DC voltage divider is an important measurement equipment in converter station, the insulation failure of DC voltage divider will directly affect the operation of HVDC system. Two typical insulation faults of ±800 kV DC voltage divider are described, the disassembly status and insulation structure are discussed, and the potential and electric field distribution under different operating conditions of the voltage divider are calculated and analyzed, then the cause of faults is proposed as follows: under wicked external insulation operating environment, the insulation resistance of polymeric housed epoxy cylinder of the voltage divider nonlinearly declined, which makes the axial resistance of epoxy cylinder and resistance capacity units unsuitable, and further results in axial potential difference and causes partial discharge, creeping discharge of the epoxy cylinder, and radiate partial discharge and SF₆ gas-gap breakdown of the voltage divider. Based on the above analysis, the countermeasures are proposed such as improving the external insulation potential distribution, enhancing the threshold of partial discharge and breakdown, and carrying out the specific operation and maintenance. The research achievements will be of great significance to the selection and operation maintenance of DC voltage divider, and the improvement of operation reliability of ±800 kV DC voltage divider.

The system commissioning of Xiamen flexible HVDC transmission project is analyzed and summarized. The design and preparation of the system commissioning program and the implementation of field system commissioning are introduced. The problems found during the system commissioning are analyzed and rectification methods are given. Three innovation test methods in the process of commissioning are elaborated including test method for true bipolar passive inverter, short time de-block technology, system commissioning isolation technique which effectively guarantee the safety of equipment and improve the quality of system commissioning. The summarized commissioning experience and methods are good guidance and reference for the construction of following projects.

DC fault detection and DC fault isolation based on change rate of DC voltage in DC grid are studied. The principle of change rate of DC voltage is introduced. The influence factors on change rate of DC voltage are analyzed, including current limited reactor, fault location, fault type, fault resistance and measurement time constant. A four-terminal MMC-MTDC is established in PSCAD/EMTDC and setting values of direct current circuit breakers(DC CBs) are chosen. When change rate of DC voltage exceeds setting values, internal DC faults are judged and DC CBs receive the tripping singal to isolate the DC faults. The feasibility of the proposed protection method is proved by simulating pole-to-ground DC fault and pole-to-pole DC fault.

Based on typical structure of voltage source converter based HVDC (VSC-HVDC) station and its parameters, the impact of startup process of VSC-HVDC station on AC grid is analyzed in this paper. According to the characteristic of voltage and current during station startup, it is concluded that AC grid voltage might drop abruptly because of transformer excitation inrush current or incomplete charge of DC capacitors at the time of closing AC circuit breaker or bypassing charging resistor. A control method to avoid the voltage drop of AC grid is proposed which decreases over current through phase selection switchs and delayed charging resistor bypassing. The method is verified through simulations based on real VSC-HVDC station.

For harmonic and reactive compensation of shunt active power filter (SAPF), the higher the DC link voltage is, the better comthepensation performance will be. However, higher SAPF DC voltage will cause bigger switching loss and switching noise, which is bad for the long-time running of SAPF. Thus, an optimal DC link voltage control strategy is proposed based on the equivalent energy model of three-phase three-wire system of SAPF. According to the reactive powers which is consisted in power grid and conpensated by SAPF, the compensated result would be better when the reactive power is near to zero in power grid side. Moreover the optimal DC link referent voltage is calculated to decrease switching loss and switching noise in the strategy. Simulation and experiment results validate the correctness of the theoretical analysis.

The component contents of silicone rubber composite insulators play a very important role in their quality and service life, but the detecting method of component contents is still inadequate for the electric power department. In this paper, TG-DSC technology is employed to study the thermal decomposition behavior of silicone rubber and its main components (aluminum hydroxide, organic silicone compounds, inorganic materials such as silica), and a method is developed to calculate the component contents according to the thermal weight loss rate in a certain temperature range. The method has been applied to the quality control, operation state evaluation and aging invalidation analysis for composite insulators. A series of composite insulators from several companies are evaluated by this method, and the results indicate that the contents of organic silicone compounds are about 35.9%~40.7%. Layer by layer sections analyses are conducted to running composite insulator skirts, and it is found that the polydimethylsiloxane (PDMS) contents vary with the depth, which reflects the aging state of the housing surface. In addition, this method also provides the component contents information at a selective silicone rubber housing region around fault locations, which can be used for failure analysis for the broken composite insulator. So TG-DSC method for silicone rubber component contents analysis is helpful for the operation and maintenance management of composite insulators, and also is helpful for ensuring the safety and stability of electric power network.

In order to make full use of the efficiency of composite material tower,it is studied to cancel the overhead grounding wire and downward leading wire to form fully insulated tower. Considering loss of discharging path when insulated tower is stroked by lightning, overvoltage caused by resulting intruding wave may do damage to equipment in substation, iron tower is proposed to be used in inlet line to relieve the overvoltage. Lightning withstanding levels of insulated tower and inlet line iron tower are simulated by ATP-EMTP, and the impact of lightning intruding wave on inlet line iron tower and substation, and the necessity of arrester is also studied. The results show that when arresters are not installed, the lighting intruding wave overvoltage(LIWOV) caused by lightning current of 9 kA on 110 kV insulated tower could result in flashover of inlet iron towers and about 800 kV overvoltage on a typical 110 kV substation, while LIWOV withstanding level of iron tower is improved up to about 40~45 kA lightning current and consequential overvoltage of less than 300 kV stressing the substation after installing arresters, which fulfills the requirements of the standard.

The uncoordinated charging strategy of massive electric vehicles (EVs) will threaten the safe operation of the grid, this situation can be relieved if coordinated charging/discharging strategy is developed. Based on classical battery-wear model and time-of-use price, a multi-objective optimal model for EVs’ charging/discharging process is proposed to reduce the daily load fluctuation and the charging cost considering EV’s charging demand. The Pareto front and the compromise solution are calculated by equilibrium-inspired multiple group search optimization with synergistic learning (EMGSS). Rolling optimization is adapted to deal with the day and night random variance of charging demand and reach the double-win of grid and EV owners. The simulation results demonstrate that daily load fluctuation is reduced effectively and EVs’ charging cost is also decreased.

To deal with power distribution problems of multiple parallel inverters in microgrid, the interaction mechanism between circulating-current and power distribution is elaborated firstly. Under the situation that the low-voltage microgrid line parameters is equivalent in resistance and reactance, by adding virtual reactance to compensate microgrid transmission line and achieve the resistance and inductance ratio like high-voltage transmission lines, the coupling problem of active power and reactive power is solved. Then the conditions are studied that the control strategy should meet for precise power distribution and circulating-current restraint with inductive impedance line. Improved droop control is put forward aiming at the coupling of reactive power distribution and inductive line impedance, which can realize reactive power distribution and circulating-current restraint. Finally, the correctness of the theoretical analysis and the proposed control strategy is verified by PSCAD/EMTDC simulation.

Under the background of smart grid, the two-way interaction of grid side and user side keeps upgrading continuously. An automatic demand response strategy considering load characteristics and suitable for different users is proposed based on intelligent communication and automatic management system. Firstly, based on user’s historical data and real-time price, the strategy calculates the available electric power in every period of a day. Then an optimal scheme dicision model is established to choose optimal strategy of different period from a strategy set of various demand response schems. Different demand response strategies have their own advantages on priority, fairness and flexibility. The decision factor of the optimal decision model can be set differently according to users’ different preference,thereby users’ preferences and requirements are satisfied. The analysis results of example show that the proposed strategy can help user obtain favorable effect of energy saving, cut the electricity expenses, and decrease the load difference between peak and valley load of grid.

Central air-conditioning load of public buildings has become one of the most important peak load regulation objects of electric power company with the features of concentrated using time, large load capacity, various adjustable methods and little influence on customer, etc. Firstly, the technology architecture of large scale central air conditioning load participating in day-ahead peak load regulation is proposed. Then, aiming at minimumizing the compensation fees of electric power compay, considering the constraints of adjustable stragies, the total load, load deviation of peak load regulation, etc., the optimal dispatch model of central air-conditioning load for day-ahead peak load regulation are built, Lastly, taking Jiangsu Province demonstration project with non-productive air-conditioning load as an example, the dispatch schedule are obtained by CPLEX for morning, middle and evening peak load periods.

Facing the rapid change of structure and scale of distribution network, this paper presents an improved minimal path method for distribution networks based on GIS Data to analyze the reliability of actual complex distribution networks accurately and rapidly. In this method, a complete set of simplification of network topology data, construction and equivalent transformation of minimal path matrix, process of calculating distribution networks reliability is designed to achieve the calculation of massive complex distribution network reliability based on GIS topology sheet. This method simplifies distribution network structure by eliminating component, and reduces total components in searching by extracting components selectively. This method achieves directed search from buses to distribution transformers by adjusting topology data in the process of search.The feasibility and accuracy of this method are illustrated by contrasting the calculation results of the improved method and traditional method on an actual distribution network.