Terfenol-D based optical current transducer

The authors have developed and tested a prototype magnetostriction based, passive optical current sensing device for high voltage applications. The sensor contains a ferromagnetic yoke, a modulator of magnetostrictive Terfenol-D that responds to the magnetic field, and a fiber Bragg grating that converts this response into a wavelength modulated optical signal and transmit it via an optical fiber to ground level electronics. To linearize the output the modulator material was subjected to both mechanical and magnetic bias. The prototype CT was found to have a useable linear range of 100-1000A with a measured phase shift of around 30 degrees for a steady state 60 Hz excitation. Both the gain and the phase response have been found to be dependent on mechanical prestress and magnetic bias. The authors also report on materials characterization and modeling that support the actual design process.