Rejuvenation of Retired Power Cables by Heat Treatment: Experimental Simulation in Lab

Abstract

In this work, heat treatment was performed on three retired 110 kV AC cables with service years of 0, 15 and 30, and the effects on the thermal and electrical performance of the cable insulation were investigated. First, each cable with a length approximately of 5 m was prepared and cut into five equal segments. Four segments of each cable were annealed at a temperature of 90, 95, 100, or 105 • C by building a small circuit to simulate cable operation. Then, a section at the middle of each segment was cut out, and the insulation layer was peeled away. The peeled-off layers from the inner, middle and outer positions were selected as the test samples. Subsequently, Fourier transform infrared spectrometry (FTIR), and differential scanning calorimetry (DSC) were performed, and the DC conduction current and dielectric breakdown strength were measured. The best thermal properties of the highest melting point, crystallinity, and smallest melting range were found when the cables were annealed at 100, 105, and 105 • C for the inner, middle, and outer positions, respectively. The highest dielectric breakdown strength and lowest electrical conductivity were found at temperatures of 95 or 100 • C for the inner and middle positions, respectively, and at 105 • C for the outer position. The FTIR results showed that thermal annealing for hundreds of hours did not adversely affect the molecular chains. It is found that this type of heat treatment could be a feasible method to rejuvenate retired cables, and a conservative temperature of 95 • C is regarded as the optimum annealing temperature. INDEX TERMS Cable, DSC, melting point, crystallinity, electrical conductivity, dielectric breakdown strength.

Correlation Between Thermal Parameters and Morphology of Cross-Linked Polyethylene

“…H m is the enthalpy of fusion of an ideal polyethylene crystal per unit volume; and L is the lamellar thickness. The used values for calculation were as follows: H 0 f = 293 J/g, T m0 = 414, 6 K, H m = 2, 88 × 10 8 J/m 3 and σ e = 93 × 10 −3 J/m 2 .…”

“…Fourthly, the parameters of T 1 ' and T 2 ' in Figure 2 can be measured from the temperature recorder of the platform, and the parameter of P' was approximately equal to P 0 'due to R 0 ', P 1 ' and P 2 ' can be ignored comparing with P 0 '. Fifthly, the parameters of R 1 and ρ 1 at 50, 70 and 90 • C were derived from Formula (1) and (3).…”

“…Cross-linked polyethylene (XLPE) is playing an increasingly important role in high voltage cable insulation due to its high performance on electrical and thermal properties [1]- [3]. The insulating state (thermal history, operating period or material characteristic) of the XLPE has a profound effect on the safety and reliability of the cable operation because the external properties of the XLPE are determined directly by its morphology.…”

Assessment of Thermal Aging Degree of 10kV Cross-Linked Polyethylene Cable Based on Depolarization Current

“…To detect the cable insulation condition, the commonly used methods include 50Hz dielectric loss, leakage current, partial discharge, etc. [9]- [13]. These methods have been widely recognized in actual cable detection, but there are still shortcomings.…”

An Equivalent Heat Transfer Model Instead of Wind Speed Measuring for Dynamic Thermal Rating of Transmission Lines

“…In the contact thermometry, the temperature sensor is installed directly on the conductor surface. This thermometry also has high measuring precision and anti-interference capability [23,24]. However, as the sensor is in direct contact with the conductor, it is difficult in terms of sensor maintenance [25].…”