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.

Advanced sensing and measurement technology is the key to realize transparent power grid and power Internet of Things. In order to meet the measurement needs of the power Internet of Things, this paper developed a micro current sensor device based on giant magnetoresistance effect, including the design of the sensor architecture, signal processing circuit, digital processing circuit, self energy, wireless communication, temperature compensation and other functional modules, the sensor shell structure is designed and the special protection design of IP and insulation is carried out. Finally, the sensor has been applied in the field of low-voltage distribution for a long time. The results show that the current sensor can work stably and reliably for a long time. It has the advantages of miniaturization, high integration, convenient installation and remote management. It can provide more comprehensive and real-time information support for the operation of the distribution network and lay the foundation for the transparent management of the smart grid.

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.

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.

Integrated design technology of external cooling system of voltage source converter (VSC) valve and water-cooled transformer is suitable for the design of key equipment external cooling systems such as converter valve and water-cooled transformer. This paper proposes a optimal design scheme for VSC valve and transformer external cooling system, which shares one water spray pool and one spray water treatment system, and also gives spray water yield analysis and calculation based on one stage and two stage of first level reverse osmosis system. This scheme can save water and reduce pollution, and is convenient for the converter station maintenance and management. It can be widely used in the equipment cooling system design of HVDC converter station on land and offshore wind power HVDC station.

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.

A modular multilevel converter (MMC) parallel system based on half-bridge sub-module (HBSM) is applied in order to build the integrated test equipment for large-capacity offshore wind turbine generator.The operation principle of the device and its primary parameter selection method are elaborated in detail. Power electronics technology is adopted to send low/high voltage signals. The voltage signal is synthesized from the reference voltage, the fundamental frequency voltage difference, and the harmonic command voltage, which are given by split-phase V/F control, and consequently the amplitude, phase and frequency of the output AC voltage can be adjusted. PSCAD /EMTDC simulation results show that the system designed can meet the grid-interconnection requirements for both fault ride-through and grid adaptability tests, including high/low voltage ride-through, voltage imbalance, frequency deviation, harmonic output, voltage fluctuation tests for large-capacity offshore wind turbines.

Manual instantaneous grounding test of transmission lines is a key procedure in HVDC project commissioning. This paper describes the manual instantaneous grounding test method of transmission lines applied to multiple HVDC projects of CSG, and simulates the influence of grounding current and soil resistivity on regional step voltage using CDEGS software. Simulation results show that when the grounding current is 10 kA, the soil resistivity of the short circuit area is 1 500 Ω·m, and the grounding device of current divergence tower is typically radial, the maximum step voltage of the test field within 30 m horizontal distants away from the tower base will exceed the safe limit, then the safe distant should be improved to reduce the test risk.

Since 2012 three cross-linked polyethylene (XLPE) insulated HVDC cables with rated voltage level of ±160 kV, ±200 kV and ±320 kV have been tested or successfully commissioned in HVDC transmission projects. They are Nan’ao three-terminal VSC project for island wind farm connection to China Southern Power Grid, with a total length of 37 km submarine and land cable of rated ±160 kV, which has been put into operation in December 2013; Zhoushan five-terminal VSC project with 294 km ±200 kV DC submarine power cable and has been in operation since June 2014; and another VSC project at the voltage level of ±320 kV is under construction in Xiamen, with a cable in length of 21 km deployed in cable tunnel. On the completion of these three projects within three years of time, China has realized triple leap in its HVDC submarine and land cable development. This paper presents the technical achievement of XLPE insulated HVDC cable development in detailed material characterization, space charge behavior, degassing processing and testing considerations. Their application in the three projects are introduced as well to illustrate the insulation and coordination design by considering each individual transmission system.

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.

Dynamic simulation package(DSP) is a new power system analysis software developed by Electric Power Research Institute CSG. It has four basic modules: power flow calculation, electromechanical transient calculation, short circuit assessment and dynamic equivalence. This paper introduces the main function of each module of DSP. The features and advantages of improvedment algorithm for power flow convergence, DC model and custom modeling capabilities in electromechanical transient calculation module are introduced in detail. The accuracy of DSP is verified by comparing the examples’ results with widely used commercial softwares.

HVDC circuit breakers whth ability to interrupt large DC fault current in a very short period of time and high reliability and economics are urgently needed for flexible DC power transmission and multiterminal DC grid. In this paper, DC circuit breakers including the mechanical, all-solid-state and hybrid ones are reviewed, their advantages and disadvantages, as well as application scopes are analyzed. It is concluded that hybrid constraint circuit breakers and mechanical pre-charged artificial current zero point circuit breakers are more likely to meet the requirements. For the former, it should be in focus to increase the operation speed, optimize the structure, enhance the reliability and economic effectiveness; and for the latter, more attentions should be paid in detailed topoloty, maximum breaking current of the mechanical switch at the artificial current zero point, parameter optimization of tank circuit, and high speed mechanism.

With the increase of power electronic equipment in the power grid, harmonics and their hazards gradually appear, and have drawn more and more attention. As converters are the main harmonic sources in DC transmission system, it seems particularly important to further analyze them on harmonics. Taking the line commutated converter high voltage direct current (LCC-HVDC) system as the objective, the paper uses an harmonic calculation model based on the switching function to analyze characteristic harmonics. Firs-tly, based on the modulation theory, AC-DC harmonic calculation equations considering the switching function are established, while the switching functions of voltage and current are solved based on the working principle of the converter. Then the equivalent harmonic impedance model of DC system is obtained by structure analysis of DC system. Based on the above analysis and flow analysis on the AC side, the harmonic equations are solved to obtain the LCC characteristic harmonics of AC and DC sides. Finally, by comparing with the PSCAD simulation model, the feasible and accurate of harmonic calculation method are verified. The paper can provide theoretical basis and method reference for power system harmonic analysis, harmonic suppression and so on.

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.

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.

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.

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.

Valve-side bushing of the converter transformer undertakes the internal and external insulation of the valve-side outgoing line, and is the core element to ensure long term stable operation of the converter transformer. According to the bypast fault characteristics of the converter transformer valve-side bushings and the deficiency of industry standards, based on investigation on the typical structure and technical requirements of three typical converter transformer valve-side bushings in operation of DC transmission projects, six type selection technical points of converter transformer valve-side bushing such as insulation construction design, heat resistance current-carrying capacity and material selection, docking matching consideration to the valve-side outgoing line, sealing structure and mechanical strength design, plugging combination to the valve hall, and connection matching to the outdoor fittings are systemically concluded. Pertinent quality control measures and suggestions to converter transformer valve-side bushings are proposed. Relevant research results conduct the type selection and application of converter transformer valve-side bushings for DC transmission projects under construction.

Aiming at the problem that in certain cases, traditional failure protection settings of 220 kV circuit breaker cannot meet the fault clearing time requirements to keep system stable, based on the characteristics of 220 kV breaker failure protection, the factors affecting fault clearing time such as main protection action time, breaker opening time, arc extinction time and current element return time and their time boundaries are analyzed. The matching necessity of the two-stage of bus coupler breaker tripping, feeder retripping and adjacent breaker tripping is evaluated. The delay optimization scheme of circuit breaker failure protection considering critical limit clearing time of the system and lower limit time of failure protection is proposed, giving consideration of both failure protection and power system stability, and the calculation method of the fault duration is provided.

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.

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 development process of grid operational risk management of China Southern Power Grid Company is described in this paper, the basic concepts of grid operational risk and risk management of power grid operation is presented, and the main content of risk management is given, specifically the main approaches to risk identification, the main calculation procedure of risk assessment as well as the classification of risks are described. The main content and emphasized points at different time scales for risk identification and assessment are listed. The operational matters of risk management and critical management processes are also presented. For specific risk and annual basis risk, closed-loop risk control is illustrated. Finally recommendations to promote the development of risk management of grid operation are provided.

XLPE (cross-linked polyethylene) insulated cable is an important component of power transmission lines. In allusion to the operating status of HVAC and HVDC cables, the paper introduces the electrical ageing model of XLPE cable insulation based on the typical V-t characteristics (the relationship between breakdown voltage and breakdown time) and the research method of V-t characteristics both of HVAC and HVDC XLPE insulated cables. Previous research show that the electrical aging lifetime index n of AC XLPE cable is between 9 and 25, while the electrical aging lifetime index n of DC XLPE cable from very limted research shows that it’s between 13 and 20. And there is no research on V-t characteristics of DC cables having been reported yet in China.

With the continuous advancement of China’s electricity market construction, a complete comprehensive evaluation system and method for electricity market plays an important role in ensuring that the electricity market can operate safely, stably, efficiently and reliably. Fully considering the principles of index system construction and the rules of market design, this paper constructs a complete comprehensive evaluation index system of electricity market from four dimensions: fairness, safety, economy and environmental friendliness. Meanwhile, based on the multi-level fuzzy evaluation method, the Guangdong mid and long-term electricity market public data is employed as an example to verify the effectiveness of the index system. The results show that the constructed comprehensive evaluation index system is applicable.

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.

Nan'ao VSC-MTDC Demonstration Project is the first VSC-MTDC project in the world.The design scheme of the system access and converter station is introduced.The sending converter stations, Jinniu station and Qing'ao station, are built at Nan'ao island while a accepting converter station, Shucheng station, is set up near Shucheng substation in the mainland.The wind power of the wind farms at Nan'ao island is sent out through DC lines of Qing'ao-Jinniu and Jinniu-Shucheng, and integrated into the AC system at Shucheng substation.In comparison of three grounding schemes, one of them is adopted, in which the △/Yn form is for transformer interconnection, and a grounding point with a neutral resistor in the Yn transformer side is chosen.According to the principles of clear function zoning, compact process, energy saving and coordination with the surrounding environment, the general electric layout plan of the converter station is designed.

Facing the increasingly severe problems like short circuit current exceeding limit, serious AC-DC interaction and difficulty in setting up the third defensive line, system partition in multi-DC infeed receiving power grids like Guangdong power system is urgently required. In order to solve the contradiction between system partition and system stability and reliability, and support regional power consumption growth and large-scale clean energy access, an idea of building the outer ring of the Guangdong-Hong Kong-Macao Greater Bay Area is proposed. Key issues like coverage of the outer ring of the Bay, partition scheme of Guangdong power grid and capacity selection of the outer ring are specifically discussed. Then the flexible DC interconnection network scheme based on the outer ring of the Guangdong-Hong Kong-Macao Greater Bay Area is formed. Simulation analysis indicate that the scheme could meet the relevant safety standards, the capacity of Guangdong power grid could be increased to the expected level and problems such as short circuit current exceeding standards, serious AC-DC interaction and difficulty in setting up the third defensive line are effectively dealt with.

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.

Nan'ao VSC-MTDC Demonstration Project is the first VSC-MTDC project in the world.The MMC (modular multilevel converter) topology and the integrated system design scheme of Nan'ao VSC-MTDC project are introduced.The converter station of the project adopts a single converter and bipolar connection, and is able to operate in the modes of AC/DC paralled, DC only and STATCOM.The present project consists of three terminals with branch type parallel connection, and in the near future, it will be upgraded into a system of four teminals.The main device parameters and protection configuration of the project as well as the starting process of the three converter stations are also presented.

The system commissioning of Xiamen flexible HVDC transmission project is analyzed and summarized. The design and preparation of the system commissioning program and the implementation of field system commissioning are introduced. The problems found during the system commissioning are analyzed and rectification methods are given. Three innovation test methods in the process of commissioning are elaborated including test method for true bipolar passive inverter, short time de-block technology, system commissioning isolation technique which effectively guarantee the safety of equipment and improve the quality of system commissioning. The summarized commissioning experience and methods are good guidance and reference for the construction of following projects.

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.

The development of new power system requires higher efficiency of power system simulation. In order to effectively deal with the massive computing needs from multiple users, this paper proposes a construction scheme of power system computing and analysis platform based on modern internet technology. Based on the leading Kubernetes cluster management system and docker container deployment technology, a real-time dynamically scalable cluster system architecture is proposed to construct an efficient, reliable, green share computing platform. The platform has been deployed in Power Dispatch and Control Center of China Southern Power Grid, and the reliability and efficiency of the system are verified by the actual data. Results show that the efficiency gain is close to the upper limit of the theoretical optimal value. The platform provides a powerful computing system to the operators at grid, province and city level dispatching departments, and provides technical support for resource sharing and integrated management.

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.

Residents’ living condition and project environment evaluation are affected greatly by noise and electromagnetic pollution caused by substation corna discharge, which must be suppressed. According to the actual layout and structural drawings of related equipment and fittings, taking measured results of substation corna discharge as reference, and considering the effects of three phases and surrounding conductors, an electric field finite element simulation model for 220 kV substations’ typical discharge positions is built by the finite element method ( FEM ) software ANSYS. The maximum surface electric field magnitudes of the fittings are calculated, the surface electric field distribution conditions are obtained, the structure of those corona fittings is optimized based on the calculation results and corona noise suppression measures are put forward. The results show that after structure optimization, the distortion of electric field distribution of the fittings is declined greatly, and the maximum surface electric field magnitudes are reduced to less than 3 000 V/mm. This research provides important reference for prevention of corona and reduction of substation noise, and supplies basis for construction of green grid and substation.

With the wide application of modular multilevel converter (MMC) power electronic devices and the rapid development of AC&DC hybrid power grid, the higher demand is required for the power system simulation technology. A multi-time scale hybrid real-time simulation system for AC & DC large-scale power grid is presented, which is based on the “FPGA+RTDS+PC(parallel computer)” heterogeneous platform and is able to carry out hybrid simulation of fast electromagnetic transient, electromagnetic transient and electromechanical transient. The simulation system is composed of several simulation sub-systems such as VSC device, HVDC system and AC power system. Connected together by closed-loop interfaces, the system can implement multi-mode united calculation in multi-time scale and multi-grain parallelism. The system can also be interfaced with the EMS (energy manage system) as well as the dispatch control and characteristics display platform. Thus an accurate and efficient simulation tool for the test and study on complex AC&DC large-scale power grid is provided.

It is of great practical significance to establish the evaluation system of power equipment utilization efficiency aiming at power grid capacity optimization for collaboration of power grid planning and construction. An evaluation system of power equipment utilization efficiency aiming at power grid capacity optimization is introduced. Four major evaluation indices, including capacity-load ratio, maximum load rate, annual equivalent mean load rate and annual mean utilization time, and power grid capacity optimization limits are given. Considering the key factors influencing utilization efficiency, and a capacity optimization method is adopted to enhance the overall utilization efficiency. Case study in Yunnan power grid verifies the reasonability and effectiveness of the evaluation system and the optimization method proposed in this paper.

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.

This paper investigates the dynamic characteristics of active power and reactive power during HVDC commutation failure period. The quantitative index for assessing voltage supporting capability of AC system for HVDC system is introduced. The influence of simultaneous commutation failures of Guangdong multiple HVDC on the secure operation of the power grid is analyzed from three aspects: AC area where AC fault may cause multiple HVDC simultaneous commutation failure; multi-infeed effective short circuit ratios and the number of power grid instability under severe AC system failure conditions. Technical countermeasures including HVDC control strategy optimizing, dynamic reactive power compensation installation, AC power grid topology reconfiguration and VSC HVDC utilization are proposed for dealing with voltage instability risk of Guangdong power grid.

Traditional transformer oil-paper composite insulation is becoming increasingly difficult to meet the demands of insulation system with large capacity and miniaturization at ultra-high voltage level. To improve the insulation properties of oil-paper insulation, the effect of nanoparticles on insulation properties of oil-paper composite insulation system is investigated. The withstand voltages of traditional and nanoparticle modifying oil-paper composite system are tested and compared. The streamer discharge in transformer oil is simulated. Based on the model, the electric field and space charge distributions, and the surface charge density on the paper insulation are obtained and analyzed in this paper. The results show that the nanoparticle modifying transformer oil-paper system has better insulation property than the traditional oil-paper system (10% increase) and the surface charge density decreases from 0.020 C/m² in pure oil-paper system to 0.016 C/m² in nanoparticle modified oil-paper system. The nanoparticles in transformer oil not only restrain the streamer development in the oil, but also restrain surface streamer and decrease the surface charge density on the paper insulation, which are beneficial for the improvement of the oil-paper insulation.

Driven by the rapidly growing application of distributed generation (DG) and DG based user-side microgrid, bidirectional power flow between user and power grid forces the traditional measuring method to be changed accordingly. Bidirectional metering demand of user-side microgrid and user with DGs and independent metering issues of DGs are analyzed in this paper. The impact of power quality issues caused by the integration of DGs, such as harmonic wave, voltage sag, temporary shortage and voltage flicker, on the inaccuracy of metering system are sorted out. Present situation and developing tendency of communication interface, protocol and precise metering algorithm for smart meters are summarized with introduction of smart meter’s application in future smart grid. The development tendency and modes of bidirectional metering are presented.