actual service life meaning in English

实际使用寿命
行驶里程

139 synchromotors for the south - to - north water transfer and taihu harnessing project has been installed in jiangsu province technically , synchromotors are designed to have a service life of about 20 years while , according to statistics , most of the actual service life can not be as long as 20 years . to make matters worse , some of the synchromotors could only work for about 10 years and for those running a relatively a long time needed overhauling every year
同步电机的正常使用寿命（指线圈）应在20年以上，但据统计，各地大泵站同步电机运行寿命多在20年以下，有的仅10余年；部分运行时间较长的大型泵站同步电机每年均需大修；有的泵站泵机组起动困难或无法起动。