Current transformers (CTs) are essential components to measure system current for safe operation and protection of railway substations. Many studies have been conducted related to low-power current transformers (LPCTs) to meet increasing demand for digitalization of substations. This study proposes a newly developed LPCT to replace conventional CTs in gas-insulated switchgears (GISs) for railway substations. The prototype LPCT consisted of a Rogowski current sensor (RCS) and a passive module; it was designed to have an output of 150 mV at the rated current of 1250 A according to IEC 61869-10. The LPCT was also assembled in a metal shield enclosure to reduce the external influence, which could affect output accuracy. According to the performance evaluation tests, the prototype LPCT was confirmed to satisfy the accuracy class of 0.2, with a maximum corrected ratio error and corrected phase error of -0.368% and 25.65 minutes, respectively. In addition, the temperature correction coefficient was calculated to minimize the output variation of the LPCT, and the output was improved by up to 0.02% over the widest temperature range of -40 °C to 40 °C. It is expected that the prototype LPCT can replace conventional bulky CTs and help in the miniaturization and digitalization of GISs with built-in GIS spacers.