真空有载分接开关在高压直流换流变压器中的运用

有载分接开关（on-load tap-changers,OLTC）是高压直流输电线路中现代换流变压器不可或缺的设备,可对系统的电压变化进行补偿,优化变频器控制角,并使高压直流系统降压运行成为可能。但开关操作时产生的电流具有陡峭的非正弦波形,不仅增加了开关切换的负荷,也增加了开关的容量和尺寸,而且开关频繁操作对维护提出了很高的要求。比较了换流变压器和电力变压器OLTC的操作条件。真空开关技术的引入使得真空OLTC除了可以消除油的污染外,还具备独特的优势,可承受高切换负荷,可用在高压直流换流变压器上,OLTC的容量配置可以优化调整等。真空OLTC免维护的操作次数可高达600 000次,维护工作可降至最低限度,大幅提升了换流变压器的可靠性和可用率。通过优化OLTC额定容量可以节省开关的体积和重量,有助于开发超高压直流换流变压器。

Application of Vacuum OnLoad TapChangers in HVDC Converter Transformers

Onload tapchangers (OLTCs are indispensable components in modern converter transformers for HVDC transmission lines. They compensate the system voltage variation, optimize the control angle of converter valves and realize the operation with reduced DC voltage. But the nonsinusoidal current waveshape with the high rate of rise during tapchange operation augments the switching duties and leads to an over sizing of the OLTC, and the frequent tapchange operations result in high maintenance demand. The switching condition of OLTCs in converter transformers is compared to that of power transformers in this paper. The introduction of vacuum switching technology in OLTCs provides, besides the elimination of oil contamination, the unique advantage for heavy switching duties as that in converter transformers for HVDC applications. The rating of the OLTC can be adjusted optimally to the service duties. Since this new OLTC technique is maintenancefree up to 300,000 operations, the maintenance work can be reduced to a minimum. The reliability and the availability of converter transformers are therefore considerably improved. The sparing in volume and weight through the optimized rating of OLTCs makes a contribution to the future effort in ultra HVDC development.