Purpose/Aim
The oil-SF₆ bushing is an important equipment connecting GIS and transformers, and its model under very-fast transient overvoltage(VFFO) plays a key role in evaluating the VFFO level of substations. In this paper, on the basis of analyzing the structure and capacitance of oil-SF₆ bushings, and relying on the UHV AC bushing full-condition test research platform, a real-type test is carried out to measure the overvoltage level on the oil-SF₆ bushing side. Finally, combined with simulation and actual measurement, the electromagnetic transient model of oil-SF₆ bushing for VFFO simulation available in the project is established.
Experimental/Modeling methods
In the UHV AC test base, a test and research platform for AC bushings under full conditions including transformers, overhead lines, SF6 bushings, disconnectors, and oil-SF₆ bushing s has been established, and a measurement system that meets the VFFO test requirements has been developed and installed. The electromagnetic transient model of oil-SF₆ bushing for VFFO is established and perfected by combining the test data of the disconnector opening and closing operation with the structural analysis of the oil-SF₆ bushing.
Results/discussion
The real test shows that there is a certain difference between the overvoltage on the oil side of the oil-SF₆ bushing and the overvoltage waveform in the GIS. The oil-SF₆ bushing in the project can be modeled as a transmission line model plus a capacitor to evaluate the overvoltage waveform at the transformer entrance in the project.
Conclusions
Through the establishment of UHV AC bushing full-condition test research platform, the experimental study of VFFO caused by disconnector operation was carried out. At the same time, the capacitance of oil-SF6 bushing is analyzed in detail, and on this basis, models of oil-SF6 bushings such as transmission line model, lumped capacitance model and multi-layer equivalent model are explored and established. By comparing the measured and simulated waveforms, it is proposed that the oil and gas bushing model in the project can be in the form of a transmission line model plus a capacitor, which can be used to evaluate the overvoltage waveform at the transformer entrance in the project.

modeling; VFFO; GIS; oil-SF6 bushing; test