The first IOPC sensor was successfully deployed in a phase measurement application in 1998 at a BC Hydro substation. Shortly after, Carmanah began the search for a partner with a compatible current sensing technology to fully exploit the market potential of the technologies. The move toward optical sensing has been heating up as NxtPhase and other companies are introducing new optical instrument transducers that offer many advantages over existing CTs and VTs. The fibre CT is a derivative of a Sagnac interferometer that is widely used in navigational gyro systems. Instead of sensing rotation as it does in gyro applications, the sensor encircles a current carrying conductor and detects magnetic field.
Light travels from a source that is remotely located in the control building.
It splits into two paths and propagates in both directions around the fibre-sensing loop. Both paths are recombined and travel back to a photo detector. The speed of propagation of the light is affected differentially depending on which way it travels around the current sensing loop. The resulting signal is really two signals that are out of phase proportionately with the strength of the magnetic field encircling the conductor. According to Ampere's law this field is directly proportional to the current flowing through the conductor.