Fiber-optic current sensor
 | This article contains content that is written like an advertisement. It's not horrible, but quotes extensively and uncritically from ABB marketing material.. (December 2015) |
Fiber-optic current sensor (FOCS) is a device designed to measure direct current. Utilizing a single-ended optical fiber wrapped around the current conductor, which exploits the magneto-optic effect (Faraday effect), the FOCS can measure uni- or bidirectional DC currents up to 600 kA with an accuracy within ±0.1% of the measured value.<ref name="IOPref1">Ye, W., Dong, Z., Ren, R., Liu, J., Huang, K., & Zhang, C. (2020). Application research on fiber-optic current sensor in large pulse current measurement. In Journal of Physics: Conference Series (Vol. 1507, Issue 7, p. 072015). IOP Publishing. https://doi.org/10.1088/1742-6596/1507/7/072015</ref><ref name="brochure">"FOCS – Fiber-Optic Current Sensor: make light work of DC current measurement" (PDF). 2011. Retrieved 24 August 2021.</ref>: 2 <ref name="ABB">"Fiber-Optic Current Sensor FOCS". Retrieved 3 July 2013.</ref>
Fiber-optic current sensor uses an interferometer to measure the phase change in the light produced by a magnetic field. As it does not require a magnetic yoke, the FOCS is smaller and lighter than Hall effect current sensors, and its accuracy is not reduced by saturation effects. The inherent insulating properties of the optical fiber make it easier to maintain electrical isolation. It also does not need recalibration after installation or during its service life.<ref name="brochure"/><ref name="ABB" /> Because the optical fiber is inherently insulating, electrical isolation is easier to maintain.
The optical phase detection circuit, light source and digital signal processor are contained within the sensor electronics; this technology has been proven in highly demanding applications such as navigation systems in the air, on land and at sea.<ref name="brochure"/>: 5
Applications
In 2013, ABB introduced a 420 kV Disconnecting Circuit Breaker (DCB) that integrates FOCS technology replaces many conventional current transformers, engineering and design of the substation is simplified. By reducing the material needed, including insulation, A 420 kV DCB with integrated FOCS can reduce a substation's footprint by over 50% by minimizing the need for materials, including insulation, compared to conventional solutions involving live tank breakers with disconnectors and current transformers.
