High Voltage Insulation Systems Research Articles

Epoxy/BN micro- and submicro-composites: dielectric and thermal properties of enhanced materials for high voltage insulation systems

Hexagonal boron nitride (h-BN) is a very promising material for application in high voltage insulation engineering due to its high thermal conductivity and good electrical insulating properties. In order to study the effect of incorporating BN particles in epoxy resin, composites with different filler sizes and several BN loadings have been fabricated. Two different filler sizes, one micrometric with an average grain size of 9 μm and a submicrometric one with 0.5 μm, have been used to form composites. The amount of either type of BN in the matrix has been varied from 1 to 5 wt%. Dielectric and thermal performances of the test specimens have been assessed by means of Dielectric Spectroscopy, Differential Scanning Calorimetry, surface erosion, AC breakdown tests and thermal conductivity measurements. It has been found that incorporation of BN particles in the epoxy resin resulted in significant improvements of parameters such as resistance to electrical discharge, as well as diminished dielectric losses for the composites at higher temperatures. Furthermore, BN composites with 5 wt% filler loadings have shown a noteworthy enhancement of thermal conductivities, which was more distinct for the submicrometric BN composite.

Application of HFCT and UHF sensors in on-line partial discharge measurements for insulation diagnosis of high voltage equipment.

Partial discharge (PD) measurements provide valuable information for assessing the condition of high voltage (HV) insulation systems, contributing to their quality assurance. Different PD measuring techniques have been developed in the last years specially designed to perform on-line measurements. Non-conventional PD methods operating in high frequency bands are usually used when this type of tests are carried out. In PD measurements the signal acquisition, the subsequent signal processing and the capability to obtain an accurate diagnosis are conditioned by the selection of a suitable detection technique and by the implementation of effective signal processing tools. This paper proposes an optimized electromagnetic detection method based on the combined use of wideband PD sensors for measurements performed in the HF and UHF frequency ranges, together with the implementation of powerful processing tools. The effectiveness of the measuring techniques proposed is demonstrated through an example, where several PD sources are measured simultaneously in a HV installation consisting of a cable system connected by a plug-in terminal to a gas insulated substation (GIS) compartment.

Determination of partial discharge time lag in void using physical model approach

Repetition of partial discharge (PD) activities within a dielectric insulation of high voltage equipment may lead to dielectric breakdown, eventually resulting in failure of the whole equipment. Thus, PD measurement is essential in high voltage insulation system. Modeling of PD activity may increase an understanding of PD phenomenon. One of the parameters which can be determined from PD modeling is the statistical time lag. In this work, a physical model of PD using finite element analysis (FEA) method has been developed to determine the relationship of statistical time lag with different applied stresses; these include different applied voltage, frequency and temperature. The statistical time lag as a function of different applied stresses was determined through comparison between measurement and simulation results. The proposed experimental-modeling approach may increase an understanding on the physical explanation about the statistical time lag.

Experimental Investigations and Ageing Studies on Effects of Insulating Barriers in Transformer Oil during High Frequency High Voltage Transients in Inhomogeneous Field

Insulating barriers utilized in complex high voltage insulation systems has been exploited widely by manufacturers of power apparatus. Barriers have found utility in a variety of power apparatus for protection against direct lightning strokes, as an interface at the boundaries of composite insulation materials etc. Though investigations have been carried out by researchers on the breakdown characteristics, barrier position in the gap, influence of space charge etc these characteristics have been analyzed based on aspects pertinent to classical testing procedures only. Advent of high speed switching devices in power systems provides avenues to investigate the effect of insulation performance due to High Frequency High Voltage (HFHV) also. Further, uncharacteristic failures in oil filled distribution transformers have been reported indicated fast transients as the major cause for failures which was not revealed during classical laboratory testing. This research focuses on the influence and effects of solid insulating barriers placed in transformer oil due to HFHV in inhomogeneous fields. Test cell arrangement has been fabricated for carrying out experimental investigations to adhere international standards. Exhaustive experimentation has been performed to infer the influence of the position of barrier, nature of field and breakdown voltage, erosion characteristics of the barrier at an appropriate range of frequencies. A detailed comparison between HFHV and classical power frequency voltage has been carried out. The nature of ionization at the barrier interface and the subsequent increase in the breakdown voltage as explained by Double Electric Layer (DEL) theory has been cross validated. In addition, a study has also been carried out to assess and characterize the ageing of oil based on Dissolved Gas Analysis (DGA) analysis using Weibull distribution.

The influence of ultrasound signal parameters on sonoluminescence light intensity

Abstract Topics of this article concern the study of the fundamental nature of the sonoluminescence phenomenon occurring in liquids. At the Institute of Electrical Power Engineering at Opole University of Technology the interest in that phenomenon known as secondary phenomenon of cavitation caused by ultrasound became the genesis of a research project concerning acoustic cavitation in mineral insulation oils in which a number of additional experiments performed in the laboratory aimed to determine the influence of a number of acoustic parameters on the process of the studied phenomenona. The main purpose of scientific research subject undertaken was to determine the relationship between the generation of partial discharges in high-voltage power transformer insulation systems, the issue of gas bubbles in transformer oils and the generated acoustic emission signals. It should be noted that currently in the standard approach, the phenomenon of generation of acoustic waves accompanying the occurrence of partial discharges is generally treated as a secondary phenomenon, but it can also be a source of many other related phenomena. Based on our review of the literature data on those referred subjects taken, it must be noted, that this problem has not been clearly resolved, and the description of the relationship between these phenomena is still an open question. This study doesn’t prove all in line with the objective of the study, but can be an inspiration for new research project in the future in this topic. Solution of this problem could be a step forward in the diagnostics of insulation systems for electrical power devices based on non-invasive acoustic emission method.

Condition monitoring and diagnostics [Editorial

This special issue of the IEEE Transactions on Dielectrics and Electrical Insulation (TDEI) is devoted to Condition Monitoring and Diagnostics (CMD) of high voltage insulation systems. Our intension was to pinpoint actual trends in this area of research and engineering. Especially the diagnostics of insulation systems of power equipment becomes particularly important, driven by multi-stress operational conditions and the strive for higher transmission capacity. Also the increasing requirements with respect to safety and reliability in electric power and industrial networks as well as their environmental compatibility set new and special demands.

Partial discharge analysis using energy patterns

Partial Discharge detection is an important tool for diagnosis of High Voltage insulation systems. The Phase Resolved Partial Discharge (PRPD) data obtained from Partial Discharge (PD) detectors is used to construct the energy versus phase angle plots called as Energy Patterns. The energy patterns in case of three types of discharges viz. delamination, void and slot discharges for High Voltage rotating machines are discussed in this paper. The energy patterns are correlated with tanδ measurements.

Conductivity Variation Observed by Polarization and Depolarization Current Measurements of High-Voltage Equipment Insulation System

Conductivity Variation Observed by Polarization and Depolarization Current Measurements of High-Voltage Equipment Insulation System

Conductivity Variation Observed by Polarization and Depolarization Current Measurements of High-Voltage Equipment Insulation System

Nondestructive and time domain dielectric measurement techniques such as polarization and depolarization current (PDC) measurements have recently been widely used as a potential tool for determining high-voltage insulation conditions by analyzing the insulation conductivity. The variation in the conductivity of an insulator was found to depend on several parameters: the difference between the polarization and depolarization currents, geometric capacitance, and the relative permittivity of the insulation material. In this paper the conductivities of different types of oil-paper insulation material are presented. The insulation conductivities of several types of electrical apparatus were simulated using MATLAB. Conductivity insulation was found to be high at high polarizations and at the lowest depolarization current. It was also found to increase with increasing relative permittivity as well as with decreasing geometric capacitance of the insulating material.

High voltage insulation system monitoring and diagnostics: generators, power transformers

During last decades a variety of different practices having the main intention to assess the expected reliability and remaining life span of large units in the power system have been introduced and implemented. During the first period a so called Timely Based Diagnostics (TBD) with a defined periodicity was practiced. Further on the development and introduction of improved testing and measuring methods and tools brought on the Condition Based Diagnostics (CBD). Finally, the Reliability Oriented Diagnostics (ROD) fostered by appropriate methods and tools is practiced by many utilities. The article depicts the most important testing and measuring procedures reported during the last years and particularly those which were long-term practiced in the Milan Vidmar Electric Power Research Institute contributing to an appropriate and efficient asset management.

Compact power supplies for tokamak heating

As extension of power transformers, efficient large-scale contactless power transfer between stationary and reference frames is a problem of world-wide importance, to such applications as electric vehicles, materials handling and plasma heating for fusion science. Tokamak is the common developed fusion device where heating is recognized as one of its key technologies for its future reactor roadmap. Snubber is often used as protection device in NBI system for Tokamak heating [1-3]. The present NBI generally use 50/60 Hz High Voltage (HV) Insulation Transformers to configure its dc power supply to offer the bias current to the snubber, which could use the full flux swing of the core from the negative saturation point to the positive one of its BH major loop. The snubber weight could then be decreased to its half by using the bias power supply. But this 50/60Hz HV insulation transformer is much heavier than High Frequency (HF) High Voltage (HV) Insulation system. The paper gives the requirement, design and test of this Compact Power Systems based on HF HV Zero Current Switching (ZCS) technologies for Experimental Advanced Superconducting Tokamak (EAST) NBI snubber as well as its potential for its compact HVDC power supply. Its new control strategy is also implemented with one macro pulse composed by the digital defined continuous micro pulses. Some experimental evaluations have been done to verify the analysis results, which have been extended to over 100s and could be used for detail engineering design of power supplies for EAST based on IGBT.

Adapting particle swarm optimisation for charge simulation method

The charge simulation method (CSM), owing to its favourable characteristics, is commonly used for electric field analysis of high-voltage insulation systems. In order to improve the precision of the electric field calculation and to minimise the reliance on personal experience, a novel combination of particle swarm optimisation (PSO) and CSM is proposed. In this, the optimum allocations of the simulating charges can be obtained using PSO. The conventional CSM is briefly considered and the optimised version is formulated. The potential distribution between two spherical electrodes is determined as a sample problem. Also, the solution of field distribution with non-axial symmetry resulting from a floating spherical conductor between the spheres is considered. The optimised CSM using PSO proved to be more efficient and there is no need for the experience that was required to set up and implement a solution of this kind.

Cellular Neural Network on Digital Signal Processor: An Algorithm for Object Recognition

In this article, an attempt is made to pictorially analyze certain images pertaining to partial discharge in a high-voltage insulation system. The data obtained is in pictorial form, which can be represented in its equivalent pixel value and is stored in a file. These files are categorized and labeled. A cellular neural network is used to analyze these labeled files, and the convergence obtained before and after training is tabulated. Convergence will be faster after training, and the cellular neural network learns from each sample; hence, better classification is possible after training. A digital signal processor is used to simulate the cellular neural network, as the architecture of the digital signal processor is “multiply and accumulate,” which is ideal for all matrix-based calculations. A fixed-point digital signal processor is used (TMS320C542, Texas Instruments, Dallas, Texas, USA) for the present analysis. All programming for the cellular neural network is done in C language and converted to assembly language using Code Composer Studio (Texas Instruments, Dallas, Texas, USA).

Impregnating compounds of the H—C temperature classes

A review has been carried out of electrical-insulating compounds of the H—C temperature classes in Russia and abroad. A lack of electrophysical data on hardened compounds at operating temperatures is noted. The results of tests of some compounds using procedures used in Russia are presented. The necessity of using compounds with low dielectric loss tangents for high-voltage insulation systems applied at higher temperatures is shown.

Phase-resolved rise-time-based discrimination of partial discharges

The novel discrimination method of partial discharges (PDs) based on the analysis of PD pulse waveform with special focus on the rise time is presented. This parameter of PD current pulse has various values for different forms of discharges in insulation systems. The time waveforms and the rise time represent an important attribute of a PD pulse, which might be used as a distinctive factor between types of discharges. The composition of phase-resolved rise-time (PRRT) images has been described and for phase-resolved PD rise-time registration, the dedicated measuring systems have been developed. The PRRT registration of PD created a new approach to the description of PD mechanisms and their identification and discrimination for diagnostics of high-voltage insulation systems.

Dielectric response measurements utilizing semi-square voltage waveforms

Dielectric response measurements belong to the group of diagnostic tools used for quality evaluation of high voltage insulation systems. A measurement system called arbitrary waveform impedance spectroscopy (AWIS) is presented here which is capable of utilizing the harmonic content of repetitive voltages with a semi-square waveform and the corresponding current response to perform dielectric response measurements. Extensive circuit modeling and calibrations are required in order to perform accurate measurements. AWIS could offer new possibilities, especially for continuous monitoring of the dielectric properties of high voltage components and systems. The accuracy of the technique in both low and high voltage applications is verified by comparison with results obtained by means of the frequency domain spectroscopy (FDS) technique.

분포 통계 해석에 의한 계면 결함 부분방전 진단

Most of the high voltage insulation systems, such as the power cable joint having hetero interface, are composed of more than two different insulators to improve insulating performance. The partial discharge(PD) in these hetero interface is expected to affect the total insulation performance. Thus, it is important to study electrical properties on these interfaces. This study described the influence of copper and semiconductive substance defects on -q-n distribution between the interface of the model cable joints to classify PD source. PD was sequentially detected for 600 cycles of the applied voltage. The K-means cluster analysis has been analyzed to investigate the -q-n distribution. The skewness-kurtosis(Sk-Ku) plot from K-means clustering results was defined to quantify cluster distribution and classify distribution patterns. The Sk-Ku plot is composed of skewness and kurtosis along abscissa and ordinate which indicate the asymmetry and the sharpness of distribution. As a result of the Sk-Ku plot, it was confirmed that the data was distributed in 1st 2nd and 3rd quadrant at copper foreign substance defect, but in case of semiconductive foreign substance, the data was distributed in 2nd quadrant only.

Surface tracking in polymers: a pattern discrimination technique using fractals

The geometrical patterns of dielectric breakdown like electrical trees, surface discharges and lightning are known to be fractal in nature. These fractal patterns can be analysed numerically using fractal dimensions and lacunarity. Surface tracking occurring in high voltage insulation systems is a very complex phenomenon and more so the shapes of tracking patterns. It has been fairly well established that the shapes and the underlying parameters causing tracking have a one-to-one correspondence and therefore methods to describe and quantify these patterns must be explored. This contribution reports preliminary results of such a study wherein two-dimensional (2D) tracking patterns of gamma irradiated ethylene propylene diene monomer (EPDM) were analysed and found to possess fairly reasonable pattern discriminating abilities. This approach appears promising and further research is essential before any long-term predictions can be made. It is also interesting to note that the ac tracking resistance of EPDM decreases with an increase in the radiation dose. The erosion depth affected by radiation was also studied.

Discussion of "Practical Value of Internal Partial Discharge Measurements on High-Voltage Insulation Systems for Rotating Machines"

Discussion of "Practical Value of Internal Partial Discharge Measurements on High-Voltage Insulation Systems for Rotating Machines"

An HTS SQUID picovoltmeter used as preamplifier for Rogowski coil sensors

In the design and development of high voltage insulation systems, partial discharge measurements are often used for system characterization and evaluation. One commonly used sensor for such measurements is the Rogowski sensor, which is a type of induction coil. Since the sensor itself has low resistance it produces very little voltage noise. Hence, the noise limit of the measurement is often set by the preamplifier. Recent development of SQUID picovoltmeters shows excellent noise performance, especially for sensors with low source impedances. We have evaluated the possibility to use the SQUID picovoltmeter as preamplifier for Rogowski type sensors. The designed voltmeter has a voltage noise of 110 pV/ Hz and a bandwidth of 250 kHz. Measurements of sensors with inductances between 0.5 and 40 μH have been performed.