To reduce the probability of both commutation failure and continuous commutation failure in HVDC power transmission system, the main reasons causing commutation failure are analyzed, which include the voltage amplitude drop of commutation bus, direct current uprush and commutating voltage zero-cross phase shift. An optimal control strategy in which the extinction angle setting value can be adjusted dynamically considering zero-cross phase shift of commutation bus voltage at the inverter side and delayed trigger is allocated at the rectifier side is proposed. The influence of the optimal control strategy on system operating parameters is also analyzed. Based on the CIGRE benchmark model of HVDC, the proposed control strategy is developed in PSCAD/EMTDC. Simulation results show that the proposed optimal control strategy, to some extent, has the ability to mitigate the commutation failure and continuous commutation failure under single-phase and three-phase grounding fault conditions. Thus, the fault recovery performances of HVDC can be effectively improved.

Based on the structure characteristics of China Southern Power Grid(CSG) after asynchronous interconnection, this paper proposes the black-start scheme of CSG based on Luxi Back-to-back VSC-HVDC System. Firstly, from the characteristics of asynchronous interconnection of Yunnan power grid and its impact on the target framework of the black-start stage of CSG, the advantages of Luxi Back-to-back VSC-HVDC being applied to power grid black-start are analyzed and the black-start strategy of VSC-HVDC system is proposed.Then, the VSC-HVDC based black-start scheme suitable for CSG is put forward, meanwhile the start-up paths and operation steps to restore Yunnan power grid and the main grid of CSG with Luxi Back-to-back VSC-HVDC system are presented. At last, field test and RTDS simulation verify the validity and effectiveness of the proposed black-start strategy.

Under the influence of flames with high temperature, high conductivity, solid particles and other factors, the electric field around UHVDC transmission lines increases significantly, which may cause trip of the transmission line. In this paper, taking Yun-Guang UHVDC transmission lines as the example, simulation studies are conducted to analyze the influence of charge density and particulates in forest fire on electric field under ±800 kV transmission line through Comsol software. Research shows that the maximum electric field strength increases significantly, up to 47 times higher than that under normal operating conditions when the flame charge density reaches 10¹⁴ m^-3 under stable combustion condition, the particles may cause distortion of the electric field, when the flame charge density reaches 10¹⁴ m^-3,the distortion value can reach 7.5 times of which under normal operating conditions, the distortion of the electric field caused by solid particles increases with the increase of the long axis and the decrease of the short axis.

In order to master the lightning strike characteristics of distribution network arrester and propose economic and reliable improvement measures, firstly, the lightning strike conditions of arresters for distribution transformer and arresters for distribution line in typical 10 kV distribution network are classified and simulated, the change rule and numerical level of residual voltage, discharge current and absorbed energy of arrester are obtained. Then, the absorbing lightning surge energy level of D3, D4 and D5 varistor arresters are calculated. Meanwhile, combined with the arrester electric characteristic data, the overload lightning current range and the corresponding overload probability of arresters are given. Furthermore, the technical and economic evaluation of the configuration of MOA with different varistors is carried out. Results show that the use of D4 or D5 varistors arrester can reduce annual average operating costs, improve power supply reliability and reduce maintenance pressure.

Regular insulator contamination online monitoring systems can only work under normal pressure and temperature condition, which are not applicable for severe cold areas like northeast of China and east of Inner Mongolia with below-40 ℃ of extreme low temperature weather in winter. Hence, an insulator contamination online monitoring system for severe cold condition is developed in this paper. Firstly, the advantages and disadvantages of mainstream insulator contamination sensors are compared and severe cold experiment is carried out, then optical sensor is selected for contamination monitoring. Secondly, based on the characteristics of severe cold condition, measurement of salt and non-soluble deposit densities, insulation methods and stable power supply technology are studied, then an insulator contamination online monitoring system for severe cold condition is developed. Finally, relevant tests and operation research in grid are carried out to verify the performance of the system. The results show that insulation measures are feasible and stable power supply can effectively work in extreme low temperature, and the online monitoring system can work reliably under severe cold condition with ±10% detection accuracy of salt and non-soluble deposit densities.

With the diversification of requirements in transmission line construction and renovation projects, augmented capacity conductor will be applied to AC/DC transmission line project with multiple voltage levels. In existing transmission line design, the sag of transmission line are evaluated by empirical formula, which is verified merely in a 60 meters small span test in laboratory, and is quite different from the actual project. To understand the temperature rise and sag characteristics of typical conductors and provide basis for the selection of transmission line conductor, the first domestic 200 m large span transmission line on actual strain tower for full scale test is built in Kunming UHV engineering technology lab to study on the temperature rise and sag characteristics of four kinds of conductors, including one kind of ordinary aluminum clad steel conductor and three kinds of typical augmented capacity conductor: carbon-fiber aluminum conductor composite core (ACCC), aluminum clad invar core aluminum alloy wire, and aluminum clad steel core aluminum alloy wire. Results show that ACCC and aluminum clad invar core aluminum alloy wire have better arc sag characteristics, and there are obvious temperature transfer points. The temperature transfer point of ACCC is about 75 ℃, and the transfer point of aluminum clad invar core aluminum alloy wire is about 105 ℃.

In order to make better use of the Cole-Cole dielectric mathematic model to diagnose the damp-state of oil-immersed bushing, it is necessary to analyze the effect of temperature on the Cole-Cole dielectric model paremeters of oil-immersed bushing. In this paper, 72.5 kV oil-immersed bushings are produced in laboratory, and the frequency-domain dielectric response tests of oil-immersed bushings are carried out at different test temperatures. The experimental data are fitted by using the modified double relaxation Cole-Cole dielectric model, and the influence of temperature variation on the Cole-Cole dielectric model parameters is analyzed. Results show that the relationship between the DC conductivity σ_dc and the thermodynamic temperature T in the Cole-Cole dielectric model of oil-immersed bushing is consistent with that in transformer, the Arrhenius relation is satisfied; however, the relaxation time and relaxation strength are quite different from those of transformer; the relaxation time τ₁ decreases exponentially with the increase of test temperature; τ₂ decreases with the temperature rise and there is a slowdown in the process of change; the relaxation strength Δε₁ exponentially increases with the increase of test temperature; Δε₂ shows a tendency to increase first, then decreases and then increases with the increase of test temperature.

The digital value inputs and the trip command outputs of smart substation secondary system depend on the highly reliable operation of GOOSE circuits, of which the on-line monitoring and fault diagnosis are important functions of smart substation. Aiming at the fault diagnosis for GOOSE circuits interruption of smart substation, this paper proposes a fault diagnosis method for GOOSE circuits of smart substation based on Petri net, which accurately locate the fault points by model calculation. In this paper, according to GOOSE circuits of smart substation with the feature of decoupling in bays, GOOSE circuits of line bay and GOOSE circuits of busbar bay are chosen as study representatives to establish Petri net models. Finally, two scenarios, including a GOOSE interruption of the intelligent terminal as well as the line protection and busbar measurement and control device in a line bay, are studied in this paper, which can precisely locate faults and verify the effectiveness of proposed Petri net model of GOOSE circuits.

The feasibility of integrating traveling wave fault location function into transmission line protection device is discussed, the design, key technologies and solution scheme of the integrated device with both transmission line protection function and traveling wave fault location function are proposed, prototype of the integrated device is developed. The device integrates traveling wave fault location function module based on transmission line protection device, uses DSP component to collect input signals from current transformer of the line protection device, takes bulk cache technology to improve the coverage rate of traveling wave fault location record, diagnoses traveling wave triggers by protection triggers to ensure the reliability of the traveling wave trigger, communicates through longitudinal protection channel by transparent frame transmission technique, and verifies the reliability and precision of traveling wave fault location with impedance fault location of the line protection device. The device also adopts traveling wave speed correction technology to minimize the error between traveling wave fault location results and actual results. The performance of the integrated device prototype developed by this paper meets the design requirement and engineering application requirement, and provides a developing trend of integration of line protection and traveling wave fault location in high or ultra-high voltage lines.

The applicable occasion and effectiveness of demand response(DR) changes with different decision time-scales. Response behavior of customers is described based on the principle of consumer psychology, and constraints of the price difference ratio and customer satisfaction index are both considered in priced-based DR decision. Beside, the impacts of response capacity, continuous response time, limits of total response time in cycles are considered in incentive-based DR decision as well. With analysis on DR resource configuration in different time scales, a day-head and day-in two-stage scheduling model is established considering the participation of the priced-based and incentive-based DR. Taking the minimization of costs of general units operation, wind curtailment and incentive-based DR dispatching as the objective, unit commitment and economic dispatch are respectively determined in day-head and day-in time scale. Customers response behaviour and its effectiveness on scheduling are analyzed in cases, which verifies the effectiveness of the modeling and solution.

In order to reduce the impact of fluctuation and intermittence of renewable energy generation on the power grid, a two-stage optimal dispatching strategy for wind-photovoltaic-coal-energy storage system considering virtual power plant and time-of-use electricity price is proposed. In the first stage, the output power of virtual power plant is decomposed by extreme-point symmetric modal decomposition, energy storage is used to stabilize the output power after decomposition, and the stabilized power is transmitted to the second stage as the output power of the virtual power plant. In the second stage, time-of-use electricity price is used to guide power users to reduce the power system load fluctuations, and chance constraints are used to solve spinning reserve capacity. An adaptive particle swarm optimization algorithm is proposed to solve the dispatching strategy. Taking a regional distribution network as an example, the results show that the fluctuation of the wind and photovoltaic output power and the economy of the system operation are improved obviously. The validity of the dispatching strategy is verified.