Carbon emission reduction, as one of the core drivers of energy transformation, can effectively promote clean energy development and mitigate the global greenhouse effect. In the context of the development of the global energy internet, large-length HVDC cables for long-distance and cross-regional power transmission occupy an essential position in the power internet. However, the accumulation of electric charges in the large-length HVDC cables is inevitable, and would threaten the safe operation of the cables, reduce their service life and might even cause insulation fault. Therefore, it is indispensable to study the electric charges in large-length HVDC cables. This article provides a brief overview of electric charge generation, measurement and dissipation in HVDC cables, and summarizes the important research issues in recent years, which can provide informative guide for both online monitoring and life assessment of large-length HVDC cables.
Auxiliary power system of substation is the key to ensure the safe and stable operation of substation,but the leakage current in the cable may cause serious accidents such as channel fire.And the fixed monitoring device has many disadvantages,such as high cost and difficult popularization.Aiming at the problem of accurate detection of leakage current of auxiliary power system,a new leakage current detection system of auxiliary power system is developed.This system is composed of multiple wireless acquisition terminals and has the functions of multi-channel synchronous acquisition,automatic data communication,current vector sum calculation,which can realize the accurate detection of leakage current and the accurate positioning of defects in auxiliary power system,so as to eliminate the potential accidents in time.In order to verify the effectiveness and accuracy of the proposed system,the actual detection is carried out in the substation site,and many potential current leakage problems in auxiliary power system are found and processed.The results show that this system can quickly,effectively and accurately detect the operation of auxiliary power system and is helpful to ensure the safe and stable operation of substation,which has high economy and practicability.
The hybrid cascaded ultra-high voltage direct current (UHVDC) transmission system, which combines the advantages of the line commutated converter (LCC) based and modular multilevel converter (MMC) based UHVDC system, has good engineering prospects. In this topology, the rectifier side adopts LCCs, and the inverter side adopts an LCC connected in series with three paralleled MMCs. In this paper, the mechanism of unbalanced current among the paralleled MMCs induced by commutation failures of LCC is analysed. Firstly, the cause of unbalanced current is explained by combining the control strategy and the change of the inverter equivalent topology after commutation failures. Furthermore, the main factors affecting the unbalanced current are analysed, including the smoothing reactor, the constant current control on the rectifier side and the voltage dependent current order control (VDCOL). Finally, the validity of the mechanism analysis is verified by simulations based on PSCAD/EMTDC platform. The technical route and key points of limiting unbalanced current are also put forward.
以汶川地震强震区岷江干流及渔子溪沿岸的 42 个泥石流为研究对象,提取泥石流流域中物源存储量、暴发频率、流域面积等 7 个重要因子,运用CRITIC法建立电网降雨诱发泥石流灾害识别模型,将识别结果划分三级:15 条泥石流流域属于高易发性泥石流灾害;11 条泥石流流域属于中易发性泥石流灾害;16 条泥石流流域属于低易发性泥石流灾害.然后,选取研究区内 26 条泥石流曾经一次冲出物源量来验证电网泥石流灾害识别模型的可行性.最后,通过ARCGIS平台生成电网泥石流灾害易发生分区图.
针对目前没有成熟的交流电缆中间接头载流量校核方法,搭建了土壤直埋 110 kV电缆中间接头和电缆本体稳态载流量三维仿真模型,利用有限元对比研究环境温度、土壤导热系数和敷设深度对电缆中间接头和本体稳态载流量的影响规律.结果表明:在不同环境温度、土壤导热系数和敷设深度下,电缆中间接头载流量始终小于电缆本体载流量,土壤导热系数为 0.5 W·(m·K)-1、环境温度为 293 K以及敷设深度为 1.75 m时的中间接头载流量相较于相同条件下的本体载流量减小了 10.8%.因此,如按照电缆本体载流量校核电缆载流能力,将导致中间接头主绝缘处于加速热老化状态.为确保电缆长期稳定运行,建议以本体载流量确定电缆载流时应留有一定裕度.
