Dielectric Response Spectroscopy Research Articles

Effects of Temperature Gradient Induced Aging and Moisture Distribution on Dielectric Response Measurement for Transformer Insulation

Internal temperature distribution of an oil-immersed transformer is not uniform, resulting in an axial moisture gradient. Thus, the internal insulating paper ages unevenly with the synergetic impact of temperature and moisture. To examine the aging characteristics and moisture dispersion mechanism of insulating paper in a nonuniform system. A discretized aging kinetic model is proposed to analyze the nonuniform aging impact of insulating paper. Then, dielectric response spectroscopy (DRS), including frequency-domain spectroscopy (FDS) and polarization and depolarization current (PDC), is measured to illustrate the effect of nonuniform effect on the DRS test. Findings indicate that: 1) temperature gradient is a more important factor in nonuniform aging of paper than moisture distribution; 2) both the amplitude of FDS and PDC decrease as the moisture distribution becomes more uniform; and 3) the conductance of insulating paper with diverse nonuniform moisture content and aging degrees can be interpreted by the proposed mathematical model, in which the identified parameters are positively correlated with the deterioration degree of internal insulation materials.

Dielectric Response Spectroscopy as Means to Investigate Interfacial Effects for Ultra-Thin Film Polymer-Based High NA EUV Lithography.

Extreme ultra-violet lithography (EUVL) is the leading-edge technology to produce advanced nanoelectronics. The further development of EUVL is heavily based on implementing the so-called high numerical aperture (NA) EUVL, which will enable even smaller pitches up to 8 nm half pitch (HP). In anticipation of this high NA technology, it is crucial to assess the readiness of the current resist materials for the high NA regime to comply with the demanding requirements of resolution, line-edge roughness, and sensitivity (RLS). The achievable tighter pitches require lower film thicknesses for both resist and underlying transfer layers. A concern that is tied to the thinning down is the potential change in resist properties and behavior due to the interaction with the underlayer. To increase the fundamental understanding of ultra-thin films for high NA EUVL, a method to investigate the interplay of reduced film thickness and different patterning-relevant underlayers is developed by looking at the glass transition temperature (Tg) of polymer-based resists. To minimize the ambiguity of the results due to resist additives (i.e., photoacid generator (PAG) and quencher), it was opted to move forward with polymer-only samples, the main component of the resist, at this stage of the investigation. By using dielectric response spectroscopy, the results obtained show that changing the protection group of the polymer, as well as altering the polymer film thickness impacts the dynamics of the polymer mobility, which can be assessed through the Tg of the system. Unexpectedly, changing the underlayer did not result in a clear change in the polymer mobility at the tested film thicknesses.

From the editors

This issue of the Magazine presents articles related to cable diagnostics and technology. Two of them, written by authors from Canada and Australia, summarize experiences and research activities on the use of dielectric response spectroscopy for diagnoses of insulation condition in medium voltage cables. The third article presents work performed in the USA on development of superconducting gas insulated cable system for power transmission at voltage level above 10 kV. Finally, the fourth article, from Norway, raises the importance of mesoscale material effect on the performance of cable joints.

Effects of alkyl group size on the structure and dynamics of poly(n-alkyl methacrylate)-based ionomers

The effects of alkyl group size on the structure and dynamics of poly(n-alkyl methacrylate)-based ionomers were investigated in this study. Ionomer samples were synthesized via the reversible addition–fragmentation chain transfer copolymerization of sodium styrene sulfonate and alkyl methacrylate with different alkyl groups (methyl, butyl, hexyl, lauryl, and octodecyl groups) and with varying ion contents. The samples were characterized by dielectric response spectroscopy (DRS), X-ray scattering, and linear viscoelasticity (LVE) measurements. X-ray scattering revealed ionic peaks indicative of spacing between ion aggregates. The interaggregate spacing decreased with increasing ion content when the alkyl groups were methyl, butyl, or hexyl groups. This observation is in accordance with the trend reported for sulfonated polystyrene, which has been extensively studied. In contrast, the interaggregate correlation peak merged with the backbone correlation peak when the alkyl groups were lauryl or octodecyl groups, suggesting that the steric repulsion of the long side chains partly suppressed the interchain association. Quantitative analysis of LVE showed that the sol-to-gel transition occurred at a higher number of ions per chain for samples with longer alkyl groups, lending support to the idea that long side chains generated increased steric repulsion. In addition, the plateau region broadened gradually with increasing alkyl group size, reflecting an increase in electrostatic interaction energy among the ionic groups. This increase was attributed to a reduction in the polarity of the polymer medium as the size of the nonpolar alkyl group increased, as detected by DRS.The effects of alkyl group size on the structure and dynamics of poly(n-alkyl methacrylate)-based ionomers were investigated in this study. Ionomer samples were synthesized via the reversible addition–fragmentation chain transfer copolymerization of sodium styrene sulfonate and alkyl methacrylate with different alkyl groups (methyl, butyl, hexyl, lauryl, and octodecyl groups) and with varying ion contents. The samples were characterized by dielectric response spectroscopy (DRS), X-ray scattering, and linear viscoelasticity (LVE) measurements. X-ray scattering revealed ionic peaks indicative of spacing between ion aggregates. The interaggregate spacing decreased with increasing ion content when the alkyl groups were methyl, butyl, or hexyl groups. This observation is in accordance with the trend reported for sulfonated polystyrene, which has been extensively studied. In contrast, the interaggregate correlation peak merged with the backbone correlation peak when the alkyl groups were lauryl or octodecyl gro...

Investigation on Insulation Performance of Thermally Aged Natural Ester Oil Impregnated Pressboard

An attempt is made to understand the effect of thermal ageing on natural ester oil impregnated pressboard material. Surface discharge inception voltage of natural ester oil impregnated pressboard material is reduced drastically under AC, harmonic AC voltages and with DC voltages with high ripple content. Phase-resolved partial discharge studies show an increase in the number of discharges for natural ester oil impregnated pressboard (OIP) aged at higher temperature, under AC and harmonic AC voltages with different total harmonic distortions. Surface potential measurement study complies with results obtained by surface discharge inception voltage. It indicates the presence of high-density charge traps evolved as a function of ageing time and temperature. Laser-induced breakdown spectroscopy analysis is carried out to understand the characteristic variation with thermally aged OIP material. A decrease in plasma temperature is observed for sample aged at higher temperature. Differential scanning calorimetric studies indicate reduction in peak temperature with thermally aged specimens. Ageing observed to affect mechanical strength of the cellulosic material, as indicated by tensile test. Dielectric response spectroscopy study indicates that with an increase in thermal ageing, the permittivity, tan(δ), DC conductivity and relaxation time have increased. A reduction in activation energy of the aged material is observed, which indicates the status of the OIP material.

Investigation on thermal ageing impact on dielectric properties of natural ester oil

Ester oils are evolving as next-generation transformer insulants, and it is essential to understand their characteristic variation upon thermal ageing. Corona inception voltage reduces with thermally aged ester oil under AC and DC voltages. The UHF signal generated due to corona discharge activity has energy content in the range 0.4–4 GHz. The magnitude and energy content of the UHF signal formed due to corona activity increases with thermally aged oil. Ionic mobility studies are carried out to understand the impact of thermal ageing on polarization and depolarization current, ion concentration, and ionic radius formed in the oil. Thermal ageing of ester oil leads to an increase in the ionic mobility of oil samples along with an increment in the ionic concentration. The conductivity of oil is observed to increase with ageing, accompanied by a reduction in ionic radii. The effect of voltage stress shows enhanced conductivity for thermally aged oil samples. Dielectric response spectroscopy exhibits higher loss and permittivity values for thermally aged oils. The physicochemical analysis shows a gain in viscosity, moisture content and turbidity, and a marginal loss in thermal conductivity due to the formation of new molecular species. UV analysis exhibits a significant redshift in the oil sample aged at a higher temperature.

Form II to I transformation of polybutene-1 and copolymer of butene-1 and ethylene: A role of amorphous phase

Polymorphic transformation from the form II to form I crystal was investigated for isotactic polybutene-1 (PB) and butene-1/ethylene copolymers (PBE) with differential scanning calorimetry (DSC) and dielectric response spectroscopy (DRS). DRS detected the so-called α relaxation of segments within the amorphous phase, and DSC traced a degree of form II to I transformation with time. It turned out that incorporation of the ethylene comonomers in PBE suppressed the crystallization and plasticized the amorphous phase, and the II to I transformation was greatly accelerated in particular at low T close to Tg. To normalize Tg enabled normalization of the α relaxation frequency (detected in DRS), but not the II to I transformation rate (detected in DSC): extra acceleration was noted for samples with a number fraction of ethylene monomers of 4.3% or higher. The extra acceleration is attributed to (1) heterogeneity of segmental mobility that facilitates the crystal growth and (2) crystal defects accumulating at the fold surface that cause internal stress to accelerate the nucleation.

Linear and non-linear dielectric spectroscopy on ammonium doped rochelle salt

In this work we present a thorough investigation of the mixed system of Rochelle salt doped with ammonium, with 0 ≤ x ≤ 1 for [Na(K1-x(NH4)x)C4H4O6 · 4H2O]. This interesting system is known to exhibit a rich phase diagram with a variety of polar and non-polar phases. However, most of the earlier investigations date back many decades and the experimental advances made since then should enable new insight into the physical nature of its phase diagram. We studied single crystals of 18 doping concentrations using linear and non-linear frequency-dependent dielectric response spectroscopy. In the low field measurements a variety of relaxation features are detected and analyzed in detail. The results for two concentrations of x = 0 and x = 0.15 are described qualitatively with a simple model. The most important outcome of the present work is the detection of a new electrically ordered phase for concentrations 0.18 < x < 0.89.