SSSC Starting and Stopping Method for Overvoltage Suppression
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Solution Overview
Problem
The existing starting and stopping methods for Static Synchronous Series Compensators (SSSCs) result in excessive voltage and current fluctuations, leading to transformer saturation and overcharging, which compromises safety and stability in power transmission systems.
Innovation Solution
A method involving a series-connected SSSC with a converter, shunt transformer, start circuit, series transformer, and bypass switch, where the bypass switch is connected in parallel to the series transformer and the converter is charged through a shunt transformer, allowing for gradual current reduction and zero-current control to stabilize the starting and stopping processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the series transformer is put in use but the converter is blocked, then the SSSC can be started, but excessively high voltage is generated at the transformer and converter, the transformer is saturated, and the capacitor is overcharged
Solution Approach 1:
The patent applies preliminary action by charging the converter capacitor through a dedicated charging circuit before connecting the series transformer to the power transmission line. This ensures the capacitor is pre-charged to the required voltage level, preventing excessive voltage generation and transformer saturation when the transformer is subsequently connected. The charging circuit is disconnected after charging is complete, maintaining normal operation without the charging path.
Solution Approach 2:
The patent introduces a charging circuit as an intermediary component that provides a controlled path for charging the converter capacitor before the series transformer is connected to the power transmission line. This intermediary charging circuit allows gradual capacitor charging without causing excessive current or voltage spikes that would occur with direct connection, thereby preventing transformer saturation and overvoltage conditions.
2Ease of operation
If the bypass switch is opened when line current changes drastically, then the transformer can exit service, but the power flow of the alternating-current system is severely affected
Solution Approach 1:
The patent applies preliminary action by controlling the bypass switch to close before the series transformer is disconnected from the power transmission line. This ensures the bypass path is established in advance, allowing line current to smoothly transition through the bypass switch rather than causing drastic current changes. The bypass switch remains closed during transformer disconnection, maintaining stable power flow throughout the stopping process.
3Ease of operation
If the converter is blocked immediately during stopping, then the SSSC can be stopped, but voltage and current oscillations occur affecting system stability
Solution Approach 1:
The patent applies preliminary action by controlling the bypass switch to close before the converter is blocked during the stopping process. This preliminary action establishes a safe bypass path for line current before the converter is disabled, preventing voltage and current oscillations that would occur if the converter were blocked immediately. The bypass switch remains closed during converter blocking, ensuring stable system operation throughout the stopping process.
Data Source
Figure 1~2
Figure 3
AI summary
A starting and stopping method for a static synchronous series compensator (SSSC) is provided. A starting process includes: first, connecting a converter (4) to a shunt transformer (2), and closing an incoming line switch (1) of the shunt transformer to charge the current converter until a direct-current voltage is stable; then, opening the incoming line switch of the shunt transformer, and connecting the converter to a series transformer (5) through a change-over switch (3); deblocking the converter, and controlling a current of a bypass switch (6) of the series transformer to approach zero; further, opening the bypass switch of the series transformer, and enabling the converter to enter a normal operation mode after a line is stable; and in stopping the SSSC, first, switching a control mode of the converter to make the current of the bypass switch approaches zero when closed the bypass switch, then controlling a current of the series transformer to be gradually reduced to zero to make the series transformer out of service, and then blocking the converter. By means of the method, an overvoltage and an overcurrent of a converter when a series transformer is put into use and exits can be effectively suppressed, and current oscillation of an line and impact on the series transformer can be reduced, thereby achieving stable starting and stopping of an SSSC