Abstract
Space charges accumulate easily at insulation interface of cable accessories, which cause different electric field distribution and aging characteristics compared to single-layered cable. To explore the space charge behavior in double-layered insulation of cable accessories, a one-dimensional (1D) axisymmetric model for bipolar charge transport is built in this work, in which the effects of temperature gradient and electric field gradient in the radial direction are considered. Then the influences of electric field/temperature gradient and interface position on transport behavior of space charges are investigated. The simulation results suggest that the charges accumulate easily at the interface, which severely reduce the electric field in the inner layer of insulation and further inhibit the injection and migration processes of charges. The charge density at the interface increases with temperature and voltage, which accelerates the decay of the charge injection, furthers the interface charges to reach the dynamic equilibrium state quickly. The charge density at the interface and the electric field distribution are closely related to the interface position, and the electric field is more uniform when XLPE occupies the 1/3 to 1/2 inner part of the whole insulation.
Highlights
High voltage direct current (HVDC) cables are widely used in key fields such as long-distance transmission, submarine cables and power links in isolated areas [1], [2]
Since Ethylene Propylene Diene Monomer (EPDM) and XLPE present different electrical properties, the interface plays an important role in space charge dynamics, which causes different electric field distribution and aging characteristics compared to single-layer cable [6], [7]
Delpino et al investigated the charge distribution in XLPE/EPR double-layered insulation, and the results show that when the electric field is lower than the threshold electric field of charge injection, the interface charge density is mainly determined by the permittivity and conductivity [14]
Summary
High voltage direct current (HVDC) cables are widely used in key fields such as long-distance transmission, submarine cables and power links in isolated areas [1], [2]. J. Li et al investigated the space charge and electric field distribution characteristics of cable accessories considering the interface effect, and the results show that the charge distribution could be improved by reducing the interface barrier and matching the charge mobility of the two materials [17]. Based on the geometrical characteristic of DC cables, a 1D axisymmetric model for the bipolar charge transport in double-layered insulation cable accessory structure is built, in which the gradient distributions of temperature and electric field in the radial direction are considered. BIPOLAR CHARGE TRANSPORT MODEL One-dimensional model with thickness of 150-500μm is usually used to investigate the dynamic behavior of space charges in dielectric materials [21]–[23] Since these models are different from the geometric characteristics of cables, the temperature gradient and electric field gradient in the radial direction are rarely considered. Where ρd is the density of the material, Cp is heat capacity at constant pressure, k is the thermal conductivity, q is the heat flux density of conduction, Q is the heat source, N is the cross-section area of the conductor, I is the DC current within the conductor and ρal is the resistivity of the cable core
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