Study and analysis of conduction mechanisms and space charge accumulation phenomena under high applied DC electric field in XLPE for HVDC cable application

Abstract

The development of High Voltage Direct Current (HVDC) cables requires design according to specific criteria and materials with appropriate properties. Cross-linked polyethylene (XLPE) has established itself over the past 20 years as the most used insulation material for HVAC cables, but also more recently for HVDC cables. If the electrical properties of this polymer have been widely studied under AC stress, the behavior of these materials under high DC stress is less known and needs thorough investigation. It is well known that, in DC conditions, the electric field distribution is highly dependent on operating conditions (thermal gradient and electric field) and can be affected by electric charges trapped in the insulation. The resulting space charge accumulation is able to increase significantly the local electric field, thus accelerating ageing and increasing the risk of breakdown. Consequently, the influence of electrical and thermal stresses on the material properties could be a key parameter on the ageing law for HVDC insulating material.The purpose of the present work is to investigate the dielectric behavior of XLPE insulation under different combined thermal and DC electrical stresses. The first step is to evaluate the volume electrical conduction and interface injection mechanisms by using current versus voltage (I-V) measurements. The second step is to investigate the development of space charges by using a non-destructive space charge measurement technique (the Thermal Step Method).

Behavior of XLPE for HVDC Cables under Thermo-Electrical Stress: Experimental Study and Ageing Kinetics Proposal

“…Electrical volume resistivity values measured during ageing conditions under 30 and 60 kV/mm at 70, 80 and 90 • C for 857 days are presented in [22,23]. Electrical volume resistivity did not show any significant evolution as a function of ageing time, for all temperatures and electric fields studied [22].…”

“…Electrical volume resistivity values measured during ageing conditions under 30 and 60 kV/mm at 70, 80 and 90 • C for 857 days are presented in [22,23]. Electrical volume resistivity did not show any significant evolution as a function of ageing time, for all temperatures and electric fields studied [22]. In this section, we present only results for ageing tests under 30 kV/mm and 60 k V/mm at 90 • C. Values for ageing under 30 kV/mm measured under 2 kV/mm were between 10 14 Ω × m and 10 15 Ω × m, whatever the ageing temperature, while those measured under 30 kV/mm were lower than those under 2 kV/mm and are on average of the order of 10 12 Ω × m and 10 13 Ω × m. For ageing under 60 kV/mm, electrical volume resistivity was in the order of 10 14 Ω × m and 10 15 Ω × m when measured under 2 kV/mm, and between 10 13 Ω × m and 10 15 Ω × m when measured under 30 kV/mm.…”

Contributed Review: Review of thermal methods for space charge measurement

“…The obtained results have shown that the space charge accumulation grows with the increase of both electric field and temperature. 48 …”

Effect of injection barrier height on charge transport under bipolar injection

“…Dielectrics are widely used as insulators in electrical engineering and are subjected to many constraints: temperature, electric field, and pressure . The insulating properties of these dielectrics can then be modified under these constraints.…”