This is the accepted version of the paper.This version of the publication may differ from the final published version. Permanent repository link ABSTRACT This position paper, prepared by the IEEE DEIS HVDC Cable Systems TechnicalCommittee, illustrates a protocol recommended for the measurement of space charges in full-size HVDC extruded cables during load cycle qualification tests (either prequalification load cycles or type test load cycles). The protocol accounts for the experimental practices of space charge measurements in the thick insulation of coaxial cables in terms of poling time, depolarization time, heating and cooling of specimens, as well as for the experience gained very recently from such kind of measurements performed in the framework of qualification tests relevant to ongoing HVDC cable system projects. The goal of the protocol is not checking the compliance with any maximum acceptable limit of either space charge or electric field. Rather, this protocol aims at assessing the variation of the electric field profile in the cable insulation wall during poling time at the beginning and at the end of load cycle qualification tests for full-size HVDC extruded cables. Indeed, in the design stage the electric field distributions are determined by the cable geometry and by temperature gradient in the insulation. Thus, the design is based on macroscopic parameters conductivity and permittivity and how they depend upon temperature. Any disturbance of the electric field due to space charge accumulation will only be revealed during space charge measurements either in as-manufactured state or in the aged state after load cycle qualification tests.

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This position paper by the DEIS HVDC Cable Systems Technical Committee provides a review of existing diagnostic electrical and dielectric techniques for testing the insulation of polymeric extruded HVDC cable joints in the present Part 1. Here, the state of the art on the insulation of HVDC extruded cable system joints is covered with reference to types, design and testing techniques. This helps to identify routine tests as the first target for the onset of new testing procedures, AC-PD measurements as the readily-available measurement from manufacturers' practices for quality control of the insulation of accessories during routine tests and VHF/UHF wireless sensors as the best tool for performing such measurements on joints in the noisy factory environment. Thereby, a novel protocol for the measurement of partial discharges using AC voltages and VHF/UHF sensors, for quality control during routine tests on such joints, is derived in the next Part 2. This protocol is the main novelty of this investigation.

The effect of DC poling time upon the time-dependent decay of space charge in insulation peelings of Cross-linked Polyethylene (XLPE) cable that had not previously experienced either electrical or thermal stressing is investigated. Two DC poling durations were used, two hours and twenty six hours at an electric field of 50kV/mm and at ambient temperature. Space charge was measured in the two samples investigated both during space charge accumulation and throughout its subsequent decay. The results show that the length of DC poling plays an important role in the subsequent decay. Despite the fact that both samples have had the same amount of space charge by the end of both short and long poling durations the time dependence of the space charge decay is different. Most of the charge stored in the sample that had experienced the short time poling decays rapidly after voltage removal. On the other hand the charge that is stored in the sample with the long DC poling duration decays slowly and its decay occurs in two stages. The data, which is analysed by means of the detrapping theory of space charge decay, implies that the charge stored in the material has occupied energy states with different trap depth ranges. The two poling durations lead to different relative amounts of charge in each of the two trap depth ranges. Possible reasons for this are discussed. Voltage on Volt off SC-2min Volt off SC-14min

This paper presents the results of endurance tests that have been carried out on cross-linked polyethylene (XLPE) cable peelings. The peelings were taken from cables that were manufactured from a single batch of XLPE and subjected to electrical (up to 28 kV/mm), thermal T = 363 K (90 o C) and electro-thermal stressing for at least 5000 hours. The endurance tests of the peelings (thickness 150 μm) were carried out at the same temperature of T = 363 K as the thermally stressed cable, but at two different ac electrical fields of 55 and 70 kV/mm. The resulting life data for the different sample sets are compared to one another and to that of peelings taken from unaged cables. Weibull analysis of the failures shows that only peelings from cables that had experienced a thermal stress component during their time of stressing as a cable, exhibited a statistically significant reduction in endurance capability. Possible reasons for this reduction of life are discussed.