Surface charge accumulation on insulators in HVDC gas-insulated equipment causes electric field distortion, posing flashover risks and threatening operational safety. Precise surface charge density inversion is thus essential for equipment design. This paper proposes a hybrid regularization-based inversion method, combining Tikhonov and total variation regularization advantages for accurate charge density reconstruction. Integrating the LSMR algorithm with Golub-Kahan bidiagonalization significantly reduces computational burdens. The generalized cross-validation (GCV) criterion adaptively determines the regularization coefficient and iteration stopping criterion, effectively suppressing noise interference and preventing semi-convergence. Simulation verification confirms the method achieves high inversion accuracy under varying noise levels, demonstrating excellent robustness. Further validation via insulator charge accumulation simulations using the bipolar charge transport model shows high agreement between inversion results and steady-state charge distributions. The method accurately reconstructs charge discontinuity regions in distributions with abrupt transitions. In conclusion, this hybrid regularization-based inversion algorithm provides an effective solution for precise surface charge density inversion on HVDC gas-insulated equipment insulators, offering significant theoretical value for optimizing insulation design.

The modular multilevel converter (MMC) is widely used in flexible direct current projects. The fault clearance speed of hybrid MMCs is closely related to the proportion of full bridge sub-modules (FBSMs). To address the issue of sub-module overvoltage caused by unbalanced energy absorption between half bridge sub-modules (HBSMs) and FBSMs during the clearance of a bipolar short-circuit fault, this paper designs an energy-assisted isolation branch suitable for hybrid MMCs with a low FBSM ratio. By bypassing the HBSMs before blocking, the energy released by the submodules is reduced, thereby lessening the transient energy absorption burden on the FBSMs and suppressing FBSM overvoltage. To shorten the fault clearance time, this paper proposes a dual-branch coordinated operation strategy. A transient energy absorption branch is connected in parallel at the port side to assist in absorbing the fault's transient energy and accelerate fault clearance. A two-terminal hybrid MMC-based flexible direct current transmission system model is built on the PSCAD/EMTDC platform to verify the effectiveness of the proposed scheme. Simulation results show that the proposed dual-branch coordinated operation strategy can effectively suppress sub-module overvoltage, shorten the fault clearance time, and reduce the operational cost associated with rapid self-clearing of faults in hybrid MMCs.

Conventional auto-reclosing schemes, relying on fixed delays, exhibit operational blindness that risks secondary system impacts or prolonged outages. This study addresses these limitations through adaptive reclosing technology. The variation characteristics of the fault-pole voltage before and after arc extinction are first analyzed in this study. Fourier decomposition of recovery voltage revealed frequency-specific variations, leading to the definition of a 50 Hz incremental percentage parameter (H₁) as the arc extinction identifier. Adaptive reclosing logic was developed by monitoring H₁ against adaptive thresholds. Implemented in a four-terminal MMC-HVDC PSCAD/EMTDC model simulating DC-side faults, The simulation results demonstrate that this arc extinction time identification method achieves rapid recognition and can accurately capture the moment of fault arc extinction within several milliseconds. The identification error of arc extinction time under various fault conditions is less than 10 ms. The adaptive reclosing strategy, which accounts for arc extinction time identification, enables reliable recognition of the arc extinction moment, effectively shortens the reclosing process, and enhances system reliability.

With the continuous increase in voltage levels and transmission capacity of modern power systems, traditional hybrid reactive power compensation (HRPC) can no longer fully meet the stability requirements of ultra-high-voltage (UHV) transmission. During short-circuit faults, controllable HRPC introduces high-amplitude, low-frequency oscillations in the fault current, intensifying the transient recovery voltage (TRV) and posing a serious threat to system insulation. To address this issue, this study establishes an equivalent double-fault model of the UHV HRPC line based on its compensation principle, derives the TRV mechanism under different fault locations and initiation times, and analyzes the effects of compensation degree on TRV peak and rate of rise. The deterioration characteristics of TRV under double faults are revealed, and a high-speed grounding switch (HSGS) suppression scheme is proposed. Simulation results show that double faults on HRPC lines can cause TRV to exceed standard limits, hindering reliable circuit breaker interruption, while a properly configured HSGS effectively reduces both TRV peak and RRRV, enhancing breaker reliability and overall system stability.

Modular Multilevel Converters (MMCs) are widely employed in voltage-source converter-high voltage direct current (VSCHVDC) transmission projects. Capacitor voltage imbalance in hybrid MMCs is closely related to the differences in the charging and discharging processes of their submodules (SMs). To address the issue of submodule voltage imbalance caused by uneven energy absorption between half-bridge and full-bridge submodules during over-modulation conditions, a detailed analysis of the impact of second-order harmonic current and third-order harmonic voltage injection on the arm voltage is provided. A dynamic modulation index incorporating multiple harmonics is proposed to enable operation under high modulation ratios across various working conditions. Based on the system power factor, the phase of the multiple harmonic injections is adjusted, thereby shifting the phase of the arm voltage. As a result, the MMC arm current distribution is optimized, the formation of DC circulating currents is counteracted, and circulation uniformity is improved. A double-terminal hybrid MMCHVDC system model was built on the PSCAD/EMTDC platform to validate the effectiveness of the proposed strategy. It is demonstrated by simulation results that the operating range of the capacitor voltages is effectively confined by the proposed dynamic modulation index. Furthermore, the electrical angle at which the HBSM is compelled to discharge energy is adjusted, the excess energy absorbed by the FBSM is reduced, the capacitor voltage imbalance issue is mitigated, and system operational stability is enhanced.

To save line corridors and increase the transmission capacity, the co-tower erection of AC/DC transmission lines has broad prospects for development. However, due to the thyristor controlled series compensation (TCSC) on the AC side of the co-tower lines, the fault current during a single-phase ground fault contains high-amplitude low-frequency components, which are not conducive to the rapid extinction of the arc. To address this issue, based on the mechanism of the formation of the post-fault arc in the AC side of the co-tower lines with series compensation, a simulation model for ultra-high and extra-high voltage AC and DC co-tower transmission is established. The low-frequency components of the post-fault arc are analyzed using power spectrum analysis. Considering the frequency characteristics of the post-fault arc, the suppression effect of short-circuiting the fault phase series compensation with a small resistance on the low-frequency components is studied. The research results show that the post-fault arc mainly consists of the fundamental frequency component, the low-frequency component generated by the discharge of the residual voltage of the TCSC, and the induced direct current coupled from the DC side of the co-tower. After suppression, the amplitude of the post-fault current and the recovery voltage significantly decrease.

DC circuit breakers are one of the key equipment of photovoltaic(PV) DC systems. Aiming at the problems of insufficient fault current limiting ability, severe breaking arc, and serious contact ablation of traditional circuit breakers in the junction box of PV system, a current injection DC circuit breaker topology based on coupling reactor is proposed in this paper. The thyristor device is used to transfer the fault current of the mechanical switch branch in this topology to suppress the breaking arc from the perspective of energy transfer. At the same time, a coupling reactor is added between the main branch and the mechanical switch branch, and a resistance-capacitance hybrid current limiting branch is added to the main branch. The rising speed of the fault current is suppressed effectively, the transfer speed of the fault current is accelerated, and the breaking arc time is shortened. The principle analysis and parameter design of the proposed circuit breaker topology are completed in this paper, the influence of the parameters of the coupling reactor and the resistance-capacitance hybrid current limiting branch on the fault current transfer time is analyzed and verified by the MATLAB/Simulink platform. The results show that the topology can suppress the arcing and accelerate the arc extinguishing speed significantly, which can reduce the fire hazard of the junction box and improve the operation reliability of the PV system effectively.

With the rapid development of the global energy transition and the carbon emissions trading market mechanism, the penetration rate of distributed photovoltaics in distribution transformer areas has increased year by year. Due to the early rapid deployment of distributed photovoltaics systems, many installations were mismatched with the existing feeder topology or exceeded the capacity limits of local transformer areas, resulting in voltage violations and abnormal network losses. To address the above issues, an optimized configuration method for DES under multiple scenarios based on improved Affinity Propagation clustering is proposed. By considering the characteristics of distributed energy storage and distribution network operation. A multi-objective bilevel optimization configuration model is established, with daily average lifecycle cost, line loss cost, and photovoltaic utilization rate as objectives. The power flow model is transformed using second-order cone programming relaxation, converting the original non-convex model into a convex one. Finally, a multi-objective particle swarm optimization algorithm is used for solution. Verification is conducted using two actual substations in Hebei as case studies. The results show that the proposed method can improve voltage compliance, reduce grid losses, and increase the integration capacity of distributed photovoltaic systems.

Aiming at the safety threat posed by metal particle contamination inside DC gas-insulated transmission line (GIL), where metal particles tend to adhere to the surface of basin insulators, a simulation model reflecting the actual operating conditions in DC GIL is established, and the impact mechanism of metal particles on the insulator's surface electric field is analyzed. In this paper, the millimeter-sized particle is selected, and the effect of various factors, such as particle size, shape, attachment location, and the aggregation of multiple particles, is researched on the electric field distribution of basin insulators. The findings indicate that the safety threshold of the insulator surface electric field strength is exceeded with a single metal particle adhesion defect. There is a boundary-diminishing effect of particle size on electric field distortion. The potential and curvature of particle attachment location are positively correlated with the degree of electric field distortion on the insulator surface. Furthermore, when particles are irregularly shaped, such as conical or linear, or when multiple particles aggregate longitudinally, there is a significant increase in the degree of electric field distortion on the insulator surface. The electric field distortion near the particles becomes more severe under the condition of voltage polarity reversal.

Direct current circuit breakers (DCCBs) are extensively utilized in flexible DC transmission systems, with their cost being intricately related to the breaking current. An adaptive current-limiting control structure tailored for half-bridge modular multilevel converters (MMCs) has been developed with the aim of reducing the breaking current of circuit breakers. By examining the short-circuit current characteristics on DC side of MMC, the variation in the input impedance amplitude of the converter station is utilized to indicate the extent of the fault. The coefficient Kf, which defines the fault depth of the converter station, is determined. Kf is incorporated into the control structure of MMC to align it with the reference value of the bridge arm voltage. A proposed method for adaptive current limiting control addresses DC side short circuit fault of MMCs. The model of the half-bridge MMC flexible DC transmission system is created using power systems computer-aided design/electromagnetic transients including DC (PSCAD/EMTDC) platform to model the clearance of DC side short-circuit faults and validate the effectiveness of current limiting control. The simulation results demonstrate that the proposed adaptive current limiting control technique can effectively implement differentiated current limiting control depending on the diverse fault depths of MMC. The breaking current of DCCB is reduced and the fault clearing speed is improved by this approach.

The influence of thyristor controlled series compensation (TCSC) on the transient characteristics of transmission lines needs to be studied urgently. Firstly, the structure and function of compound FCL and TCSC are analyzed. Secondly, based on the background of 500 kV extra-high voltage demonstration line, a single-phase ground fault equivalent model of ultra-high voltage line with FCL and TCSC is established. The influence of FCL hybrid multiplexing TCSC on the breaking characteristics of circuit breakers is studied. Based on the Laplace transform and the equivalent parameter concentration circuit, the influence of the fast switching time and the current limiting ratio of the FCL on the transient recovery voltage is analyzed. The influence mechanism of different modes of FCL on transient recovery voltage is obtained. The research scheme of FCL instead of FSC is proposed, and the change rules of transient recovery voltage and rise rate RRRV under different compensation degrees are compared. The results show that under the same compensation degree, the FCL replaces the FSC to reduce the peak value of the transient recovery voltage and reduce the RRRV over-standard condition, which verifies the feasibility of replacing the FSC with FCL. A new design scheme for extra-high voltage series compensated transmission lines is provided.

The AC/DC hybrid transmission line is affected by electromagnetic coupling. After the line is failed, the secondary arc is difficult to extinguish, which posed a serious threat to the stable and reliable operation of the line. Taking a 500 kV AC double-circuit and ± 800 kV Yun-Guang UHV DC transmission line on the same tower as an example, this paper is built an AC/DC hybrid transmission line model through PSCAD, studied the influence of coupling section length and fault point location on the transient characteristics of the secondary arc, and analyzed the suppression effect of the DC line coupling operation mode on the secondary arc. According to the findings, the secondary arc current of AC and DC lines is greatly influenced by the length and location of the coupling section. The AC line fault is located at the midpoint of the coupling section. When the length of the coupling section is 400 m, the amplitude of the secondary arc current has reached the minimum value. When the DC line fault is located at the midpoint of the coupling section, the amplitude of the secondary arc current has reached the maximum value. In addition, the bipolar coupling operation mode of DC lines can effectively limit the amplitude of secondary arc current and recovery voltage of AC and DC lines, and the suppressive effect of secondary arc is obvioused.

Hybrid reactive power compensation(HRPC) has broad development prospects in UHV transmission lines. However, due to extreme weather conditions, the interaction of complex faults on HRPC lines needs to be studied urgently. Based on the analysis of the function of HRPC structure, considering the double fault condition, the influence of double fault of UHV HRPC line on the breaking characteristics of circuit breaker is studied. Based on Laplace transform and equivalent parameter concentrated circuit, the double fault equivalent model of UHV HRPC line is established. The mechanism of transient recovery voltage (TRV) of HRPC line is deduced and calculated when double fault occurs at different fault positions and different moments. The influence of double fault on the breaking characteristics of circuit breaker of HRPC line is revealed, and the suppression scheme of high speed grounding switch is proposed. The simulation results show that the TRV is prone to exceed the standard when double faults occur in the hybrid line, and the normal breaking of the circuit breaker is affected. Reasonable configuration of high speed grounding switch can effectively reduce the TRV and the breaking current of circuit breaker, and the expected effect of normal breaking of circuit breaker can be achieved.

可控型混合无功补偿(hybrid reactive power compensation,HRPC)对输电线路暂态特性的影响亟待研究.在分析可控型混合无功补偿结构功能的基础上,以晋东南-南阳-荆门特高压示范线路为背景,建立特高压混合无功补偿线路单相接地故障等效模型,研究可控串联补偿+可控并联电抗器(thyristor controlled series compensation+thyristor controlled transformer,TSCT+TCT)混合无功补偿对断路器开断特性的影响.基于拉氏变换和等值参数集中电路,分析瞬态恢复电压(transient recovery voltage,TRV)影响因素,得出瞬态恢复电压随可控型混合无功补偿度变化规律.利用PSCAD/EMTDC,研究安装可控型混合无功补偿前后对瞬态恢复电压的影响,验证分析方法的有效性.结果表明:随着可控型混合无功补偿度的增加,TRV峰值和上升率RRRV不断增大,而TCT对瞬态恢复电压影响较小.

针对部分配网不能采集所有节点电压相角信息的情况,提出通过分析配电网现有量测设备可获取的功率电压数据,采用数字化的方式映射物理系统实现配电网拓扑结构和线路参数可视化.为实现这一目标,首先,基于多组时间断面下的量测数据,根据潮流方程建立线性回归的拓扑与线路参数辨识模型,采用最小二乘法求解模型中导纳参数.其中,考虑实际数据获取过程中存在不可控因素导致部分数据缺失,利用最小方差填补缺失数据,保证信息完整性;其次建立修正模型,采用改进的牛拉法迭代修正拓扑和线路参数初值,对拓扑结构和线路参数精度进行调整;最后利用IEEE 33节点算例验证该方法可行性.

Zero insulators directly reduce the electrical performance of insulator strings, affecting the safe and reliable operation of transmission lines. The grounding current of the insulator string contains the characteristic information of insulator electrical performance. Extracting the characteristic information of grounding current can realize the detection of zero value insulator, which is of great significance to ensure the safe operation of transmission lines. In this paper, the composite insulator used on ultra-high-voltage (UHV) lines is studied to analyze the influence of zero insulators on the electric field distribution. Furthermore, the corresponding characteristics of the zero insulators at different locations are extracted. The fitting relationship between the characteristic quantity and the zero insulator position is analyzed. The effective characteristics of grounding current are selected as training sample to establish the zero insulator position prediction model based on probabilistic neural network (PNN). The research result is meaningful for the detection of zero insulators.

混合串联补偿对输电线路暂态特性的影响亟待研究.为研究串联补偿混合复用对瞬态恢复电压(transient recovery voltage,TRV)暂态特性的影响,以500 kV超高压示范工程线路为研究背景,利用PSCAD/EMTDC建立可控串补与固定串补的电磁暂态仿真平台,分析系统发生单相接地故障时瞬态恢复电压变化规律,得到恢复电压上升率与短路电流变化曲线;采用对比分析方法,针对可控串补与固定串补不同配置方式,研究不同串补度对TRV特性的影响,并得出最佳串补配比.仿真表明:相比固定串联补偿(fixed series capacitor compensation,FSC)双平台分段布置,系统采用可控串联补偿(thyristor controlled se-ries compensation,TCSC)与FSC混合复用时,TRV超标工况大幅增加;合理配置TCSC+FSC线路串补度,能够有效降低TRV与断路器短路电流,且能够满足断路器正常开断的国家标准.

针对研究生现代电力系统分析课程特点实施课程建设改革,提出了双线双语、教师授课与工程实践双向并行的创新教学模式,并对 2020 级电气专业研究生展开教学实践验证.研究生综合学习能力得到提高,为培养具有国际视野和专业素养的研究生奠定了扎实的基础.

Abstract The DC side fault of the high voltage DC transmission system based on modular multilevel converters high voltage DC (MMC-HVDC) is easily affected by the double influence of AC transient electrical quantity infeed and overvoltage and overcurrent, seriously threatening the safe operation of the power grid. Aiming at the problem above, a fault suppression strategy in dual mode of isolation and current limiting is proposed. Based on the half-bridge-full-bridge hybrid MMC, the fault transient mathematical model considering AC feed and sub-module switching feed is analyzed. AC isolation module with double conduction self-resistance structure and current-limiting control module is constructed, which can be adaptively adjusted to the system’s direct current parameters. The ±500 kV double-ended hybrid MMC system model is established to verify the scheme’s effectiveness. In addition, the influence of high AC modulation parameters on the suppression effect is investigated. PSCAD/EMTDC simulation results show that AC active and reactive power feed-in peaks are reduced by 388.69 MW and 119.82 Mvar, respectively, under dual-mode control. The peak value of DC overvoltage and overcurrent is reduced by 1211.53 kV and 22.5 kA, respectively, the fault self-clearing time is shortened by 43 ms, and the fault suppression effect is remarkable. In the high AC modulation ratio operating state, the modulation parameters are positively correlated with the AC power feed and negatively correlated with the overvoltage and overcurrent of the DC system. The research results provide support for the fault protection scheme of the hybrid MMC flexible and direct power grid.