A single mode of linearly polarized light is coupled into an electro-optic crystal. Like the current sensor, the speed of propagation of light in the crystal is differentially influenced, this time based on the strength of the electric field. The resulting output from the sensor is elliptically polarized light. The polarization state is measured to derive the electric field. Optical voltage sensors have been challenging to develop because deriving an accurate voltage measurement is dependent upon the geometry of the conductors relative to ground.
Any sensor based on an electric field measurement is sensitive to perturbations in the field.
By deploying more than one of the field sensors in a nitrogen-filled composite polymer insulator, the overall electric field is integrated to determine the voltage measurement. This concept has been tested as a 230kV voltage class prototype at Powertech Labs. It successfully maintained accuracy while exposed to a variety of severe electric field perturbations. The voltage transducer is unique in its dielectric design. The electrodes are widely separated resulting in a safe design with low dielectric stresses.