Abstract
The most severe partial discharges and main insulation failures of 10 kV cross-linked polyethylene cables occur at the joint due to defects caused by various factors during the manufacturing and installation processes. The electric field distortion is analyzed as the indicator by the charge simulation method to identify four typical defects (air void, water film, metal debris, and metal needle). This charge simulation method is combined with random walk theory to describe the stochastic process of electrical tree growth around the defects with an analysis of the charge accumulation process. The results illustrate that the electrical trees around the metal debris and needle are more likely to approach the cable core and cause main insulation failure compared with other types of the defects because the vertical field vector to the cable core is significantly larger than the field vectors to other directions during the tree propagation process with conductive defects. The electric field was measured around the cable joint surface and compared with the simulation results to validate the calculation model and the measurement method. The air void and water film defects are difficult to detect when their sizes are less than 5 mm3 because the field distortions caused by the air void and water film are relatively small and might be concealed by interference. The proposed electric field analysis focuses on the electric field distortion in the cable joint, which is the original cause of the insulation material breakdown. This method identifies the defect and predicts the electrical tree growth in the cable joint simultaneously. It requires no directly attached or embedded sensors to impact the cable joint structure and maintains the power transmission during the detection process.
Highlights
The power cable has been extensively used in power transmission and distribution systems due to its large ampacity and ability to be installed underground [1,2]
The average length of the trajectories was small because the electric field around the air void defect decreased (Table 1) and the field distortion was mild
The electrical tree simulated based on and random walk theory to analyze the pattern of electrical tree trajectories
Summary
The power cable has been extensively used in power transmission and distribution systems due to its large ampacity and ability to be installed underground [1,2]. Many studies have been conducted to investigate the electric field distribution and aging process of main cable body, whereas studies of the cable joint are inadequate due to its complicated structure and multiple installation procedures [9,10]. Most existing methods adopted the thermal or ultrasonic signal as the indicator to detect the internal defects of cable joints [19,20] These signals are the derivative consequences of the insulation material breakdown and susceptible to interferences in the environment, while the electric field intensification is the original cause of the insulation material breakdown. Since the electrical tree propagation is a stochastic process creating different trajectories even the electric field distributions remain the same, the random walk theory is more consistent with the physical phenomena in the cable.
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