Solid Insulation System Research Articles

Partial Discharge in Capacitor Model at Low Temperature

The partial discharge plays an important role in the ageing and the rupture process of solid or mixed insulation systems. It has been recognized that the failure of this insulation can be joined to the presence of partial discharge often in inclusions sparkling. Liquid filled cavities can be considered as the most likely defects that can exist in capacitors. In this paper we describe the partial discharge evolution at low temperatures in all-PP film capacitors according to the time and the applied voltage. We distinguish two regimes of discharges for all the range of temperature and the low temperatures encourage the breakdown of capacitors at weak voltage, we assign this phenomenon to the increase of the viscosity of filling liquid.

Computer aided partial discharge testing of thin solid insulation systems

For the assessment of thin insulation films in electrical equipment and components a computer aided partial discharge (PD) measuring system is presented. Those insulations are e. g. used in optocouplers, transformers, capacitors and all kind of coating, for instance on printed circuit boards (PCB). The test specimen are taken out of industrial production and are typical for the present manufacturing standard. Two types of test results are presented: Type I shows the PD-behaviour for long time stress with the test voltage kept constant at a value not higher than ].5 times the PD-inception voltage (Uj). Type 2 shows the PD-behaviour for short time stress when the test voltage is increased continuously up to the breakdown voltage of the test specimen. The results are discussed for coated printed circuit boards.

Water in oil-filled high-voltage equipment part II: water content as physicochemical tools for insulation condition diagnostic

In the first part of this investigations, we examined the current state of knowledge of the effect of water on paper and liquid-insulating materials. Demonstrated that the scientific representation of the states of water in insulating liquids has a direct practical application as a diagnostic tool for electrical equipment, at least for the dielectric properties of the insulation. The work presented in this second part of these investigations is divided into four sections. The first section deals with the influence of water on the electrical characteristics of the oil/paper insulating materials, followed by a critical review of up-to-date water quantification methods. Based on the physicochemical criteria of the limiting state discussed in the third section, this article proposes some analytical expressions that can help electrical engineers monitor and/or diagnose oil-filled, high-voltage equipment. Our investigations show the advantage of diverse methods for measuring humidity in insulating liquids, and a variety of analytical expressions for calculating the condition of liquid/ solid insulation systems.

A fuzzy logic algorithm to detect electrical trees in polymeric insulation systems

Inter-time (i.e., the time that separates a PD event from the next one) distribution analysis has been recently proposed as a tool to infer the presence of trees in solid insulation systems. In this paper, inter-time distribution analysis is improved to infer more accurately trees at an early growth stage. Measurements from both artificial specimens as well as practical objects are presented to support the effectiveness of this tool. Moreover, considerations on inter-time analysis robustness with respect to both noise interference and other partial discharge sources are reported.

Advanced pd inference in on-field measurements. part 2: identification of defects in solid insulation systems

Results of investigations performed to evaluate the effectiveness of a new inference method for the diagnosis of solid insulation systems, based on partial discharge (PD) measurements, are reported in this paper. Signal separation, noise recognition, and PD source identification are the main features of the proposed inference method. Techniques for signal separation and automatic noise rejection are reported in the 1st part of this paper, while the problem of the identification of PD phenomena, occurring in defects of insulation systems, is approached in this 2nd part. The identification is based on fuzzy logic and enables the recognition of PD generated from different basic sources, such as internal, surface and corona discharges. It is shown that the different source typologies can be identified by means of fuzzy rules applied to a selection of parameters derived from PD-pulse phase and amplitude distribution analysis, once PD phenomena have been clustered in homogeneous class through a fuzzy algorithm based on PD-pulse shape. The proposed identification procedure is finally applied to rotating machines and cables, affected by insulation defects, showing promising on-field applications.

A new approach to the diagnosis of solid insulation systems based on PD signal inference

The authors have developed digital instrumentation that can measure the amplitude, shape, phase, and number of pulses per cycle. Examples are given of results obtained from an induction motor, a hydrogenerator, a polymeric cable system with a defective joint, and a high-voltage current transformer.

On the statistical testing of solid insulation systems

Solid insulating materials are not self-restoring due to electrical discharges; a separate test piece is needed for each individual test. Even with no discharge observed, polarization and conductivity processes can produce space charges that exist for a long time and that can affect the results of a subsequent test on the same test piece. The solution is to use one test piece per stress. Since solid test pieces are relatively expensive, a small number of test pieces is recommended. Consideration of the choice of sample size should be exercised with great care. The statistical nature of high-voltage testing of electrical insulation has long been recognized. A brief overview of the application of statistical methods to establish the insulation strength and lifetime of solid dielectrics is reported. Accelerated aging tests on solid dielectrics are statistical tests that have to be rigorously analyzed in order to justify any valid conclusions. The application of Weibull statistics for the description of dielectric breakdown is presented. The breakdown probability of the test voltages is a function of the test method, of their parameters, of the nature of the breakdown probability function, and of the assumed physical processes. Proper test methods and their parameters can be selected to determine the breakdown voltages and time to breakdown.

Protection measures for selected ITER magnet system off-normal conditions

The International Thermonuclear Experimental Reactor (ITER) magnet systems provide the magnetic field intensity and field geometry to contain and control plasma during the various phases of pulsed operation. During these pulses, the toroidal field (TF) coils operate with a constant current. The central solenoid (CS) and poloidal field (PF) coils, on the other hand, are each independently powered. The maximum terminal voltages during plasma operation and protective discharges are 15 kV for CS and 10 kV for TF and PF. The energy stored in the 20 TF coil system is 103 GJ; in each of the other coils it is approximately 10 GJ or less. This paper describes the protection requirements and selected design concepts being considered for the large superconducting coils for the ITER. Ground faults, short circuits and helium leaks are the major serious accidents to be prevented in the coils. All coils use a solid insulation system to avoid ground faults. The electrical circuits including coil and power supply are grounded through resistors that limit current in the event of a ground fault. In the case of a short circuit within the coil winding, a large energy would be dissipated close to the small shorted volume. The impact of the short circuit can be reduced by using a potential screen. Inside the cryostat, helium leakage is most likely at the electrical insulating breaks in the cryogenic cooling lines between the coils and helium manifolds. A double containment (metallic shield and glass-epoxy) is therefore provided for the insulation breaks to allow for the detection of small leaks and to limit the spread of helium to other locations.

Partial discharge. IX. PD in gas-insulated substations-fundamental considerations

For pt.VIII see ibid., vol.7, no.5, p.9 et seq. (1991). The physical aspects of partial discharge (PD) in SF/sub 6/ gas-insulated substations (GIS) are reviewed. The orientation is toward present and developing techniques for evaluating defects in solid and gaseous insulation systems on the basis of PD measurement. Standard evaluation methods provide an indication of PD in GIS, but cannot quantitatively determine the type and size of defect. Statistical analysis of PD activity, together with physical models for the various types of discharge and defects, provides the basis for more advanced interpretation. Measurements of PD activity that do not require an absolute calibration are of greatest utility. >

An approach to calculate insulation resistance (IR) at different temperatures and voltages

Analytical methods for determining insulation resistance (IR) for solid insulation systems at various ambient temperatures and applied voltages are presented. The methods used are based on trending of the IR at various temperatures and voltages. A model for insulation resistance, which precisely shows the trend of its variation under the influence of a single environmental parameter while all other parameters are held constant at a fixed defined environment, is developed. Experimental data are used to validate the proposed analytical methods. >

The Space Charge Behavior and Luminescence Phenomena in Polymers at 77 K

Electroluminescence phenomena were observed at the needle tip in polymer samples with a point-plane electrode system under an applied ac voltage at liquid nitrogen temperatures. This luminescence was considered to be caused by the recombination between positive and negative charges injected from the point electrode. The nature and behavior of the charges injected into the polymer became clear through a detailed study of luminescence. A degenerate rate region of polymer was also found at the needle tip after prolonged ac voltage application, which may indicate a depolymerized region caused by the attack of then injected charges. The fact that tree channels started from the degenerate region in the polymer led us to theon conclusion that the injection of charge can be hazardous for polymer solid insulation systems.

A Solid Insulation System for Airborne High-Voltage Components and Systems

A method for the design of a high-voltage solid insulation system used in airborne or satellite high-voltage components and systems is presented, and illustrated with a successful system now used in these applications. The design is based on the elimination of corona in the solid, and principally involves making an insulation with a very high corona inception voltage and then controlling the electric field stress below that level. Examples of actual components and systems designed in this way are shown.