Under the background of the new power system, parameter identification and correction based on measurement data are key requirements for the digitalization and intelligence of distribution networks. A parameter identification method is proposed that integrates the mathematical model of the distribution network with measurement data collected from the low-voltage side of distribution transformers, aiming to address the online identification and correction of line and transformer parameters. Firstly, the topology is obtained by parsing CIM files, and the initial parameters of components are set according to asset data. Then, a quasi-Newton-Raphson method is employed to construct the Jacobian matrix based on multiple sets of measurement data, enabling iterative parameters updated by solving underdetermined or overdetermined equations. Finally, the identified parameters are used to recalculate the low-voltage side voltages, which are then compared with the measured values for validation. Experimental results based on data from a practical distribution network in South China demonstrate that, with increasing data sets and iteration times, the average relative errors converge to a stable level. This verifies that the proposed method achieves high accuracy and practicality, and can provide effective support for power flow calculation, state estimation, and digital twin construction in distribution networks.

Along with the growing integration of renewable energy resources, the new power systems, which are dominated by inverter-based resources （IBRs）, are facing critical challenges in both planning and operation stages. The conventionally used system strength metric, short-circuit ratio （SCR）, exhibits limitations in assessing connections of new IBRs due to their unique dynamic behaviour and control interactions. In this paper, the definition of system strength is reviewed. The underlying principles of conventional SCR and its variants are then discussed, with their constraints explained. To describe the system strength in a more comprehensive way, this paper further classifies system strength into three categories: quasi-static, small-signal, and large-signal. For each category, relevant metrics are introduced and their relative merits are discussed. Electromagnetic transient simulations are presented to illustrate key insights.

The cryptographic device generates a large amount of physical information such as electromagnetic，energy consumption，heat，etc. during encryption and decryption. The attackers use these physical information to perform a side channel attack on the cryptographic device and steal the key of the cryptographic device. In the case of a traditional simple power analysis attack of elliptic curve cryptography algorithm，the attacker recovers the key by manually identifying similar modules in the power consumption data of the double point calculation. But this way results in low attack efficiency and low attack accuracy. This paper proposes the SPAMD algorithm based on the time series of motif discovery. The algorithm realizes the automatic recognition of similar modules in the power consumption data of the double point calculation，and completes the conversion of the attack mode from manual recognition to automatic recognition. Experiment results show that SPAMD attacks have a significant improvement in efficiency and accuracy.

With the increasing complexity of "high-proportion renewable and high-electrification" power systems, traditional model-driven stability analysis methods face growing limitations. Artificial intelligence （AI） techniques, offering advantages in both speed and accuracy, have emerged as a key research focus. This paper focuses on the development path of power system stability analysis technology from model driven to data-driven, and further to hybrid intelligence integrating domain knowledge and data. Firstly, the technical requirements of typical stability analysis tasks are outlined, and traditional model driven methods are reviewed.Subsequently, the application results of artificial intelligence methods in different scenarios are summarized, and their advantages and disadvantages are analyzed. Further the information driven methods and research progress of integrating power system knowledge and mechanisms are explored. Finally, based on the power system characteristics under the background of "double high", the current challenges faced are analyzed, and future research directions are discussed.

Traditional communication technology between substations of security and stability control (SSC) system has some inherent shortcomings, it does not conform to the trend of current technological development and restricts the expansion and application of SSC. Using intelligent substation process layer GOOSE communication technology, a new communication technology between substations based on IEC 61850 in SSC is proposed in this paper. The key technology of communication network architecture, communication capacity control, data flow control and visualization of decoupling configuration are deeply researched, and the typical project of Brazil Belo Monte SSC application is introduced. This technology has several advantages, such as stable and reliable communication, data transmission capacity, reusability and interoperability. It can meet the demand of information exchange between substations, and it represents the development direction of the communication technology of SSC.

Driven by the "dual carbon" goals, the user side of the new power system faces multidimensional security risks due to the large-scale integration of new grid-connected entities such as distributed photovoltaic systems, electric vehicle charging stations, and energy storage equipment.Firstly, the challenges to equipment safety, grid security, and societal safety posed by the massive integration of these new entities are systematically analyzed, core bottlenecks at the technical and managerial levels, such as uneven equipment quality, difficulties in cross-modal data fusion, and insufficient safety protections, are highlighted. To address the heterogeneity, semantic differences, and correlation characteristics of multimodal data, a multimodal large model construction technology is proposed, incorporating data augmentation generation, cross-modal semantic alignment, and parameter-efficient fine-tuning methods to enhance risk perception accuracy. Furthermore, integrated security prevention and control strategies are introduced from three perspectives: grid optimization, intelligent operation and maintenance, and resilience enhancement. These measures provide theoretical support and practical pathways for the security governance of the new power system, facilitating the coordinated development of energy transition and security under the "dual carbon" objectives.

Multi-infeed effective short circuit ratio (MIESCR)is a common index to evaluate the voltage supporting capacity of AC power grid in multi-infeed systems, but its physical significance and applicable scope are not clear enough. In this paper, the multi-infeed system is equivalent to a single-infeed system with the same external characteristics, and the definition of the generalized multi-infeed equivalent effective short-circuit ratio (MEESCR)is proposed. It is proved that effective short circuit ratio (ESCR)and MIESCR are special cases of MEESCR under certain operating conditions after some approximations, and the applicable scope and the error source of MIESCR and ESCR are explained theoretically. The mechanism analysis and PSCAD simulation results show that MEESCR can more accurately evaluate the voltage support capability of AC grid in multi-infeed system compared with MIESCR and ESCR.

When interior point method is used to solve the problem of reactive power optimization in large scale power system, the feasible solution may not be obtained because of the unreasonable part of the constraint conditions. In this paper, a practical relaxed reactive optimal power flow method (Relax ROPF) is proposed to restore the solvability of reactive optimization by interior point method. In the iterative process, the ill-condition constraint which causes failure of OPF can be automatically identified, the problem is restored by introducing minimum relaxation into those ill-condition constraints. Test results on IEEE 39-bus system and an actual power grid show that the proposed method can identify unfeasible constraints very well, and can effectively restore the optimal power flow.

Roof insulators of high-speed electric multiple units (EMUS) are important mechanical supporting component for high voltage equipment, which in addition isolates the catenary from the train’s roof in electric, the flashover of roof insulators may lead to interruption of power supply or even outage. However, due to the specificity and severity of operation environment for high-speed railway in China, accidents caused by the flashover of insulators often occurred, which seriously affect the safe operation of high-speed railway. Through deep research on revelant scientific problems, accidents of trains result from insulator flashover have been greatly reduced, but these kinds of problem haven’t been solved fundamentally. In this paper, research progresses of roof insulators used for high-speed EMUS are reviewed from the follwing aspects: structure and material property, pollution flashover characteristics, sand dust flashover characteristics under strong wind, insulation online monitoring, methods for accelerated aging test and aging test platform. In the end, this paper forcasts future research key points.

The asynchronous interconnection mode between Yunnan Power Grid and China Southern Power Grid is planned to be put into practice in 2016. However, during the practical experiment of raising DC power in asynchronous mode, the frequency of Yunnan Power Grid oscillates in ultra-low frequency for a long period. In this paper, through detailed analysis of the experiment data, the governor systems of hydropower units are found to be the direct reason of the oscillation, and the mechanism of governor systems offering negative damping during the oscillation is analysed. Furthermore, off-line data simulation is carried out to reproduce the process of this practical experiment, the results prove the correctness of the theory, finally some preliminary recommendations are proposed for further work.

Microgrid system is a small power system made up of distributed generations, energy storage devices, converters, loads and monitoring and protecting devices. According to the diversity of distributed generation and the complexity of microgrid system operation mode, a stability control strategy combining droop control and V-f control for microgrid system based on converter of energy storage devices is presented. When microgrid system is in grid-connected mode, droop control is used for converter of energy storage devices. When microgrid system is in islanded mode, if voltage and frequency are beyond the variation range of stability control strategy, V-f control is used for converter of energy storage devices to ensure the voltage and frequency stability of microgrid. Simulation results demonstrate the effectiveness of the stability control strategy for grid-connected mode, islanded mode and the transfer process between the two modes.

The development and test of China’s first ±525 kV cross-linked polyethylene （XLPE） DC cable are introduced. A type of heteromorphic copper conductor with a section of 3 000 mm² was designed， and a water-blocking tape was chosen as filler material. After calculation， the filling factor of the conductor reached 95.5%. Longitudinally permeability tests on the insulated conductor have proceeded under the condition of 2 MPa hydraulic pressure for 10 d and 1 m water column with thermal cycling for 10 times， the length of permeability was 7.2 m and 0.9 m respectively. Copper wires were twisted as a metallic shield of the ±525 kV XLPE DC cable， among the copper wires， two optical fibers were implanted in to achieve the requirements of communication and thermometry online. A composite waterproof sheath was compounded with aluminum-plastic tape and PE， hence， the outer diameter of cable has been minished 10% compared to corrugated aluminum-sheathed cable in the same voltage and section. To verify its electrical properties， voltage test and partial discharge test under AC 525 kV were carried out， then a whole performance type test was taken in National Center of Testing and inspection for Electric Cable and Wire （TICW） referred to CIGRE TB496—2012 and GB/T 31489.1—2015， including load cycle test， DC withstand voltage test， superimposed impulse test and so on， and the conductor passed all the tests. During the load cycle test， the maximum temperature of the conductor was over 70 ℃， and the temperature gradient in insulation exceeded 30 ℃.

With the maturity of power cable technology and updating of new technology of cable accessories, the failure characteristics of high voltage cable systems and fault causes have changed significantly. In this paper, detailed statistics are carried out for the characteristics and fault cause proportions of 132 failures for 110 kV and above power cable in China Southern Power Grid(CSG)during 2006 and 2016, and 99 failures in the literatures, and the fault characteristics and main reasons of the high voltage cable system in recent years are analyzed. The statistical results show that the present operation reliability of high-voltage cable system in CSG has been improved significantly, while the failure rate has decreased by an order of magnitude compared to 2001. Cable accessories have now already become the weakest part of high-voltage cable systems, the failures of which account for as high as 85.5% without taking external damage into account. For cable, more than 70% of the cable failures are due to external damage, while more than 84% cable accessories failures are due to product quality and improper installation. The statistical result of power cable system can provide a basis for the development of differentiated operation and maintenance strategy.

Ultra-high-penetration distributed photovoltaics （PV） in distribution networks pose significant challenges, including severe reverse power flow overloads and voltage violations. Addressing the strong coupling characteristics between active-reactive power （P/Q） and voltage under complex network impedances of distribution networks, a active-reactive power coordinated voltage support optimization method is proposed. This method achieves multi-objective collaborative optimization operation of distributed renewable energy and energy storage, balancing low operational costs with high power quality. Firstly, a rolling optimization method for three-phase power flow voltage model predictive control （MPC） based on active-reactive power coupling is proposed. Via a multi-period voltage MPC framework, the number of decision variables and constraints is effectively reduced, which improves solution efficiency while ensuring solution accuracy and achieves fast solution of the online voltage control problem. Furthermore, a pre-iterative method based on fixed-point iteration is proposed for the strongly coupled three-phase power flow model. By distributing multi-step iterations across the rolling optimization horizon, the solution accuracy is significantly improved without increasing the number of per-step iteration. Finally, the effectiveness of the proposed control system in suppressing voltage exceeding limits is verified by integrating an IEEE 13-node system with ultra-high-penetration PV.

Aiming at the practice of intelligent robot inspection of transmission lines, four key control technologies of the robot’s automatic inspection operations are developed including automatically passing over obstacles, automatically positioning, automatic fault diagnosis and restoration, automatic inspection The principle and implementation method of the control technology are introduced in detail. Three typical failure modes of the robot, i.e., the self recovery fault, the replacement fault and the fault need to repair, and their diagnosis and repair strategies are established. The robot inspection test on real outdoor line is carried out. Robot inspection demonstration application of 500 kV live line in China Southern Power Grid is completed for the first time. The robot inspection control technology, fault diagnosis and repair strategy, as well as the independent inspection process are verifid and assessed. The robot has a single time inspection mileage of over 10 km, and the inspection application has achieved good results.

The wide area response based transient stability detection and control technology has become a hot research area in power system stability studies. Currently several different technologies have been proposed, but lots of problems still need to be solved before they can be applied to practice. In order to effectively analyze and compare the validity and practicability of these transient stability detection technologies, a wide area measurement system (WAMS) based prototype system is developed for power system real-time transient stability detection and control. Based on real-time measured data from PMU, the system simultaneously implements various response based transient stability detection and control technologies and provides visual presentation of results. The design of framework structure, implementation of function modules and engineering applications of the system are presented. Meanwhile, suggestions on future orientation of wide area response based transient stability control are given in the following aspects including time delay, data acquisition and control schemes generation. Engineering application demonstrates that the prototype system has a good perspective and is an effective tool for analysis and comparison of the wide area response based transient stability detection methods.

When the partial discharge in SF₆ insulated equipment ceases or the concentration of decomposition products are sampled and delivered to laboratory examination, the concentration of decomposition products will decay with a certain degree over time in despite of the stationary equipment or sample.To improve the accuracy and reliability of the detection of decomposition products, the standing effect of the decomposition products decaying over time is studied.By analysis of the SF₆ decomposition mechanism, the SOF₂、SO₂F₂、CO₂ are considered typical components of the decomposition products.Model with floating potential defect is setup in a 90 L chamber suspension, and then a voltage twice larger than an initial partial discharge voltage is applied to the model to cause SF₆ to decompose.The varying tendency with time and initial content of the three concentrations of decomposed products and the concentration ratio are studied.The results show that contents of SOF₂ and SO₂F₂ decreases gradually over time, and the higher their initial content, the bigger the rate of decrease will be.On the contrary, the content of CO₂ remains steady.The level of SOF₂ falls more quickly than that of SO₂F₂.The ratio of two gas composition contents, φ(SOF₂)/φ(SO₂F₂), decreases with standing time at the initial 12 h, and then comes into stable state gradually after 24 h.

Featured with long distance, large capacity, extra high voltage and AC-DC interconnected operation, China Southern Power Grid is interconnected with surrounding areas and countries through multiple AC lines, and has complex operation characteristics. In combination with the operation practice of Southern China regional power system during recent years, the operation characteristics of complex AC-DC interconnected power grid is discussed in depth. This paper reveals the main security risks in the operation of Southern China regional power system, including: the prominent risk of single-cause common mode fault, the prominent stability problem caused by the primary and secondary equipment failure in the AC-DC close coupling scenario; and the security of main power grid caused by the stability problems of frequency and rotor angle seriously. On the basis of summarizing the stability control methods, this paper proposes to build the power system security and stability defense lines based on wide-area information, which will make the China Southern Power Grid more secure and stable in the future.

In power market environment, the competition mechanism has been extended to the distribution side. Distribution company regulation methods for market competition have become important research the topics of power market reform. In this paper, the methods of distribution regulation the power market environment, involving the traditional rate-of-return regulation method, the revenue-cap regulation method, the price-cap regulation method, the yardstick competition regulation method and the quality regulation method, together with their advantages and disadvantages are summarized. Finally, the experiences of distribution company regulation in the world are discussed, which provides a good reference for the adjustment of regulatory approach and the establishment of a modern electricity regulatory system in our country.

The quality of the power system state estimation and the practical level of advanced power application softwares would be reduced by the wrong parameter.It is very important to ensure the effectiveness of results of the state estimation when multi bad remote sensing data and parameter errors exist.A diagnosis method for the doubtful parameters of the power grid is proposed.The parameter errors and measurement errors are uniformly modeled in the information space.The measured percentage residuals are calculated according to the weighted least square method, and the suspicious measuring point set is obtained by comparison with the threshold.The relevant indexes of all suspicious measuring points and branches are calculated, then Newton Downhill Method is introduced to determine the optimal estimation of each suspicious parameter according to all suspicious branches, and the corrected parameters are regarded as the returned values.Simulation results show that the network parameter errors and measurement data errors can comprehensively be considered through the proposed method, which can also be applied to the situation where there exist multi error parameters simultaneously, and the accuracy of the parameter identification and diagnosis is effectively improved, and the quality of basic operating data and the practical level of advanced applications of the power grid are improved.

The influence of distributed photovoltaic (PV) integration on Hainan Power Grid is studied with DIgSILENT/ PowerFactory software in terms of power quality, ecnomic operation, protection, etc. The integration capacity of distributed PV is evaluated for various typical connection forms and operatioin modes of Hainan Power Grid based on constraints of safety and economy. The results show that the PV integration capacities of the evaluated distribution networks are in the range of 20%~40% of the networks peak load; and the main factors restricting the PV integration capacity are the power factor decrease of medium-voltage distriubution networks and the three-phase imbalance of low-voltage distribution network.

Due to the special laying environment, the loss of submarine cables is one of the focuses in the design and model selection stage, especially the loss in the landing parts of the cables which generates heat and becomes a bottleneck to constrain the transfer current. Basod on analysis of structure and loss influence factors, the calculation model is set up. For Hainan interconnection project II, the loss and economic operation cost of four different armoring 500 kV cables at three laying environment (the bottom of the sea, tidal flats, landing parts) are calculated, and the flat copper wire armoured cable is proposed as the first choice for submarine project. Finally, the effective energy saving measures for the landing parts are analyzed.

The coordinated control and management of distributed generators in active distribution network(ADN) provide distribution system operators with more approaches to control voltage actively and make coordinated voltage control(CVC) possible in ADN.The impacts of distributed generators on existing voltage level and control strategies of distribution network are analyzed, based on which a hierarchical CVC framework and corresponding trategy of ADN are proposed.On one hand, the closed loop voltage control of single feeder is realized by means of CVC controller on the basis of accurate voltage estimation, on the other hand, transformer tap adjusting and capacitor switching are employed to ensure the voltage level and quality of multiple feeders.The effectiveness and practicability of the proposed CVC strategy are verified on a 2-feeder ADN.

In order to analyze the air gap flashover characteristics of switching impulse voltage of fittings in Xinsong converter station at the altitude of 2 400 m, according to the fittings structure size of valve hall in Chuxiong converter station, this paper selects Φ750 mm/Φ880 mm cap, Φ1 200×300 mm/Φ1 600×300 mm/Φ1 900×300 mm grading ring and Φ1 100 mm/ Φ1 600 mm/ Φ2 000 mm equalizing ball, all in typical size, and carries out an experiment in Kunming UHV base at the altitude of 2 100 m. On this basis, this paper checks the air clearance of transmission side valve hall in Xinsong station and presents the discharge voltage curves for different altitudes after altitude correction. The study of air gap discharge characterstics and altitude correction provides a reference for practical engineering.

Converters as the key equipment for HVDC transmission systems have the features of giant capacity, strongly controllability and highly reliability. Conventional thyristor converter is featured with great transporting capability, high cost and heavily harmonics.Voltage source converter (VSC), based on controllable power electronics elements and PWM technology, overcomes some problems of conventional thyristor converter and is developing rapidly. Typical converters for HVDC transmission systems, including conventional thyristor converter, two twelve-pulse converters per pole, capacitor commutated converter (CCC) and voltage source converter, etc. are reviewed in detail on their structure, basic principle and control strategy. Moreover, technology characteristics and application fields of these converters are also surveyed. It is shown that conventional thyristor converters are still the perfect candidates for long distance and giant capability HVDC transmission system, and voltage source converters have a good application prospect of future HVDC transmission applications.

With the proposal of dual-carbon target, energy storage is an important way to promote distributed PV local balanced consumption and reduce carbon emissions from the distribution network, but the traditional energy storage configuration scheme usually only considers the electric power balance, and how to comprehensively consider the electric-carbon characteristics puts forward higher requirements for the optimal configuration of energy storage. Firstly, a cluster division method based on electrical distance and net load carbon flow rate is proposed by introducing the node net load carbon flow rate index for cluster division of distribution networks, which improves the efficiency of distribution network management and the accuracy of carbon emission management. On the basis of the cluster classification, an energy storage allocation method that takes into account the carbon emission cost of the distribution network is further proposed, which takes into account the carbon emission cost and network loss cost, as well as the economic cost and benefit of energy storage allocation, establishes a carbon balance mechanism for energy storage, quantifies the impact of the change of the carbon content within the energy storage on the distribution network, and avoids carbon dioxide emissions into or out of the energy storage equipment. Finally, the results of an arithmetic simulation in a distribution network in Anhui province show that the proposed method reduces the total carbon emissions of the distribution network by 11.12 % compared to the unconfigured energy storage system.

Driven by the "dual carbon" goals and energy transition, distributed photovoltaic systems with their characteristics of "numerous points and extensive coverage" are connected to distribution networks, making power interactions between distribution network levels more complex. Traditional supply-side regulation methods struggle to meet the operational demands of multi-source collaboration and multi-objective coordination. To address this, a multi-level multi-objective collaborative optimization method for distribution networks-substation areas-users is proposed, considering dynamic comfort zones. Firstly, a multi-level structure and hierarchical scheduling framework for distribution networks, transformer areas, and users is established. The distribution network is divided into the distribution network layer, transformer area layer, and user layer. Within each layer, source-grid-load-storage resources achieve collaborative interaction, while bidirectional power transfer and information exchange occur between layers, promoting rational resource allocation and utilization. Secondly, a flexible resource model incorporating dynamic comfort zones is developed to quantify residential users′ resource regulation potential under varying electricity prices, enabling real-time adjustment of regulation boundaries. Then, a multi-level multi-objective collaborative optimization model for distribution networks-substation areas-users is formulated, comprehensively considering optimization objectives across different levels to establish a bottom-up coordination mechanism. Finally, the proposed strategy is validated through case simulations. The results demonstrate that the method effectively maximizes and utilizes source-grid-load-storage resources across all levels, significantly improving photovoltaic integration, optimizing load curves, reducing user electricity costs, and ensuring safe and economical distribution network operation

Based on typical structure of voltage source converter based HVDC (VSC-HVDC) station and its parameters, the impact of startup process of VSC-HVDC station on AC grid is analyzed in this paper. According to the characteristic of voltage and current during station startup, it is concluded that AC grid voltage might drop abruptly because of transformer excitation inrush current or incomplete charge of DC capacitors at the time of closing AC circuit breaker or bypassing charging resistor. A control method to avoid the voltage drop of AC grid is proposed which decreases over current through phase selection switchs and delayed charging resistor bypassing. The method is verified through simulations based on real VSC-HVDC station.

The lightning strike is an important influencing factor to the operation of China Southern Power Grid (CSG), the lightning location system is one of the effective means to research lightning pattern and guide the lightning protection of power transmission and transforming equipment.CSG Lightning Location System Interconnection System is introduced with the necessity of interconnection, structure, site optimization, application systems, and with the applications in lightning fault point searching, transmission and transforming equipment fault analysis and lightning pattern research.The lightning detection data of the five southern provinces are interconnected. A lightning information WEB application system and a lightning parametric statistical analysis expert system are developed to serve the whole CSG. The entire network probing station locations are optimized on the basis of the whole network probing station distribution and the lightning detection precision requirements. Thus the coverage of lighting location deviation less than 1 km in Guangdong, Guangxi and Yunnan province is improved by 14.9%,1.6%, and 10.3% respectively.The system has been accumulated massive lightning activity data within CSG region since it was put into operation, and can provide guidance to the transmission and transforming equipment lightning fault analysis, the lightning activity pattern research, and the transmission line differentiation lightning protection.

At present, the communication between dispatching and substation is mainly protected by the power vertical encryption authentication device. The power vertical encryption authentication device at both ends of the dispatching and substation can protect the confidentiality and integrity of data transmission at both ends. However, the communication protocol IEC 60870-5-104 (IEC104) between dispatching and substation does not have a corresponding security mechanism. The protocol data is easy to be forged, tampered, replayed and stolen before the encryption device of the dispatch and after the encryption device of the substation, which poses certain security risks. Therefore, this paper extends the protocol security domain on the basis of IEC 104 protocol, and solves the problem of communication security between dispatch and substation from the protocol level. The identity-based cryptographic algorithm SM9 provides algorithmic support to achieve this goal. According to the characteristics of the algorithm and the protocol, the security of the protocol can be realized by a little extension of the protocol in this paper. The highlights of this paper are as followes: 1) based on the identity-based cryptographic algorithm the security communication between dispatching and substation is achieved, which is fundamentally different from the digital certificate based security communication in other documents, without certificate management and other complicated matters; 2) the end-to-end security authentication of the communication between the dispatching master station and the substation is achieved; 3) the security hidden dangers of the protocol are solved through the identity-based cryptographic algorithm, and the two-way identity authentication between the dispatching and the substation and the confidentiality, integrity and non-repudiation of the communication data are realized.

In order to achieve low-carbon hydrogen production under diversified demands, a comprehensive energy management method based on hydrogen energy hub is proposed. Firstly, a comprehensive energy system management framework is constructed considering new energy units, electrochemical energy storage, gas generator units, hydrogen energy hubs and hydrogen loads. Then, based on the oxygen complementary utilization principle of hydrogen production by water electrolysis and rural biomass gasification, the design of hydrogen hub is introduced and the optimal operation model of hydrogen hub is established. Based on the energy management framework of the integrated energy system and the hydrogen energy hub model, the energy optimization management model of the integrated energy system is established, considering the constraints of hydrogen supply and demand balance, power balance, and operating characteristics of each equipment, in order to achieve efficient, economical, and environmentally friendly hydrogen production and energy management under diversified hydrogen demand. Finally, the numerical simulation of an integrated energy system with hydrogen energy hub verifies the effectiveness of the proposed method.

The sub-synchronous oscillation （SSO） incidents caused by the dynamic interactions between wind farms and the rest of power system threaten the safe and reliable operation of practical power grids. Firstly， this paper introduces several incidents occurred in practical power systems caused by wind farms， and several key factors of wind turbine types， mechanism， and the consequences are described. Secondly， the paper illustrates the commonly used analysis methods which are frequency-domain method （complex torque coefficient analysis and impedance-based method） and model analysis method for analyzing SSO caused by grid-connected wind farms in terms of principles， applicability， and characteristics. Thirdly， the paper summarizes the researches which have been carried out in the area of SSO caused by grid-connected wind farms on the basis of the analysis methods and the object system types adopted in the literature. In addition， the current research status of mechanism investigation on the issue of SSO caused by grid-connected wind farms has been demonstrated. Finally， the analysis methods and issues to be addressed urgently for mechanism study of SSO caused by grid-connected wind farms are discussed.

The structure, mathematical model and control strategy of permanent magnet direct-drive wind turbines are analyzed. A new scheme of RTDS dynamic equivalence for permanent magnet direct-drive wind power systems is proposed to adapt to the response in large scale power systems. Hainan Power Grid is selected as a demonstration grid with integration of new energy sources and a model including four voltage levels is established. The interface between the power system and the VSC model of wind turbines is designed. Simulation results demonstrate that the proposed model with high penatration of renewable energy sources has good response performance.

Under voltage load shedding (UVLS) is one of the efficient measures of emergency control to prevent transient voltage collapse of power systems. UVLS schemes used in some foreign and domestic power grids are introduced in this paper. The configurations and setting methods of UVSL are analyzed and summerized in the aspects of control mode, installation location, action condition, time delay, scale of load shedding and simulation calculation. Centralized control mode is usually adopted in foreign power grids, while distributed control mode is usually adopted in domestic power grids. For the action condition and the delay time of UVSL, voltage level is usually used as action condition in centralized control mode while more complicated comprehensive criterias are usually used as action condition in distributed control mode. UVLS should be of coordination with not only the security and economy of power grid but also the UFLS, and meets the development requirement of both AC/DC hybrid power grid and intelligent power grid.

Recently the issue of voltage stability has become a major challenge for the safe operation of the power grid. The new generation synchronous condenser and STATCOM are receiving more and more attention due to their excellent voltage support capabilities. This paper first briefly introduces the basic principles and characteristics of the new generation synchronous condenser and STATCOM. Then, these two types of reactive power compensation equipment are compared technically from three aspects:coping with system voltage sag, voltage surge, and impact on short-circuit current. Based on the comparison results, the reactive power compensation equipment choice suggestion in different application scenarios are given from a technical perspective. Finally, the paper compares the economics of the new generation synchronous condenser and the chained STATCOM using the isochronic method, and gives suggestions for the selection of reactive power compensation equipment in different application scenarios from the perspective of economics.

With the development of power electronic devices towards high frequency, large power and lightweight, high frequency becomes one of the important reasons of the high frequency transformers failures. In this paper, a high-frequency electrical aging experiment system is built, and the surface potential attenuation method is used to measure the surface charge accumulation and attenuation characteristics of oil paper insulation with different aging degrees. The results show that as the applied frequency increases, the amount of charge accumulated on the surface of the insulating paper decreases, and the charge attenuation rate increases first and then decreases. After high-frequency aging, the surface charge accumulation and attenuation rate of oil-paper insulation decreases with the increase of aging degree. When the frequency is lower than 5 kHz, the high-frequency heating effect on the surface of the insulating paper plays a leading role, and when the frequency is higher than 5 kHz, the charge dissipation time caused by the high frequency plays a leading role, causing the surface charge attenuation rate to increase first and then decrease. As the degree of high-frequency electrical aging increases, the probability of initial electron generation of oil-paper insulation decreases. Understanding the characteristics of surface charge accumulation and dissipation provides a theoretical basis for revealing the electrical aging mechanism of oil-paper insulation under high frequency.

On-line monitoring plays a more and more important role in maintaining the safe and reliable operation of power grid. In order to supply power to on-line monitoring equipment in a convenient and efficient way, this paper presents a power tapping method to collect power from ground wires using the magnetic induction effect of transmission lines. Cases show that this power tapping method can satisfy the power demand of on-line monitoring equipment. Also, factors such as line current, length of span, grounding resistance and spatial position relationship between transmission lines and ground wires may affect the power tapping efficiency. This paper discusses on the groundwire magnetic induction power tapping scheme, which lays the foundation for further optimization and practical use of power tapping from the ground wire.

The mechanism of the effects of external short circuit current on oil flow inside the transformer is analyzed, and a SFPZ11-120 MVA/220 kV transformer transient electromagnetic-force-flow field coupled model is built in ANSYS Workbench. The vibration of windings caused by short circuit current is studied, and the effect of external fault on transformer oil surge is simulated accurately by finite-element method, from which the distribution of oil flow under external faults can be achieved. The simulation results show that the transformer oil surge caused by external short circuit current has great effect to gas protection, which may cause gas protection maloperation.The simulation models and methods can be generalized to oil transformers of other voltage level and can provide reference to analysis of transformer oil surge.

Aiming at the application situation of XLPE insulated submarine cable in the field of China’s offshore wind power, firstly the typical applications of mid-voltage AC submarine cable to offshore wind farms are summarized. The technical breakthrough of three-core HVAC submarine cable, the structure improvement and performance upgrade in the developing process of cable voltage level from 35 kV to 110 kV and 220 kV are introduced. Fabricating costs are compared between three-core and one-core submarine cables. Then the product features and insulation structure design method of VSC-HVDC submarine cable are briefed. Finally, according to the trend of large capacity and high seas construction for future offshore wind farm, it is proposed that the application of XLPE insulated submarine cable should focus on wet type structure array submarine cable and VSC-HVDC submarine cable in the future.

Digital technology is leading the development and evolution of the fourth industrial revolution, promoting the gradual transformation of industrial economy into digital economy.In the era of digital economy, digital power grid is a new idea, new way and new insight for the construction and development of smart grid driven by technological evolution and demand upgrading. The definition, composition and characteristics of digital twin are expounded. The paper first proposes the digital power grid based on digital twin, analyzes the concept, characteristics of digital power grid and its derivative relationship with smart power grid, constructs the digital power grid architecture including physical power grid, perception layer, transmission layer, data layer, platform layer and application layer, and summarizes the key technologies of digital power grid.The digital power grid realizes the twin interaction between the physical world and the digital world, supports the digital operation of the power grid and constructs the digital energy ecology by constructing the power grid data closed-loop empower system.