Parametric change in Insulation Resistance and Breakdown Voltage of Underground PVC Cables under Accelerated Multistress Aging Conditions

Abstract

PVC is widely used as an electrical insulation for low-voltage indoor wiring and underground cabling. These cables are attacked by contaminants and chemicals present in the soil. The elevated temperatures and pressures inside the soil also adds up to stresses and deteriorates their insulations and sheaths and this eventually goes on damaging the conductors. So their performance in the contaminated service environment should be investigated considering extreme conditions in order to predict and ensure reliable service life. In this research 4 different PVC cable samples (2 core 10 mm2, 4 core 10 mm2, 4 core 120 mm2 and 4 core 240 mm2) were subjected to mechanical (via small punches), thermal, chemical and electrical stress over each core of the cable. Electrical stress was applied with 1 kV AC transformer. These samples were aged for 1000 hours under International Electrotechnical Commission (IEC) 1000 hours multistress aging conditions. Visual inspection and electrical characterization was done by Breakdown Voltage and Insulation Resistance Test for insulation and sheath at different intervals to investigate early stage degradation and reduction in lifetime. The results were compared with the characterizations already reported in the literature. Physical appearance and chemical degradations were apparent from the visual inspection of end aged samples. Quantitatively the results also indicated the continual decline in the breakdown voltage and insulation resistance over the aging time. Our findings inferred that the depreciation in quality of PVC cables (insulations and sheaths) is likely due to the chemical stresses which also instigates all other stresses