In view of the possible inconsistency between the excitation current value used in the configuration of overexcitation limit and rotor overload protection in the actual system and the excitation current definition in the rotor overcurrent curve in the national standard, the relationship between the excitation AC current and the excitation system DC excitation current was obtained by solving the equation of the rotor control link according to the mathematical model of the rectifier of the excitation system of the unit. Finally, the simulation was carried out for the theoretical part, and the influence of fault types on the action time of the overexcitation limit was compared and analyzed. The final conclusion has guiding significance for the coordination and configuration of overexcitation limit and rotor overload protection in practice.

This study focuses on the problem of leak localization in high-pressure oil-filled submarine cables. These cables employ oil-immersed insulation technology, which not only provides excellent insulating performance and high current-carrying capacity but also adapts to complex and harsh seabed conditions. Despite this, oil-filled submarine cables still face significant challenges in leak detection. Traditional methods involving manual inspection and underwater robots are costly and thus not widely applicable. Additionally, advanced sensor technologies are limited due to the unique structure of the cables. Existing leak detection methods mainly rely on analyzing the flow state of insulating oil, but the accuracy of this approach needs improvement, and it cannot determine the leak damping at the leak point. To address this, the study develops an efficient leak localization and leak damping identification model that combines a reduced-order leak flow model with deep neural networks. This model aims to quickly locate the leak points and digitally twin the leak conditions. Research results show that this identification model has high accuracy and feasibility, effectively reducing the cost of leak localization in oil-filled submarine cables.

In recent years, buffer layer failures of high-voltage corrugated aluminum cable have occurred many times. The typical characteristics are ablative holes, white powders on the surface of water blocking tape, while the failure mechanism of buffer layer ablation has not been clearly stated. In this paper, a finite element simulation model of 110 kV corrugated aluminum cable with cross-section of 800 mm 2 is built, and the influence of volume resistivity and relative permittivity of water blocking tape and air gap distance on the electric field of buffer layer is studied. The results demonstrates that the maximum electric potential and field intensity of the buffer layer rise with the increase of volume resistivity and decrease of relative permittivity. With the air gap distance between water blocking tape and aluminum sheath decreases from 0.6 mm to 0.01 mm, the maximum potential of the buffer layer remains constant when the air gap is larger than 0.1 mm, while increases when the air gap is smaller than 0.1 mm. But for the water blocking tape without white powders, the change of air gap distance has little effect on the field intensity.

1 Abstract-As the protection device of submarine cable of new energy offshore wind power transmission system in new power system,J-tube has such problem as hinders the external heat dissipation of cable and restricts the carrying capacity of the whole wind power transmission line. Since the heat dissipation condition of cables in seawater is much better than that in air, the limiting effect of the air section of the J-tube on the carrying capacity is more significant. This paper takes ± 400 kV DC submarine cable under the J-tube laying environment as the research object, and a three-dimensional simulation model of the air section of J-tube is established using COMSOL Multiphysics software to study the influence of ambient temperature and pipe's outer diameter on cable's steady-state carrying capacity. The results show that with the increase of ambient temperature, J-tube submarine cable's carrying capacity will be significantly lower, from 2015A in 10°C down to 1386A in 40°C. And as the outer diameter of J-tube increases, the current carrying capacity of the cable also increases, because air flow in the tube also becomes more intense.

To solve the single time-frequency resolution problem of time domain reflectometry (TDR) and frequency domain reflectometry (FDR) in the localization of cable defects, a cable location method based on joint time-frequency analysis is proposed. Firstly, the basic principles of the joint time-frequency location method are briefly explained in terms of time-frequency distribution, reference signal selection, time-frequency offset, and time-frequency cross-correlation function. Then, the method proposed in this paper is used to achieve high-precision location of local defects, and the feasibility of the method is tested by modeling and simulation of 10 kV long cables with local defects. The simulation results show that the method can effectively locate cable local defects in different locations and degrees, and the error of the location results is only about 0.02%. Compared with the traditional TDR and FDR methods, this method utilizes the time limit and band limit characteristics of reference signals and introduces the time-frequency cross-correlation function to achieve higher precision location, which combines the advantages of TDR and FDR.

Interfacial pressure is one of the key factors that determine the insulation strength of cable accessories. However, the cable accessories will relax due to the temperature cycling during operation. Therefore, it is worth to study the change regulation of the interfacial pressure of the cable accessories with the temperature. In this study, an interfacial pressure acquisition device is designed by the built-in pressure sensor. The interfacial pressure of 10 kV cold shrinkable cable joint is measured by the device at 25°C and 130 °C respectively. Meanwhile, the joint thickness and inner diameter is recorded to compare the changes of joint geometry before and after aging. Then, the cable joint is built by the finite element simulation software, and the simulation results are compared with the measured data to verify the validity of the data. With the increase of the temperature cycle time, the interfacial pressure of the cable joint at room temperature decreased by 15.9%, while the interfacial pressure at high temperature increased by 11%. Experimental results proved that after the temperature cycle of the cable joint, the geometric dimensions of the cable joint changes, and the stress relaxation increases. When the cable joint work at high temperatures, the interfacial pressure of the cable accessories increases, while the cable accessories work at room temperature, the interfacial pressure decreases, resulting in a decrease in the electric field strength of the cable accessories.

Functionally graded materials (FGMs) used in electrical insulation have spatially inhomogeneous dielectric properties (i.e., permittivity or conductivity), which can be applied to relieve localized electric field (E-field) intensification and improve insulation performance. However, previous research shows some limitations in inadequate considerations on the material feasibility, and insufficient universality on material grading type and voltage form. In this study, a material study of silicone rubber (SiR) nanocomposites containing carbon nanotubes (CNTs) is conducted to determine the practical variation range of dielectric properties (both permittivity and conductivity) in joint insulation materials. Then, the optimal design of both multilayer and pointwise FGM joint insulation is investigated under both AC and DC voltage, in which the lower and upper limits of permittivity and conductivity were derived from the experimental results. Experimental results on SiR/CNT nanocomposites indicate that low-amount doping of the CNTs (0-0.5% wt%) can effectively increase the permittivity and conductivity of joint insulation materials. The successive simulation study indicates that compared to uniform joints, cable joints employing optimally designed FGM insulation show a considerable increase in the E-field utilization factor (from 0.08-0.17 to 0.23-0.56), indicating elevated E-field uniformity. Finally, the optimal range of CNT doping ratios is determined to be 0-0.3 wt% from both experimental and simulation results. This study systematically verifies the applicability of FGMs in enhancing the performance of power cable accessories, which can show some guidance to the design and fabrication of advanced power cable systems.

The oil-impregnated paper in the converter transformer, especially in the valve side bushing, is suffered by the complicated electric field. By reason of the power electronics and non-linear equipment, the oil-impregnated paper is subject to the harmonic voltages. The insulating aging is more prominent in contrast with the power transformer. Under this condition, the charges are capable to accumulate on the surface of oil-impregnated paper, which will lead to the distorting the electric field and accelerating the insulating degradation. Consequently, the performance deterioration of oil-paper insulation is inevitable. Surface fluorination is an effective approach of modifying the chemical components of polymer matrix. Hence, this paper is dedicated to research effects of thermal aging on the surface charge dynamic characteristics of fluorinated oil-paper insulation under the harmonic superimposed DC voltages. Some conclusions can be drawn that the comprehensive effect of harmonic voltage and thermal aging can significantly enhance the de-trapping of the surface charge in deep traps, the deep trap energy level density is greatly affected by the proportion of harmonic. As the thermal aging time is prolonged, the trapped charge becomes more difficult to detrap, the charge accumulation increases.

Partial discharge (PD) is one of the main causes of the interface insulation deterioration of cable accessories. Studies have shown that temperature has an important influence on the PD development, but the effect of temperature on the PD initiation is still not fully understood. This paper investigated the developing regularity of PD at the interface defects of the cable accessories under thermal cycling. An electro-thermal co-aging platform with a cable accessory having semiconductive-layer protrusion defect was firstly designed and introduced in the paper. The experiment loop in the platform was thermally cycled in air by using a current transformer to induce a current in the cable conductor. Cycle duration was 9.5 h with 8h/ON and 1.5h/OFF. Afterwards, PD numbers, PD amplitude and PRPD (Phase Resolved Partial Discharge) spectrum were collected and analyzed comparatively. Obtained results show that temperature change caused by current on-off control will result in temporary PD excitation. PD numbers and amplitude increase rapidly as the temperature rises or falls quickly. When temperature stabilizes, however, the increment slows down. Phenomenon above can be interpreted to the interface pressure change caused by thermal expansion and contraction of the interface insulation, namely “Breathing Effect”. The research revealed that PD signals in the interface defect are more easier to be detected when cable accessories are operating under high temperature gradient, which may provide practical references for PD field test of cable accessories.

Recently, there have been many breakdown faults of 220kV one-piece pre-molded silicone rubber joint. The faults occurred in the closing process of the cable line. The faulty phases are B and C. The main difference of the three-phase cable line is that the electromagnetic voltage transformer (VT) is installed in Phase A. In order to study the influence of electromagnetic voltage transformer on 220 kV cable line, the residual voltage of cable conductor and the operating overvoltage level of cable line are simulated and analyzed by ATP-EMTP. The results show that the switching over-voltage level has little to do with whether the line is equipped with VT. When the cable line is equipped with VT, the residual charge can be released quickly through the electromagnetic voltage transformer, and the reclosing over-voltage of the line is significantly reduced. In addition, for silicone rubber insulation materials, there will be space charge accumulation under the DC field of residual voltage, which will cause the change of material electric field distribution. The abrupt change of the local electric field may lead to the breakdown of the insulation.

Application of functionally graded materials (dielectric materials with spatial variated permittivity or conductivity distribution) is a promising approach for the electric field optimization in cable accessories. In this paper, we uses a multi-layer optimization approach to design the permittivity and conductivity distribution in cable joint insulation, which are intended to be applied in AC and DC applications, respectively. The results shows that the electric field intensification phenomena were inhibited after the optimization process. Moreover, the degree of E-field optimization is affected by the permittivity/conductivity range, the layer number and the direction of layered permittivity/conductivity gradient.

The fast parsing technology of IEC61850 SCD configuration file of intelligent substation is studied in this paper. According to the parsing results, various complex logic modules and their correlations are established within the system, such as IED, data set, virtual channel and virtual loop, besides, the fast search index is formed within the system. According to the fast data processing technology of SCD model, a high visualization of SCD model is formed and network connection diagram and logical connection diagram are automatically generated, which provides a model basis for the massive real-time data analysis needed for debugging and analysis work.