Abstract
The gas-insulated line (GIL) is one technical solution to allow the transmission of electricity underground at a high voltage level, yet its equivalent model is quite complicated. Based on an examination of the geometrical structure of the GIL and the way the metallic enclosure is grounded, this paper analyzed the electromagnetic and electrostatic coupling among the inner conductors and the metallic enclosures of the three phases. Then, the paper proposes a modeling method for the widely-used short-distance GIL based on the PI-model (the model consisting of two lumped admittance at each terminal and a lumped impedance in between). The GIL parameters were later simplified with the coupling effect of the metallic enclosure considered, and a simplified PI-model was produced. Finally, the proposed PI-model and its simplified version were built on the Power Systems Computer Aided Design (PSCAD) platform, and their effectiveness verified by simulation results.
Highlights
The Gas-insulated Line (GIL) is a transmission system for the transmission of electricity at a high voltage level, with SF6 or SF6 -N2 gas mixture as the insulating medium and the conductor kept in the center of the metallic enclosure [1]
The typical structure of the GIL is shown in Figure 1: At the center lies the hollow conductor made of an aluminum alloy of high electrical conductivity; the metallic enclosure is made of an aluminum alloy, coated with an insulating material; and the conductor and enclosure are coaxial, with a SF6 -N2 gas mixture filled in between
Vco and Ven are defined as the voltages on the inner conductor and the metallic enclosure respectively; correspondingly, Ico and Ien are the currents flowing through the two; Zco-co, Zen-en and Zco-en are the matrices of per-unit length conductor impedance, of the per-unit length metallic impedance and of the per-unit length mutual impedance between the conductor and the enclosure, respectively; and correspondingly, Yco-co, Yen-en, and Yco-en are the matrices of the per-unit length admittance
Summary
The Gas-insulated Line (GIL) is a transmission system for the transmission of electricity at a high voltage level, with SF6 or SF6 -N2 gas mixture as the insulating medium and the conductor kept in the center of the metallic enclosure [1]. [17] proposed a model of a three-phase GIL transmission system with the earth return current considered; reference [18] adopted the finite-element method in building a model of a three-phase GIL system; reference [19] proposed an approximate model based solely on the mutual inductance among the GIL inner conductor and the metallic enclosure; reference [20] suggested a modeling method for the simulation of a long-distance. To reduce the complexity and computation of the model, the equivalent parameters of the inner conductor are deduced and a simplified PI-model of the GIL is produced
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