Exploring the Design and Application of Photoelectric Current Transformers in GIS

1.Design and Application Example of Photoelectric Current Transformer in GIS

This article takes a 126kV GIS project as a specific example to deeply explore the design ideas and practical application of photoelectric current transformers in the GIS system. Since this GIS project was officially put into operation, the power system has remained stable, with no major failures occurring, and the operation status is relatively ideal.

1.1 Design and Application Ideas of Photoelectric Current Transformer

In the initial stage of the project, the GIS project team had intense discussions on the layout plan of the photoelectric current transformer. The core controversy focused on: whether to arrange it in the sulfur hexafluoride SF₆ gas environment or in the conventional air environment.

Scheme 1: Arranged in the Sulfur Hexafluoride Gas Environment

If this scheme is adopted, the photoelectric current transformer will be in a high - pressure sulfur hexafluoride gas environment, and the electrical connection between it and the control room needs to rely on optical fibers. However, in the high - pressure environment of sulfur hexafluoride, it is rather difficult to introduce optical fibers into the control box. If optical fibers are to be made into terminal ports similar to the form of cables, professional seamless welding technology must be adopted; but the welding process will not only interfere with the transmission of optical signals, but also the conductive path formed by welding may affect the electrical insulation performance of the current transformer, with many unfavorable factors.

Scheme 2: Arranged in the Air Environment

This scheme does not need to consider the impact of high pressure, so there are no concerns related to welding. However, it is necessary to focus on how to ensure the tightness of the current transformer, as well as the impact of eddy currents on the measurement accuracy and other potential impacts that may occur.

After rigorous analysis and comparison, the GIS project team finally selected Scheme 2. This scheme takes the safety, reliability and stability of system operation as the primary consideration, and fully takes into account the operability during the implementation of the scheme.

2. Solution to Scheme Problems
Structural Design and Connection

By comparing and analyzing the design structure of the photoelectric current transformer with that of the traditional electromagnetic current transformer, it is determined to arrange the photoelectric current transformer in the air environment, and carry out the following design work:

Produce an adapted large - scale flange, place the photoelectric current transformer inside the flange, and lead out the optical fiber from the side of the flange. In this way, the connection part between the optical fiber and the photoelectric current transformer is located inside the transformer, and this area is adjacent to the large flanges of other external transformers, and the photoelectric current transformer and the sulfur hexafluoride gas are isolated by metal.

Since eddy currents will be generated during the operation of the current transformer, which will interfere with the measurement accuracy and voltage of the photoelectric current transformer. To solve this problem, electrostatic spraying treatment is adopted on the metal contact surfaces of the two large flanges, so as to block the eddy current loop and ensure the tightness of the sulfur hexafluoride gas.

Electric Field Simulation and Verification

Due to the adoption of the flange structure in the design, the electric field distribution of the photoelectric current transformer will change. To verify the effectiveness of the scheme, it is necessary to use mature simulation calculation tools (such as ANSYS software) to carry out testing and analysis work. Use ANSYS to conduct field strength experiments on the metal rings and conductors of the two flanges. The lightning impulse voltage used in the experiment is 150kV. Through precise analysis by ANSYS software, it is concluded that the field strength at the edge parts of the flange and the shielding cover is the largest, and the maximum value reaches 20kV/mm. This result has passed the test and acceptance after in - depth research and scientific and precise simulation calculations by the project team.

At present, this project has been running stably for a long time, and the effect is good. Currently, certain achievements have been made in the research of photoelectric current transformers in China. However, in the application scenarios of high voltage levels, there are still problems such as reducing the influence of birefringence caused by stress and temperature, ensuring the long - term stable operation of the system, and further improving the measurement accuracy, which need to be solved in the follow - up.

3. Conclusion

Through the discussion of the whole process from scheme selection, implementation to problem solving of the photoelectric current transformer in the GIS system, it can be seen that remarkable results have been achieved in the field of GIS design and application. Compared with the traditional electromagnetic current transformer, the photoelectric current transformer has obvious advantages, and its application range is becoming wider and wider. Many manufacturers and users have already adopted it. It is foreseeable that in the near future, the photoelectric current transformer is expected to completely replace the electromagnetic current transformer, and with the continuous development and maturity of technology, it will make greater contributions to the progress of transformer technology.