The Formation Mechanism of White Substances on Water-blocking Buffer Layer of HV XLPE Cables

The ablation failures of the water-blocking buffer layer in HV XLPE cables have occurred frequently, causing widespread concern in the industry. In this paper, a 220 kV faulted cable was dissected to observe the distribution and characteristics of the ablation points, and the samples of white substance were taken from the ablation points to be tested by Fourier transform infrared spectroscopy and scanning electron microscope energy disperse spectroscopy. At the same time, a simplified experimental device was set up and simulated experiments were conducted to reproduce the formation of the white substance and to investigate the relevant influencing factors. By combining the results of the faulted cable and the simulated experiments, it was found that sodium bicarbonate was the main constituent of the white substance, and it was produced by the chemical reaction between the aluminum sheath and the water-blocking powder under a humid condition. Since the moisture is necessary for the formation of the white substance, which is thought to be the start point of the ablation of the buffer layer, it is important to keep the water-blocking layer from moisture during manufactory and installation of HV XLPE cables, and to develop new water-blocking material for them.