By Topic

Electrical Insulation Magazine, IEEE

Issue 5 • Date September-October 2012

Filter Results

Displaying Results 1 - 20 of 20
  • Table of contents

    Page(s): c1 - c2
    Save to Project icon | Request Permissions | PDF file iconPDF (104 KB)  
    Freely Available from IEEE
  • IEEE Electrical Insulation Magazine

    Page(s): 3
    Save to Project icon | Request Permissions | PDF file iconPDF (92 KB)  
    Freely Available from IEEE
  • Editorial

    Page(s): 4
    Save to Project icon | Request Permissions | PDF file iconPDF (118 KB)  
    Freely Available from IEEE
  • From the editors' desk

    Page(s): 6 - 7
    Save to Project icon | Request Permissions | PDF file iconPDF (286 KB)  
    Freely Available from IEEE
  • A perspective on online partial discharge monitoring for assessment of the condition of rotating machine stator winding insulation

    Page(s): 8 - 13
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (594 KB) |  | HTML iconHTML  

    Partial discharges (PD) are small electrical sparks that can occur in liquid or solid insulation systems in high-voltage equipment, and can eventually cause failure of the equipment [1]?????????[3]. Partial discharge testing has been used for more than 80 years as a factory quality control tool to find manufacturing defects that could eventually lead to equipment failure. We believe that Johnson was the first to measure PD on operating high-voltage equipment, in the 1940s [4]. His aim was to find an online method to determine whether stator winding coils or bars were vibrating excessively in the stator magnetic core. These vibrating coils lead to abrasion of the high-voltage electrical insulation and to eventual failure. A symptom of the insulation abrasion process was that PD (or what he referred to as slot discharge) occurred between the surface of the coil and the stator core. By measuring the PD online, he could indirectly detect the movement of coils, which indicated that failure was likely. The measurement had to be made online because, if the generator were not operating, no magnetic forces would be acting on the coils; thus, the air gaps that are a necessary precursor of PD would not be as large. Johnson was successful in identifying those generators that were suffering the most from this problem, which was caused by the introduction of the first thermoset insulation systems and by workmanship variations that were magnified by an inadequate method of securing the coils in the stator slots for the novel insulation system. The success of the Johnson online PD measuring system inspired other machine manufacturers and even a few utilities to develop their own methods [5], [6]. The main reason Johnson needed online PD measurement was that loose windings do not produce as much PD when the motor or generator is not operating. Thus one of the important reasons for performing online PD tests is to monitor the condition of the equipment under normal operating electri- al, thermal, and mechanical stresses. However, with the current emphasis on extending times between maintenance outages, and the push to reduce testing costs in general, the main reason now given for online PD measurement is to avoid shutdown of the equipment, which would be necessary for an off-line PD test or other diagnostic test. Although we believe online PD monitoring was first applied to rotating machines, the same reasons are valid for other electrical equipment, such as oil paper cable joints or terminations, distribution class switchgear, gas-insulated switchgear, and power transformers [2], [3]. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Cell membrane electroporation- Part 1: The phenomenon

    Page(s): 14 - 23
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2251 KB) |  | HTML iconHTML  

    Each biological cell, trillions of which build our bodies, is enveloped by its plasma membrane. Composed largely of a bilayer (double layer) of lipids just two molecules thick (about 5 nm), and behaving partly as a liquid and partly as a gel, the cell plasma membrane nonetheless separates and protects the cell from its surrounding environment very reliably and stably. Embedded within the lipid bilayer, also quite stably, are a number of different proteins, some of which act as channels and pumps, providing a pathway for transporting specific molecules across the membrane. Without these proteins, the membrane would be a largely impenetrable barrier. Electrically, the cell plasma membrane can be viewed as a thin insulating sheet surrounded on both sides by aqueous electrolyte solutions. When exposed to a sufficiently strong electric field, the membrane will undergo electrical breakdown, which renders it permeable to molecules that are otherwise unable to cross it. The process of rendering the membrane permeable is called membrane electroporation. Unlike solid insulators, in which an electrical breakdown generally causes permanent structural change, the membrane, with its lipids behaving as a two-dimensional liquid, can spontaneously return to its prebreakdown state. If the exposure is sufficiently short and the membrane recovery sufficiently rapid for the cell to remain viable, electroporation is termed reversible; otherwise, it is termed irreversible. Since its discovery [1]?????????[3], electroporation has steadily gained ground as a useful tool in various areas of medicine and biotechnology. Today, reversible electroporation is an established method for introducing chemotherapeutic drugs into tumor cells (electrochemotherapy) [4]. It also offers great promise as a technique for gene therapy without the risks caused by viral vectors (DNA electrotransfer) [5]. In clinical medicine, irreversible electroporation is being investigated as a method for tissue ablation (n- nthermal electroablation) [6], whereas in biotechnology, it is useful for extraction of biomolecules [7] and for microbial deactivation, particularly in food preservation [8]. This article, the first in a series of three focusing on electroporation, describes the phenomenon at the molecular level of the lipid bilayer, and then proceeds to the cellular level, explaining how exposure of a cell as a whole to an external electric field results in an inducement of voltage on its plasma membrane, its electroporation, and transport thorough the electroporated membrane. The second article will review the most important and promising applications of electroporation, and the third article will focus on the hardware for electroporation (pulse generators and electrodes) and on the need for standards, safety, and certification. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Water ingress in high-voltage cross-linked polyethylene (XLPE) cable terminations

    Page(s): 24 - 31
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2200 KB) |  | HTML iconHTML  

    In Norway, there are 6000 to 7000 oil-filled high-voltage cable terminations in the transmission network, most of which are constructed following the old design shown in Figure 1. Although the number of reported failures of medium-voltage cross-linked polyethylene (XLPE) cables and cable accessories is low, during the last few decades some severe explosive failures with potential for personnel injury have been reported [1]. Examination of some of the failed cable terminations showed that the most likely cause was the presence of water in the housing. Water can enter the housing through defective O-rings or through an air ventilation screw on the top cover of the termination housing. As part of their regular maintenance programs, some Norwegian utilities measure the water content of the filling oil. Liquid water was found in some installations, and in one case, the stress cone was found to be covered in ice when the porcelain housing was removed [2] (Figure 2). Similar breakdowns have been reported in other European countries [3], [4]. The main purpose of the work described in this article was to investigate the effect of water ingress in oil-filled high-voltage cable terminations, in particular the associated breakdown mechanisms. The work was performed using full-size and model cable terminations. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Adaptive neuro-fuzzy inference system approach for simultaneous diagnosis of the type and location of faults in power transformers

    Page(s): 32 - 42
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (670 KB)  

    Electrical, mechanical, and thermal stresses can degrade the quality of the insulation in power transformers, causing faults [1]. Several methods are used for fault diagnosis in transformers, e.g., dissolved gas analysis (DGA), measurement of breakdown voltage, and tan ??????, pollution, sludge, and interfacial tension tests [2]. Of these, DGA is the most frequently used. Thermal and electrical stresses result in fracture of the insulating materials and the release of several gases. Analysis of these gases may provide information on the type of fault. Various standards have been suggested for the identification of transformer faults based on the ratio of dissolved gases in the transformer oil, e.g., International Electrotechnical Commission (IEC) standards [3]?????????[7], and these standards has been quoted in many papers, e.g., [8]?????????[15]. However, they are incomplete in the sense that, in some cases, the fault cannot be diagnosed or located accurately. Intelligent algorithms, e.g., wavelet networks [16], neuro-fuzzy networks [17], [18], fuzzy logic [8], [12], and artificial neural networks (ANN) [2], [9], [10], [19], [20] have been used to improve the reliability of the diagnosis. In these algorithms, the type of fault is diagnosed first, and the fault is then located using the ratio of the concentrations of CO2 and CO dissolved in the transformer oil [21], [22]. The algorithms are not entirely satisfactory. The wavelet network has high efficiency but low convergence, the fuzzy logic method has a limited number of inputs and, in some cases, it is very difficult to derive the logic rules, and the ANN need reliable training patterns to improve their fault diagnosis performance. In this paper, we present a new method for simultaneous diagnosis of fault type and fault location. It uses an adaptive neuro- fuzzy inference system (ANFIS) [23]?????????[27], based on DGA. The ANFIS is first ?????????trained????????? in accordance with IEC 599 [3], so that it acquir- s some fault determination ability. The CO2/CO ratios are then considered additional input data, enabling simultaneous diagnosis of the type and location of the fault. The results obtained by applying it to six transformers are presented and compared with the corresponding results obtained using ANN and some other standards and methods. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Preparation of a vegetable oil-based nanofluid and investigation of its breakdown and dielectric properties

    Page(s): 43 - 50
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2299 KB) |  | HTML iconHTML  

    Investigations during the last decade have shown that conductive nanoparticles can be dispersed in transformer oils to form nanofluids. Well-dispersed nanoparticles are capable of increasing the breakdown voltage of the oil under power frequency and lightning impulses. They also increase the inception voltages for partial discharge [1]. With increasing moisture content, reduction of the breakdown voltage of the nanofluid at power frequency is significantly smaller than that in the corresponding transformer oil [1]. The electrical and thermal properties of four types of nanofluid, prepared by dispersing Al2O3, Fe3O4, SiO2, and SiC nanoparticles in transformer oils, were described in [2]. It has also been reported that the thermal conductivity of such oil was enhanced by 8% when aluminum nitride nanoparticles were dispersed in it at a loading of 0.5% by weight, and its cooling capability was improved by about 20% [3]. An electrodynamic model has been developed describing streamer formation in transformer oil-based nanofluids, which presents generation, recombination, and transport equations for each charge carrier type [4]. Vegetable insulation oils are based on natural ester oils, which are environmentally friendly and fire resistant [4]?????????[9]. At the moment, little is known about the preparation of nanofluids using natural ester oils and their dielectric, breakdown, and aging properties. Surface modification of nanoparticles is a very effective procedure to avoid nanoparticle agglomeration in insulating nanofluids [10]?????????[14]. However, the surface modification procedures used for mineral oils cannot be applied to vegetable oils because of their very different molecular structures. We therefore investigated new approaches to the preparation of vegetable oil-based nanofluids. This paper presents some of the results of a study of the breakdown voltages and dielectric properties of a vegetable oil-based nanofluid. The nanofluid was prepared by dispersing Fe- O4 nanoparticles in a vegetable insulation oil obtained from a laboratory at Chongqing University. Oleic acid was used for surface modification of the nanoparticles. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • EIC 2013 call for papers

    Page(s): 51
    Save to Project icon | Request Permissions | PDF file iconPDF (104 KB)  
    Freely Available from IEEE
  • Report on 2012 IPMHVC

    Page(s): 6
    Save to Project icon | Request Permissions | PDF file iconPDF (2221 KB)  
    Freely Available from IEEE
  • Report on ISEI 2012

    Page(s): 56 - 59
    Save to Project icon | Request Permissions | PDF file iconPDF (2112 KB)  
    Freely Available from IEEE
  • IEEE division delegate/director position description

    Page(s): 60 - 63
    Save to Project icon | Request Permissions | PDF file iconPDF (267 KB)  
    Freely Available from IEEE
  • Director-elect nomination process

    Page(s): 64 - 65
    Save to Project icon | Request Permissions | PDF file iconPDF (779 KB)  
    Freely Available from IEEE
  • Development of a high- performance transfer mold power module

    Page(s): 66 - 67
    Save to Project icon | Request Permissions | PDF file iconPDF (803 KB)  
    Freely Available from IEEE
  • Book reviews [7 books reviewed]

    Page(s): 69 - 72
    Save to Project icon | Request Permissions | PDF file iconPDF (175 KB)  
    Freely Available from IEEE
  • IEEE media advertising sales offices

    Page(s): 73
    Save to Project icon | Request Permissions | PDF file iconPDF (209 KB)  
    Freely Available from IEEE
  • Meetings calendar

    Page(s): 74 - 75
    Save to Project icon | Request Permissions | PDF file iconPDF (143 KB)  
    Freely Available from IEEE
  • IEEE Electrical Insulation Magazine - Cover

    Page(s): c1 - c2
    Save to Project icon | Request Permissions | PDF file iconPDF (676 KB)  
    Freely Available from IEEE
  • Author's guide

    Page(s): c3
    Save to Project icon | Request Permissions | PDF file iconPDF (39 KB)  
    Freely Available from IEEE

Aims & Scope

The EI Magazine is specifically concerned with publishing articles in the development and characterization of the dielectric, chemical, mechanical, and environmental properties of all vacuum, gaseous, liquid, and solid electrical insulation, and with utilization of these materials in circuits and systems under conditions of use.

Full Aims & Scope

Meet Our Editors

Co-Editor-in-Chief
Edward Cherney

Co-Editor-in-Chief
Robert Fleming