A New Method for Detecting Defects of XLPE Insulated Cables

XLPE insulated cables have the advantages of easy installation, simple maintenance, excellent insulation performance and large transmission capacity, so they are widely used in urban power grid systems.

Although XLPE insulated cables have superior electrical characteristics, due to the uneven manufacturing processes and technical levels of various manufacturers, it is inevitable that there will be defects such as air gaps and inclusions in the finished XLPE cables, which is easy to cause electric field stress concentration inside the cable insulation layer, so that seriously affects the insulation performance of the XLPE cables and forms a discharge micro-channel. In this way, it is prone to cause the breakdown of the power cable insulation layer and even lead to accidents such as explosions.

Therefore, controlling strictly the factory quality of XLPE insulated cables as well as detecting and positioning accurately the insulation layer defects are conducive to the timely detection of safety hazards, providing guarantee for the reliability of power supply.

At present, the detection methods for cable insulation layer mainly include AC withstand voltage test, dielectric loss angle method, partial discharge detection method, however, these traditional methods generally require the experimental environment of high-voltage and high-current for detection, which are not only more complicated and cumbersome in operation as well as have higher requirements for safety, but also can not detect information such as air gap size and shape.

Terahertz Time-Domain Spectroscopy (THz-TDS) technology, as a new detection technology, uses terahertz pulsed electromagnetic waves to reflect the properties of matter, and has been widely used in many fields. Terahertz waves are between microwaves and infrared, having high penetrability to non-conductive dielectric materials, which can be used to easily detect defects such as impurities and gaps in dielectric materials.

Terahertz time-domain spectroscopy detection technology has the characteristics of high resolution and high sensitivity. By using its spectral data, physical information such as refractive index and dielectric constant of materials in terahertz frequency band can be directly and conveniently extracted, and then the characteristics of the sample can be studied; On the one hand, compared with X-rays, terahertz waves have extremely low photon energy, only one millionth of the former, which can guarantee the personal safety of inspectors.