Thermal Aging Time-temperature Effects on Low Voltage EPR/XLPE Insulated Cables

Abstract

Low-voltage (LV) insulated cables are widely used in nuclear power plant environments in critical applications such as power transmission, control of equipment and instrumentation, and signal and data communication. Since the majority of nuclear power plants are nearing reaching their end-of-life, extending their operating life by up to 40 years is critical. As a result, assessing the health of LV cables has become a critical issue, as this is typically accomplished through destructive techniques.

Most cables are made with polymer insulation and jacket materials, which can become brittle, crack, or degrade over time due to exposure to harsh environmental conditions such as high temperatures, moisture, and radiation. Degradation of the properties of these materials, particularly the insulation, can result in a significant decrease in the overall health and performance of the cable, eventually leading to failure. Aging assessments are performed on cable polymers exposed to harsh conditions in service to identify and quantify the severity of degradation and determine when they will reach their end of life.

Cross-linked polyethylene (XLPE) and ethylene propylene rubber (EPR) insulated cables are among the most commonly used in the industry, and their use is continuing to increase. A variety of cable samples are thermally aged at 130 °C for different periods of time in this paper. These samples are subjected to frequency-domain dielectric spectroscopy (FDS) and polarization/depolarization current (PDC) measurements. The dielectric response characteristics of FDS and PDC are examined, and a variety of diagnostic ”metrics” derived from variable frequency dielectric response and polarization and depolarization current data have been trended as a function of aging time.