Fiber-optic Current Sensor (FOCS): Fully Digital Non-conventional Instrument Transformer

The Fiber-Optic Current Sensor (FOCS) is a non-conventional instrument transformer (NCIT) founded on the Faraday Effect. Compared to the conventional magnetic system, this well-proven, field-tested optical technology brings radical benefits over conventional CTs and enables the introduction of a digital process bus in HV substations.This new NCIT exceeds traditional magnetic CT technology in terms of safety of operation, current measurement and frequency response, footprint/weight savings, and having a lower environmental impact. The faster response of the FOCS and the precise measurement of both AC and transient DC result in improved substation protection and monitoring functions. The digital interface of FOCS is designed for IEC 61850-9-2LE communication for integration into digital substation automation systems.This paper discusses the differences between conventional CTs and FOCS and lists the growing applications as well as the benefits of these applications to customers in the utility industry and renewables and generation sectors.