Rohitha Dhara

Comparative study of synthetic and natural clay filled PP films under surface discharges

It is known from literature that addition of small wt% of nanofillers into pure polypropylene matrix improves the electrical characteristics by many folds. This study is intended to compare the effect of natural and synthetic nanocomposites on the PD resistance when introduced in small concentrations in the base PP material. This work investigates the effect of type of nanofiller and its content on the PD resistance of PP films under surface discharges. The sample aging is performed under a voltage that constantly increases with time (Ramp voltage) to minimize the effect of space charge redistribution during the aging process on the sample PD behavior and PD characteristics. Samples with 0, 2, 6 wt% of natural organoclay nanocomposites and 2, 4, 8 wt% of synthetic organo clay nanocomposites are considered for this purpose. These samples are subjected to surface PDs and the degree of surface erosion is quantified by Optical microscope and surface Profilometer.

Comparative analyses of partial discharge characteristics of polypropylene films with natural and synthetic nanocomposites

Homogeneous incorporation of nanofillers into the polymer matrix improves electrical properties of polypropylene film. In this research work, step voltages were applied on natural and synthetic nanofilled PP and corresponding PD characteristics were recorded and analyzed systematically. In order to quantify PD Resistance, Surface Erosion was also measured for each sample. Weibull Scale Factor analyses indicates that discharge magnitude is higher in synthetic nanofilled PP than in natural nanofilled one, when filler concentration is similar. For both types of samples PD Resistance increases as filler concentration increases but the effect is more significant in natural than in nanofilled samples.

Evaluation of aging in nanofilled polypropylene by surface discharges

Literature indicates conflicting results on improvement/degradation of electrical characteristics due to introduction of nanofillers into polymers. Since polypropylene has superior electrical, mechanical and thermal properties and has significant utility in electrical industry, this work investigates the effect of nanofiller content on the partial discharge resistance and breakdown strength of the polypropylene films with 0%, 2% and 6% organoclay nanofillers. Since the surface discharges are random in nature, the overall partial discharge behavior is quantified in terms of temporal behavior of the Weibull parameters of the partial discharge pulse amplitude spectra obtained during sample aging and analyzed within the framework of time series analysis. Experiments indicate that the partial discharge characteristics are affected by the percentage of nanofiller content. Microscopic examinations indicate that on exposure to aging by partial discharges, the defect volume decreased in nanofilled polymer and was found to be least in samples where nanofiller content was below the percolation threshold. Profilometric studies indicate that the partial discharge resistance increases with increase in filler content. Results indicate that in fresh unaged samples, the breakdown strength improves with nanofiller content. However, the reduction in breakdown strength due to aging in nanofilled samples is noticeably higher as compared to unfilled samples.

An investigation into the effect of varying the main field and local field on the PD characteristics of nanofilled polypropylene films

When a rod - plane electrode system with a dielectric barrier is subjected to a power frequency voltage, the progression of partial discharges is dependent on the combined field due to applied voltage and local field caused by residual charges resulting from earlier partial discharges. The goal of this paper is to investigate the effect of variations in main (applied) field in comparison to variations in local field due to space charges on the progression of surface partial discharge behavior in polymer nanocomposites. In the first set of experiments, keeping all the other conditions constant, the effect of variation in gap spacing on the partial discharge behavior and its effect on depth of erosion in unfilled polypropylene is studied. In the second set of investigations, keeping the main field constant, composition of the polymer nanocomposite (i.e. content of the nanofiller) of the dielectric barrier is varied thereby altering the local fields by virtue of their difference in response to PD occurrence. The results of our investigations and their analysis is presented.

Effect of type of aging voltage on the residual breakdown strength of polypropylene films with natural and synthetic nanofillers

The aging conditions play a prominent role on the remnant breakdown strength of the samples as the partial discharge characteristics which affect the sample performance change drastically with the type of aging voltage. During aging, the formation of space charge that causes change in partial discharge characteristics depends on the electric field applied during aging. In this work, an investigation into remnant breakdown strength of natural and synthetic nanofilled and unfilled PP is done when aged under different types of voltage profiles. Synthetic (2, 4 and 8 wt-%) and natural (0, 2 and 6 wt-%) organoclay samples were used in this experiment. The nanocomposites were aged under different aging conditions. Samples of same composition were exposed to constant voltage aging, step voltage aging, and ramp voltage aging. The various types of voltages were applied to the nanocomposites to observe how they would behave under different aging conditions. Breakdown strength analyses was done on aged and unaged samples to evaluate the effect of PD on the remnant breakdown strength of samples with and without nanocomposites.

Statistical analysis of partial discharges evolved during aging of synthetic nanofilled polypropylene

Introduction of nanofillers into polypropylene matrix has shown to improve the partial discharge resistance and breakdown strength. This work details the various statistical techniques that can be used to effectively analyze and forecast PD data obtained. PP samples made of base polymer and loaded with 1%, 2%, 4% and 8% synthetic nanofillers were aged under surface partial discharges. The acquired partial discharge pulse amplitude spectra were quantified in terms of Weibull scale (α) and shape (β) parameters. The sequential observations of these parameters collected at regular intervals of time constituted the two time series which are used here to analyze the PD data. The theoretical framework for analyzing & forecasting time series of Weibull shape and scale parameters of partial discharge pulse amplitude spectra using the auto & cross correlations to arrive at parsimonious models that can be used to analyze and forecast the data are presented.

Effect of variation in main field and nanoparticle content on the partial discharge characteristics of polypropylene nanocomposites

Abstract. The effect of varying the main and local field on the partial discharge characteristics of polypropylene film is studied by analyzing the temporal behavior of partial discharge parameters. In the first set of experiments, keeping the applied voltage constant, the gap spacing is varied altering the applied field. When the gap is relatively small, discharges appear in quick succession deepening the craters in front of the rod tip where space charges are widely distributed, precipitating discharges of wide range of amplitudes. At relatively larger spacing, the discharge behavior is largely controlled by electric field distribution. In the fixed gap experiments, the local field is varied by introducing polymer nanocomposites that have different filler content. For a fixed gap and constant voltage, discharge magnitudes are lower in samples with nanofiller content below the percolation threshold than in the base polymer. The scatter in discharge magnitudes is lower in samples with nanoparticle content below the percolation threshold than in samples with nanofiller content above the threshold. The major conclusion is the maximum advantage of adding nanofillers is gained only when the particle content is below the percolation threshold.

Effect of aging with partial discharges on the remnant breakdown strength of polypropylene films with natural and syntheticnanofillers

Uniform dispersion of small amounts of nanofillers into Polypropylene (PP) base polymer have shown to improve the dielectric properties such as Partial Discharge (PD) resistance and breakdown strength (BDS). A comparative analyses of the effect of addition of natural and synthetic nanofillers on the PD characteristics and the BDS prior to and after aging with PD have been performed. Results indicate that addition of both type of fillers significantly reduce maximum PD magnitude (Qmax). The Weibull characteristic BDS magnitudes were observed to improve with addition of nanofillers.

Investigation into the effect of space charges on the surface erosion of synthetic and natural organoclay nanofilled PP films

Literature indicates space charge formation in the polypropylene (PP) films when subjected to Partial Discharges (PD). The space charge thus formed also alters the PD characteristics in turn altering the PD resistance. The main focus of this work is to investigate the effect of space charge formed during the PD aging process on the main field with minimal space charge redistribution times. AC Ramp voltage that constantly increases with time at a rate of 667 V/s was applied across the samples for 20 second duration. PP films with natural organo clay nanofillers (0 (wt/v) % referred to as PP+N0% (base polymer) and 2 (wt/v) % referred to as PP+N2%), and synthetic organo clay nanofillers (2 (wt/v) % referred to as PP+S2%) were considered for experimentation. Results indicate that with the inclusion of the either natural or synthetic organo clay nanoparticles, with in the percolation threshold limit of nanofiller concentration, the final electric stress is reduced thus enhancing the resistance to surface PDs.

Study of partial discharge characteristics of nano filled polypropylene films according to the variation in electric field distribution on the sample

In this work, partial discharge (PD) measurements of natural nanofilled polypropylene (PP) films have been performed by systematically varying the air gap between rod and plane electrodes to study the effect of field variation on PD characteristics. Results indicated that Partial Discharge Inception Voltage (PDIV) increases when either the nanofiller concentration or air gap is increased. Further, during aging, average PD magnitude and Weibull Scale Factor of PD pulse distributions decrease with increase in air gap. Electric field simulation results agree with our experimental findings.