Life Estimation of HVDC Cables Under the Time-Varying Electrothermal Stress Associated With Load Cycles

Abstract

In this paper, a new procedure is presented for life estimation of HVDC cables subjected to the time-varying electrothermal stress associated with load cycles and voltage. The electric-field inversion phenomenon in the insulation of dc cables is accounted for by updating the field profile as the temperature profile changes with the load. The thermal transients due to load cycles are modeled via the CIGRÉ transient thermal network adapted to dc cables. The life fractions lost during each cycle because of the cyclic variation of the electrothermal stress are computed via an adequate electrothermal life model for the insulation of HVDC cables. The Weibull hypothesis is made for relating cable life to failure probability. The procedure is applied to the load cycles of the prequalification test for HVDC extruded cables after CIGRÉ Technical Brochure 496 that does not consider the effect of thermal and synergistic electrothermal aging. It is thus shown that this test might be less severe than it should be. Index Terms-DC power transmission, electrothermal effects, high-voltage direct-current (HVDC) insulation, life estimation, testing. I. INTRODUCTIONH IGH-VOLTAGE direct-current (HVDC) cable systems are often the best or the only option for bulk long-distance subsea or underground transmission [1], and their improved performances gave rise to an increased growth of installed HVDC cable lines worldwide [2], [3]. As for the HVDC extruded cable systems, in particular, their voltage and power ratings have reached 300-350 kV and 1000 MW, respectively, and commercial HVDC extruded cable system projects at the 320-kV level are on their way to commissioning [3]- [8].With this background, the CIGRÉ Technical Brochure (TB) 496 [9] has broadened the "Recommendations for testing dc extruded cable systems" after former TB 219 from the 250-kV to the 500-kV level. TB 496 emphasizes long-term reliability by prescribing the prequalification (PQ) test-one year of daily load cycles under dc voltage-"in order to demonstrate satisfactory long-term performance of the cable system" [9].Commonly, the accessories (joints and terminations) are the "weak link" of HV cable systems from the viewpoint of longterm reliability [3], [10]. However, as for HVDC extruded cable Manuscript

The Effect of Insulation Characteristics on Thermal Instability in HVDC Extruded Cables

“…The algorithm followed in this paper depends on an iterative method of electric field calculation and reliability estimation of HVDC cables subjected to load cycles according to CIGRÉ Technical Brochure 496 [6]. It was first developed by Mazzanti by developing a reliability estimation model of HVDC cables subjected to prequalification test (PQ) considering a steady state electric field as a simplification [13], then it was improved to include the transient electric field calculation in [14] instead of the steady state electric field. Later in [15], it was improved to include the type test (TT) load cycles in the algorithm.…”

“…The flow chart presented in Figure 1 explains step by step the algorithm implemented for such assessment. First, the temperature profile of load cycles according to CIGRÉ Technical Brochure 496 [6] is calculated using the CIGRE transient thermal network model following the guidelines of Standard IEC 60853-2 [16] (for more details, see [13,14]). Then, the transient electric field inside the insulation of the cable subjected to load cycles is calculated using both Maxwell's Equations (1)- (3) and conductivity Equation (4) as mentioned in detail in [15], followed by the calculation of insulation losses and the Then, the transient electric field inside the insulation of the cable subjected to load cycles is calculated using both Maxwell's Equations (1)- (3) and conductivity Equation (4) as mentioned in detail in [15], followed by the calculation of insulation losses and the resulting temperature rise.…”

Research of temperature destruction effect on cables insulation operation life

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Influence of Endurance tests on Space Charge Distribution of 160kV HVDC XLPE Cable

“…Flexible HVDC technology has provided a solution for large scale of renewable energy integration. Since the flexible HVDC doesn't involve the polarity inversion problem, the extruded XLPE cable has made rapid progress in recent years [1,2]. Several HVDC XLPE cables have been in service for decades in the worldwide [3,4].…”