Two-Stage Transformer Assembly for Lightning Impulse Withstand
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Solution Overview
Problem
Medium frequency transformers (MFTs) in solid state transformers face challenges in reducing size and weight due to high insulation requirements for withstanding lightning impulse tests, leading to large and voluminous components, which compromises the space and weight savings potential.
Innovation Solution
A two-stage transformer assembly is introduced, where the first stage has MFTs optimized for nominal operation without lightning impulse withstand requirements, and the second stage has MFTs designed to meet the high lightning impulse breakdown voltage, allowing for reduced insulation distances and component size in the first stage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If MFTs are designed to meet high lightning impulse breakdown voltage requirements, then insulation reliability is improved, but volume and weight increase
Solution Approach 1:
The transformer assembly is divided into multiple transformer cells (e.g., 9 cells) connected in series, where each cell handles a portion of the total voltage. This segmentation allows each individual MFT to be designed with smaller insulation distances while the series connection collectively achieves the required lightning impulse withstand capability.
Solution Approach 2:
Different insulation designs are applied to different parts of the system. Each transformer cell has its own optimized insulation configuration suitable for its specific voltage stress, rather than designing all components for the maximum system voltage. This allows local optimization of each MFT's insulation to match actual operational requirements.
2Reliability
If MFTs are designed to meet high lightning impulse breakdown voltage requirements, then insulation reliability is improved, but weight increases
Solution Approach 1:
The transformer assembly is divided into multiple transformer cells (e.g., 9 cells) connected in series, where each cell handles a portion of the total voltage. This segmentation allows each individual MFT to be designed with smaller insulation distances while the series connection collectively achieves the required lightning impulse withstand capability.
Solution Approach 2:
Different insulation designs are applied to different parts of the system. Each transformer cell has its own optimized insulation configuration suitable for its specific voltage stress, rather than designing all components for the maximum system voltage. This allows local optimization of each MFT's insulation to match actual operational requirements.
3Reliability
If insulation distances are increased to meet lightning impulse test requirements, then insulation reliability is improved, but device complexity increases
Solution Approach 1:
The transformer assembly is divided into multiple transformer cells (e.g., 9 cells) connected in series, where each cell handles a portion of the total voltage. This segmentation allows each individual MFT to be designed with smaller insulation distances while the series connection collectively achieves the required lightning impulse withstand capability.
Solution Approach 2:
Multiple transformer cells are combined in series to achieve the cumulative insulation capability required for lightning impulse tests. Rather than creating one large complex insulated MFT, several simpler MFTs are combined, where the sum of their individual insulation capabilities meets the system requirement.
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 configuration results in significant volume and weight savings, improved component optimization, and reduced complexity in design and cooling systems, particularly beneficial for low power applications up to 500 MW.
Implementation Method 1
Each of the transformer cells 10 has an input converter 12, an MFT 14, and an output converter 16. In each cell 10, the output of the input converter 12 is connected to the input winding of MFT 14 at the MFT's frequency; and likewise the input of the output converter 16 is connected to the output winding of MFT 14 at the MFT's frequency.
Data Source
Figure 1
Figure 2
AI summary
Transformer assembly comprises a first transformer stage (100) having a plurality of first-stage transformer cells (110); and a second transformer stage (200). An input (201) of the second transformer stage (200) is connected to an output (102) of the first transformer stage (100). A lightning impulse breakdown voltage of a transformer cell (210) of the second stage is at least double of a lightning impulse breakdown voltage of transformer cells (110) of the first stage.