Internal defects inside power cable joints due to unqualified construction is the main issue of power cable failures, hence in this paper a method based on thermal probability density function to detect the internal defects of power cable joints is presented. First, the model to calculate the thermal distribution of power cable joints is set up and the thermal distribution is calculated. Then a thermal probability density (TPD)-based method that gives the statistics of isothermal points is presented. The TPD characteristics of normal power cable joints and those with internal defects, including insulation eccentricity and unqualified connection of conductors, are analyzed. The results indicate that TPD differs with the internal state of cable joints. Finally, experiments were conducted in which surface thermal distribution was measured by FLIR SC7000, and the corresponding TPDs are discussed.

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Water tree is the predominant defect in high-voltage crosslinked polyethylene cables. The microscopic mechanism in the discharge process is not fully understood; hence, a drawback is created towards an effective method to evaluate the insulation status. In order to investigate the growth of water tree, a plasma-chemical model is developed. The dynamic characteristics of the discharge process including voltage waveform, current waveform, electron density, electric potential, and electric field intensity are analyzed. Our results show that the distorted electric field is the predominant contributing factor of electron avalanche formation, which inevitably leads to the formation of pulse current. In addition, it is found that characteristic parameters such as the pulse width and pulse number have a great relevance to the length of water tree. Accordingly, the growth of water tree can be divided into the initial stage, development stage, and pre-breakdown stage, which provides a reference for evaluating the deteriorated stages of crosslinked polyethylene cables.

Submarine cables have complicated structures and high production process requirements. In order to make sure the submarine cables to operate safely and reliably, this paper takes into account how the different laying conditions of submarine cables affect the maximum allowable ampacity. A 110kV YJQ-1×500 XLPE submarine cable is taken as the research object, based on the finite element method, the electromagnetic-thermal coupling models of the submarine cable laying in underwater soil, seawater and pipeline is established respectively in Comsol Multiphysics to study their thermal field and ampacities. The results indicate that the laying conditions would affect the cables’ heat dissipation, submarine cable lays in seawater has the highest ampacity and lays in the pipeline in landing section of the cable has the lowest ampacity. Moreover, the variation of temperature of seawater would also influence the ampacity of the submarine cable.

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