Security Constrained Distributed Optimal Power Flow of Interconnected Power Systems

The security constrained distributed optimal power flow (DOPF) of interconnected power systems is presented. The centralized OPF problem of the multi-area power systems is decom-posed into independent DOPF subproblems, one for each area. The dynamic security region (DSR) to guarantee the transient stability constraints and static voltage stability region (SVSR) constraints, and line current limits are included as constraints. The solutions to the DOPF subproblems of the different areas are coordinated through a pricing mechanism until they converge to the centralized OPF solution. The nonlinear DOPF subproblem is solved by predictor-corrector interior point method (PCIPM). The IEEE three-area RTS-96 system is worked out in order to demonstrate the effectiveness of the proposed method.

Prediction of Instability Separation Modes and Its Application in Practical Dynamic Security Region

The transient critical boundary of dynamic security region (DSR) can be approximated by a few hyper planes correlated with instability separation modes. A method to fast predict instability separation modes is proposed for DSR calculation in power injection space. The method identifies coherent generation groups by the developed K-medoids algorithm, taking a similarity matrix derived from the reachability Grammian as the index. As an experimental result, reachability Grammian matrices under local injections are approximately invariant. It indicates that the generator coherency identifications are nearly consistent for different injections. Then instability separation modes can be predicted at the normal operating point, while average initial acceleration is considered as the measure of the critical generator group to amend the error. Moreover, based on these predicted instability separation modes, a critical point search strategy for DSR calculation is illustrated in the reduced injection space of the critical generators. The proposed method was evaluated using New England Test System, and the computation accuracy and speed in determining the practical DSR were improved.

Surface Breakdown of Printed Circuit Board under Magnetic Field with Reduced Pressure

Epoxy resin laminate onto which a pair of copper foil was printed was employed as test samples.The samples were placed in an artificial atmospheric chamber, which was vacuumed by a rotary pump from 100 kPa to 5 kPa.The magnetic field was produced by permanent magnets that were assembled to make E×B drift away from, into and parallel to the sample surface, respectively.Magnetic flux density was adjusted at 120 mT, 180 mT and 240 mT respectively.By applying a negative bias voltage between the electrodes, the time to surface breakdown was recorded.Obtained results show that when E×B is into the surface, the time to the breakdown is shortened;when E×B is away from the surface, the time to the breakdown is delayed;when E×B is parallel to the surface, the time to the breakdown remains approximately the same as the case without magnetic field.With the decrease of pressure, the time to the breakdown increases and the effect of magnetic field on breakdown appears to be strengthened.

Chaos Analysis of Discharge Current Based on Tracking Test of Phenolic Resin

In tracking test, discharge is a complicated process and comparative tracking index (CTI) has wide varia-tion. To evaluate tracking resistance, the chaos analysis of discharge current is presented based on the tracking test of phenolic resin in accordance with IEC60112. According to the characteristics of statistical self-similarity and complexity of discharge current, the largest Lyapunov exponent is calculated, and the 2-dimensional attractor of discharge current is reconstructed. Moreover, the attractors of discharge current and recurrence plots of different discharge states are reconstructed. The results indicate that the chaos attractors have different characteristics in evo-lutionary tracks, the topological structure and grain direction of recurrence plots show significant differences. The chaos attractor can describe the tracking process, the recurrence plot can identify the tracking state clearly, while its arithmetic is simple.

Single Phase-to-Ground Fault Line Identification and Section Location Method for Non-Effectively Grounded Distribution Systems Based on Signal Injection

A diagnostic signal current trace detecting based single phase-to-ground fault line identifica- tion and section location method for non-effectively grounded distribution systems is presented in this paper.A special diagnostic signal current is injected into the fault distribution system,and then it is detected at the outlet terminals to identify the fault line and at the sectionalizing or branching point along the fault line to locate the fault section.The method has been put into application in actual distribution network and field experience shows that it can identify the fault line and locate the fault section correctly and effectively.

Island partition of the distribution system with distributed generation

In this paper, a novel optimum island partition model based on Tree Knapsack Problem (TKP) is presented for the distribution system integrated with distributed generation (DG), and a Depth-first Dynamic Programming Algorithm (DPA) is used to solve this model. With the considerations of the load priority, controlled/uncontrolled loads, and the constraints of power balance, voltage and equipment capacity, the model can meet the practical engineering requirements very well. The island partition problem of the distribution system integrated with multiple DGs is first decomposed into multiple TKPs, each of which is solved by DPA respectively. Then, the initial optimum island partition scheme is gained through an island combination procedure, and the final island partition scheme is obtained after feasibility checking and adjustment. Since the algorithm proposed owns the advantages of strong theoretical foundation and low computational complexity, it can find the approximate optimal solution within a limited time. The results of examples demonstrate the validity of the new model and algorithm.

A new method of frequency-dependent network equivalence for power system

Electromagnetic transient simulation for large-scale power system is a time-consuming problem.A new frequency-dependent equivalence method is presented in the paper,which might significantly accelerate power system electromagnetic transient simulation.In the method,an effective algorithm is designed to directly transfer the port admittance determinant of external system's mixing matrix into admittance rational function;and the step-by-step strategy for the equivalence of actual large system is put forward,which further reduces the calculation quantities needed.Moreover,the study of multiple real root pole characteristics of admittance transfer function of two-port network is performed and a proposition is achieved.Based on the proposition and residue theorem,the equivalence system for external system corresponding to the admittance rational function is obtained.The computation complexity of the step-by-step equivalence method is about o(┌n/np×T┐)(┌┐ is upper integral operation,n is the total buses number of external system,N P is the total buses number of single step equivalence network,T is single step equivalence time),which indicates that the computation complexity of the method proposed has nearly linear relationship with the buses number of external system,and the method proposed has satisfactory computation speed.Since the mixing matrix of external system includes all the information of external system,therefore,port admittance rational function derived from it can reflect its full frequency characteristic and the equivalence network achieved has high equivalence precision.Moreover,since the port rational function is gained at the condition of the external system without source,which equals stable passive network,it could not show any unstable pole and need not extra measure to make the equivalence system stable.The test results of the samples and comparison with other methods demonstrate that the new method proposed is valid and effective.

Frequency-Feedback Based Islanding Detection Algorithm for Micro-Grid

The unintentional islanding of micro-grid may cause negative impacts on distribution loads and distributed generations,so it must be detected within the acceptable duration.In this paper a new islanding detection algorithm is proposed.This algorithm introduces the frequency feedback method by the reactive power compensation to derive the frequency continuous shift. Accordingly,the islanding can be detected by monitoring the frequency within 0.1 s.The simulation results prove that this algorithm has extremely small non-detection zone,and meanwhile it presents an excellent islanding detection speed as well.

Equivalence of stability criteria for time-delay systems

During the past few decades,there have been a number of new delay-dependent stability criteria based on linear matrix inequalities published in the literature.These criteria,to some extent,can reduce the conservativeness.In fact,some criteria are equivalence.In this paper,we aim to theoretically establish equivalence of two stability criteria.One was obtained by Sun et al.[Sun et al.In:Proceedings of IEEE Power&Energy Society General Meeting.2009,1–7]and the other was given by Xu et al.[Xu et al.IEEE Transactions on Automatic Control,2005,50(3):384–387].Also,we theoretically establish equivalence of the robust stability criterion presented by Jia et al.[Jia et al.Automation of Electric Power Systems,2010,34(3):6–11]and the one given by Xu et al.(2005).

Overvoltage Suppression for UHV Transmission Lines

The overvoltage phenomena of ultra high voltage (UHV) transmission lines are analyzed and verified by EMTDC/PSCAD simulation. Referring to the theoretical analyses and operating experiences of extra high voltage (EHV) transmission lines in China and UHV transmission lines in Russia and Japan, the methods to suppress the internal overvoltage in UHV transmission lines by protection and control strategies are discussed. Through the cooperation among the recloser, shunt reactor, tripping and closing resistance, and metal oxide varistor(MOV), the overvoltage can be restrained within an acceptable level.