A protocol for space charge measurements in full-size HVDC extruded cables

Abstract

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.

DC Model Cable under Polarity Inversion and Thermal Gradient: Build-Up of Design-Related Space Charge

“…The space charge measurement on samples of full-size cables, with several cm thick insulation, has been demonstrated [8,9]. The challenges are now to adapt these techniques for type tests and online measurements under high voltage, on full-size cables [7,[10][11][12].…”

Contributed Review: Review of thermal methods for space charge measurement

“…55 The TSM has been applied by Mazzanti et al to the cables during both pre-qualification and type tests. 56 The same article reports the most relevant problems related to this method. A relevant challenge for this method can be identified by the significant space occupied by the test setup, which is also composed by an additional cable (namely "compensation cable"), identical to the cable under measurement and connected to its terminals, in order to avoid the problems related to the current amplifier, as described in Section II C. Another problem consists in the test procedure, because before the space charges measurement the DC source must be disconnected, while the cold liquid must begin to flow.…”

Factors Affecting Pulse Injection from Measuring Electrode Based on the Pulsed Electroacoustic Technology for Coaxial Cables

“…10, a clear high-frequency oscillation appears on the coupled pulse, which is due to the impedance mismatch when the pulse spreads to the cable terminal and then reflects repeatedly. (20,21) If the pulse injection point is located in the middle of the cable, the propagation of the pulse along the cable conductor can be illustrated in Fig. 14.…”