To respond to the national "One Belt, One Road" initiative, and support the “going out” strategy by power companies, this paper briefly introduces and analyzes the history and present application of HVDC, both in the world as well as in China. It also analyzes the latest development trends and market prospects of HVDC, focuses on plan and prospect of the global HVDC market. Through the analysis of HVDC planning in China, Europe, North America and other emerging economies, it is known that the global HVDC will grow rapidly in the future, and the demand for DC transmission technology is strong. Compared with the State Grid, the analysis of the competition of China Southern Power Grid (CSG) in the global HVDC market, this paper gives some suggestions for CSG, as the active development of HVDC internationalization, the implementation of flexible HVDC standards, strengthening institutional innovation and business management, and strengthening relevant planning strategies, and so on.

In order to improve receiving-end frequency stability of AC power grid with MMC based HVDC (MMC-HVDC), a frequency stability enhancement control strategy based on frequency limit controller (FLC) and modified virtual synchronous generator (VSG) is proposed in this paper. When power disturbance occurs in the receiving-end grid, the receiving-end MMC adopting the proposed control strategy can provide emergency power support for the disturbed power grid, which can not only improve system damping and frequency oscillation, but also realize the steady-state transmission power of DC system controllable. The effectiveness of the proposed control strategy is verified by theoretical analysis and simulation in PSCAD/EMTDC.

Flexible multi-terminal DC system has significant advantages in terms of renewable energy and island power supply. To ensure the safe operation of flexible DC grid, it is necessary to research and develop a high-voltage DC circuit breaker capable of breaking the fault current in milliseconds. In this study, a low-stray inductance power electronic branch series topology is proposed based on the breaking parameters of the high voltage DC circuit breaker used in South Australia ±160 kV flexible DC system with the introduction of high voltage DC circuit breaker topology design based on coupled negative voltage circuit. After the checking analysis of key components and series structure design of valve string in power electronic branch, the modular design of power electronic branch valve string is completed, and after the verification of design strength of each parts by seismic analysis of integrated circuit breaker, the designing of ±160 kV high voltage DC circuit breaker prototype based on coupled negative voltage circuit is completed.

Transient stability detection technologies based on wide-area response are important means for real-time warning of transient instability. Based on the changing track of oscillation center voltage, a transient instability warning strategy for interconnected power grid is proposed. Firstly, the transient instability criterion based on ucosϕ trajectory integral is improved to overcome the relative lag of instability detection under some complex faults. Secondly, a ucosϕ trajectory penetration identification algorithm is proposed to form the ucosϕ composite criterion without increasing measurements, which further improves the reliability of instability detection. Finally, combined with the transient instability characteristics of China Southern Power Grid (CSG), a scheme of regional transient instability warning is designed. The transient stability is evaluated in real time by synthesizing wide-area and multi-station information. Simulation results show that the proposed method can identify the transient instability more quickly and accurately, and it would provide basis for emergency control after extreme contingencies.

Cascading failure is one of the main causes of blackout failure. Based on the OPA cascading failure model (ORNL-PSERC-Alaska, OPA), this paper analyzes the evolution mechanism of cascading failures and discusses the complex characteristics of blackouts. The OPA model is further improved by considering the hidden faults of relay protection and the complete derivation of failures chain. Multiple system-level risk assessment indicators are introduced to process the simulation results and the indicators can assess the risk of target system cascading failures at the macro level. the weak links of the target system are identified by counting the frequency of line faults. The related programs are written on MATLAB and the IEEE RTS96 system is taken as an example. The simulation results of cascading failure under different operating conditions are obtained, and the risk assessment indicators of the blackouts are calculated which prove the feasibility of this model.

The stray current generated by the massive operation of subway transit will affect nearby power transformers by DC bias, threaten the safe and stable operation of transformers and AC grid systems. In order to solve such problems, the static distribution model of subway stray current, the multi-layer block soil model of Shenzhen and the simulation model of Shenzhen AC power grid are established for simulation analysis. The variation of the ground potential of the AC power grid substation and the distribution characteristics of the neutral point DC current of the transformer caused by the stray current are calculated and analyzed. The results show that the change of ground potential and DC current through transformer neutral point is related to the operating conditions of the subway. The distance between the substation and the dense area of the subway line and soil resistivity are the main influencing factors. For the autotransformer, combined with test results, it is pointed out that the installation of the capacitive blocking device at only the DC over-standard site cannot eliminate such DC magnetic bias problems, and it is necessary to properly arrange the blocking device from the perspective of the entire regional power grid.

Combined cooling, heating and power (CCHP) microgrid is a typical application of integrated energy system, microgrid planning is the basis to improve the performance of microgrid system considering the integrated demand response.Based on the coupling, complementarity, alternation and interaction among different forms of energy such as gas, electricity, cold and heat in the microgrid, the specific models of energy storage equipment, controllable load (reducable load, translatable load),convertible load are established which are the integrated demand response (IDR) implementation in microgrid system, the system energy flow is established, and an optimal allocation model of microgrid capacity considering IDR is established, costs are considered comprehensively, including annual equivalent investment cost, annual fuel cost, annual operation and management cost and annual IDR cost, the IDR constraints and reliability constraints are taken into account in the constraints. The results of multi-scenario comparison in the example show that IDR improves the allocation economy and reliability of system, promotes the consumption of renewable energy, the correctness and rationality of the model are verified.

In order to study power cable of different arrangements for same-phase parallel multi-cable, ampacity calculate mode of the same-phase parallel multi-cable is set up by using COMSOL multiphysics finite element analysis software and MATLAB; For the four typical layouts, sub-cable load current and ampacity of cable groups are calculated and analyzed, and the phase sequence of the cable is optimized by genetic algorithm based on the maximum ampacity of the cable groups. The results show that cables are arranged in a regular triangle with a higher ampacity than horizontal arrangement, and the cable loops adopt the longitudinal arrangement mode with a higher ampacity than the horizontal layout; For the cables of the same arrangement, the smaller the uneven distribution of the load current of the sub-cable, the larger the ampacity of the cable groups; The optimal phase sequence ampacity analysis shows that the optimal cable arrangement is mode 4 (cable loops longitudinal arrangement, cable triangle arrangement), and the optimal phase sequence is ABC-BCA-ABC-BCA.

In order to help the operation and maintenance personnel set up the priorities of high-voltage cables, a high-voltage cable state evaluation method based on the weight-space Markov chain Monte-Carlo (MCMC) sampling is proposed. Firstly, the weight space of the multi-attribute comprehensive evaluation is defined, and the boundedness, normalization and equivalence of the prioritized probability of the evaluated object under multi-weight vector are discussed. Then, the constraint condition of high-dimensional weight space is analyzed, and the MCMC method is used to simulate the constrained weight space. Considering the on-line monitoring, off-line test, operation and maintenance and environmental data of high-voltage cables, the cable with obvious abnormality is judged by a single index, and then the weight vector is obtained by MCMC sampling, and then the priority ordering probability matrix of each evaluated cable is constructed to calculate the overall priority probability of each object, thereby a state evaluation result of the high voltage cable is obtained; Finally, the effectiveness of the proposed method is verified by the actual data of a 220 kV cable.

The cathead composite tower has been firstly used in domestic 500 kV circuit transmission line. Owing to its compact arrangement of post insulators and tension insulators at the end of cross-arm, the uneven electric field distribution is a prominent problem in practical operation that needs to be solved. A 500 kV cathead composite tower is chosen as the research object, and the 3D simulation model has been established with finite element software. The electric field concentration regions of middle phase and side phase are computed and then analyzed with finite element method (FEM). The potential distributions of composite cross-arm are compared and analyzed with normal 500 kV line insulators. The grading and shielding devices for this 500 kV cathead composite tower are designed. The influences of different structural parameters of each grading ring on the field strength at the key position of the composite cross-arm are studied with submodeling technology to save computing time. The results show that the key positions beard very high electric field intensities in initial scheme. It is not conductive to the long term stable operation of composite tower. The 500 kV composite cross-arm has better potential distribution than that of normal 500 kV line insulators. With the configuration of reasonable grading and shielding devices, the electric field distribution on key positions could meet with the critical value.

In this paper, the reliability of transmission line tower-line structure system under combined ice-wind condition is modeled and analyzed. Firstly, the reliability indices of pole-tower structure, insulator, fittings and grounding wire are calculated by checking point method of first-order second-moment method. Then, the reliability calculation method of series structure system is used to calculate pole-tower structure, insulator, fittings and grounding wire. Finally, taking a 220 kV straight tower and tension tower as examples, the system reliability indices of pole-tower structure, insulator, fittings and ground wire under combined ice-wind condition are calculated and analyzed, which can provide reference and guidance for disaster prevention of transmission lines.

Aiming at the influence of meter clock drift on electricity spot market settlement, this paper carries out quantitative analysis of settlement deviation under different drift time and different price curves based on actual user load data and time-sharing price data. Firstly, the calculation model of settlement deviation under time-sharing price in electricity spot market is analyzed. Then, the influence of forward and backward clock drift of different users on settlement deviation is analyzed by different time clock drift scale. The influence of clock drift by different types of users' consumption habits on settlement deviation is studied. In consideration of the frequent fluctuation of electricity spot market price, the influence of different fluctuation levels of electricity price on settlement deviation is studied and analyzed. Finally, the influence of meter clock drift on settlement result in spot market is summarized and analyzed.