Dielectric Dissipation Factor Measurements Research Articles

Insulation evaluation of MV underground cable with partial discharge and dielectric dissipation factor measurements

Insulation evaluation of MV underground cable with partial discharge and dielectric dissipation factor measurements

Bilateral Comparison of High-Voltage Capacitance and Dielectric Dissipation Factor at 50 Hz

NIM (National Institute of Metrology, China) and NMIA (National Measurement Institute, Australia) carried out a comparison program, which included low-voltage capacitance, the voltage dependence of high-voltage capacitance and the dielectric dissipation factor (DDF) at 50 Hz. The travelling standards included a low-voltage standard capacitor, a dissipation factor standard and a 100 kV compressed-gas capacitor. The capacitance and DDF of the standard capacitor, measured by the two institutes, agreed within 2 μF/F and 2×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> , respectively, at 50 Hz and 500 V. DDF measurements at nominal values of 0.00000, 0.0001 and 0.001 agreed within 6×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> at 50 Hz and 10 kV. The capacitance change of a 100 kV compressed-gas capacitor measured by the two institutes agreed within 2 μF/F over the voltage range from 10 kV to 100 kV. The success of the program proved comparisons using a re-filled high-voltage compressed gas capacitor and a low-voltage standard capacitor can be conveniently used to validate the complete traceability chain of the measurement of high-voltage capacitance at 50 Hz. The program also proved that DDF measurements with different implementations of traceability chain via capacitance and resistance would agree well within the uncertainties required by industrial measurements and a commercial DDF standard that has undergone international air travel would be sufficiently stable.

A modified dielectric dissipation factor measurement technique for transformer insulating oil

This paper proposes a low cost mechanism to accurately measure the dissipation factor and its allied effect over transformer insulating oil. The measuring circuit is a modified De Sauty bridge network where the accurate parameter measurement can been performed. The effect of stray capacitance over dielectric loss and dissipation factor has been nullified by the application of operational amplifier in the circuit. Different samples of transformer insulating oil have been tested based on their aging and moisture content to check the reliability of the proposed measuring technique. Experimental result shows the efficacy of the proposed method when compared to existing IEC and ASTM standard procedures and commercial measuring devices. Measurement error analysis with repeatability and uncertainty calculation shows promising result and is within the acceptable limits.

Reducing Hydrophilic Characteristics of Kraft Paper Insulation by Reinforcing With Surface Modified Rutile-TiO2 Nanoparticles

The hydrophilic nature of cellulose compromises the dielectric properties of kraft paper insulation when exposed to water and moisture. The effort to address this setback is an ongoing research enquiry. In the present work, surface-modified rutile-titanium dioxide nanoparticles (rutile-TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> NPs) are reinforced into cellulose pulp to fabricate a nanocomposite kraft paper insulation. Surface modification of the nano-filler particles is intended to reduce the hydrophilicity of the resultant nanocomposite kraft paper insulation. The nanoparticles (rutile-TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> NPs) improve other dielectric properties of the insulation. The chemicals used for the surface modification of the rutile-TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> NPs were the alkyl ketene dimer (AKD) and alkenyl succinic anhydride (ASA). The nanofiller retention, r dispersion and hydrophobic properties of the resultant reinforced kraft paper were experimentally analyzed. The results show that more than 50% of the nanofillers were retained within the reinforced kraft paper. Scanning electron microscopy (SEM) images showed evenly distributed nanofillers, with some traces of agglomeration. The moisture absorption property of the kraft paper specimen modified with rutile-TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> NPs containing 5 vol/vol% ASA improved by 74% compared to the control (reference) specimen. Water vapor transmission rate of the surface-modified nanoparticles reinforced kraft paper insulation decreased by 30%. Compared to the unfilled paper, the contact angle of water droplets on the surface of the reinforced kraft paper improved by 12%. Water absorption rate improved by being 4 times slower in paper specimens containing rutile-TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> NPs 5 vol/vol% ASA. Dielectric dissipation factor measurement results showed that the specimen modified with rutile-TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> NPs containing 5 vol/vol% had 40% lower dielectric losses than the reference samples. This study, therefore, has successfully improved the hydrophobic properties of kraft paper by filling it with surface-modified rutile TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> using 5% ASA as the nanoparticle surfactant.

Dielectric Dissipation Factor Measurements on New Stator Bars and Coils—Results from a Global Survey

This article presents analysis of the dielectric dissipation factor over a collection of more than 20,000 measurement records of new stator bars and coils.

DIELECTRIC DISSIPATION FACTOR IN THREE-CORE POWER CABLES

This article is devoted to the analysis of components of variance of the results of measurements of dielectric dissipation factor of insulation layers between the conductive elements of the construction of three core power cables with paper impregnated insulation in a common sheath. The analysis of components of variance was carried out by applying presented relations for the direct calculation of the dielectric dissipation factor. The accuracy of presented relations for the calculation of variance components was verified. The results of carried out analysis have shown that the variance of the dielectric dissipation factor measurements is mostly determined by the variances of multiplication of measurements of aggregate values of dielectric dissipation factor and coefficients depending on the partial capacitances of tested three core cable.

Modeling of dielectric dissipation factor measurement for XLPE cable based on Davidson-Cole model

Dielectric response analysis is one approach for the condition assessment of high voltage insulation systems, and measurement of the dissipation factor or tan δ is widely used in practice. This article presents an experimental study of DF measurement over the frequency range from 1 mHz to 50 Hz. Three different short sections of service-aged 11-kV cross-linked polyethylene cable are used as test specimens. Low-voltage polarisation / depolarisation current and frequency domain spectroscopy techniques are employed in the investigation. Following the experimental work, numerical analysis is carried out utilizing the Davidson-Cole (D-C) model. To optimize the final parameters of the model, numerical simulation is performed using 3 or 4 R-C branches with different values of Jonscher and D-C constants. It is shown that results from numerical simulation agree well with the experimental results over the tested frequency range.

Modeling of dielectric dissipation factor measurement for XLPE cable based on Davidson-Cole model

Dielectric response analysis is one approach for the condition assessment of high voltage insulation systems, and measurement of the dissipation factor or tan δ is widely used in practice. This article presents an experimental study of DF measurement over the frequency range from 1 mHz to 50 Hz. Three different short sections of service-aged 11-kV cross-linked polyethylene cable are used as test specimens. Low-voltage polarisation / depolarisation current and frequency domain spectroscopy techniques are employed in the investigation. Following the experimental work, numerical analysis is carried out utilizing the Davidson-Cole (D-C) model. To optimize the final parameters of the model, numerical simulation is performed using 3 or 4 R-C branches with different values of Jonscher and D-C constants. It is shown that results from numerical simulation agree well with the experimental results over the tested frequency range.

Stability of mineral oil and oil–ester mixtures under thermal ageing and electrical discharges

This study summarises the results of an experimental investigation on the stability of mineral-based oil mixtures when they are confronted with different ratios of synthetic ester under conditions of electrical discharge, electrical breakdown and a combination of both. The condition of the oil samples was assessed using diagnostic techniques such as gassing tendency, turbidity, dissolved decay products (DDP) and dielectric dissipation factor (DDF), according to ASTM standards. A comparison is made between the performances of fresh and aged samples. The results provide experimental evidence that the chemical composition of hydrocarbon blend is contributing factors to oil gassing. It was observed that aged oils release more gases than new one. It was also observed that the gassing tendency increased with increasing amount of ester for the mixed fluids. The pressure and the absorbance of gases vary proportionally with ester content. Under thermal stress, an increase in pressure is observed especially for the mineral oil sample. The turbidity, DDP and DDF measurements revealed higher values for mineral oil. Importantly, the stability improved with increasing ester content in the blends. Mixed mineral oil/ester therefore offers many advantages with concomitant cost reductions compared with pure synthetic esters.

Comparison of the mineral oil lifetime estimates obtained by differential scanning calorimetry, infrared spectroscopy, and dielectric dissipation factor measurements

In this study, improved observables and new endpoint criteria were developed to assess the remaining useful life of mineral transformer oil using differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FT-IR). The tested oil was exposed to thermal ageing at temperatures of 110, 120 and 130°C for times ranging from 100 to 2400h. The intensity of the infrared spectral band of the low-temperature inhibitor and the temperature of the thermo-oxidative DSC peak were considered for evaluation. The obtained results were correlated with standardized dielectric dissipation factor (tan δ) measurements. The results indicated that the analysed observables changed continuously during the applied thermal ageing. The endpoint criteria were subsequently determined and Arrhenius diagrams were constructed. The results demonstrated that the determination of the actual state or the lifetime of the transformer oil via DSC or FT-IR may be beneficial in terms of reducing the measurement time, the influence of moisture on the measurement results and the oil volume required for the tests. Thus, DSC and FT-IR represent promising alternatives to dissipation factor measurements.