Study of a future metropolitan electric network adapted to introduction of cryogenic high-power cables

The authors have investigated the operational feasibility of a future metropolitan electric power system associated with highly densified cryogenic cables. A new concept of power system configuration with cryogenic cables and its operation have been proposed. Three different models of future power transmission systems in large cities of Japan have been constructed as the background systems prior to introduction of cryogenic cables in the 21st century. This paper considers one of the three models which is characterized by its conventional transmission system constructed mainly by 154-kV transmission lines stepping down directly from the 500-kV outer ring without any intermediate voltage class. This paper also discusses whether or not the power system model will be operated effectively together with cryogenic cables to supply demands forecasted in the period subsequent to the first decade of the 21st century. The computer simulations are carried out to obtain power flow and bus voltage distributions for a peak load period as well as for an off-peak one in the power system model. These simulations reveal that the conventional background power system should be arranged very carefully before introducing the cryogenic cables to facilitate their operations. (1) On a contingent trip of a cryogenic cable in the peak in the peak load period, not all bus voltages are expected to be kept within a tolerant zone due to the high impedance of 154-kV conventional transmission lines in the power system model. (2) Thus it is proposed that the background conventional system prior to introduction of cryogenic cables should be developed not only by extension of 154-kV conventional transmission lines but also by introduction of 275-kV lines. (3) Bus voltage rises induced in the off-peak load period are reduced by effective utilization of 275-kV conventional transmission lines.     

Ex-ante transmission-service pricing based on load-flow patterns

In this paper, a new pattern-based transmission-service pricing technique is reported. It is based on power-flow tracing techniques that determine the power contributions of participants in line power flows throughout the whole network. Since producers supply a consumer through the transmission paths considering Kirchoff's Laws, it is obvious that the actual paths are not strongly correlated with the contractual paths. This means that instead of financial paths, only the actual power-flow paths should be considered when calculating the transmission-service price. Power-flow data from previous years can be utilized for this purpose. Several power systems and different operating states that realistically represent actual system operating conditions were statistically analyzed. The analysis showed a constant pattern of power-flow shares in lines to consumers, which can be utilized in ex-ante transmission pricing for a network. Since the new approach reflects the characteristics of transaction- and nontransaction-based methods, it combines their benefits too.     

Improved Three-Phase Power-Flow Methods Using Sequence Components

The paper presents the formulation and the solution of the three-phase power-flow problem using sequence components. An improved sequence component transformer model and a decoupled sequence line model were used. As a result, the three sequence admittance matrices are decoupled with three-phase power system features in sequence components. The sequence power-flow algorithm has been formulated such that the single-phase power-flow programs can be called as routines for solving the positive sequence network. The results for the proposed sequence power-flow methods are identical to those obtained from three-phase power-flow programs developed in phase components. The computational efficiency and convergence of the proposed sequence three-phase power-flow methods show that they are as fast and as robust as conventional the Newton–Raphson method.     

A novel out of step relaying algorithm based on wavelet transform and a deep learning machine model

Out-of-step protection of one or a group of synchronous generators is unreliable in a power system which has significant renewable power penetration. In this work, an innovative out-of-step protection algorithm using wavelet transform and deep learning is presented to protect synchronous generators and transmission lines. The specific patterns are generated from both stable and unstable power swing, and three-phase fault using the wavelet transform technique. Data containing 27,008 continuous samples of 48 different features is used to train a two-layer feed-forward network. The proposed algorithm gives an automatic, setting free and highly accurate classification for the three-phase fault, stable power swing, and unstable power swing through pattern recognition within a half cycle. The proposed algorithm uses the Kundur 2-area system and a 29-bus electric network for testing under different swing center locations and levels of renewable power penetration. Hardware-in-the-loop (HIL) tests show the hardware compatibility of the developed out-of-step algorithm. The proposed algorithm is also compared with recently reported algorithms. The comparison and test results on different large-scale systems show that the proposed algorithm is simple, fast, accurate, and HIL tested, and not affected by changes in power system parameters.     

Behaviour of three-node power networks

The real power-flow equation for a three-node network is analysed in terms of its topology and geometry. It is shown that the set of feasible power injections is convex and that, for each feasible injection, there is a corresponding uniwue stable solution. Certain aspects of the behaviour of the associated swing equations are studied. This behaviour is quite different from that of a two-node network; in particular, the system may not be completely stable even when the damping is made arbitrarily large.     

Steady-state operating conditions of very long EHVAC cable lines: Two case studies

The paper deals with the operation of very long EHV AC cable lines in a well-developed bulk power system, by simulating two 400 kV-50 Hz single circuit cable lines, 80-100 km long, installed at different locations of the Italian transmission network, both standing alone and in parallel to an existing overhead line. The power transmission limits of the considered cable lines are assessed analytically, as well as the required amount of shunt compensation and its location, at line terminals or also at mid-line; a criterion for sizing mid-line shunt compensation is also proposed. In order to check theoretical analyses carried out by analytical formulas, AC load flow simulations of the transmission network with the hypothetical cable lines in place are evaluated, referring to severe loading conditions in both normal and post-contingency operation. Open-ended cable operation and shunt compensation contingencies are also addressed. Results show that power transmission limits due to cable ampacity and higher active power flows due to low cable reactance do not pose special constraints on the operation of the powerful network under examination. Appropriate shunt compensation minimizes the effects of surplus cable reactive power, allowing to operate long 400 kV-50 Hz cable lines (up to 100 km at least) with reactors at line terminals only. Moreover, if shunt compensation is installed also at mid-line, operating capabilities of the long cable lines are enhanced and losses reduced.     

New transmission planning model

A model for optimal long-range transmission planning is proposed. The model is capable of dealing with both static and dynamic modes of transmission planning. Given the existing network and anticipating a requirement for future facilities and loads, an accurate nonlinear cost function for the system is formulated. It includes both the fixed and the variable costs for all planned lines, in addition to the cost of the power losses. The cost function is minimized subject to demand satisfaction and overloading constraints. The model includes security constraints on bus voltage magnitudes and swing angles. The AC load flow solution is included in the optimization model. The results of applying the model to a previously reported power system from the literature are discussed     

交直流系统的动态无功优化

考虑直流输电系统对功率与电压的调节能力,建立了交直流系统的动态无功优化模型。模型的目标函数为交直流电网的全天网损最小,约束包括交直流系统的潮流约束、所有直流变量的控制约束、离散控制变量动态调节次数约束及节点电压的安全约束。模型求解是一个多时段非线性混合整数规划问题。以混合算法为基础,提出了交直流系统的动态无功优化混合智能算法。以PSASP 36节点系统为例,通过仿真计算验证了所建模型和算法的有效性,说明了动态无功优化在交直流输电网络中具有更大的降损潜力。     

不对称电力系统相序混合建模与三相潮流算法

由于参数不对称元件和不平衡负荷的存在,电力系统中可能出现三相不对称运行的情况。为此,文中提出一种新的不对称电力系统三相潮流计算方法。该方法采用相序混合建模方法对电网建模,并采用分解协调方式实现全网三相潮流的求解。所述方法兼具相分量法的灵活性和对称分量法的计算高效性,适用于输电网和中高压配电网三相潮流分析和故障计算。针对...     

Data-mining model based adaptive protection scheme to enhance distance relay performance during power swing

The paper presents a data-mining model based adaptive protection scheme enhancing distance relay performance during power swing for both compensated and uncompensated power transmission networks. In the power transmission network, the distance relays are sensitive to certain system event such as power swings, which drive the apparent impedance trajectories into the protection zones of the distance relay (zone-3) causing mal-operation of the distance relay, leading to subsequent blackouts. Further, three-phase balanced symmetrical fault detection during power swing is one of the serious concerns for the distance relay operation. This paper proposed a new adaptive protection scheme method based on data-mining models such as DT (decision tree) and RF (random forests) for providing supervisory control to the operation of the conventional distance relays. The proposed scheme is able to distinguish power swings and faults during power swing including fault zone identification for series compensated power transmission network during stress condition like power swing. The proposed scheme has been validated on a 39-bus New England system which is developed on Dig-Silent power factory commercial software (PF4C) platform and the performance indicate that the proposed scheme can reliably enhance the distance relay operation during power swing.     

Estimation of transmission line parameters from measurements

This paper describes the method of estimating the transmission line parameters from voltage, current, and power measurements at the two ends of the line. This becomes necessary if a new parallel transmission line is constructed between two substations due to load growth or if an underground cable replaces an overhead line and the overall parameters of the paralleled lines or the cable are desired to be determined. The parameters of the equivalent pi network of the line are obtained from the measurements at the line ends by using the Newton–Raphson method to solve the non-linear equations. The proposed method then gives the resistance/m, inductance/m, and capacitance/m, considering the distributed nature of the transmission line. The technique to determine the conductance parameter is also presented.     

电气化铁路新型电缆供电方案

电分相和电能质量问题是制约我国高速铁路发展的主要技术问题,为了适应高速铁路发展的需要,可采用新型电缆供电方式。在考虑电缆间耦合作用的基础上,计算了单相电缆的电气参数。基于电缆牵引网等值电路推导了单、复线电缆牵引网的电流分配规律与等效阻抗。以实际线路为例完成了新型电缆供电方案的设计,确定了主变电所容量、牵引变压器容量和各区段的电缆选型,并就所提方案进行了可行性验证和经济性分析。仿真结果表明,所提新型电缆供电方案在空载和负载条件下,电缆和接触网的电压水平均在相应的电压允许范围内,满足牵引供电需求;与已有牵引供电方案相比,新型电缆供电方案具有较明显的经济效益。     

基于参数识别的继电保护原理初探

从网络分析理论出发,通过建立网络响应和网络参数之间的数学模型,利用网络的全响应信号,采用模型参数识别的方法得到故障网络的故障参数信息构成保护原理。参数识别的保护原理不受系统运行方式变化的影响,不受过渡电阻和系统振荡的影响。初步研究表明,利用该原理可以解决单端电气量无系统误差的准确故障定位、快速方向元件、串补电容线路故障位置的可靠识别和小电流接地系统准确故障选线等工程难题,具有良好的应用前景。     

SDH ATM在电力系统综合业务信息网中的运用

有线电视网、电信网、计算机网三网融合正在成为全球的趋势。针对目前国内电力系统通信网络改造,利用电力系统本身特点建议以OPGM、ADSS光缆为传输媒体,以SDH、ATM以及IP设备进行组网,电力通信开始了与互联网最大限度和最快速的结合演进与渗透。     

Estimating the saddle-node bifurcation point of static power systems using the holomorphic embedding method

Voltage stability studies have been progressively gaining importance in the power engineering community. Predicting the saddle-node bifurcation point (SNBP) of a power system has become more critical as the power-system loading has increased in many places without a concomitant increase in transmission resources. Since a Newton–Raphson power-flow method is inherently unstable near the SNBP, adaptations such as continuation methods have been used as stabilizers. A new class of nonlinear equation solvers known as the holomorphic embedding method (HEM) is theoretically guaranteed to find the high-voltage solution to the power-flow problem, if one exists, up to the SNBP, provided sufficient precision is used and the conditions of Stahl’s theorem are satisfied by the equation set. In this paper, four different HEM-based methods to estimate the saddle-node bifurcation point of a power system, are proposed and compared in terms of accuracy as well as computational efficiency.     

高峰运行模式下动态优化调度的网损修正

电网高峰运行模式下在优化调度时进行网损修正，这不单纯是一个经济分配问题。高峰时供求矛盾尖锐，通过网损修正降低网损，还有助于缓解供求矛盾，缓和拥塞线路的潮流。对电网高峰运行模式在地域分布方面的特征进行的分析表明，发电机组的网损修正系数宜逐时段加以更新。文中给出了用潮流法逐时段更新网损修正系数的简捷算法。     

光纤复合相线的电气性能研究与试验方法探讨

OPPC光缆是光缆和导线的复合体,在电力网络中起到通信和电能传输的双重功能,在110 kV及以下电压等级的输配电网络中有着广阔的应用前景。文章设计并实施了OPPC光缆电气性能试验（包括耐压性能试验和载流性能试验）,检测了试验过程中OPPC光缆的光纤传输损耗及光缆表面温度的变化趋势,对OPPC光缆的电气性能及部分光缆表面温升过高的应对措施进行了研究和分析,为OPPC的实际应用和入网检测试验方法提供了有意义的参考。     

广东—海南500 kV海底电缆输电系统电磁暂态研究

海南联网工程是中国第一个500kV超高压、长距离、较大容量的跨海联网工程,也是继加拿大本土与温哥华岛交流跨海联网工程之后、世界上第二个同类工程。文章研究了广东—海南500 kV海底电缆输电系统的电磁暂态问题,主要包括电缆参数、工频过电压、单相重合闸过程中的潜供电流和恢复电压、工频谐振过电压、操作过电压等,并在此基础上分析了500 kV海底电缆可选择的绝缘水平,为国内500 kV海底电缆输电工程的建设提供了依据。     

配电系统电力电子变压器的研究

供电可靠性及电能质量一直是用户和供电部门密切关注的问题。在电网中，变压器是电能转换的最基本的元件，但常规变压器难以对供电可靠性的提高和电能质量的改善作出贡献。本文介绍了一种全新的产品一电力电子变压器，它具有提高供电可靠性、改善电能质量并且体积小、重量轻、环保效果好等一系列优点，可以较好地解决这些问题。在对电力电子变压器现有方案进行分析的基础上，本文提出了一种新的实现方案，计算机仿真结果表明：变压器原方可以实现输入电流波形为正弦称功率因数接近于1，变压器副方可以获得良好的输出电压、电流。     

基于网络分割及旁侧路径搜索的输电断面识别方法

在潮流转移特性分析的基础上,提出一种基于网络分割及旁侧路径搜索的输电断面识别方法。该方法立足图论思想构建电网拓扑模型及关系矩阵,利用网络分割简化系统结构,准确限定开断支路的输电断面存在范围;基于提出的删除添加算法建立旁侧通路路径库,获得各支路分流系数,据此识别输电断面并得到其敏感度排序。仿真结果证明所提方法的正确性与有效性。