Overview
Fiber Optic Current Transformer (FOCT) is an all‑fiber optoelectronic current measurement device developed based on the Faraday magneto‑optic effect. It consists of a PM fiber sensing coil, an SLD broadband light source, a PM fiber splitter, an optoelectronic signal processing unit, and a merging unit, forming a complete optical measurement system. The magnetic field generated by the current‑carrying conductor induces a phase difference proportional to the current between two orthogonally polarized light beams propagating in opposite directions within the fiber sensing coil. The primary side current value is accurately retrieved through an interferometric demodulation algorithm, achieving passive, all‑optically isolated current detection on the high‑voltage side.
The entire optical path of this product is manufactured using mature batch‑packaging processes. Core optical components (SLD light source and PMFS) feature wide‑temperature stability and low‑noise characteristics. The sensing fiber coil adopts an integrated flexible coil structure, paired with a standardized electrical enclosure and a 6U rack‑mount merging unit, meeting various power industry standards. It is suitable for 110kV to 750kV AC substations, UHV converter stations, and other engineering scenarios, simultaneously fulfilling both high‑precision metering and relay protection requirements. It is a core piece of equipment for next‑generation digital measurement in smart grids.
Applications
High‑Voltage / Ultra‑High‑Voltage Smart Substations
110kV, 220kV, 330kV, 500kV, 750kV AC GIS and air‑insulated substations. Integrated into circuit breakers or GIS tank interiors for busbar, feeder, and main transformer current measurement.
UHV / Flexible HVDC Converter Stations
High‑current detection for DC converter valves, smoothing reactors, and DC busbars. Suitable for wide‑bandwidth, large‑range transient current acquisition requirements.
Power System Relay Protection and Energy Metering
Measuring circuits meet Class 0.2S high‑precision metering accuracy; protection circuits meet Class 5P protection accuracy. Suitable for fault/short‑circuit current recording, harmonic monitoring, and power quality analysis.
Renewable Energy Power Stations
High‑current monitoring for wind and PV step‑up substations and energy storage converters. Resists complex electromagnetic interference and adapts to outdoor wide‑temperature harsh environments.
Industrial Special High‑Current Detection
Current sensing for metallurgical electrolysis, railway traction power supply, shipboard power systems, and aerospace high‑power equipment.
Laboratory and Optical Test Platforms
Paired with SLD light sources and PM splitters to build fiber optic sensing test systems for Faraday effect and fiber optic path calibration experiments.
Product Features
Superior Safety and Insulation Performance
All‑fiber passive structure on the primary side. Fiber is naturally insulating, with no oil‑immersed or iron‑core flammable components, completely eliminating the risk of explosion or oil leakage found in conventional CTs. Full optoelectronic isolation between primary and secondary sides eliminates the danger of open‑circuit high voltage on the secondary side. Meets stringent power‑frequency withstand voltage and lightning impulse insulation standards, suitable for 330kV and above UHV insulation conditions.
Outstanding Measurement Accuracy and Dynamic Performance
No iron‑core saturation. Excellent linearity across the full range from 40A to 4000A, with no distortion under 50kA short‑circuit fault currents. Dual‑accuracy compatible: Class 0.2S for metering and Class 5P for protection. Wide frequency response enables simultaneous acquisition of power frequency, harmonics, and transient fault currents. Supports 4kHz / 5kHz high‑frequency sampling with complete and undistorted fault recording waveforms.
Wide‑Temperature Stability and Strong Environmental Adaptability
Equipped with self‑developed low‑ripple SLD light sources and low‑temperature‑drift PM splitters. Optical path loss and wavelength drift are well controlled across the full temperature range (-40°C ~ +65°C). Long‑term temperature drift errors are minimal. Operating temperature: -40°C ~ +65°C; storage: -55°C ~ +85°C. Withstands ≤95% non‑condensing humidity. Passed thermal cycling, vibration, and EMC full‑suite testing.
Digital Interface for Smart Grid Compatibility
Direct output of standard digital sampled‑value (SV) messages. ST‑interface 850nm multimode fiber for one‑to‑many communication, seamlessly interfacing with merging units (MU), eliminating analog conversion stages and reducing transmission errors. Sampling rates configurable at 4kHz / 5kHz, with synchronized pulse triggering support, fully compliant with next‑generation digital substation communication standards.
Lightweight Structure and Flexible Installation
Lightweight sensing fiber coil (330kV version weighs only 2.0kg). Flexible coil design adapts to various busbar sizes. Electrical enclosure and 6U rack‑mount merging unit feature modular design for easy on‑site cabling and integration. Low total power consumption (<30W). Supports DC110V / 220V wide‑range DC power supply, compatible with substation DC operating power sources.
High Reliability and Mature Mass Production
Core optical path components are manufactured using mature batch‑packaging processes with excellent device consistency. Full optical path features low polarization noise and low power noise, with long‑term zero‑drift stability. Meets national standards for EMC, insulation, and dynamic/thermal stability testing. Supports large‑scale engineering deliveries. Sensing coil dimensions and overall system specifications can be customized according to voltage levels and primary current ranges.
Please log in to view the full article.
