The Infona portal uses cookies, i.e. strings of text saved by a browser on the user's device. The portal can access those files and use them to remember the user's data, such as their chosen settings (screen view, interface language, etc.), or their login data. By using the Infona portal the user accepts automatic saving and using this information for portal operation purposes. More information on the subject can be found in the Privacy Policy and Terms of Service. By closing this window the user confirms that they have read the information on cookie usage, and they accept the privacy policy and the way cookies are used by the portal. You can change the cookie settings in your browser.
This paper presents an experimental investigation on frequency acceleration of water treeing and on the effect of different factors, such as humidity content, different contaminants, temperature and field strength on tree growth in PE and XLPE. For this investigation model test specimens have been used to supplement cables for testing. Coloured trees and their points of initiation have been analysed...
This paper presents a progress report on a continuing investigation into the voltage endurance of cast and molded resins, particularly cast epoxy resins. The relation of gas cavity size to the observable discharge magnitude and the stress level on the resin at which discharges can be expected to occur within internal cavities is estimated. This illustrates that, with small cavities, the discharge...
Electrical discharges in various gases may produce chemical species which can cause damage to solide surfaces of different materials. In air, for example, ozone, metastable states of molecular oxygen, atomic oxygen and nitrogen oxides are produced. Furthermore, in the case of corona discharges,those species are pushed in preferred directions by electrical wind. As a matter of fact, in the case of...
Corona discharge study has been made considering discharge as a streamer like process. After to have compared the effect of uv radiations and low energy particles like electrons and positive ions, by means of an infrared analysis, experiments have been carried out with ions lower than 30 eV. Though the ions seem to be the more effective particles, their impact did not give a degradation so important...
Failures of high-voltage oil-polypropylene insulated capacitors during operation at 20 kHz were experienced after the capacitors had been filled with new transformer oil. Examination indicated that air pockets trapped in the insulation system during the oil fill had ionized with subsequent damage to the polypropylene. An investigation of the behavior of ionizing air pockets was carried out by means...
The need for partial discharge (corona) measurements at very low frequencies is explained and the results of tests on epoxy resin samples are given for the frequency range 0.1 Hz to 50 Hz. As no suitable commercial generator was available, a new type of low-frequency low-noise generator has been developed and this is described. The discharge detection system is also explained in the paper. This includes...
The paper describes the study of simple experimental models of partial discharges. The characteristics of discharges in point to plane gaps with air or air and solid dielectric, in parallel-plane cells with open air gap and solid dielectric or with artificial voids in the dielectric are studied with a view to contribute to a better interpretation of partial discharges in H. V. equipments.
An extremely sensitive overheating detection technique has been developed using special “sacrificial” coating materials in conjunction with an ion chamber detector or a nuclei condensation monitor. Several distinct “families” of sacrificial coatings based on diazonium compounds, malonic acids, metal acetylacetonates, blocked isocyanates, and special fluorocarbon greases have been formulated for this...
From the testing results on the electrical breakdown phenomena of various epoxy micaceous insulations for form-wound coils of a high voltage rotating machine, electrical failure properties such as breakdown voltage and voltage endurance time were analyzed statistically using Weibull distribution.
Some problems associated with the drying of large power transformers are studied in this paper. It is shown that the conventional end-of-drying criteria cannot be used as dryness criteria when moisture is deeply embedded in the insulation. The solution proposed here consists in introducing into the drying transformer paper probles that are representative of the transformer insulation, and in monitoring...
The structure and shape of the coils in high-voltage apparatus have a pronounced effect upon their electrical life expectancy because of the dielectric stress concentration at the edges and corners of the conductors. In these regions, as a result of the high dielectric stress, accelerated damage to the insulation can occur due to the partial discharges on the surfaces and in minute voids created during...
The advantages of direct-current (DC) over alternating-current (AC) for the transmission of electric power have long been recognized. Considering the transmission line per se, and neglecting terminal equipment, the advantages of DC are overwhelming, and include the following: 1. Improved utilization of the transmission corridor or cable. 2. Complete control over power flow. 3. Absence of phase-angle...
A model for the life of a high tension polymer insulator material was postulated to be dependent on the temperature (T), ultraviolet (U.V.) radiation (I), energy of activation (E), gas law constant (R) as: Life Ln(L)=c + E−BI/RT, where c and B are constants. This model was derived by modifying the Arrhenius equation of reaction rates to r =A − E−BI/KT to take into account U.V. radiation. The validity...
The basic concept of the test method and its main advantages are recalled in the first Section. In particular, it is noted that the test technique used by us allows determination of the “intrinsic” value of voltage endurance. In the second Section many data pertinent to some of the most important plastic insulating materials are reported. It is so possible to make an interesting comparison among these...
A short review of the constructive solutions generally adopted in recent years in manufacturing high voltage current transformers is given, and the problems involved in designing the insulation of such equipment are discussed.
Set the date range to filter the displayed results. You can set a starting date, ending date or both. You can enter the dates manually or choose them from the calendar.