal flexible DC transmission system. The method includes selecting a STATCOM operation mode for the non-operating station; opening a bypass switch at an AC side and connecting a charging resistor to an AC line; closing the AC incoming-line breaker, and pre-charging a converter valve of the non-operating station through the resistor; closing the bypass switch after the pre-charging; selecting a constant-DC voltage control mode for the non-operating station to perform deblocking; controlling the difference between a non-operating station DC voltage value and an operating system direct voltage value to be within an allowable range; closing the pole-connection device at the DC side of a converter of the non-operating station; and switching the non-operating station from the STATCOM operation mode to a DC operation mode, and incorporating the non-operating station into the operating system.