Method for OCS current capacity calculation in AC railways

The current capacity of an overhead contact system (OCS) is a basic design parameter for electric railways. When the OCS current capacity is being calculated, only the influences of the self and mutual impedances of the OCS conductors are considered in the traditional method. A new method for OCS current capacity calculation, which considers the influences of the return circuit, is proposed based on the multiconductor transmission line model. The OCS current capacity and current distribution among the conductors are calculated for a direct feeding system and an autotransformer (AT) feeding system. The results reveal that there are nonnegligible errors in the current distribution ratios by the traditional method when there are return conductors near the OCS in the traction network.