A Steady-State Contingency Analysis of the SADC Regional Grid Using the N-1 Criterion

Southern Africa has experienced electric power deficits over the last decade. This has been due in part to the member countries＇ inadequate electrical power supply system, as well as load growth in areas which were not adequately planned for. This has induced the formation of organizations such as SADC （Southern African Development Community） and SAPP （Southern African Power Pool） that have the common goal of achieving development and economic growth in the region which comprises of 15 member countries. This paper presents results from a security analysis of the region＇s electric power supply system using a baseline level of performance. This was carried out by performing a steady-state contingency analysis on a SADC power network model subject to the N-1 criteria which expresses the ability of the power network to experience a contingency without causing an overload or failure in any other part of the network. Simulations were carried out using DigSilent.

Transmission network expansion planning with embedded constraints of short circuit currents and N-1 security

An approach of transmission network expan-sion planning with embedded constraints of short circuit currents and N-1 security is proposed in this paper.The problem brought on by the strong nonlinearity property of short circuit currents is solved with a linearization method based on the DC power flow.The model can be converted to a mixed-integer linear programming problem,realizing the optimization of planning model that considers the constraints of linearized short circuit currents and N-1 security.To compensate the error caused by the assump-tions of DC power flow,the compensation factor is pro-posed.With this factor,an iterative algorithm that can compensate the linearization error is then presented.The case study based on the IEEE 118-bus system shows that the proposed model and approach can be utilized to:opti-mize the construction strategy of transmission lines;ensure the N-1 security of the network;and effectively limit the short circuit currents of the system.

配电系统安全域的体积

该文提出了配电系统安全域(distribution system security region,DSSR)体积的概念与算法,分析了DSSR体积对电网的意义。首先,对DSSR体积进行了定义,DSSR描述了配电系统满足N-1安全的运行范围,体积是DSSR大小的度量。其次,提出了DSSR高效运行区的体积定义。再次,提出了基于蒙特卡罗仿真的DSSR体积算法。最后,通过算例验证了体积算法,并进一步研究了体积的用途。DSSR体积能提供一些最大供电能力(total supply capacity,TSC)无法给出的重要信息,选取TSC相同但DSSR体积不同的电网比较,发现体积大的电网具有更好的安全性能,在各个负荷增长方向上的安全裕量更均衡。该文提出的DSSR体积是反映配电网安全性能的新指标,对未来配电网的规划和运行具有重要的应用价值。

基于最优潮流并计及静态电压稳定性约束的区域间可用输电能力计算

可用输电能力(ATC)是衡量电力系统在安全稳定运行的前提下区域间功率交换能力的指标。文中基于最优潮流(OPF)方法,建立起符合电力市场交易机制的ATC计算模型,其中考虑到输电线路故障对系统静态电压稳定性的影响,加入线路N-1故障时广义参数化形式的潮流方程及相应的不等式约束条件,使系统在故障时仍有负荷裕度,以保持电压稳定;以支路功率和系统负荷裕度之间的灵敏度指标进行预想故障选择,并用原对偶内点法计算得到输电线路N-1安全约束下的区域间可用输电能力。IEEE30和IEEE118节点系统算例表明该模型和算法的正确性与有效性。

兼顾供电能力和安全裕度的智能配电网协调运行优化方法

配电网的供电能力直接影响到其供电可靠性,而现有供电能力模型解均是资产效率最大化下的N?1安全临界值,未达到配电网实际运行所需满足的安全裕度要求,使得其在负荷波动等不确定因素影响下适应性较差。针对这一问题,提出一种兼顾供电能力和安全裕度的配电网协调运行优化方法。首先,基于配电网安全距离模型,定义了安全距离均值、安全距离均衡度和安全距离均衡比3个量化描述N?1安全裕度的指标。其次,将供电能力充盈度最小和安全距离均衡比最小作为目标函数,给出了相应的优化模型,并利用正态边界交点联合序列二次规划算法对模型加以求解。最后,通过算例仿真,与现有文献方法对比,给出了2个不同情景下的N-1安全裕度校验分析。结果表明,该方法协调优化了社会经济性和供电安全性,提高了配电网抵御负荷波动的能力,对调度运行人员具有指导意义。

MLRM法预估含风电场系统静态电压稳定裕度

对含风电场的复杂电网,计及负荷及风电场出力的随机性,快速预测电网稳定性有利于电力系统安全运行,并为电网调度提供参考。多元线性回归法(MLRM)可在离线计算的基础上,利用离线计算结果快速、在线预估电网的静态电压稳定性。具体过程是:基于连续潮流,采用蒙特卡罗仿真法离线计算系统静态电压稳定裕度(SVSM)真值,作为SVSM预估样本空间;采用MLRM建模,将影响系统电压的发电机节点无功备用作为解释变量,蒙特卡罗法所得SVSM为被解释变量,建立多元线性回归方程,求得回归系数;在线预估系统SVSM。对接入风场的改进IEEE-14及IEEE-118算例进行仿真计算,结果说明了MLRM方法用于在线预估电网静态电压稳定的有效性。

Distribution management system framework based on security region for future low carbon distribution systems

In this paper,a new Distribution Management System(DMS)framework based on security region is proposed.First,the concept of Distribution System Security Region(DSSR)is introduced.DSSR is capable to describe the N-1 security boundary of the whole distribution network,including the secure output range of DGs.This new theoretic tool provides a chance for the implementation of real-time security analysis and active controls in DMS.Second,this paper proposes and describes five security states for distribution system.Third,an upgraded DMS enhanced with DSSR is proposed,which consists of advanced security functions such as preventive and predictive control of the trajectory of operating points.Finally,a practical case is presented to simulate the proposed DSSR-enhanced DMS,in which both the security region of network and the output range of DGs are calculated.Typical security functions are also demonstrated.In conclusion,the new DMS framework aims to help operate the system closed to its security boundary in order to improve the efficiency significantly within same security standard.This work is beneficial for future low carbon distribution systems with high penetration rate of DGs.

Total Quadrant Security Region for Active Distribution Network with High Penetration of Distributed Generation

The region-based method has been applied in transmission systems and traditional passive distribution systems without power sources. This paper proposes the model of total quadrant security region(TQSR) for active distribution networks(ADN) with high penetration of distributed generation(DG). Firstly, TQSR is defined as a closed set of all the N-1 secure operation points in the state space of ADN. Then, the TQSR is modeled considering the constraints of state space,normal operation and N-1 security criterion. Then, the characteristics of TQSR are observed and analyzed on the test systems with different DG penetrations. TQSR can be located in any quadrant of the state space. For different DG penetrations,the shape and security features of TQSR are also different. Finally, the region map is discovered, which summarizes the features of different types of distribution networks.

Reconfiguration in the Transmission System of the Slovak Republic

Topology changes （reconfigurations） in the transmission system are effective remedial actions to restore fulfilling N-I security principle. In the transmission system, Slovak Republic prepares several scenarios of possible reconfigurations, especially in the substation Varin and substation Lemesany. The paper describes reasons of reconfiguration necessity, preparation process, testing process, test results and comparison with expected results from simulation calculations. The conclusion summarizes advantages and disadvantages of the reconfiguration implementation in the transmission system, recommendations for real-time operation, including coordination with neighbouring transmission system operators and affected distribution system operators.

Dynamic-decision-based Real-time Dispatch for Reducing Constraint Violations

This paper proposes a dynamic-decision-based realtime dispatch method to coordinate the economic objective with multiple types of security dispatch objectives while reducing constraint violations in the process of adjusting the system operation point to the optimum.In each decision moment,the following tasks are executed in turn:①locally linearizing the system model at the current operation point with the online model identification by using measurements;②narrowing down the gaps between unsatisfied security requirements and their security thresholds in order of priority;③minimizing the generation cost;④minimizing the security indicators within their security thresholds.Compared with the existing real-time dispatch strategies,the proposed method can adjust the deviations caused by unpredictable power flow fluctuations,avoid dispatch bias caused by model parameter errors,and reduce the constraint violations in the dispatch decision process.The effectiveness of the proposed method is verified with the IEEE 39-bus system.

A diagnostic method for distribution networks based on power supply safety standards

In order to overcome the shortages of diagnostic method for distribution networks considering the reliability assessment,this paper proposed a method based on power supply safety standards.It profoundly analyzed the security standard of supply for urban power networks,and established quantitative indicators of load groups based on different fault conditions.Then a method suitable for diagnostic evaluation of urban distribution networks in China was given.In the method,“N-1”calibration analysis of the distribution network was conducted.Then the results are compared with quantitative indicators of load groups on different conditions deriving the diagnostic conclusions and the standard revision is discussed.The feasibility and accuracy of the method is finally verified in the case study.

Exploiting Flexibility of Integrated Demand Response to Alleviate Power Flow Violation During Line Tripping Contingency

Multi-energy integrations provide great opportunities for economic and efficient resource utilization. In the meantime, power system operation requires enough flexible resources to deal with contingencies such as transmission line tripping. Besides economic benefits, this paper focuses on the security benefits that can be provided by multi-energy integrations. This paper first proposes an operation scheme to coordinate multiple energy production and local system consumption considering transmission networks. The integrated flexibility model, constructed by the feasible region of integrated demand response(IDR), is then formulated to aggregate and describe local flexibility. Combined with system security constraints, a multi-energy system operation model is formulated to schedule multiple energy production, transmission, and consumption. The effects of local system flexibility on alleviating power flow violations during N-1 line tripping contingencies are then analyzed through a multi-energy system case. The results show that local system flexibility can not only reduce the system operation costs, but also reduce the probability of power flow congestion or violations by approximately 68.8% during N-1 line tripping contingencies.