阿里与藏中联网工程联网通道故障后保网方案

2020年,阿里与藏中联网工程投运,结束了西藏阿里地区孤网运行的历史。阿里电网与藏中电网通过长链式通道互联,联网通道故障中断后,阿里电网频率与电压稳定问题交互影响,电网面临失稳风险。建立联网工程的仿真模型,分析联网通道故障后阿里电网的稳定特性,研究五种保网方案的可行性,提出合理的解列控制措施和保网方案。从保障电网安全稳定运行和提高资源利用效率的角度,提出整合日喀则和阿里地区现有稳定控制系统的工程建设方案和运行策略。

Design and testing of a centralized protection scheme for micro-grids

Micro-grids comprise low voltage distribution systems with distributed energy resources(DERs) and controllable loads which can operate connected to the medium voltage grid or islanded in a controlled coordinated way. This concept aims to move from "connect and forget" philosophy towards a full integration of DERs. Micro-grids can provide numerous economic and environmental benefits for end-customers, utilities and society. However, their implementation poses great technical challenges, such as a new philosophy in design of protection systems. In this work, a micro-grid protection scheme is presented based on positive-sequence component using phasor measurement units(PMUs) and a central protection unit(CPU). The salient feature of the proposed scheme in comparison with the previous works is that it has the ability to protect both radial and looped micro-grids against different types of faults with the capability of single-phase tripping. Furthermore, since the CPU is capable of updating its pickup values(upstream and downstream equivalent positive-sequence impedances of each line) after the first change in the micro-grid configuration(such as transferring from grid-connected to islanded mode and or disconnection of a line, bus, or DER either in grid-connected mode or in islanded mode), it can protect micro-grid against subsequent faults. Finally, in order to verify the effectiveness of the suggested scheme and the CPU, several simulations have been undertaken by using DIg SILENT Power Factory and MATLAB software packages.

Additional Overloading Assessment for Future Low Voltage Networks Based on Smart Metering

The purpose of this article is to present an additional overloading assessment scheme to the current protection scheme, which can be applied in the low voltage distribution network to prevent overloading of network assets. As higher penetration of distributed generators is envisioned among distribution networks, the network operators will have an challenging task in the future to maintain the reliability and quality of supply. The distribution networks are going to be challenged simultaneously by increasing penetration of distributed generators and by increasing loading （inter alia heat pumps, air conditioners or electric vehicles）, which will change the operational perspective of the future distribution networks. Presented simulation results show that the increasing penetration of those appliances can jeopardize the functionality of current protection scheme in distribution networks. Therefore, an additional scheme for assessment of network overloading applicable at low voltage distribution networks is proposed and the application of this scheme, supported by smart metering infrastructure, is demonstrated in a case study. The proposed overloading assessment scheme should help the network operators to increase the flexibility of distribution networks, their hosting capacity, safety and reliability.

A secure routing scheme based on social network analysis in wireless mesh networks

As an extension of wireless ad hoc and sensor networks, wireless mesh networks(WMNs) are employed as an emerging key solution for wireless broadband connectivity improvement. Due to the lack of physical security guarantees, WMNs are susceptible to various kinds of attack. In this paper, we focus on node social selfish attack, which decreases network performance significantly. Since this type of attack is not obvious to detect, we propose a security routing scheme based on social network and reputation evaluation to solve this attack issue. First, we present a dynamic reputation model to evaluate a node's routing behavior, from which we can identify selfish attacks and selfish nodes. Furthermore, a social characteristic evaluation model is studied to evaluate the social relationship among nodes. Groups are built based on the similarity of node social status and we can get a secure routing based on these social groups of nodes. In addition, in our scheme, nodes are encouraged to enter into multiple groups and friend nodes are recommended to join into groups to reduce the possibility of isolated nodes. Simulation results demonstrate that our scheme is able to reflect node security status, and routings are chosen and adjusted according to security status timely and accurately so that the safety and reliability of routing are improved.