H. St-Onge

Electrical conduction of polyethylene below and above its melting point

The electrical conduction of low-density polyethylene (LDPE) has been investigated between 20 degrees C and 150 degrees C and up to 1 MV/cm. Special molded specimens and a self-compensating test cell were used; particular care has been taken in the control of experimental conditions. Absorption currents show broad maxima, while resorption currents display polarity reversal. Steady-state currents increase with a power law of the electrical field, and they tend to saturate at high fields and temperatures. Results are discussed in the framework of space-charge-limited conduction and dispersive hopping transport models. >

The Dielectric Properties of Silicone Fluids

Silicone fluids constitute a very diverse family of organosiloxane liquids having the general structure (CH<inf>3</inf>)<inf>3</inf>-Si-[O-Si-(R)<inf>2</inf>]<inf>n</inf>-0-Si-(CH<inf>3</inf>)<inf>3</inf> in which R may represent almost any organic group. These fluids are coming increasingly in use in dielectric and insulating systems because of their thermal, electrical and chemical characteristics and particularly as they are becoming economically competitive.

Thermal Capability Of Solid Dielectric Cable Materials

This paper describes a study of the temperature behavior of chemically cross-linked polymer materials used in conventional extruded cables. An extensive :study has been carried out into the electrical, mechanical, thermal and physico-chemical behavior of extruded dielectric materials as a function of temperature. Materials studied include XLPE filled XLPE, EPR compounds and semiconducting XLPE and data was obtained on specimens cut from full size extruded cables as well as laboratory molded specimens. The results are presented in a form that emphasizes differences and similarities between the behavior of XLPE and EPR materials at elevated temperatures. The use of those materials at elevated termperatures is discussed as regards to satisfactory cable operation under emergency conditions.

HPLC and DSC Analysis of Crosslinked PE from HV Cables

High performance liquid chromatography (HPLC) has beenused to simultaneously determine the amounts of antioxidant(Santonox(R) R), peroxide, acetophenone and ¿-methylstyrenepresent in crosslinked-polyethylene cable samples andmolded specimens, as well as to detect some other peroxidedecomposition products.It was found that the antioxidant is grafted to thepolymer chains after curing (even after partial curing).Results also seem to suggest that a reduction of the phenoliccharacter and perhaps of the effectiveness of thentiantioxidant might result from this grafting process. Peroxidedecomposition products were found to depend on the curingconditions used and to affect the dielectric behavior insome cases.Various XLPE and EPR materials have also been examined bydifferential scanning calorimetry (DSC), and experimentalprocedures were developed for evaluating the degree ofcrosslinking by DSC.This work was part of a program supported by the Electric Power Research Institute.

Dielectric Breakdown in Polyethylene at Elevated Temperatures

A two-terminal dielectric test cell for the study of the dielectric properties of viscous polymers above their softening temperature was used to perform 60 Hz breakdown measurements in polyethylene between 23 and 150°C. Molded specimens of polyethylene with embedded electrodes of parallel-plane configurations were employed. The interelectrode spacing was kept constant over the entire temperature range by suitable compensation of differential thermal expansion effects in the test cell. Low density (0.919 g/cm3) polyethylene was used for this study. The results show a marked decrease of the breakdown strength as a function of temperature between room temperature and the crystalline melting temperature, Tm. Above Tm the breakdown strength appears to be only weakly dependent on temperature. The results are analyzed with the help of Weibull statistics. The temperature dependence of the breakdown strength is discussed in the light of Artbauers theory of free volume breakdown.

Electrical Conduction in 3-Percent Carbon-Filied Polyethylene-Part 11: High-Field Results

The high-field conduction properties of 3% carbon-filled polyethylene were investigated. Detailed step-response measurements were made as a function of temperature and applied field. A near-quadratic dependence of the steadystate conduction current upon applied voltage was observed. The steady-state and transient absorption and resorption currents are discussed in the framework of physical models of space-charge limited conduction and charge carrier trapping.

A critical evaluation of analytical. techniques for the characterization of extruded dielectric cables

Various analytical techniques used to characterize cables are reviewed. It is shown that cable morphology can be evaluated simply by density and differential-scanning-calorimetry (DSC) measurements and that oxidation is best evaluated by Fourier-transform-infrared (FTIR) spectroscopy. Elemental contamination is best evaluated by neutron activation analysis and proton-induced X-ray emission (PIXE) measurements, whereas ions can be detected by ionic chromatography. It is shown that the water content of cables can be reliably measured by commercial instruments relying on coulometry and Karl-Fischer titration. >

Physical Behavior of Paraffinic Oils at Low Temperatures

This paper presents a study and an analysis of the low-temperature physical properties of a paraffinic oil refined from Canadian feedstock. The study demonstrates that a significant attribute of this oil is the mechanism of wax formation below the cloud point, This wax formation can explain the higher low temperature viscosity of the oil as compared to that of a naphthenic oil, its non-Newtonian behavior, and a critical temperature zone where the oil gels. Finally , DSC analysis was found successful to analyze this wax formation.

Space charge limited conduction in polyethylene

In a previous study of the electrical conduction properties of 3% carbon loaded polyethylene,1 a near quadratic dependence of the dc current on voltage was observed between 104 and 5 × 105 V/cm. This type of behavior is usually associated with space charge limited conduction and has been observed by several workers in unfilled polyethylene.2,3 This report deals with a detailed study of the time, voltage, and temperature dependence of this conduction regime in 3% carbon loaded polyethylene. By extending the measurements to higher temperatures than previously reported, new features of the current transients were observed.

A Study of Morphology in Polyethylene Filled with 3-Percent Carbon

Samples of polyethylene filled with 3-percent carbon were cooled from the melt at rates ranging from 104 to 10-1 C/min. The resulting degree of crystallinity, as measured from wide angle X-ray diffraction and density, was studied. Variations in the degree of crystallinity between 46 and 68% were observed. The role of morphology on the conduction properties of partially crystalline polymers is discussed.