When power cables are loaded under high voltage direct current (HVDC), an accumulation of space charge and a radial distribution of temperature gradient are developed across the insulation material. Such existence and accumulation of space charge within the insulating material poses a threat to the reliability of the operation of dc power cables. The electric field of a practical dc power cable is affected by the conductivity of the material, which is a function of both temperature and electric field. This causes difficulties in identifying the electric field distribution. In this paper, a method of determining the electric field distribution in dc power cables was proposed by considering the influence of space charge on the conductivity of the insulating material under different temperatures. Commercial 11 kV ac cross-linked polyethylene (XLPE) power cables were used and the space charge in these cables under dc conditions was measured using a modified pulsed electroacoustic (PEA) system with an attached current transformer. Therefore, a replica of a power cable under load conditions is obtained, which allows an investigation of the formation, migration and accumulation of space charge in a power cable with and without temperature gradients across the insulating material. COMSOL Multiphysics software package was used to accurately determine the electric field distribution in the dc power cable with consideration of the influence of electric field on the conductivity of the insulating material. The numerical modelling is based on the hopping conduction mechanism and its parameters were obtained from experiments carried out on the XLPE insulation material.

Abstract:A well-known fact of the existence and accumulation of space charge within the insulating material poses threat to the reliability in the operation of dc power cables. When power cables are loaded under high voltage direct current (HVDC), temperature gradient is developed across the insulation. Results of space charge evolution in commercial ac XLPE power cables under an application of 80 kV dc supply at different temperature gradients and during external voltage reversal are discussed in this paper. The space charge distributions were measured across the insulation of the cable by means of a modified pulsed electroacoustic (PEA) system with a current transformer attached. Therefore, a replica of a power cable under load conditions could be obtained, which allows us to investigate the formation, migration and accumulation of space charges in a power cable both without and with different temperature gradients consideration across the bulk of the insulating material during voltage reversal. Discussion will be made thoroughly in order to understand the space charge phenomenon of power cable under its service temperature as space charge accumulation during polarity reversal plays an important factor on the electric field distribution within the insulation material.

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Abstract--In direct current (dc) power cable the electric field is affected by conductivity of the material, which is a function of both temperature and electric field. Loading in high voltage direct current (HVDC) cable results in a temperature gradient across the insulation and hence a radial distribution of the insulation conductivity. A direct consequence is the accumulation of space charge within the insulation bulk, which modifies the electric field across the insulation. The coupled problems due to electric field and temperature inflict difficulties to identify the electric field distribution in HVDC cables, which therefore poses threat to the reliability in operation of dc power cables. Space charge in a commercial 11 kV ac XLPE power cable has been measured under a voltage application of 80 kV dc. Space charge distributions were obtained across the insulation of the cable by means of a modified pulsed electroacoustic (PEA) system. In this paper, COMSOL Multiphysics software package is also used to accurately determine the electric field distribution in the dc power cable by considering the influences of both the effects of temperature and electric field on the conductivity of the insulating material.

Abstract:The pulsed electroacoustic (PEA) technique was used to perform space charge measurements in polymeric power cables. However, for a practical dc power cable the electric field is affected by conductivity of the material, which is a function of both temperature and electric field. The coupled problems inflict difficulties to identify the electric field distribution in high voltage (HV) cables, which therefore poses threat to the reliability in operation of dc power cables.In this paper we proposed a method of determining electric field distribution in XLPE power cable, where under temperature gradient the existence of space charge density of the cable is determined by means of a modified PEA system. Commercial 11 kV ac XLPE power cable is applied and measured under an applied dc voltage of 80 kV. The space charge across the insulation was obtained and COMSOL Multiphysics software package is used to accurately determine the electric field distribution in the dc power cable by considering the influences of both the effects of temperature and electric field on the conductivity of the insulating material. Therefore, the results of the numerical modelling shall give us a clearer representation of the electric field distribution in HVDC cables.