A Contribution to Everlasting Electrical Insulation for DC Voltage: PD-Phobic Materials

Abstract

This paper focuses on the design of insulating materials candidate from DC-supply applications, proposing viable solutions that may increase the defect-tolerance of an insulation system and avoid the presence of highly energetic phenomena, specifically partial discharges, which can cause premature insulation breakdown. It is shown that, in principle, polymeric materials for DC insulation can be structured, possibly through nanotechnology, to avoid partial discharge inception in steady state even in UHVDC cables and high-field design insulation systems, which would exclude partial discharge degradation from the aging factors that can affect insulation reliability and life. This approach may provide basic tools to design DC insulation having electro-thermal life and reliability of virtually unlimited extent, thus of so-called PD-phobic materials. INDEX TERMS Cables, electro-thermal life, HVDC, insulation reliability, nano-filled materials, partial discharge (PD), partial discharge inception voltage (PDIV), polymeric materials.

Designing a HVDC Insulation System to Endure Electrical and Thermal Stresses Under Operation. Part I: Partial Discharge Magnitude and Repetition Rate During Transients and in DC Steady State

“…where is the gas pressure inside the cavity. This holds approximately also for cylindrical cavities, replacing with cavity height, ℎ , [2,3,5,13,[21][22][23]. For voltage transients, the PD repetition rate as a function of time, ( ), from beginning of the voltage transient (cable energization/voltage polarity inversion), 0 , to DC steady state condition, d , and can be estimated roughly as: (15) where d corresponds to steady state condition and 0 to the PD repetition rate in the initial instants of electric field variation, hence 0 = (0 + ).…”

“…The steady-state dependence of electrical conductivity on temperature and electric field can be exploited using a wellknown empirical model [3][4][5][6]:…”

“…During electrical and thermal transients, the electric field profile in insulation and internal defects may vary significantly. There might be a significant difference in field profile between the conductivity-driven distribution, in DC steady-state, [5], and the permittivity-driven one, which establishes at the beginning of voltage (and sometimes load) transients [2,3]. PD might incept in insulation defects (cavities) during transients, but not in DC steady-state, if the insulation is designed properly to work (at any operating temperature) at nominal voltages below the DC steady-state partial discharge inception voltage, PDIVDC.…”

“…In [5] the authors considered insulation system design in DC steady-state, that is, when electric field transient rate is negligible during operation life.…”

Charging and Discharging Current Measurements and Impact of Polarization Dynamics on Electric Field Modeling in HVDC Paper-Insulated Cables

“…Even though the HVDC cable insulation technology has been moving recently towards solid and homogeneous dielectrics [13,14], oil-paper and laminated insulation has been and is still used, especially at the largest values of supply voltage. Therefore, this paper deals with the mature impregnated oil-paper insulation technology.…”