An optical sensor using the Pockels effect can be a useful measurement tool in electrical applications where mapping distributed E-fields is required. Results from electric field tests with a 2 m sphere, and the voltage distribution of a 1100 kV cascaded test transformer are presented to demonstrate its utilisation. These results show that the optical sensor, due to its inherent dielectric link to the data acquisition electronics, can be utilized as a research tool in the measurement of the voltage distribution on high-voltage insulation systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>