Development of Future Compact and Eco-Friendly HVDC Gas-Insulated Systems: Shape Optimization of a DC Spacer Model and Novel Materials Investigation

Abstract

Testing and validating the electrical insulation performance of full-size compact high-voltage direct current (HVDC) gas-insulated systems, gas-insulated transmission lines (GIL) and gas-insulated switchgears (GIS) is very costly and take long time. Therefore, a reduced scale system was designed and constructed to study thoroughly the spacer’s performance when subjected to higher electric fields under HVDC with different shapes, made of new advanced materials, and housed in new SF6-free gas environment. Since the stationary DC electric field distribution along the spacer is controlled by spacer material conductivity and strongly depends upon its shape, this, the first part of two articles, proposes in a first step based on electric field calculations with COMSOL Multiphysics software, an optimized shape of a spacer model using a standard high-voltage alternating current (HVAC) alumina-filled epoxy material. Then, two novel types of materials were introduced and investigated: (i) modified filled epoxy material with a lower temperature-dependent conductivity than that of the standard HVAC material, which is interpreted by a lower thermal activation energy; and (ii) nonlinear resistive field grading material with a low nonlinearity coefficient, with and without the presence of a temperature gradient which occurs under operating service load. The numerical results show that, despite that the DC optimized profile of the spacer made of standard HVAC, alumina-filled epoxy is very effective in relaxing the electric field magnitudes along the spacer under uniform temperature—its distribution is significantly affected by the presence of a high temperature gradient causing the maximum electric field shifts along the spacer surface towards the earthed flange. Under this condition, the modified filled epoxy material with a weaker temperature-dependent conductivity results in a significant reduction of the electric field enhancement, representing thus a relevant key solution for HVDC GIL/GIS applications. Nonlinear resistive field grading material is also effective but seems unnecessary. The optimized DC spacer models are being fabricated for tests verification with C4-Perfluoronitrile (C4-PFN, 3MTM NovecTM 4710)/CO2 and Trifluoroiodomethane (CF3I)/CO2 gas mixtures in the reduced scale gas-insulated test prototype.

Development of HVDC Gas-Insulated Components for the Power Supply of Neutral Beam Injectors

“…Generally the electrical conductivity of solid parts depend both on temperature T and electric field E, that is σ I = σ I (T , E). As an example, for the Alumina (Al 2 O 3 )filled epoxy resin through relation [11] σ…”

“…When dealing with nonlinear resistive field grading materials (FGM), for electric fields below the switching value E 1 kV/mm the material behaves as dielectric, while for stresses E > E 1 the material become conductive and consequently a significant increase of Joule heating takes place. The electrical conductivity of such materials can be expressed as [11] σ…”

Automatic Optimization of Gas Insulated Components Based on the Streamer Inception Criterion

“…As reported in [7], the surface charging depends on normal and tangential components of the electric field on the solid insulator at the initial capacitive state [51]. With the purpose of reducing the charge accumulation and mitigate the probability of surface flashover, the field components can be minimized through a shape optimization of the insulator [52]. In this case, the minimization problem can be defined as a multiobjective optimization problem [53], where the design variables define the shape of the insulator surface and the objective function becomes a vector constituted by the normal E n and tangential E t (or its gradient ∇E t ) components of electric field on solid insulator, i.e.,…”

Shape optimisation of basin insulator for DC gas insulated switchgear/gas insulated transmission lines based on artificial bee colony algorithm

“…Liang et al optimised the shape of the insulator by adjusting the tilt angle to change the surface normal electric field [18]. Instead of employing any optimisation algorithm, Zebouchi et al performed a parametric sweep of selected geometric control parameters to obtain the optimal insulator shape [19]. Hasegawa et al [20] and Ma et al [21] both achieved shape optimisation by comparing the surface charge and electric field distributions of insulators with different shapes.…”

“…Instead of employing any optimisation algorithm, Zebouchi et al. performed a parametric sweep of selected geometric control parameters to obtain the optimal insulator shape [19]. Hasegawa et al.…”