The Effect of pH and Temperature in the Propagation of Water Treeing in XLPE Insulated Underground Cable

Boonruang Marungsri

Abstract


Water treeing has become the major problem in XLPE insulated underground cable caused by the moisture penetration. Despite several studies performed, this problem is still not clear on how the moisture can fast damage the XLPE insulated cable under certain operating conditions. This work has studied the effect of pH and temperature of the ionic solutions to the degradation of the XLPE insulation. The study focused on the XLPE cable used in the 22 kV underground distribution systems in Thailand. The ionic solutions involved a 0.1 mole/L of NaCl and CuSO4 solutions for degrading the XLPE cable at ambient and 50 °C in 1000 hours and 4000 hours with the electric stress of 22 kV 50 Hz continuously.  CuSO4 and NaCl revealed a pH of 4.04 to 3.70 and 6.49 to 6.74 from ambient to 50 °C respectively. The higher strength of acidity resulted by CuSO4 at 50 °C was observed to be more effective in the propagation of water treeing across the XLPE insulation. The propagation of water treeing across the XLPE was strongly dependent on the pH level. Temperature above ambient was concluded to be detrimental for XLPE insulation when a CuSO4 ionic solution exists over a long period due to the significant propagation of water treeing.


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