Abstract
Space charge behavior has a strong impact on the long-term operation reliability of high voltage–direct current (HVDC) cables. This study intended to reveal the effect of trap density and depth on the space charge and electric field evolution behavior in HVDC cable insulation under different load currents and voltages by combined numerical bipolar charge transport (BCT) and thermal field simulation. The results show that when the load current is 1800 A (normal value), the temperature difference between the inside and the outside of the insulation is 20 °C, space charge accumulation and electric field distortion become more serious with the increase in the trap depth (Et) from 0.80 to 1.20 eV for the trap densities (Nt) of 10 × 1019 and 80 × 1019 m−3, and become more serious with the increase in Nt from 10 × 1019 to 1000 × 1019 m−3 for Et = 0.94 eV. Simultaneously decreasing trap depth and trap density (such as Et = 0.80 eV, Nt = 10 × 1019 m−3) or increasing trap depth and trap density (such as Et = 1.20 eV, Nt = 1000 × 1019 m−3), space charge accumulation can be effectively suppressed along with capacitive electric field distribution for different load currents (1800 A, 2100 A and 2600 A) and voltages (320 kV and 592 kV). Furthermore, we can draw the conclusion that increasing bulk conduction current by simultaneously decreasing the trap depth and density or decreasing injection current from conductor by regulating the interface electric field via simultaneously increasing the trap depth and density can both effectively suppress space charge accumulations in HVDC cables. Thus, space charge and electric field can be readily regulated by the trap characteristics.
Highlights
High voltage–direct current (HVDC) power transmission is becoming more and more attractive for the wide-area energy interconnection of asynchronous networks, renewable energy utilization, subsea power transmission and island power supply, etc. [1]
We mainly focused on the effect of trap depth and density on the space charge and electric field evolution in the HVDC cable insulation considering the influence of load current and the applied voltage
For space charge suppression, increasing trap density is more effective at low temperatures and high electric field, while increasing the trap depth is more effective at high temperature and low field
Summary
High voltage–direct current (HVDC) power transmission is becoming more and more attractive for the wide-area energy interconnection of asynchronous networks, renewable energy utilization, subsea power transmission and island power supply, etc. [1]. Giuseppe et al developed a two-dimensional numerical model to simulate space charge behavior in the time domain, considering the effect of nonhomogeneous electrical conductivity distributions due to the temperature gradient. They demonstrated that the variations of the external heat exchange conditions along the axis will obviously enhance the maximum electric field in HVDC cables [10]. Zhou et al measured the space charge distribution in XLPE cable insulation under DC electric field and temperature gradient (TG) using the PEA method They used both the microscopic charge transport model and the macroscopic conductivity model based on a modified cylindrical geometry. Compared to the conduction model, which can be performed by commercial software (such as COMSOL and ANSYS), the BCT model has the advantages of providing deep insight into the microscopic process of space charge behavior, such as charge injection, charge trapping and detrapping, charge transport, the effect of trap characteristics and so on
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