In the functional performance tests (FTP) of Dianxibei UHVDC project, after 700 ms two-phase metal short-circuit fault on AC line at the rectifier side, it is found that valve misfire protection misoperation leads to instant outage of pole 2 in Xinsong Station. In this paper, the cause of valve misfire protection misoperation is analyzed theoretically. It is found that the AC voltage waveform distortion is caused by the interaction between the wave trap coil and the lightning arrester after the unbalanced fault at the AC side of the rectifier station of the Dianxibei UHVDC project. The original low AC voltage criterion of valve misfire protection cannot match the condition and causes misoperation. Finally, two solutions are proposed in which the true RMS and the fundamental component of the AC voltage are used to judge low AC voltage, and the effectiveness is verified.

Security and stability control system (SSC) is an important guarantee for the safe operation of power grid, and for HVDC system modulation function is an important kind of stability control measures. Combined with Tianshengqiao-Guangzhou HVDC safety strategy transformation, RTDS simulation test is conducted. In allusion to the exposed defects about SSC handling with multiple DC power modulation orders and sequence coordination between SSC and pole control system, the processing means for the stability control device of Mawo converter station and control characteristics of DC power downhill for pole control system are analyzed in detail. An optimization method of control sequence coordination for stability control system and pole control system is proposed and tested on the SSC test platform. Test results show the effectiveness of the proposed method, and this method can provide guidance for the design and implementation of SSC scheme of HVDC project with similar techniques.

The input stage, isolation stage and output stage of modular multilevel converter (MMC) based power electronic transformer contain a large number of IGBTs and freewheeling diodes. The circuit topologies and fault characteristics of IGBTs and freewheeling diodes under open-circuit and short-circuit faults are analyzed. According to the characteristics of each stage of power electronic transformer, the corresponding redundancy methods are designed to help the system to achieve fault ride-through. The input stage adopts sub-module spinning reserve redundancy. The dual active bridge of isolation stage is improved to be used for the isolation of the single stage double active bridge by means of parallel half bridge module in the series capacitors, on this basis, spinning reserve redundancy is configured for the isolation stage. The output stage inverter adopts bridge leg redundancy. Finally, the effectiveness of the proposed fault ride-through strategy is verified though simulation.

Aiming at the application situation of XLPE insulated submarine cable in the field of China’s offshore wind power, firstly the typical applications of mid-voltage AC submarine cable to offshore wind farms are summarized. The technical breakthrough of three-core HVAC submarine cable, the structure improvement and performance upgrade in the developing process of cable voltage level from 35 kV to 110 kV and 220 kV are introduced. Fabricating costs are compared between three-core and one-core submarine cables. Then the product features and insulation structure design method of VSC-HVDC submarine cable are briefed. Finally, according to the trend of large capacity and high seas construction for future offshore wind farm, it is proposed that the application of XLPE insulated submarine cable should focus on wet type structure array submarine cable and VSC-HVDC submarine cable in the future.

Considering the universally decreased insulation resistance of high voltage cable sheath and the possibility of its decreased withstand voltage level, the paper studies whether the protector can act correctly without damage to protect the sheath with decreased insulation under lightning overvoltage, operation overvoltage and short circuit when configuring protectors with low voltage-current characteristics by establishing ATP-EMTP simulation models of single-ended grounding and crossbonding grounding. The results show that reducing the voltage-current characteristics of protector can reduce the residual voltage acting on the outer sheath, and the current flowing through the protector is still below its nominal discharge current; in the case of single-phase short circuit, under the condition of single-end grounding, the protector needs to absorb a large amount of short circuit energy, reducing the voltage-current characteristics will lead to protector explosion; under the condition of crossbonding grounding, whether the protector explode or not depends on the magnitude of short circuit current, while a larger short-circuit current will cause the protector to explode. Finally, suggestions of the protector configuration of the outer sheath with decreased insulation are proposed.

To accurately guide the insulation design of coaxial bus duct of 500 kV GIS, it is necessary to study the dynamic distribution characteristics of electric field caused by structure and different voltage waveform. Taking the L-type and T-type bus bars in 500 kV GIS manufactured by a company as examples, the transient electric field characteristics under very fast transient voltage and lightning wave are studied based on time domain finite difference method. Results show that under very fast transient overvoltage, the peak value of the electric field in the L-type bus is smaller than that of the electric field under steady state, but the reflection of the wave front should be paid attention to. In the T-type bus, the reflection of the electric field is larger than that in the L-type bus. The maximum value of electric field is about 1.13 times as large as the steady-state value, and there is obvious oscillation in the wave front when 4 ns ramp wave overvoltage is applied, so it is needed to use transient electric field to check the insulation design. Under lightning wave, there is no reflection in the electric field of each node in the L-type bus and the T-type bus, and the electric field can be verified by the calculation result of the electrostatic field.

To accurately guide the insulation design of 500 kV disconnector room of GIS, it is necessary to study the dynamic distribution characteristics of electric field caused by structure and voltage waveform. The transient electric field characteristics of 500 kV disconnector room under very fast transient overvoltage (VFTO) and lightning wave are studied based on time domain finite difference method. Results show that no matter the disconnector is closed or opened, high frequency oscillations will occur in the electric field of each node, moreover, the electric field distribution will change constantly under VFTO. Oscillations have a high amplitude under 4 ns and 20 ns wavefront voltage time, which may seriously threaten equipment insulation. Especially, when the 4 ns ramp wave voltage is applied, the maximum value of electric field is about four~five times of the steady-state value and the oscillation frequency is higher than that of coaxial bus duct. So transient electric field must be calculated to check the insulation design. Under lightning wave, electric field of each node in the disconnector is almost non-reflex, and can be verified by the calculation result of electrostatic field.

It is of great significance to study the electric field and force of metal particles on the dielectrically coated electrodes of gas insulation line (GIL) to investigate the reasons of coating enhancing the lifting field strength of particles. Calculation models of the electric field distribution of particles on electrodes with or without dielectric coating are established respectively. Electric field calculation results show that the maximum value of the electric field under bare electrode appears at the top of the particle and is subjected to an upward electric field. While the maximum value of the electric field under dielectrically coated electrode appears between the particle and the coating, and the direction of the electric field force is related to the electric charge, and there are two kinds of situations, downward or upward. The partial discharge between the particles and the coating is the main mechanism of particle charging under the dielectrically coated electrode, when the electric field strength reaches the lifting field strength under bare electrode, the particle may still be uncharged, but it is subjected to the downward electric field force. Therefore, the decrease of electric charge and the downward of the electric field force are the reasons enabling coating to enhance the particle lifting field strength.

With the increasingly dense distribution of transmission lines, the possibility of fault at the crossing point of two transmission lines is intensively increasing. The existing short circuit calculation can only deal with the complex fault types with multi-point while it is unable to deal with the complex fault at the same crossing position with multi-span points. Therefore, this paper presents a short circuit current calculation method for crossing fault types with multi-span points. Firstly the sequence network equations at the fault point of two crossing transmission lines are constructed, and a general fault topology for complex fault with multi-span points is established. Then, the fault boundary condition equations for crossing fault port of two transmission lines are constructed based on phases. The phase sequence transformation is used to convert the fault boundary condition equations for each order network, and the fault current and voltage are solved by jointing the sequence network equations. Finally, a fault simulation model of power network is constructed by PSCAD/EMTDC, and the results verify the correctness of the method.

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.

Due to massive weather sensitive load in terminal equipment, the features of load changing with meteorological factors become more and more significant. Based on the virtual dummy regression forecasting model which has low complexity and strong ability to explain, the factors of human power consuming behavior, temperature and relative humidity and their across effects are introduced to the model. The dynamic mapping relationship between load and these factors is deeply mined. In terms of human power consuming behavior, dummy variables are introduced to describe the load changing rule in year, week and day. Load specificity of holidays is considered and quantified to improve the practicability of the model. In terms of temperature, cubic function model is used to describe the relationship of load and temperature, and the recency effect of temperature is put forward that means the lag hourly temperature information is introduced to the model. In terms of relative humidity, a new modeling method is put forward with quadratic function model of variables. At last, the proposed model is validated by actual historical data from 2006 to 2010 in a certain area. The prediction results show that the proposed model can reflect the load changing trend in various date types, the method is suitable for municipal power grids with little change in meteorological factors.