Abstract:With the increase of grid-connected photovoltaic generation capacity,the inherent characteristics of fluctuation and intermittence of the photovoltaic generation lead to the result that large-scale PV integration will change the distribution of power flow and even reverse it,influencing the stability and security of power grid.A steady-state model of PV generation system is established in the paper.Based on the IEEE 14-bus system and power grid of a province in Northwest China,probabilistic load flow calculation of power grid connected with photovoltaic generation system has been carried out.The influence of large scale grid-connected PV generation on load flow of power system is fully analyzed under the circumstances of different grid-connected capacity,different grid-connected spots and different output correlations of the PV generation system.The results indicate that the fluctuations and limit violation probabilities of power system voltage and load flow increase with the addition of PV capacity.What's more,power loss as well as PV penetration level is influenced by grid-connected spots and the impact of PV on load flow is directional.Additionally,the correlations among PV power stations cannot be ignored.The research does provide reference for the planning and operation of power system with large integration of renewable energy.

Abstract:With large-scale and high penetration level wind integration,stable and adjustable active power output of wind energy conversion systems like traditional power sources is an urgent requirement for the future power grid operation and dispatch.Active power control (APC) for wind turbines participating in automatic generation control (AGC) has become one of the highly-concerned issues in the main control strategy research of wind turbine.Existing APC methods mainly include the output power control base on the pitch angle control (PAC) and the rotor speed control (RSC).Base on the analysis on energy balance of wind turbine,the principles of the aforementioned APC strategies are summarized in this paper.Then,the performance of PAC and RSC are compared by simulations on the FAST (Fatigue,Aerodynamics,Structures,and Turbulence) code.Results show that RSC possesses a more stable active power output as compared with PAC.Because of the energy buffer of rotor inertia,the frequency and amplitude of pitch angle manipulation can be effectively reduced at low wind speed by RSC method.However,both methods require frequent pitch angle adjustment at high wind speed.It is also pointed out that the power reference exerts a significant influence upon APC performance.

Abstract:Through the comparison of three methods for the grid interconnection of offshore wind power,this paper pointed out the application prospects of fractional frequency transmission system (FFTS) in large-scale offshore wind power integration.Besides,this paper introduced the structure of fractional wind power system and the choice of inverter and showed the excellent performance of modular multilevel converter (M³C) as a new generation inverter.Moreover,this paper analyzed the influence of low frequency on the critical machines used in fractional offshore wind power system,which furtherly shows the feasibility,economical advantages and technological advantages of the fractional offshore wind power system.Finally,some economical and technological problems remaining unsolved of the fractional offshore wind power system were pointed out,which indicated the direction for further study.

Abstract:To enhance the power supply capacity and solve the problem for UHVDC power assumption of 500 kV power network in Suzhou,the feasibility research on the application of UPFC in 500 kV Southern Power Grid of Suzhou is carried out.Combined with the scheme of UPFC integrated and its topology structure,the capacity of UPFC is determined by system calculation and the principle for the key parameters selection of UPFC main equipment are supplied.The effect of UPFC on the power flow and voltage regulation of 500 kV power grid in southern Suzhou is verified by simulation,which indicate that under the heavy load condition of Suzhou power network in winter,the regulation of UPFC can eliminate the key section overload problem as N-1,while under the heavy load condition in summer,it can decrease the capacity of load shedding as the UHVDC bipolar blocked.The reactive power control of UPFC can provide the dynamic voltage support for power grid,which is benefit to decrease the probability and duration time of commutation failure of UHVDC.

Abstract:Emergency load shedding when serious HVDC transmission fault happens are necessary measures to prevent frequency drop of receiving-side power network.Combined with the characteristics of the stability control and marketing load control,it proposes a load control system using the load which can be interrupted as the object of precise control.It compares advantages and disadvantages of the load control by stability control device and load control by the marketing system and then introduces the overall architecture of precise load control system.It focus on the functional position of the system,load control principle and prevention for system malfunction and rejection.The precise load control system proposed in this paper has been completed and put into operation in Jiangsu Power Grid,which realizes accurate control of 3.5 million kilowatt per second and emergency control capability of 1 million kilowatt per millisecond.

Abstract:Gas-insulated metal-enclosed switchgear (GIS) has been widely used in power system,and the safe and reliable operation of the GIS are very important.Restrained by the device structure and circuit inductance,the on-site lightning impulse (LI) withstand test is difficult to be carried out in the GIS substation,especially in the ultra-high voltage (UHV) GIS substation.In this paper,the present situation of GIS impulse test is analyzed.And then the influence factors of insulation defect detecting using impulse test such as waveform parameters,polarity and interval time between two impulse tests are elaborated.Finally,based on the moveable gas-insulated impulse voltage test complete equipment,the on-site standard lightning impulse test is applied successfully in 1000 kV Nanjing substation and 1000 kV Suzhou substation.

Abstract:With the growing scale of new energy,new energy power contribute often exhibit a strong correlation,traditional random flow algorithm for strong correlation random variables was considered less.A method of probabilistic power flow algorithm based on semi-variable and Gram-Charlier series expansion was proposed in this paper.According node voltage and branch current expectations and sensitivity matrix,with wind power output,load changes,forced outages and generator fault lines and other uncertainties considered,load and conventional generators,wind turbine output and each node injection power of each order half invariant were calculated.Probability density function and probability distribution function were obtained by Gram-Charlier series expansion.IEEE-30 node test shows that the algorithm can reflect the uncertainty of large-scale new energy accessing to the system,and probability density function can be simplified to the semi-invariant algebra.Greatly reduce the computation time and it has a good convergence.

Abstract:With the continuous expansion of the interconnection scale of power grids,the number of the power electronics integrated to the power grid continues to increase,bringing new challenges to the operation reliability of the grid.As the equipment for flexible AC transmission system (FACTS) which has the strongest ability of adjusting power flow,the unified power flow controller (UPFC) has been designed,developed and applied to Nanjing western power grid successfully.In this paper,the operational reliability model considering UPFC is established and applied to perform the operation reliability analysis and benefit evaluation of Nanjing western power grid.The analysis results of the example demonstrate that UPFC can effectively improve the reliability of regional power network and positively contribute to economic benefits.

Abstract:Virtual synchronous generator (VSG) technology simulates the characteristics of the synchronous generator by power conversion system (PCS).Thus,the converter will have the characteristics of the synchronous generator such as primary frequency regulation,primary voltage regulation,damping and inertia.So the voltage and frequency regulation ability of converter for power grid will be enhanced.It can also help to improve the friendliness of grid-connection.In this paper,a new rectification method for phase angle and frequency of VSG based on phase locked loop (PLL) is proposed.The unreasonable deviation of frequency and phase is corrected in the process of starting grid connection and in the condition of strong disturbance,to reduce the oscillation and out-of-control risk under the above conditions.Finally,some experimental tests are given for correctness verification of the proposed method.

Abstract:With the development of high voltage direct current (HVDC) transmission technology,hybrid multi-infeed direct current transmission become a development trend.The mechanism of double bridge commutation failure of line commutated converter based high voltage direct current (LCC-HVDC) in hybrid double-infeed system is analysized.And the major influence factors of double bridge continuous and discontinuous commutation failure are distinguished.Through simulation under different AC system fault extent and trigger time,the effect of these two factors on commutation failure types is studied,and it is found that the AC voltage waveform distortion under slight fault is the main cause of double bridge discontinuous commutation failure.Then the control parameter of voltage source converter based high voltage direct current (VSC-HVDC) is optimized by Simplex algorithm to suppress double bridge discontinuous commutation failure of LCC-HVDC in slight fault.

Abstract:This paper studies the voltage control principle of flexible DC transmission power grid.Firstly,the main 3 voltage control strategies and their characteristics are reviewed.Then the voltage control strategy for DC grids in which primary voltage regulation and secondary voltage regulation coordinate with each other is proposed.The proposed primary voltage regulation is based on the law of voltage droop control with voltage dead band whose realization method and logic diagram have been described in the paper,while the proposed secondary voltage regulation is based on the control criterion of keeping the voltage of the benchmark voltage node constant.After introducing the concept of the benchmark voltage node,the paper describes the benchmark voltage node selection method and the implementation of the secondary voltage control.A 4 terminal DC grid is constructed as the test system.Based on the test system,the design procedure for the voltage droop control with voltage dead band is described in detail.Two operation situations are tested on the test system.One is when the load of the DC grid changes and the other is when the benchmark voltage converter drops out.The results show that the proposed DC voltage control strategy has good control performance and can be used in general DC grids.

Abstract:After analyzing the development status of distribution network communication system,a power distribution communication system common information model (CIM) is constructed according to the characteristics and application requirements of electric power communication system in China.Firstly,the principle and method of CIM modeling are discussed.Secondly,the modeling instances of topological model,equipment model and asset model of communication system are constructed and analyzed in detail.Finally,model split and merge principle are studied.This research provides a method for CIM modeling of network communication system and a solid foundation for network information.

Abstract:Reliable pull-up detection and prevention of misuse warning in the operation of heat-drop bus has been a difficult problem of daily operation and maintenance of substations.In this paper,a computation method is proposed based on research on influence of system operation and contact resistor on switch currents and unbalance of three phase.With state information in bus coupler and transmission line collected,a remote forewarning method for bus switching is studied based on switcher current and degree of three-phase unbalance.The technology combined with bus protection and background monitoring system,is integrated in the model of bus protection of traditional substation or smart substation,and installed in five-anti system to forewarning the danger in bus switching.The reliability of the method is verified by simulation and operation data of actual substation.

Abstract:A protection scheme based on the ratio of energies of direction traveling waves is presented in this paper.Firstly,the propagation characteristic of fault traveling waves in a star-connected VSC-HVDC system is analyzed,and the different propagation law between fault and non-fault lines is studied.Then modal voltage and current are transformed in discrete wavelet transform (DWT),and wavelet energies of direction traveling waves are calculated.Finally,the fault line is determined by the ratio of positive and negative direction traveling waves.Simulation results of PSCAD/EMTDC show that the proposed method can identify the fault line quickly in the star-connected VSC-HVDC system.The proposed method is insensitive to different fault lines,fault distance,fault types and fault resistance,and has good robustness.

Abstract:The isolated grid which is splitting after the grid fault has become an important part of the power system.Giving priority to the isolated grid restoration has the advantage of simplifying calculation,accelerating the recovery and restoring the important load in time.It needs to be divided into several partitions in the total black state.This paper is aimed at the rapidity and stability of the restoration,comprehensively considering isolated network partitioning strategy and the restoration skeleton,introducing the shortest path algorithm and integer linear programming,proposing a new optimization algorithm for isolated network partitioning.The algorithm makes the shortest start time of unit as the objective function,constructed by the active power and reactive power balance of the unit to simplify a complex multi objective nonlinear programming problem as a single objective and multi constrained linear programming problem.New England 10-Machine 39-Bus System is used as an example to verify the effectiveness of the proposed algorithm.

Abstract:Considering the problem that efficiency of wind generation is generally low,a hierarchical distribution strategy of reactive power for DFIG wind farm is put forward to reduce the power loss of both wind turbine and wind farm.To improve the efficiency of wind generation,,the new strategy considers the stator and gird-side converters'power limitation based on the traditional reactive power distribution strategy and realizes the optimal distribution with the aim of least power loss.A simulation model of DFIG wind farm is built on MATLAB/Simulink platform.The results prove that the strategy can greatly reduce the power loss of wind turbine,improve the efficiency of wind generation and suppress voltage fluctuation caused by load changes,improving power quality.

Abstract:Because of extreme weather conditions and the limitation of the transmission power,the DC current can not meet the requirement of de-icing.And it will lead to the formation of the DC transmission line icing,affecting the stability of the UHVDC system seriously.Combined with the de-icing function in Jiuquan-Hunan UHVDC project,the main connection topological structure and characteristics of the round resistance ice mode and hybrid de-icing mode for the UHVDC project is described in this paper,and then the strategy of bipolar synchronous tripping in round resistance ice mode and the modified scheme of UHVDC control and protection function in hybrid de-icing mode are proposed.At last,the feasibility and effectiveness of the de-icing function are verified by RTDS closed loop real-time digital simulation.Reference is provided for the design of UHVDC control and protection system for the de-icing operation mode.

Abstract:This paper presents the virtual video and real-time data demonstration for smart substation inspection based on the latest wearable services such as Google glass.The inspection operator scans a kind of Quick Response Code named QR code on electrical equipment by Google glass to automatically identify the name and Identification number of related electrical equipment.Then Google glass will transmit the information to intelligent terminal by Bluetooth.The intelligent terminal acquires the key electrical parameters such as manufacturers,nameplate,the latest maintenance time and real-time operation data of the related electrical equipment from the local database.And then it projects the real-time information on the Google glass in the form of images or video according to the need of the substation inspection operators.This method can break through the difficulty of obtaining real-time data by traditional substation inspection work and improve the automation level of substation inspection.

Abstract:Subway energy feedback system can put the subway brake energy back to the power grid,to save energy and stabilize DC voltage.The design of the charging circuit is related to not only the secure operation of the energy feedback device,but also the impact on the power grid when the device is connected to the power grid.After analyzing the working principle of subway energy feedback system,AC charging and DC charging,the two design schemes are given with their charging process.Through building 1.2 MW back-to-back test platform system,the charging experiment and the grid connection experiment have been conducted.The results show that the DC charging scheme is the ideal charging scheme,not only because it meets the cut-in requirements of the subway energy feedback system,but also because its operation process is simple and reliable.

Abstract:Life prediction based on the accelerated degradation data analysis is an effective means for the reliability evaluation of intelligent watt-hour meter.In the process of design and manufacture,the early failure problem is inevitably introduced to watt-hour meter.If the early failure analysis is ignored in the accelerated degradation test,the pseudo data will be introduced to life prediction,which will lead to wrong life evaluation and the unnecessary maintenance cost and risk.In this paper,an early failure analysis method based on the accelerated degradation test data is proposed to solve the problem of the accelerated degradation test data processing of the intelligent watt-hour meter.At last,the method is verified by the analysis of a single-phase intelligent watt-hour meter,and the life assessment accuracy of the intelligent watt-hour meter is further enhanced by this method.

Abstract:According to a cracking accident of an incoming cable GIS terminal epoxy casing in a substation main transformer,the macroscopic crack morphology,the material performance and the mechanical simulation of epoxy casing are analyzed in this paper.Thinking that the root cause of epoxy casing cracking is a large installation deviation of the connection conductor and the cable terminal.So that the groove of the epoxy casing flange is operating in a state of stress close to its material strength limit for a long time,and the safety margin is insufficient.Accordingly,replacement recommendations are presented to ensure that the installation deviation should not be greater than 0.5 mm.

Abstract:A case of the unit's abnormal outage under the situation of the manual mode operation of excitation regulator was analyzed.Based on the analysis,the relationship between active power and reactive power as well as their trend under the situation of the manual mode operation of excitation regulator were discussed.The accuracy of the analysis has been proved through a simulation which reproduce the fault process.The simulation has also verified the setting value of excitation-loss protection for generation trip.The analysis results in this paper will have important reference value for the operation and maintenance of power plant.

Abstract:Static frequency converter (SFC),as the variable frequency starting device of pumping conditions,is based on the speed regulator equipment.It is mainly used to apply the torque to the unit and drag it to the desired speed,so the unit can connect to the grid.This paper expounds the basic working principle,main equipment,and function of the SFC,also analyzes and summarizes the problems and solutions in the starting process.

Abstract:Unsteady vibration occurred in the Ultra high-pressure rotor,high-pressure rotor and low-pressure rotor for a 1000MW ultra-supercritical turbine generator unit of Taizhou power plant during the debugging process seriously affects the safety and stable operation of the unit.On the base of the detailed vibration analysis,we found that rotor-to-stator rub is the main cause of the unsteady vibration of the three rotors.The field dynamic balancing experiment was proceeded,and the starting method of the unit was changed.The unsteady vibration problem was solved.