介绍一种电力机车带电通过相分段的自动转换系统。它用可编程序控制器SIEMENS公司SIMATIC S7－200 CPU226作为系统的核心, 利用识别传感器采集机车信息, 控制两台高压真空开关, 完成机车自动过分相过程。关键词电力机车； 接触网； 相分段；可编程控制器Abstract This paper introduces an automatic conversion system for locomotive passing through the OCS phase break. This system bases on the programmable controller SIMATIC S7－200 CPU226 as system center, it collects locomotve signsls by identification sensor, it controls two high voltage vacuum switches. Then the locomotive can pass through the phase break with electricity.The system operates regularly and property is reliable.Key words power locomotive； Overhead Contact System(OCS)； phase break programmable controller