Optoelectronic current transducer

A current transducer which permits the measurement of high currents in high voltage substations by means of the Faraday effect in optical monomode fibers was developed. The measuring system has a large bandwidth and a linear signal-to-current characteristic up to high currents without saturation. High voltage insulation presents no serious problems. A V-grooved semiconductor laser is used as light source and is installed in a solid case which also houses the detection unit. The monomode fiber is placed in a teflon hose, loosely and sufficiently twisted to avoid birefringence. The fiber is coupled to the laser by gradient index lenses. Astigmatism is reduced by ellipsoidal shaping and etching of the fiber end to form a lens-like element. Part of the device was tested in the laboratory. With a 62- turn primary fiber coil, the minimum detectable signal is 0.15 Amp-turns. It is shown that the magnetooptical transducer can be improved. Measurements in a high power bus and a comparison with simultaneous conventional current measurements are planned.