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

Nugroho Adi,Gilbert Teyssèdre,Thi Vu,Ngapuli Sinisuka,Fulbert Baudoin

doi:10.3390/technologies5030046

Abstract

In the field of energy transport, High-Voltage DC (HVDC) technologies are booming at present due to the more flexible power converter solutions along with needs to bring electrical energy from distributed production areas to consumption sites and to strengthen large-scale energy networks. These developments go with challenges in qualifying insulating materials embedded in those systems and in the design of insulations relying on stress distribution. Our purpose in this communication is to illustrate how far the field distribution in DC insulation systems can be anticipated based on conductivity data gathered as a function of temperature and electric field. Transient currents and conductivity estimates as a function of temperature and field were recorded on miniaturized HVDC power cables with construction of 1.5 mm thick crosslinked polyethylene (XLPE) insulation. Outputs of the conductivity model are compared to measured field distributions using space charge measurements techniques. It is shown that some features of the field distribution on model cables put under thermal gradient can be anticipated based on conductivity data. However, space charge build-up can induce substantial electric field strengthening when materials are not well controlled.

Highlights

For energy transport purposes, the field of High-Voltage Direct Current (HVDC) technologies is booming at present due to the more flexible power converter solutions along with needs to bring energy from distributed production areas to consumption sites, including sub-sea links, and to strengthen large-scale energy networks [1]
When dealing with space charge in mass-impregnated paper insulated cables, Morshuis and Jeroense [39] distinguished microscopic space charges as due to charges trapped at imperfections in the insulation from macroscopic space charge resulting from temperature and field dependency of the conductivity of the dielectric
The field distribution within the insulation of cables under thermal gradient and polarity inversion can be obtained through simulation based on electrical conductivity data for the insulating material as a function of field and temperature

Summary

Introduction

The field of High-Voltage Direct Current (HVDC) technologies is booming at present due to the more flexible power converter solutions along with needs to bring energy from distributed production areas to consumption sites, including sub-sea links, and to strengthen large-scale energy networks [1]. The materials used for electrical insulation in the corresponding systems, being for cables, converters, bushings, etc., have specific requirements as the field distribution does not follow the same rules as for AC stress. Current (HVAC) systems, the stress distribution can be relatively well anticipated as it follows a capacitive distribution, i.e., function of the permittivity of materials. When switching to the DC case, the distribution is no longer capacitive in steady state, and moves to resistive field distribution after passing through a transient regime where space charges settle [2]. Polymers favor charge trapping phenomena which further makes uncertain the prediction of field distributions. The consequences of such features are local reinforcement of the electric field, representing possible weak points of the system with early breakdown. Addressing the above problems needs research and skills in many scientific aspects resorting to:

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Results

Discussion

Conclusion