Temperature distribution and ampacity are two important parameters to reflect the operating state of submarine cables. According to the ±160 kV HVDC submarine cable of Nan’ao project, a three-dimensional (3D) simulation model of the cable is set up and a simplification method of cable transient model is proposed by using COMSOL Multiphysics finite element analysis software. On the basis of the constant thickness, multiple thin layers and adjacent medium are used as three equivalent layers. The thermal conductivity of the equivalent layer is computed by harmonic mean method,and the specific heat capacity and density of the equivalent layer are calculated by IEC 60287 method, which solve the problem that the meshs in the thin layer of the cable are too dense. Through the simulation model, the temperature distribution of cables under different ampacity is compared before and after simplification, which verifies the correctness and effectiveness of the simplification method.

The technical scheme of a CLLC type modular input-series output-parallel DC transformer is presented, which can achieve voltage conversion and power transmission between high and low voltage of DC grid. CLLC series resonance transformer is adopted as submodule of DC transformer, which works at open loop mode, constant frequency mode and full resonance mode with high efficiency and constant voltage gain, and the input voltage and output current of each submodule are naturally equal. In order to prevent the large impact current, a soft start control strategy is proposed, in which the duty ratio D slowly increases from D_min to 0.5 by means of pulse modulation control. A 500 kW ±7.5 kV/800 V DC transformer prototype is built, the correctness and feasibility of the proposed topology and design method are verified by the experimental results.

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.

Due to the frequent occurrence of ice and snow disasters in power grid, ice-melting reconstruction is carried out for more and more EHV lines. Good anti-icing effect has been obtained, but the ground wire corrosion which cannot be ignored has also been detected during operation after ice-melting reconstruction. Aiming at the corrosion caused by different kinds of metal contacting between the outside surface of ground wire and the connecting clamp of a 500 kV AC transmission line after ice-melting reconstruction, XRD analysis of corrosion product, metallographic analysis, salt spray test and some other experiments are made in this paper and the reasons of corrosion are then analyzed in detail. Finally, feasible measures for the ground wire corrosion are proposed and planned to be applied in actual site. The proposed measures are of great reference significance for future ice-melting reconstruction of transmission lines.

The development of remote fault diagnosis of transmission line is one of the focuses of the construction of smart grid. To solve the problems of homogeneous uploaded data, enormous amount of data, and poor data utilization, naive Bayes algorithm is used together with similarity fault matching by time sequence to establish a transmission line fault warning model, based on the big data processing cluster technology provided by the background platform. The model uses collected data of electrical and switching information, event sequence information, power network topology, and data acquired by fault recorders during transmission line failure, and applies naive Bayes algorithm to excavate the occurrence factor of potential fault (i.e., fault factor), then, by cooperating with similarity fault matching by time sequence, the fault of transmission line can be forecasted. Case analysis shows that the model can excavate fault factors correctly and the forecast result is satisfactory.

In order to improve the safety and stability of Guangzhou power grid, a power transmission line monitoring system using big data technology is proposed based on analysis of the lightning activities in Guangzhou area in recent years and summary of the operational status of power transmission lines and tripping by lightning in Guangzhou power grid. The transient effect on voltage and current around the tripped transmission line can be presented for analysis directly with 3D simulation system to visualize the tripping events and the affected substations. Meanwhile, the big data mining technologies are applied to analyze the correlating factors of tripping events with transient voltage and lightning events, and search for any potential links among them. The proposed system can establish a correlative information database of lightning, tripping and other related factors for Guangdong power grid, and provide effective technical support for making protection principles of grid operation, carrying out daily maintenance of lightning protection, and improving the operation level of the grid.

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.

In order to study the electromagnetic radiated interference of electronic transformer caused by VFTO (very fast transient over-voltage) during the operation of disconnector in GIS, the simulation model of 220 kV GIS electronic transformer is established. Taking measured VFTO waveform as excitation source, the VFTO transient electromagnetic field distribution inside metal acquisition box of GIS is calculated. The results show that the transient electric field intensity and magnetic field intensity under VFTO both far exceed the existing electromagnetic compatibility test standards. Suppression methods are also proposed such as reducing the diameter of the terminal block disc and increasing the connection length between metal acquisition box and GIS tank, which can both achieve high shielding effectiveness. These research results can provide theoretical basis and technical support for VFTO electromagnetic radiation interference suppression of electronic transformer.

Capacitor voltage transformer (CVT) is widely applied to electric power system. It is beneficial to acquire the accurate transfer function of CVT for the protection and the monitoring of power system. At present, the reaserches about CVT are based on its typical equivalent circuit, however, due to the different internal parameters of CVT under different operating conditions, the transfer functions are different, which leads to inaccurate research results before. A square-wave pulse is applied to CVT when the internal structure parameters are not clear, then, the recursion method and the least square method are applied to caculate the impulse response of CVT based on convolution theorem, and Laplace transform is used to obtain the frequency transfer characteristics. The correctness of the theory and the reliability of the algorithm are verified by building the simulation circuit in PSCAD. Furthermore, the noise is added in the output signal, the anti-noise ability and noise impact factor of these two algorithms are analyzed in their algorithm structure. It is found that when noise is added, the anti-noise ability of the recursive method and the least square method are influenced by the length of convolution, both methods can get accurate results when the signal to noise ratio is larger than 40 dB.

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.

Due to the existence of power electronic devices and non-linear loads in microgrids, the power quality problem of microgrids can not be neglected. As the distributed power grid-connected inverter is essentially a three-phase full-bridge circuit, the inverter can not only delivery power, but also control the power quality problems actively. In view of this thought, an active harmonic control method based on one-cycle control is proposed to suppress the current harmonics at the points of common coupling. Aiming at the situation of multiple inverters in parallel, a control strategy of output current apportion compensation is proposed, and the traditional one-cycle control is simplified and improved. Corresponding simulation model set up in Matlab/Simulink and experiments based on dSPACE verify the correctness and validity of the proposed method.

Based on the background that demand response technology is limited by the level of information and communication in the demand side, the working principle, topology, application scenario and network mode of power line carrier communication applied to residential users are analyzed in this paper. Then the indicator requirements of different types residential user demand response service in the communication system are studied, and the specific data of indicator requirements is given. Finally, a large amount of experimental data are used to verify the feasibility of appling power line carrier communication to residential users’ demand response service. At the same time, the shortcomings of power line carrier communication are also pointed out.