The size of optical fiber current sensors with a Faraday effect can be small with greater weight savings compared with electromagnetic induction type CTs. We advanced such utilizations for power equipment, especially for optical fiber current sensors that use flint glass fiber for the Faraday element. This paper outlines the principle, the composition of optical CTs, and fault point location systems to which an optical fiber current sensor is applied as well as the practical use situations and the development status of 500-kV independence type optical CTs that are aimed at applications in all digital substations.