0102030405
Research on key technology of DC voltage support capacitor for High Voltage Direct Current Systems
2024-10-30 10:10:01
Brief introduction
Based on the research and development experience of DC support capacitors for flexible DC transmission, we proposed a test method for ESL of nH-class equivalent series inductors for DC support capacitors, and verifies its correctness, which solves the test method problem of nH-class inductors. According to the test method, the calculation method of nH-level inductance based on DC support capacitor lead line is verified, which provides a new design idea for reducing the nH-level inductance of DC support capacitor. We also analyzes and summarizes the problem of pole-to-shell AC partial discharge, which is a difficult problem of DC supported capacitors, and provides a reference for solving the AC local discharge of DC supported capacitors. Some suggestions for the study of interelectrode DC local discharge are put forward. Combined with the test and operation experience, the contact resistance test, temperature rise test, small inrush current test and large inrush current test were carried out on the current outlet terminals of DC supported capacitors. The test results show that only the thickened fine tooth round nut can pass the large inrush current test, which is of great reference value for improving the safe operation of DC supported capacitors.
Two main contents
With the development of flexible DC transmission technology in China, the problem of DC support capacitor, one of the key components used in flexible and straight engineering, has become prominent.
Starting from 2017, China's research and development of DC support capacitors for flexible DC transmission has mentioned the planning agenda. Not only the major capacitor factories in China began to lay out DC support capacitors, invested a lot of manpower and material resources for the development of this product, the State Grid Corporation, China Southern Power Grid Corporation and major universities, scientific research institutions have also been thematic research on DC support capacitors, DC support capacitors and their main raw materials polypropylene pellets have also been included in the key research and development projects. Even included in the national key projects. These measures have strongly promoted the technical progress of DC supported capacitors. Internationally, due to the development of power electronics technology, the IEC 61071 standard has also been greatly updated, which is more suitable for the research and development of DC supported capacitors. The revision of GB/T 17702, the number of participating manufacturers and personnel, the number of revised comments and suggestions collected, all reached a record high.
The rated voltage and design field strength of capacitor are the most important parameters. GB/T 24123 For the 5.8 μm thick polypropylene film most commonly used in DC support capacitors, the median DC breakdown voltage is required to be ≥350 V/μm; GB/T 13542.3 (modified to use IEC 60674-3-1) has even lower requirements, only ≥190 V/μm, which cannot meet the current design field strength of DC supported capacitors. According to the requirements of literature [1], the design field strength of polypropylene metallized film for DC supported capacitors should not be less than (220~250) V/μm. The breakdown field strength of metallized film is the basis for determining the design field strength of DC supported capacitors. There are many literatures related to DC supported capacitor technology, including self-healing theory, aging law and failure mode, temperature rise problem and loss calculation. The key technical points of this paper are the test method and improvement idea of equivalent series inductor ESL of DC supported capacitor, partial discharge test and current extraction terminal design and verification.
1 Design and verification of nH inductors
1.1 Research on test method of nH-class inductance
1.2 Nachen inductance estimation
2 Research on partial discharge problems
2.1 Terminal to Shell AC partial discharge problem
2.2 Inter-electrode DC local discharge problem
3 Terminal design and verification
3.1 Design of wiring terminals
3.2 Test verification of wiring terminals
Conclusions
1) The two-discharge method can solve the measurement problem of nH class ESL of DC supported capacitors. According to the discharge current waveform, the inductance of the test circuit can be calculated accurately, and the equivalent series inductance of the DC support capacitor can be obtained.
2) According to the size and arrangement of the current lead line of the DC support capacitor, the self-inductance and mutual inductance of the lead line can be estimated, so as to obtain the equivalent series inductance of the capacitor.
3) Research and development experience shows that the AC local discharge test of DC supported capacitors can detect whether there is a suspension potential inside the capacitor, whether the filling glue is cured well and whether there is a void inside the capacitor, but the indicators of local discharge should be rationalized and other performance indicators should be comprehensively considered. The pulse number of DC partial discharge between electrodes is very significant to determine the self-healing and performance of DC supported capacitors.
4) The test verification shows that the terminal is no problem in the contact resistance, Imax or even in the surge current of about 100 kA, but in the surge current of about 300 kA, only the thickened fine thread structure can pass the test. Therefore, how to judge whether the terminal meets the requirements needs the designer to consider according to the requirements of the buyer.
