Delta-Connected Thyristor Switched Capacitor Insulation Optimization
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Solution Overview
Problem
Static var compensators with Thyristor Switched Capacitors (TSCs) face challenges in reducing the size and cost due to the large insulation distance required between thyristor switches of different phases, caused by voltage differences when the switches are turned off.
Innovation Solution
The configuration of delta-connected three-phase series circuits with non-uniform terminal-to-terminal distances between thyristor switches, where the series circuit of one phase is opposite to the others in terms of the connection order of the thyristor switch and capacitor along the loop path, reduces the insulation distance and voltage differences between phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the thyristor switches of three phases are mounted with uniform terminal-to-terminal distance, then the mounting configuration is simple and symmetric, but the insulation distance between phases becomes excessively large due to voltage differences when switches are turned off
Solution Approach 1:
The patent applies asymmetry by intentionally designing non-uniform terminal-to-terminal distances between thyristor switches of different phases. Specifically, the distance between phases A and B is set to a first value, while the distance between phases B and C is set to a second value that is smaller than the first value. This asymmetric arrangement optimizes the insulation distance requirements by considering the actual voltage difference characteristics between phases, thereby reducing the overall size of the thyristor valve while maintaining adequate insulation.
2Reliability
If adequate insulation distance is provided between phases, then the breakdown voltage requirement is met, but the size and cost of the thyristor valve increases
Solution Approach 1:
The patent applies local quality by differentiating the insulation distance requirements for different phase combinations. Instead of uniformly providing maximum insulation distance between all phases, the patent sets the distance between phases A and B to a first value and the distance between phases B and C to a second value, where the second value is smaller. This localized differentiation of insulation quality matches the actual voltage stress distribution, ensuring breakdown voltage requirements are met where necessary while reducing unnecessary insulation elsewhere, thus downsizing the thyristor valve.
Data Source
AI summary
Three-phase thyristor switched capacitors are delta-connected to three-phase AC buses. Each thyristor switched capacitor includes a reactor, a capacitor, and a thyristor switch that are electrically connected in series. The thyristor switches of the three phases are arranged so that the terminal-to-terminal distance between respective thyristor switches of respective phases are not uniform. The three-phase thyristor switched capacitors are configured so that the thyristor switched capacitors of two of the three phases having a shortest terminal-to-terminal distance therebetween are opposite to each other in terms of connection order in which the thyristor switch and the capacitor are electrically connected along a loop path made up of the delta-connected thyristor switched capacitors.