Abstract:The reform of transmission and distribution price is an important part of the new round of power system reform. Under the supervision of transmission and distribution price, the optimization of investment scale of power supply companies will be the focus of their future work. Based on transmission and distribution price policy, this paper firstly established the quantification model of assets, costs, allowable income and taxes in the calculation of transmission and distribution price. Secondly, a two-way impact model of transmission and distribution price and grid investment contains two sub models was constructed based on the system dynamics theory, which are the transmission and distribution price to grid investment optimization model and the grid investment to transmission and distribution price simulation model. Finally, a power supply company was taken for example, the allowable investment scale under the constraints of constant transmission and distribution price and the transmission and distribution price variations under planned investment scale are calculated, and the investment optimization strategy was put forward, the results verify the feasibility of the model.

Abstract:The digital signaling cable with inner screens is transmission channel in the high-speed railway track circuit. Its multi-loop simulation model and parameters have important significance for the research of high-speed railway track circuit. Firstly, in this paper, the multi-loop model of the digital signaling cable with inner screens is set up based on its structure characteristics and transmission path. Furthermore, the parameters of cable included capacitance, inductance, resistance are calculated based on the finite element method, including a detailed description of the boundary value problem of various parameters for calculating the finite element, the necessary calculation formula and step. Finally, taking 8-core shielded cables as an example, the simulation model is established, and the validity of the calculation method is verified by the compare between the calculated values of cable and measured values. And the established multi-loop model can be used to research signal transmission and fault diagnosis of high-speed railway track circuit.

Abstract:In order to achieve the access of multi-distributed generation and efficient and reliable power supply, the microgrid can be divided into several planned sub-microgrids to reduce the complexity of control and form multi-microgrid interconnection operation. With the large-scale access of the distributed photovoltaic power generation system on the user side, the application scenario of residential multi-microgrid becomes more common. First, the typical characteristics of residential multi-microgrid from four aspects, source-load, structure, technology and operation are described. On this basis, according to the rough designing route consisting of requirement analysis, electrical design, evaluation and inspection, the general process of system engineering design is proposed. Finally, combined with the circumstances of a community, considering the requirements of security and economy, the preliminary design scheme of the multi-microgrid demonstration project is given, which provides reference value for the promotion of residential multi-microgrid.

Abstract:For the demand of transmission of bulk power through UHVDC, based on the faultiness of the equally divided current guiding system of traditional electrode design, this paper proposes a new outer-6 and inner-3 non-equally divided scheme to optimize the current guiding system design of the electrode for the UHVDC transmission system with 6 250 A rated dc current or higher. Based on the two N-1 faults which stipulated in grid code and other three N-2 faults which occur during real operation, the threshold value of current guiding capability of current guiding system of UHVDC electrode is calculated. Besides, the current loading capacity calculation of guiding system under both normal operation and fault condition with the proposed outer-6 and inner-3 scheme is analyzed. A simulation model is established in the ETTG to discuss the selection of section of current guiding cable. Moreover, an economic comparison between the non-equally divided scheme proposed in this paper and traditional equally divided scheme is conducted. The general conclusion of the electrode current guiding system design with non-equally divided scheme is summarized in the end.

Abstract:Because the wind generation has a quick starting speed and needs small cranking power, it can be employed to accelerate the restoration speed of blackout system. Because of the uncertainty of wind power output, the output power of wind farm must be scheduled to reduce the fluctuation and ensure the security of restored system, as well as enhance the efficiency of wind power utilization during system restoration. In this paper, an information-gap decision theory (IGDT) based optimization model is proposed to dispatch the power of wind farms during system restoration. Firstly, the deterministic model is established without considering the wind power uncertainty. Then the deterministic model is transferred to the robust model by IGDT considering the uncertainty of wind power, which is solved by artificial bee colony method. Lastly, the method is verified in the New England system and part of Jiangsu power grid.

Abstract:Deeply research metering data with the big data analysis platform for the distribution network operation is one of the key research directions in the power grid currently. Power outage event completion method based on SVM algorithm to solve accurate statistical problems for MV distribution network was researched in this paper. Firstly, based on summarizing the five types of power outages in the MV distribution network, the SVM completion method is mainly researched. And the power outage event completion idea based on SVM and a full-process of SVM completion model construction method for the five types of power outage events are given. Besides, the completion process of distribution network model construction, vector machine SVM construction, vector machine SVM solution and judgment of fault type are proposed. Then, the business relationship framework among the complementary modules and other related systems, the data analysis architecture based on the big data platform are designed from the perspective of engineering application. Finally, take the application of Anhui Huangshan and other three cities as an example, it verifies that the completion method can greatly improve the timeliness and accuracy of power failure event collection.

Abstract:With more and more photovoltaic generations integrated into different voltage level distribution networks, the interaction between the various voltage levels of the distribution network is more complicated. It is a great challenge for the active distribution network to improve of system security and economy capacities. Considering the effect between different voltage levels, a multi-level voltage interaction control method for active distribution network based on model predictive control (MPC) is proposed in the paper. Considering on-load tap changers (OLTC) and shunt capacitor banks (CB) future-time action plan, a medium-high voltage association model is established. Coordinated control of continuous equipment in medium voltage distribution network and discrete equipment in high voltage distribution network is achieved. In the medium and low voltage distribution network, taking into account the uncertainty exchange power and their mutual influence, a low-middle voltage association model is established. It can realize the support of medium voltage distribution network to low voltage distribution network. Finally, a case study is carried out in Matlab and the results verify the effectiveness and feasibility of the proposed approach.

Abstract:The present evaluation index system of distribution network planning cannot quantify both subjective experiences of experts and objective factors. The benefit demands of participants are analyzed and a comprehensive evaluation index system is built. A combination weighting method based on maximum dispersion and maximum coefficient entropy is utilized to obtain the indices weight. The proposed method considers both the prior knowledge of the experts and objective influence factors of indicators. The actual distribution network planning scheme is used for evaluation and verification. The case study indicates the engineering practice of the method. The method provides a reference for the planning and expansion of the distribution network.

Abstract:When the AC system of the receiving end fails, the DC transmission system based on the grid commutator has a problem of commutation failure, which will cause the DC transmission power to be interrupted. The excess reactive power at the sending end will cause the AC system to overvoltage. In turn, it is possible to cause new energy equipment such as wind turbines to be disconnected from the network. Therefore, a control strategy is proposed to suppress over-voltage at the transmitting end during commutation failure. The specific strategy is to quickly input bypass switch of the inverter side when the commutation failure occurs and calculate the DC current command value during the fault according to the reactive power consumption before the fault. The strategy can maintain a certain DC current in the mode of the active power interruption, thereby ensuring the converter valve can normally commutate and have a certain reactive power consumption to avoid the overvoltage problem of AC grid. The simulation results verify the effectiveness of the control strategy which can be applied to both strong and weak AC systems with different short-circuit ratios.

Abstract:Unreasonable excitation, speed regulation, PSS and other control system parameters in electromechanical transient simulation of power system will lead to the weakening of control system stability and the reduction of simulation credibility. A practical diagnostic method for this problem is presented based on the dominant trajectory section damping ratio sensitivity. The dominant time section, the dominant generator and its corresponding control system are determined automatically by the output variable oscillation characteristics of each control system in the simulation. After the single-machine infinite (OMIB) equivalent is performed for the dominant time section and the dominant generator, the suggestion of parameter adjustment is given by the sensitivity analysis of damping ratio. The effectiveness of the proposed method is verified by several examples. This method is an engineering application of the idea of trajectory eigenvalue. In combination with the oscillation information of the control system provided by numerical integration and the damping ratio sensitivity analytical information provided by eigenvalue technology, unreasonable control system parameters can be quickly located. It is suitable for parameter diagnosis of complex multi-machine system.

Abstract:In order to solve the problem that the large-scale security and stability control system can not be tested in the laboratory, a data conversion device is designed to interface with the on-site operation stability control device, which realizes the information exchange between the RTDS test system of the simulation laboratory and the remote operation equipment. The overall design of the data interface conversion device is introduced in detail, and combined with the typical application of the device.The application method and practical application of the data conversion device in the wide area remote testing system based on RTDS are further elaborated, extends the test system to the on-site operation equipment.The laboratory′s present situation is realized,and the closed loop test of field security and stability control system is completed. The design of the device and the application of remote test method provide the experimental basis for the remote simulation test of the the large-scale security and stability control system.

Abstract:In order to solve the problem of the current distortion under unbalanced voltage and the complexity of the phase-locked loop (PLL) of the grid-connected inverter, a strategy based on virtual synchronous generator (VSG) under unbalanced grid voltage without PLL is proposed. The control method of VSG under unbalanced grid voltage is detailed studied. An improved VSG control strategy based on PIR current control loop is designed to restrain current distortion effectively without changing output characteristics. Meanwhile, a VSG resynchronization control strategy based on virtual power is proposed to guarantee seamless switches between grid-connection mode and off-grid mode. The PLL is not used throughout the proposed strategy, which avoids the bad effect of PLL on control precision and response speed and makes the control system simplified in addition. Finally, a real-time simulation platform based on RT-LAB is built to verify the proposed control strategy.

Abstract:The distributed static series compensator (DSSC) has the characteristics of small size and low power consumption, and it can be directly connected to the power line for power flow control which makes it become one of the most promising distributed flexible AC transmission technologies. In order to solve the problem of coordinated coordination control of each sub-module in the DSSC system, the paper discusses the difference between the operating state and the adjustment performance of each sub-module, and proposes real-time optimization allocation method on the output of sub-module according to the idea of “classifying with state-setting performance with adjustment performance”, to achieve the minimum number of start-stop sub-modules and to extend the operating life of the sub-module. Based on the RTDS platform, the closed-loop simulation analysis of the optimized allocation method is carried out. It is verified that the method can meet the power flow control requirements of DSSC. Compared with the traditional average distribution method and the proportional distribution method, the method has greatly improved the adjustment speed and adjustment accuracy.

Abstract:A model of fault diagnosis for power system based on time sequence fuzzy Petri net is proposed, which mainly includes identifying blackout area, modeling for time sequence fuzzy Petri net of possible faulty components, solving faulty component set and judging operation information of protection and circuit breakers. Fault alarm error information classification and fault alarm information timing characteristics are introduced. Based on the study of operation information of circuit breakers and network topology, the method for identifying blackout area is given with BFS. Finally, take New England 10 machine 39 node system as an example, mathematical models of fault diagnosis for power lines and bus on time sequence fuzzy Petri net are established, and the overall structure of this system is given, results show that it can rapidly locate fault, and accurately give operation information of protection and circuit breakers.

Abstract:Demand response guides users to change power consumption behavior through electricity price or incentive signals,and improves efficiency and reliability of the power system.User comfort is of great significance that needs to be considered during the implementation of demand response programs.Due to the large electricity consumption and good heat storage capability,electric water heaters (EWH) are the important demand response resources.This paper proposes a flexible control scheme for the automatic water-mixed thermostat EWH aiming at balancing economical demand and demand on user comfort.The thermodynamic model of water tanks and automatic water mixing valve control system are established,an index reflecting the comfort degree of users is introduced.Based on which a multi-objective optimization is established,coping with both electricity consumption and user comfort index simultaneously.The optimal power distribution period of EWH is obtained through genetic algorithm.Results of the proposed method are compared with those by both traditional control strategy and single-objective optimization strategy aiming at minimizing electricity consumption.The effectiveness of the method is verified.

Abstract:With the continuous advancement of new power reforms and the rapid development of microgrids and multiple loads, how to ensure the comprehensive benefits of grid companies′ investment in distribution networks is the key to the comprehensive background of policies and technologies. Aiming at this problem, this paper comprehensively considers the impact of micro-grid and multi-load on the investment of distribution network, and constructs a distribution network-input benefit evaluation index system. Secondly, it combines the influence of micro-grid and multi-load on the purchase and sale of electricity. The input-output model of the distribution network after the new power reform. Finally, the evaluation of the distribution network investment and the optimization of the distribution network planning project are proposed by the scoring method and the preferred method. The scoring method uses the analytic hierarchy process and the entropy weight method to determine the synthesis. The weighting and optimization method uses the improved gray correlation method for data analysis. The practical examples verify the feasibility and effectiveness of the proposed evaluation system.

Abstract:The mixing of magnetic and electronic CTs in transmission line might affect the correction of line differential protection′s action. Recently, the virtual braking current method is the common way to solve that problem. While the virtual braking current method is fixed to the threshold value of the differential protection, and the influence of the variation of the line parameters is not considered, therefore the opening time of differential protection takes too long. Aiming to this, it proposes an improved method to identify saturation in this paper, which is based on floating threshold value. Firstly, it calculates the line parameters and floating threshold value of the reference curve by the establishment of the model of current transformer which obtains line parameter and relationship of saturation degree. Secondly, the threshold value is chosen adaptively according to the specific line parameters to ensure the differential protection disoperation, as well as reducing the locking time of differential protection. The simulation results show that the method can enhance the sensitivity, reduce the shutting time of differential protection and can apply to a large scale.

Abstract:In order to realize the observation of voltage sag at any position in power system, an optimal allocation method of voltage sag monitoring nodes based on the minimum magnitude search is proposed. Firstly, according to the analytic formula of voltage sag, the minimum node voltage magnitude when the fault location changes in each line is searched by golden section method. Based on the voltage threshold, the monitor reach area and the worst observable matrix are constructed under different fault types. Finally, with the constraint of fully observable voltage sag at any position, the optimal allocation model is established to minimize the voltage sag monitoring nodes. When constructing the voltage sag observable matrix, the worst scenario of voltage sag is considered to avoid monitoring blind area. The accuracy and effectiveness of proposed method are verified based on IEEE 30-bus system.

Abstract:The phenomenon of sharing corridor resources between AC overhead transmission lines and buried steel pipelines is becoming more and more frequent, and the resistance coupling voltage generated by short-term high current of lines will seriously accelerate the corrosion of pipelines. In order to quantitatively calculate the resistive coupling voltage of buried pipeline, a calculation method based on CDEGS simulation model is proposed in this paper. Firstly, the simulation model of large current entering the ground is established. Secondly, the calculation method of resistive coupling voltage of pipeline when power frequency current grounding is given, and the influence of current amplitude, soil resistivity and the distance between the nearest point of current entering and the pipeline on the resistance coupling voltage is analyzed. Finally, the calculation method of resistive coupling voltage taking into account frequency and time-frequency conversion are given when lightning flows into the ground. The calculation method of maximum exchange voltage is given, and the influence of lightning current amplitude, distance from the nearest point of the pipeline, soil resistivity and of lighting flow into ground through multiple towers on the resistance coupling voltage is analyzed.

Abstract:The corrosion and hazard effects of DC earth electrode on adjacent buried oil and gas pipelines are becoming increasingly prominent, and more accurate calculation methods are urgently needed. On the basis of previous research, the equivalent circuit model of pipeline and grounding device is established by moment method, and the polarization effect at the damaged surface of pipeline is considered as a non-linear controlled voltage source. A calculation method considering the non-linear polarization effect of DC earth electrode on the surface of buried metal pipeline is proposed. In the rectangular tank of grounding Laboratory of UHV AC test base, the scaling test model of HVDC earth electrode and oil and gas pipeline is built to carry out experimental research. The validity of the calculation method proposed in this paper is verified. The results show that the calculation method is in good agreement with the test results, and it can provide an estimation reference for engineering application.

Abstract:Power frequency electric field near the angle tower of double circuit transmission lines is seriously distorted, which becomes an important factor restricting the engineering design and environmental assessment of the transmission lines. This paper establishes a model for the simulation of power frequency electric field near the angle tower of 500 kV double circuit transmission lines. The validity of the model is verified by the comparison between simulation results and measured data. The distortion factors affecting the electric field on the rooftop are analyzed. Based on the electric field exposure limit, necessary control distance between the house and the transmission line is estimated. The results show that the closer the three-dimensional distance between the house and the line is, the more concentrated the electric field is and the more serious the distortion of the exposed field on the rooftop of the house is. The influence of house height on electric field decreases with distance increasing. Finally, the control distance between the houses and the lines under different house heights and turning angles is suggested, which could be referred in the planning and design of transmission lines.

Abstract:The thermal aging phenomenon that is common in power cables during operation is likely to accelerate insulation failure, limit the service life of equipment, and even cause power system failure. Nanoparticle doping modification can improve the thermal stability of polyethylene matrix materials, and related research can provide solutions for improving cable insulation life. LDPE/TiO₂ nanocomposites are studied, and the effects of nanoparticle concentration, aging time and aging temperature on the dielectric properties of the materials are studied under heat aging conditions. The experimental results show that the doping of TiO₂ nanoparticles can improve the dielectric properties of LDPE matrix materials. When the filling fraction of TiO₂ nanoparticles is 0.5%, the dielectric properties of nanocomposites are the best. The aging time and aging temperature affect the dielectric properties of materials. Two important factors of characteristic deterioration, as the aging time increases and the aging temperature increases, the dielectric properties of nanocomposites deteriorate more. Nano-modification of polyethylene materials while reducing the operating temperature of the cable is of great significance for improving cable insulation life.

Abstract:In order to meet the requirements of fine management of power grid companies and manage users pertinently,a recognition method based on fuzzy clustering algorithm and curve similarity is proposed. Taking the load in Jiangnan region as an example, it collects large amounts of power data to obtain characteristics of aquaculture load customers′ regular electricity consumption by introducing fuzzy clustering algorithm. Finally, by analyzing the similarity between the customer′s daily load curve and the characteristic curve, the possibility can be judged, and it can provide basis for precise service of power supply company. The results of case studies prove that the proposed method is feasible and effective.

Abstract:The power extraction high voltage parallel reactor,referred to as energy extraction reactor, is essentially a hollow transformer consisting of grid-side windings and auxiliary windings. It belongs to a new type of reactor which can absorb the redundant reactive power of the system and provide the power supply for the station. At present, over-current or zero-sequence over-current protection is usually used in engineering to reflect the inter-turn short-circuit fault of the auxiliary windings. This protection scheme has some shortcomings, such as poor selectivity and long operation time. Therefore, in this paper, a new scheme of inter-turn winding short circuit protection for energy extraction reactor was proposed. The scheme integrates the voltage and current of the high reactance winding on the grid side and the current in the winding ring. It consists of the criterion of out-of-zone anomaly, the criterion of core saturation and the criterion of self-produced zero-sequence overcurrent in a logical phase. RTDS simulation results show that the protection scheme can not only ensure reliable operation under various non-regional fault conditions, but also reflect inter-turn short circuit fault of auxiliary winding more than 4%, and shorten the protection operation time to about 50 ms, thus solving the problems of poor selectivity and long operation time of previous inter-turn short circuit protection schemes for auxiliary winding.

Abstract:As for the multi HVDC transmission lines on the same tower, with a wide application prospect, research on how the fault identification and protection configuration are influenced by the HVDC line layout and fault mode is important to the safe and reliable operation. Devise methods are comprehensively applied in the simulation platform establishment, including the AC grid equivalent, digital electromagnetic transient models establishment, typical line fault’s simulation scheme, and so on. The characteristics of dc line protection such as traveling wave, derivative, dc under-voltage and longitudinal difference ones,in typical faults are studied, influence mechanism and change performance are explored. The results show that the existing dc line protection can effectively identify most typical faults, while it is difficult to identify the specific fault of the specific conductor layout. In the dc lines design, specific conductor layout is suggested to be avoided aiming at improving identification and response ability of dc line protection on fault. Considering the solid theoretical foundation, clear research route, the proposed technical routine will support design, construction, operation and maintenance, is valuable for engineering application.

Abstract:In the actual power system, the load changes at all times under the influence of various factors and it can be regarded as a continuous function. The development of smart grid makes continuous time data acquisition and generator control come true, so the continuous time load dispatching is imminent. However, the economy and security of the original static and dynamic optimal power flow are limited to some extent with considering the optimization of discrete functions. The Riemann integral method is applied to expand the optimal power flow, which consider continue time change of variables. A continuation optimal power flow model is established based on Riemann integral. The precision and efficiency of the algorithm is verified through the stimulation of IEEE 5-bus system. Simulation results show that a final optimal dispatching is found in the proposed model with all the chance constraints satisfied. Moreover, the active power outputs of generators flow the fluctuation of load well.