Solving the ion current field is the basis for the electromagnetic environment analysis and the evaluation of HVDC transmission lines. This paper summarizes the research status of the ion current field calculation of HVDC power transmission lines, and analyzes the existing difficulties. Meanwhile, the related research progress is introduced. This paper is a panoramic description of the current research on the ion current field of HVDC power transmission lines, which has an important role in promoting research in this area.

Renewable energy generation forecast is important for power grid operations. As for modeling this random and volatility time series, this paper studies three representative multi-scale decomposition algorithms: wavelet transform, empirical mode decomposition, and mathematical morphology. Taking the wind power time series as an example, their decomposition performances are evaluated. Based on information entropy theory and Hilbert transform, an evaluating indices system for algorithm performance is constructed from three aspects, the complexity, amplitude characteristics and frequency characteristics of decomposition results. The proposed evaluating method is verified by the forecast models based on artificial neural network and decomposition algorithms, and the results show that the proposed evaluation system is effective, and provides guidelines for selecting decomposition algorithms.

Based on the engineering practice of Yunnan Power Grid, the 4-machine 2-area system model including DC transmission is established. The key issues of the modal analysis method applied in the frequency mode are summarized. The influences of governor model, DC model and operation mode on frequency mode are analyzed. The frequency domain and time domain characteristics of frequency mode and power angle mode are compared. Furtherly frequency mode is dominated by the governor and prime mover and appears as a coherent change in frequency. The angle mode is dominated by the PSS and the excitation system and is represented by the relative sway of the angle. If the system has both negatively damped frequency mode and angle mode, it will appear as the beat frequency oscillation phenomenon of frequency and angle. Finally, the modal analysis method is used to identify the different oscillation modes in the large power grid, to guide the adjustment of the units’ parameters. The analysis results provide technical support for revealing the oscillation mechanism of large power grid and formulating suppression measures.

The simulation control and display system for AC & DC power grid based on real-time simulation, which is developed by CSG these years, is introduced in this paper. In addition, the key technologies in the system construction are expounded, including heterogeneous platform model mapping, interface communication, simulation control and system display. Real-time simulation technology and dispatching automation technology are organically integrated in the mirror system. This system takes the actual power grid operation section as the simulation initial state, and establishes a simulated system which is highly similar to the actual operating state of the power grid, and can realize the control interaction of the simulation process and the image display of the simulation results. The mirror system would become an effective platform and a new application platform for real-time simulation calculation, dispatching and operation training, automation application testing, new technology development of AC & DC power grids.

In order to meet the urgent needs of the current government, industry and commerce for power-saving expenses, and deepen the potential of the existing policy, this paper comprehensively uses distributed energy storage and centralized energy storage for industrial and commercial users, provides flexible and economical cloud storage and rental services based on analysis on the current peak-to-valley price policy in China. Considering the scale economies of cloud storage, cloud energy storage leasing schemes that consider peak and valley electricity prices are developed. Taking the lowest total cost of electricity for industrial and commercial users as the objective function, the power balance, the interaction limit with the main network and the limitation of cloud energy storage equipment are used as constraints to optimize the storage capacity and power of the leased cloud and the economics of the schemes are furtherly analyzed. The results of the example show that the introduction of cloud energy storage service for industrial and commercial users can effectively reduce the total cost of electricity consumption; the hybrid mode of energy type and power type energy storage is more economical than the single mode. The cloud energy storage service and its corresponding leasing modes will have broad prospects in the application of industrial and commercial users responding to the city, urban area and the Internet through the development of electric energy storage technology.

Some generating power units become stranded during the restructuring of electricity industry, giving rise to the need for scientific stranded-cost subsidy mechanism that can facilitate equitable competition among various generators. In order to mitigate the stranded costs problem of the coal-fired power plants caused by the transition from the regulated to liberalized market in Yunnan, this paper presents the design of the stranded-cost subsidy to thermal power plants in Yunnan. Based on the studies related to stranded costs in the literature, the definition and category of stranded costs are proposed, then the necessity of the stranded cost subsidy of Yunnan thermal power plants is analyzed, the accounting and recovery of the stranded costs are teased out. In the end, the framework design of the stranded-cost subsidy mechanism for Yunnan thermal power plants is proposed.

The excessive temperature of STATCOM thyristor valves will lead to their cracking and even breakdown. Therefore, timely and accurate prediction of the temperature is essential to improve the safety and reliability of STATCOM thyristor valves operation. Based on the least square twin support vector regression (LSTSVR) and seven input values such as STATCOM water temperature, return water temperature, water supply flow, thermal conductivity of heat dissipating material of IGBT module, STATCOM output voltage, STATCOM output current, and collector current of gate valve set, a monitoring system is constructed to predict the temperature of STATCOM thyristor valves. The comparison with the field measured data shows that the LSTSVR model achieves the accurate prediction of STATCOM thyristor valves temperature, and the prediction accuracy of the model is better than the least square support vector regression (LSSVR) model. The effectiveness and reliability of the method are proved by practical cases.

Inside press-pack devices, protective gas is hermetically sealed to improve the insulation strength and prevent electrodes from being degraded due to oxidation. In order to clarify the convective heat transfer characteristics of different protective gas in press-pack power devices, this paper takes press-pack IEGT as an example, analyzes its power losses, and carries out iterative thermal numerical simulation in ANSYS. By comparing temperature distribution of SF₆, N₂, and SF₆/N₂ mixture, Grasof number and Nusselt number are obtained. Then the heat dissipation effect of the three different protective gas is confirmed. This paper provides a reference for the selection of internal protective gas, heat dissipation design and optimization of internal structure of press-pack power devices.

The structure of HV single core cable will change the transmission line parameters of high-voltage single-core cable. Common analytical models consider the sheath as a smooth layer. The influence of cable corrugated aluminum sheath on transmission line parameters is studied by using finite element method. The paper expounds the basic concept of cable transmission line parameters and the simulation calculation process by finite element method. The transmission line parameters are calculated and compared among smooth aluminum sheath, corrugated aluminum sheath without gravity influence and corrugated aluminum sheath structure with the influence of gravity. The calculation results show that the corrugated structure increases the characteristic impedance and attenuation, and reduces the propagation speed, while the corrugated structure along with gravity has a significant effect on the parameters.

Due to the upgrading of transmission equipment, specific structural bearing capacity requirements are put forward for transmission towers. The existing transmission tower structures in China need to be reinforced reasonably. The static axial loading tests of leg member are carried out under 24 groups of test conditions for four different connection forms of leg member of transmission tower, which are non-reinforced original section, clamps connection, cross plate connection and one-glyph plate connection. The load-displacement curve, ultimate bearing capacity and load-strain curve of leg members after reinforcement are obtained. By comparing with the bearing capacity of unreinforced members, the effects of connection type, reinforcement location and number of reinforcement points on the reinforcement effect are studied.

The 500 kV double circuit transmission line can only be operated by helicopter sling method due to the dense conductor arrangement, which makes it very difficult for the operator to choose the path to access equipotential. A feasible helicopter sling method to access the path region of equipotential is proposed by taking the double triangle and hexagonal wire arrangements of two typical same-tower double-circuit transmission lines as the objective and considering the spatial position relationship between helicopter and wire. The field decomposition method is used to decompose the three-dimensional boundless field into bounded sub-regions, and the field strength of the helicopter body at different locations during approaching is calculated by ANSYS software to obtain the safe distance between the helicopter and the wire. After specifying the combined margin of equal potential for operator, the optimal path for the operator to access the equal potential is proposed in combination with the calculation of the human body surface field strength. The practical application of helicopter sling method in live line operation of 500 kV Gufeng line A and B shows that the operators can enter the equal potential operation safely from the area 0~15 ° above the horizontal plane of the conductor while the helicopter is 8 m away from the conductor.

When two-point-successive grounding faults occurs, the accuracy of fault line selection is low. This paper proposes a fault line selection method for two-point-successive grounding of power distribution lines based on the relationship between the amplitude and phase of characteristic component amplitude of zero sequence current when fault occurs. The zero sequence voltage of bus and zero sequence current of each feeder are collected in real time, and the characteristic components of zero sequence current are extracted and processed, and their amplitude and phase relationship are compared to realize the line selection of two-point successive grounding faults. The successive grounding faults of different fault feeders are simulated and tested in a 10 kV small current grounding system. Results show that the proposed method can select the grounding line correctly and has certain engineering practical value.

In the reconstruction of urban power distribution networks, the exact location of many old directly buried cables is unknown, which has brought certain difficulties to the work of patrolling and locating faulty cables. In this paper, a method for detecting underground cables based on the analysis of magnetic field component waveforms is studied. This method is also applicable to the detection of submarine cables. The method uses a fluxgate sensor to detect the weak cable magnetic field. Three mutually perpendicular components of the magnetic field are measured separately. To simulate a real live cable, an experiment system to simulate the operation of the cable is established. Results show that at least two of the three magnetic field components have specific peaks and valleys, and these peaks and valleys are related to the location of the cable. Using the distribution characteristics of the two component waveforms can accurately locate the cable. It is found that for AC cables, the measurement results are effectively readable when the magnetic field frequency is an integer multiple of the sampling frequency. In addition, this study also uses simulation software to analyze the significant weakening effect of the cable shielding layer on the magnetic field generated by the cable.