PROBLEM TO BE SOLVED: To improve a determination accuracy of frost formation to a trolley wire by highly accurately calculating a saturated steam content around the trolley wire by estimating the temperature of the trolley wire with high accuracy.;SOLUTION: An air temperature and an air velocity measured by a measuring instrument installed in a section as an object of a frost formation prediction are accumulated, a heat transfer coefficient is calculated, and a trolley wire temperature in the prediction time of the next morning is estimated by integrating a heat-balance of the trolley wire at a prescribed time interval. A saturated steam pressure is calculated by the trolley wire temperate (S210) using the estimated trolley wire temperature and the saturated steam content around the trolley wire is calculated (S220). Further, the saturated steam pressure at a temperature at the prediction time is calculated (S240), and a steam content at the prediction time is calculated from the temperature and humidity at the prediction time (S250). When the trolley wire temperature is lower than 0°C and the steam content is higher than the saturated steam content (YES in S260), it is determined that there is the frost formation (S270).;COPYRIGHT: (C)2014,JPO&INPIT
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