Application of submillimeter wave lasers to high voltage cable inspection

An experimental device designed for real-time, nondestructive inspection of cross-linked polyethylene insulation during cable manufacture has been built, analyzed, and tested under laboratory conditions. The device detects scattered far-infrared (FIR) laser energy at 118.8 μm from imperfections, such as voids and contaminants, known to have a serious deleterious influence on cable in-service lifetime. As presently configured, the device can readily detect voids as small as 100 μm in diameter in a cable 2.8 cm in diameter moving past the sensor at 5 cm/s. Better performance of the liquid helium cooled Ga-doped Ge detectors could lead to a significant improvement in void detection capability.