Abstract:Wind energy efficiency（WEE）is used to estimate the net contribution of CO2 emission reduction from wind-generated electricity，which is an essential index to measure the efficiency of a power grid to accommodate wind energy.This paper takes into account that Chinas power grids mainly consist of coal-fired units，and it analyzes the cost components in accommodating wind power by means of unit commitment.This paper reveals how WEE changes with the operation modes and the parameters of coal-fired units，and the wind utilization proportion both in theory and by case study.The results show that the rules，approaches，prediction needs are quite unique in a coal power plant intensive grid.In addition，theory basics of wind-coal coordinating operation is provided in this paper.

Abstract:In the operation and planning of power systems，it is important to model the dependence of random wind energy in order to get accurate results.Different from the widely used linear correlation analysis，the Copula function is introduced for modeling the dependence structure of wind speed and wind power among different wind farms，and the joint distribution functions of wind speed and wind power are established respectively.By studying the actual wind speed data from four wind farms in Jiuquan of Gansu province，it is found that wind speed correlation between each two wind farms shows unsymmetrical thick tail characteristic.As this phenomenon cannot be described by a single kind of Copula function，a mixed Copula function，i.e.convex combination of some single Copula functions，is constructed based on selecting the candidate single Copula functions according to goodness of fit test.By studying the actual wind power data from two wind farms in Fujian province，it is found that Gumbel-Copula function is suitable for modeling the dependence structure between output power of two wind farms.A four-dimensional dependence structure model for wind speed is finally presented.

Abstract:In order to enhance the reliability of a generation system，battery energy storage system（BESS）is incorporated into a wind farm to constitute a hybrid wind/energy storage power station.Based on the Well-being theory，sequential Monte Carlo simulation technology is utilized to assess the reliability of the hybrid system，the probability of system integrity，of safety margin and of risk indices are obtained.Any incomplete charge-discharge cycle is forbidden，and two battery operation strategies are proposed to limit battery charge and discharge behavior.Simulation results on IEEE Roy Billinton test system（RBTS）demonstrate that incorporation of BESS can dramatically improve the reliability of generation system with wind farms;the optimized battery operation strategy mitigates the operation risk and improves the comfort of system operation;wind farms connected with suitable capacity of the battery can improve system economical performance and reliability.Finally，the results show that reliability indices based on the Well-being theory have an advantage on the reliability analysis of generation systems with BESS.

Abstract:With the ever-increasing penetration level of wind power，the impacts of wind power on the power systems are becoming more and more significant.Hence，it is necessary to systematically examine its impacts on the small signal stability and transient stability in order to find out countermeasures.As such，a comprehensive study is carried out to compare the dynamic performances of power system respectively with three widely-used power generators.First，the dynamic models are described for three types of wind power generators，i.e.the squirrel cage induction generator（SCIG），doubly-fed induction generator（DFIG）and permanent magnet generator（PMG）.Then，the impacts of these wind power generators on the small signal stability and transient stability are compared with that of a substituted synchronous generator（SG）in the WSCC three-machine nine-bus system by the eigenvalue analysis and dynamic time-domain simulations.Simulation results show that the impacts of different wind power generators are different under small and large disturbances.

Abstract:Considering the low voltage ride through（LVRT）requirement and weak-infeed feature of wind farms，the fault characteristics of a centralized wind farm is analyzed firstly based on doubly-fed wind power generation system.Since the Crowbar protection contributes to the positive and negative sequence impedances，especially the former，the wind farm weak-infeed characteristics are strengthened.On that basis，the performance of distance protection of wind farm grid connection line is analysed.The results show that the Crowbar and weak-infeed property of wind farm may cause wrong phase selection and affect the precision of impedance protection relay.Some countermeasures are also proposed.Finally，a doubly-fed wind farm is simulated，and the simulation results demonstrate the validity of the theoretical analysis.

Abstract:Owing to the inherent intermittence，fluctuation，and low predictability，integrating large-scale renewable power generation into bulk power grids has posed significant challenges to system operators.One of the key issues is how to guarantee safe operation at minimum cost where renewable power generation seriously deviates from prediction.Motivated by such considerations，this paper proposes a generalized concept and implementation framework of robust and economical scheduling，whose theoretical foundation is boiled down to the robust feasibility problem，which is actually a two-move zero sum game between nature and the decision maker.Moreover，a systematic solution algorithm is developed for the robust and economical scheduling problem.By gradually cutting off non-robust feasible solutions，the final robust solution will be immunized against all possible realization of uncertain renewable power generation and minimize the scheduling cost.

Abstract:The impact of time-varying lightning on electrical equipment fault probability is analyzed.Based on the information to be acquired for preventing lightning disaster，a spatial-temporal variation forecast algorithm for power grid fault probability is presented.First，according to the lightning information of the current time interval，the lightning subareas are duly divided，which should be associated with the subareas in the preceding time interval.Then，according to the results，the trend of lightning fault probability in the next time interval is forecasted.The spatial-temporal distributed prediction probability is used to replace the traditional average annual lightning fault probability in the method which updates the envisioned fault table of the security stability analysis software online，enables the faults with greater probability to get detailed analysis in time and realizes the integration with power system security stability analysis function.The self-adaptive ability to deal with lightning disaster is added to actual projects of the blackout prevention system to improve the early-warning ability.

Abstract:A vulnerability assessment model for cascading failures of complex power grid based on effect risk entropy and the implementation of algorithms are discussed.First，a branch vulnerability assessment model is proposed by referring to the power flow transfer and its distribution characteristics after branch outage，and the impact of disconnected branch on the power system is also taken into account in the model.Then，the vulnerability transitive relation between nodes is considered，and the method is able to overcome the existing inadequacy of currently used social network index and system science index.Finally，the risk uncertainty faced by the grids structure is identified based on vulnerable components assessment results.The test on an IEEE39-bus system demonstrates the rationality and validity of the method proposed in comparison with other methods available.

Abstract:According to the transient instability detection method based on the perturbed voltage trajectories，methods for wide-area monitoring scheme designing and instability threshold setting are discussed.Besides，the applicability and feasibility of the proposed method in the actual application process are analyzed.Numerical simulations are conducted for an IEEE39-bus system and an actual power system of China Southern Power Grid，including the vulnerability analysis of bus voltage，voltage observation scheme design and transient stability detection under different fault conditions.Compared with conventional methods，the simulation results show that the proposed method can more effectively and quickly identify the transient instability of the system，and is easy to apply in projects.This method can be used for an incomplete wide-area measurement environment.

Abstract:This paper presents a replacement strategy for an aged transformer based on condition monitoring and system risk.The condition monitoring measurements are used to estimate the insulation age of the transformer.The unavailability because of transformer aging failure is calculated using the insulation age instead of the traditional natural age.The system risk is assessed using the total unavailability from both aging and repairable failures.The expected damage cost and benefit due to delaying the replacement of the transformer are evaluated.The best replacement timing is determined as the year when the replacement of the transformer reaches the maximum net benefit.A case study for two aged transformers in a utility system demonstrates the effectiveness of the proposed method.

Abstract:The calculation accuracy of total supply capability（TSC）for power distribution network is investigated.Both the currently used model method and analytical method of TSC calculation for power distribution network as reported in literature are based on interconnections between substation transformers.Their TSC results failed to pass the N-1simulation test，which is a proof that there exist definite errors with these methods.A new model and its calculating method for TSC are proposed based on interconnections between feeders，which takes into account the contingencies of both substation transformers and feeders，plus an overall consideration of the network topology.The calculating method is capable of calculating the load of each feeder when the distribution system is operating at TSC.A case study is presented to compare the proposed method and the two typical methods available.The results of the N-1simulation show that the TSC result is on the boundary of N-1security，which means the proposed feeder-based TSC model is accurate.

Abstract:The purpose of the load aggregator（LA）is to provide demand response resources with potential product value and an opportunity to participate in electricity market regulation，make full use of demand-side resources by professional techniques and measures，and provide ancillary services to other market participants.Based on LA researches and experience across the world，an overview on the definition and function of LA is conducted from the perspective of integrating demand response resources.Control resources of LA are classified into three categories，i.e.the adjustable load，the energy storage and distributed generation.Then two key problems are discussed in detail，the operation mechanism，dispatch and control strategy，and the differences between LA and other participants are described.Finally，based on the overview of the existing aggregators and the actual situation in China，measures to promote the business model of LA in China are proposed.

Abstract:According to the new characteristics of the smart substation automation system，a model for quantitatively evaluating the capacity effectiveness of the system in task fulfillment is proposed.The evaluation system composed of a physical network architecture，a logical network architecture，and the information flow，or thetwo networks one flowplatform for short is set up firstly.The effectiveness is defined as the total index which involves reliability，availability，real time and economy in the index system.Then，an analytic network process（ANP）model is developed to describe the complex relationships of influencing factors and calculate the network synthetic rank by the weighting，test and modulation of judgment matrixes.Finally，the stability of the ANP evaluation model and the credibility of scheme rank are tested by the ANP sensitivity analytical method to help evaluation decision-making.

Abstract:The smart substation does follow the IEC61850standard and its system configuration process，but there exists the problem of version management with its configuration file.By analyzing the relevant provisions of configuration version in IEC61850Ed.2.0，a method of generating the cyclic redundancy check（CRC）code for the virtual terminal connection configuration is put forward.Based on the standard file version and CRC code，a smart substation configuration file management scheme is put forward to realize simple management of virtual terminal configuration.

Abstract:A digital simulation technique for wide area measurement system（WAMS）time delay is designed and implemented based on an analysis of the cause of WAMS time delay and the measured statistics results.Power system tasks based on WAMS are divided into soft real-time tasks and hard real-time tasks in the simulation process.The large step sub-process and the small step sub-process are adopted to simulate soft real-time tasks and hard real-time tasks at the same time，respectively.The small step sub-process produces the real-time measured values affected by the time delay at each simulation step.The large step sub-process produces measured values affected by the time delay and its time scale at each WAMS measuring step.The simulation technique presented for WAMS time delay has the following advantages:firstly，the time delay randomly generated according to a particular distribution or a sequence of measured time delay data can be simulated;secondly，on this basis，abnormal network status data，such as package loss，stick package，communication failure，can be simulated.Finally，the simulation technique for WAMS time delay is programmed in a real-time digital simulator（RTDS）.The random time delay and the measured time delay are tested in an RTDS to verify the effectiveness of the simulation technique，which is suitable for verifying the effects of time delay on the wide area controller in theory.

Abstract:The application of the power network automatic switching system in the regional power grid energy management system（EMS）is introduced.The logic modeling is built in the EMS.The logic judgment is realized by using the substation telemetering，telesignaling and other real-time information collected by EMS.In the event of a fault，the automatic switching system uses the way of remote operation to disconnect the power supply，and to switch on emergency power supply.This paper introduces the unified representation of network switching logic，the complex connection and operation mode of power grid fault recovery process，and the method for the automatic generation of model.System architecture can ensure safety with a variety of measurement ensuring the system security and reliability.Engineering application indicates that the power network automatic switching system can effectively improve the reliability of power supply.

Abstract:According to the steady state mathematical model of modular multilevel converter（MMC），a discrete mathematical model of MMC is developed.Based on which，a discrete inner-loop current controller of MMC is designed.The positive-negative sequence passive controller based on an Euler-Lagrange mathematical model of MMC is proposed to suppress negative sequence current due to DC transmission system faults.In order to maintain certain active power delivery，the active power control strategy under fault condition is adopted.Finally，a21-level system simulation model of MMC high voltage direct current（MMC-HVDC）transmission system is built in PSCAD/EMTDC.The results show that the proposed control method has a good control effect on the transient and steady state process and can provide reference to actual projects for its simple structure.

Abstract:For grid-connected inverter with LCL filter which uses active damping control strategy，the grid-connected inverter with current feedback LCL filter is able to operate stably.Its inverter-side parameter is relatively stronger and its control parameter design is relatively more simple.However，the grid current contains a lot of low-order harmonic current.The reason for producing low-order harmonic current is analyzed from the aspect of control so as to obtain the effect of suppression on low-order harmonic current from LCL filter parameters and control parameters of current loop.The design method for LCL filter and control parameters is derived based on results of above analyses.The experimental results verify that the proposed method for parameter design is accurate and valid.

Abstract:In view of the limitations of load distribution for the automatic generation control（AGC）power plant in Guangdong power grid，an optimal load distribution method based on real-time coal consumption is presented.By taking into account a variety of constraints including the regulation speed，critical load points and reserve，the problem is solved with the dynamic programming algorithm and economy of load distribution for AGC power plant is realized on the premise of satisfying the safety of power grid control.The overall architecture，mathematical model，solution algorithm and allocation process for the optimal load distribution system are described in detail.The actual system is being applied in Guangdong power dispatching center.Comparison with the traditional load distribution method shows that the proposed method can effectively reduce coal consumption of the power plant and improve economic returns.

Abstract:DC line fault recovery improves reliability of DC system.However，impacts on frequency and voltage of weak receiving systems are serious.This paper studies DC line fault recovery schemes of weak receiving systems.The operation sequence of a typical DC line fault recovery is firstly introduced，and impacts of DC line fault recovery on the second and third defensive line of power systems are analyzed.It is indicated that DC line fault recovery and low-frequency load shedding may lead to cascading faults without well coordination.Then，principles for the coordination are put forward，and a assessment of schemes for DC line fault recovery and its flow chart are proposed.Candidate schemes of DC line fault recovery are analyzed，and regulations of system operation are suggested.Finally，schemes for DC line fault recovery of a weak receiving system are studied，and operation suggestions are given.Simulation results demonstrate the effectiveness of the proposed criteria and methods.