DC networks, power quality and plant reliability

电能通过电网从发电机输送到客户，历史上一直基于高压交流(HVAC)技术。这是二十世纪的一大成功，使发达国家能够可靠和稳定地供应能源。这项技术之所以占主导地位，部分原因是能够利用变压器轻松有效地改变电压水平。高压直流输电(HVDC)的替代技术在历史上仅用于点对点链路，因为在这种情况下具有特殊的优势。然而，现在，随着电力电子技术的出现，高压直流输电系统在世界各地的使用量正在迅速增加。随着可再生分布式能源供应的增长，这一趋势得到了加速，例如英国的海上风电场。因此，当地和国际能源供应正变得依赖高压直流输电。因此，直流技术的可靠性变得至关重要，因为它们越来越多地嵌入到电源网络中。然而，与交流系统相比，对高压直流输电下的绝缘和电厂可靠性的了解还处于起步阶段。同时，直流电厂的工作环境没有很好的记录，实际上，直流系统和任何其他系统一样，具有交流纹波、脉冲和电压变化，这些时变波形可能控制工厂的老化和可靠性。该项目由来自曼彻斯特大学、斯特拉斯克莱德大学和帝国理工学院的国际领先的研究人员组成。他们带来了互补的专业知识，组成了一个独特的团队来解决这个问题。Tim Green教授(Imperial)是利用电力电子技术提高电力网络的可控性和灵活性的专家；Simon Rowland教授(曼彻斯特)是高压绝缘材料老化方面的权威；Brian Steward教授(Strathclyde)在高压系统的状态监测和绝缘诊断方面拥有独特的经验。该项目旨在将这项工作嵌入全球社区，特别是与中国的研究人员联系在一起，那里正在开发最大的系统。该项目将首先确定真实高压直流网络或链路中工厂绝缘所经历的电压分布，因为在真实系统中，网络上的电压不是恒定的固定值。作为正常运行的一部分，为直流网络供电的电源变流器会产生高频元件形式的固有“噪声”，并在响应故障条件和紧急过载时产生电压扰动。确定这些特性是全面研究直流电能质量如何影响高压绝缘寿命的第一步。然后，该团队将通过实验室探索，根据已知的直流电能质量水平，开发聚合物绝缘的寿命模型。重点将放在宽频率范围内的交流纹波上。此外，将考虑不同级别和持续时间的快速瞬变信号的影响，如上所述。第三个实验主题是开发工具，用于在实际直流电缆环境中监控暂态信号和电能质量，并支持后续解释。最后，我们将为有关可接受的直流电能质量的公用事业政策文件提供意见。我们还将为设备制造商提供最佳绝缘设计的证据，并为公用事业公司提供资产管理建议。通过这些手段，我们希望降低英国对直流网络日益增长的依赖的风险，并优化设备和系统设计和运营。

The movement of electrical energy from generators to customers, through electricity networks, has historically been based on High Voltage Alternating Current (HVAC) technology. This has been a major success of the twentieth century, enabling reliable and stable energy supplies across the developed world. The technology dominated partly as a result of the ability to change voltage levels readily and efficiently using transformers. The alternative technology of High Voltage Direct Current (HVDC) has historically only been used for point-to-point links because of particular advantages in this situation. Now however, with the advent of power electronics, utilisation of HVDC systems is rapidly increasing across the world. This has been accelerated with the growth of renewable distributed energy supplies, such as offshore wind farms in the UK. As a result, local and international energy supplies are becoming dependent on HVDC. Consequently, the reliability of DC technologies is becoming critical as they become more embedded in supply networks. However, in comparison to AC systems, the understanding of insulation and plant reliability under HVDC is still in its infancy. At the same time, the working environment for DC plant is not well documented and, in reality, DC systems have AC ripple, impulses and voltage variation just as in any other system, and these time-varying waveforms are likely to control plant ageing and reliability.This project comprises internationally leading researchers from The University of Manchester, The University of Strathclyde and Imperial College. They bring complementary expertise to form a unique team to address the problem. Prof Tim Green (Imperial) is an expert in the use of power electronics to enhance the controllability and flexibility of electricity networks; Prof Simon Rowland (Manchester) is an authority on ageing of high voltage insulation materials; and Prof Brian Steward (Strathclyde) has unique experience in condition monitoring and insulation diagnostics for high voltage systems. The project is designed to embed the work into the global community and in particular is linked to researchers in China where the largest systems are being developed.This project will firstly identify the voltage profiles experienced by plant insulation in a real HVDC network or link, because in real systems the voltage on the network is not a constant, fixed value. The power converters that feed a DC network create intrinsic "noise" in the form of high frequency elements as part of their normal operation, and also create voltage disturbances in their responses to fault conditions and emergency overloads. Characterising these is the first step in the overall study of how DC power quality impacts the lifetime of HV insulation. The team will then, through laboratory exploration, develop life models for polymeric insulation subject to known levels of DC power quality. The focus will be on AC ripple over a wide frequency range. In addition, the influence of fast transient signals of varying levels and durations will be considered, as identified above. The third experimental theme is to develop tools for monitoring transient signals and power quality in a real DC cable setting, and enable subsequent interpretation. Finally, we will develop input for utility policy documents on acceptable DC power quality. We will also provide evidence for optimal insulation design for equipment manufacturers and asset management recommendations for utilities. Through these means we hope to de-risk the UK's growing dependence on DC networks, and optimise equipment and system design and operation.