A fiber-optic current sensor (FOCS) is a
current sensor for measuring
direct current
Direct current (DC) is one-directional flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or eve ...
. By using a single-ended optical fiber around the current conductor that utilizes the magneto-optic effect (
Faraday effect
The Faraday effect or Faraday rotation, sometimes referred to as the magneto-optic Faraday effect (MOFE), is a physical magneto-optical phenomenon. The Faraday effect causes a polarization rotation which is proportional to the projection of the ...
), FOCS measures uni- or bidirectional DC currents of up to 600 kA within ±0.1% of the measured value.
Because it does not need a magnetic yoke, an FOCS is smaller and lighter than
Hall effect
The Hall effect is the production of a voltage difference (the Hall voltage) across an electrical conductor that is transverse to an electric current in the conductor and to an applied magnetic field perpendicular to the current. It was disc ...
current sensors, and suffers no reduction in accuracy due to saturation effects. Because magnetic field sensing is distributed around circumference, it is unaffected by stray magnetic fields, and there is no need for magnetic centering. It also does not need recalibration after installation or during its service life.
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.
Applications
In 2013,
ABB launched a 420 kV
Disconnecting Circuit Breaker (DCB) with integrated FOCS. Since one FOCS 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
Footprints are the impressions or images left behind by a person walking or running. Hoofprints and pawprints are those left by animals with hooves or paws rather than feet, while "shoeprints" is the specific term for prints made by shoes. T ...
by over 50% compared to the conventional solution of
live tank breakers with
disconnectors and
current transformers.
References
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Sensors
Electrical components
Electric power distribution
Electric power systems components
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