During early operation period of ±800 kV Xinsong-Dongfang UHVDC project, the construction progress of the accessory power plants at the sending-end falls far behind the original schedule, causing a lack of generation problem in sending-end power grid. In such a situation, the stability of the islanding system after Xinsong station switching into islanding mode, the overvoltage of the islanding system and the harmonic resonance risks of the islanding system are key elements which affect the transmission capability of Xinsong—Dongfang UHVDC project. All of these elements are analyzed in this paper. The analysis results show that the transmission capability of Xinsong—Dongfang HVDC project is constrained and unable to meet the demand of system commission tests. For enhancing the transmission capability of Xinsong-Dongfang UHVDC project, a stopgap according to which the UHVDC system will block itself following a preset strategy if the converter station switches into islanding mode is presented. And the transmission capability of Xinsong—Dongfang UHVDC project after adopting the stopgap is also analyzed. Finally, the quitting conditions of the stopgap, is researched under which Xinsong—Dongfang UHVDC project can reach its rated transmission capacity safely without any stopgap. The study results of this paper guarantee the security and adequacy of Xinsong—Dongfang UHVDC project’s power transmission in early operation period, and also provide valuable guidance on experiments conducting in system commissioning test periods.

The electric design of valve hall is the key and difficult point in the design of converter station, especially for UHVDC converter stations in areas with high seismic intensity. The corresponding improvement and optimization should be carried out on the basis of conventional electric layout and connections to meet the anti-seismic requirements. ±800 kV Xinsong converter station is located in the 8 degree earthquake area, and the electric equipments, electric layout and connections are fortified according to 9 degree (0.4 g) earthquake intensity. Based on the analysis of the electric equipment seismic calculation results in the valve hall, the electric layout and connections of the valve hall are optimized. On the basis of electrical and mechanical characteristics being satisfacted, special fittings connection schemes such as horizontal Z-knee busbar fittings and vertical Z-knee busbar fittings are adopted. The key electric circuit of the valve hall is seismic decoupled by the special fittings connection, which ensures the safe operation of the electric equipments in the valve hall under the earthquake condition.

With the large-scale development and utilization of renewable energy, storage and flexible transmission technologies, there are more and more grid-tied inverter power generation systems in the power grid. The low inertia and weak damping characteristics of grid-tied inverters lead to the relative reduction of the rotational inertia of the traditional power grid, and the safe and stable operation ability of the power grid is also reduced. The common stability analysis methods for grid-tied inverter systems mainly include the numerical simulation methods based on differential-difference-algebraic model, the time-domain analysis methods based on state space model, and the frequency domain analysis methods based on impedance model. This paper respectively summarizes the basic principles, main features and best application scenarios of the existing analysis methods, and points out some problems in the application. Meanwhile, this paper also introduces some new stability analysis methods such as amplitude phase dynamics analysis method, static synchronous generator model and large signal stability analysis method. Finally, this paper points out that the advantages and disadvantages of various methods and their best application scenarios should be fully considered in the practical application, the dynamic characteristics and stability of grid-connected inverter power generation system should be analyzed based on a combination of various typical analysis methods and a comprehensive understanding from different perspectives.

Take a real 500 kV straight tower as an example, the safety status of the tower is evaluated based on the insulator string tension measurement system of the ice-coated monitoring terminal. This paper proposes a method for calculating the insulator string tension considering the coupling of both spans under non-uniform ice-coated condition, and obtains insulator string tension and inclination angle under various icing conditions. By finite element simulation, the error of the proposed method is less than 1.98%. The finite element model of the straight tower is established, and the critical failure conditions under different gravity loads and unbalanced forces along the line are analyzed, and the grading critical failure curve is drawn up. The ice thickness range of the straight tower critical failure under none-uniform icing is analyzed. This paper combines the engineering practice and brings guidance for failure pre-warning of straight towers in icing areas.

At present, both the power-frequency test method and the low-frequency sine-wave test method for the excitation characteristic test of the current transformer for protection have some shortcomings. Aiming at these existing problems, this paper establishes an analysis and calculation method of excitation characteristic test for protection current transformer with ultra-low frequency arbitrary waveform signal source according to the Lucas model. In this method, the excitation current of current transformer is separated into eddy loss current and hysteresis loss current, and the related parameters are measured, such as transformer core loss, basic magnetization curve and limit hysteresis loop. The influence of voltage drop on DC resistance is fully considered, and the excitation characteristic data under power frequency are obtained by calculation. In this paper, a breakthrough have been made in the restriction of excitation characteristic test by the traditional way of using power frequency and low frequency sine wave, we fully consider the influence of the core saturation, hysteresis and direct resistance of current transformer, and establish a model and a calculation method for arbitrary waveform. Various experiments and comparisons proves that the method proposed in this paper is accurate and reliable.

In order to realize effective fault diagnosis of transformer on-load tap-changer, a fault diagnosis method is proposed, which is based on variational mode decomposition (VMD) and Fisher-Score feature selection. Firstly, the signal is decomposed into a series of modal components with narrow band and distinguishing center frequency by VMD method. Then the energy and singular values of each modal component, and the permutation entropy and singular spectrum entropy of the reconstructed signal are calculated, and Fisher-Score method is used to select the features with better discriminative ability to construct feature vector group. Finally, the feature vector group is input to the support vector machine (SVM) optimized by simulated annealing algorithm to realize the classification, recognition and fault diagnosis of the vibration signals. An experiment is carried out on the transformer on-load tap-changer simulation experiment platform and the collected signals are processed. The results show that the proposed fault diagnosis method has higher identification accuracy.

In order to reduce the safety risk in the construction of cross power transmission line, an intelligent monitoring system is designed to monitor various state parameters of crossing frame and to early warn the possible crises. In this system, the monitored data is transmitted to the ground mobile monitoring equipment to process and display through wireless communication mode, and the WiFi and wireless relay technology are used to expand the coverage of wireless signal. And data acquisition and wireless transmission process together with and the structure of data processing software for the mobile monitoring device are expounded. Field experiments show that changes in the state of the cross frame can be monitored accurately by the system.

Integrated energy system is an important trend of power and energy industry, but its basic theories still need to be further studied. The calculation of energy utilization efficiency should be based on the second law of thermodynamics and the relevant national standard is being formed. The characteristics of transfers of energy and exergy through pipelines play an important role in the plan, design and optimization of integrated energy system. The mathematical expressions of variations of electric, thermal and pressure energies and exergies along pipelines are derived from the generalized expressions of transfer and conversion equations of energy and exergy. These expressions show that the losses of energy and exergy are related with the geometrical dimensions and the material qualities of the pipelines. These dimension and quality determine the investment of the equipment, and these expressions show that the greater the investment, the smaller the losses of the energy and exergy. So the research presented in this paper will provide a theoretical foundation for optimization of integrated energy systems.

Distributed feeder automation (FA) does not rely on a large number of calculations at the primary station for fast local fault handling using only local network topology analysis. Based on analyzing topology for adapting to distributed feeder automation requirements in intelligent power distribution terminals, and comparing models of international standards such as IEC 61968, IEC 61970, and IEC 61850, the difference is found out between the whole network topology model of the power distribution main station and the local topology model of the intelligent power distribution terminal. Combining the local topology requirements of distributed FA, the local topology model of intelligent power distribution terminal and a system-wide topology model of power distribution main station are established. And self-maintenance of local topology model is implemented through model transformation.

Call auction and continuous auction are introduced into the domestic electricity market, which enrich the bidding mode, increase the transparency of market information, and improve the trading efficiency. However, they put forward higher requirements for its implementation algorithm, it is particularly important to find an efficient and reliable clearing algorithm. For this reason, a clearing algorithm which combines call auction and continuous auction is designed in this paper. Based on scalable multi-factor ordering, flexible market clearing, bidding order linking, dynamic priority queuing technology, the two-stage order linking is realized effectively, the clearing efficiency is improved, and the orderly and efficient development of the whole transaction is guaranteed. At present, the algorithm has been applied to the software platform of Kunming Electric Power Trading System, and its practicability and effectiveness have been verified by engineering.