|Source:||National Institute of Standards and Technology|
|Date:||4/1/94 Record No.: 10064|
|Contact:||Gerry Fitzpatrick, 301-975-2737; Eric Simmon, 301-975-3956|
Optical CT (HV Current Meter)
A few manufacturers (ABB, 3-M, Square-D, also Toshiba) have prototype "production" units, and want NIST calibrations. There are two types. One uses bulk glass, and the other has a glass fiber looped around the conductor a number of times. The magneto optic (Faraday) effect causes a rotation in the polarization of light along the length of the fiber, and thus a measure of the magnetic field and current. Advantages: electrically isolated, explosion-proof. Disadvantages: more complicated, sensitive to vibration and temperature. There are still problems to be overcome. Fibers need to be annealed to get rid of stresses of coiling--made for light/data transmission, not this application. ABB's unit, a bulk glass type, is now commercialized, and there are 35-40 units in service at various utilities. There's an Optical Sensor Mfg. User Group (OPSMUG), and EPRI (Jan Stein) is involved.