Appearance Of Partial Discharges Research Articles

ИССЛЕДОВАНИЕ ЭФФЕКТИВНОСТИ РЕГИСТРАЦИИ ЧАСТИЧНЫХ РАЗРЯДОВ ОПТИЧЕСКИМ МЕТОДОМ

The method of partial discharges (PD) diagnostics is used to assess the insulation condition of high-voltage equipment in order to control quality and identify the initial process of its aging. The paper presents methods for measuring PD and describes their main advantages and disadvantages. Particular attention is paid to the optical method of registering PDs. An experimental study was carried out with a cable sample and a glass insulator to measure the PD intensity in defective places and record their optical radiation. Voltage to the tested objects was applied from 0 to 26 kV. To register the PD, an electronic-optical flaw detector FILIN-6 device was used. Also, according to the results of the measurement, amplitude-phase diagrams of the PD were obtained, by which it is possible to determine the degree of the defect. It is determined that the threshold level for the appearance of partial discharges is their power of about 100 mW. In this case, an increase in the discharge power to 160 mW leads to the appearance of a discharge visible to the naked eye. The specified partial discharge pow-ers may be relatively harmless only for equipment for voltage classes from 35 kV. Thus, registration of partial discharges by optical means makes it possible to detect defects at a relatively early stage only for equipment for high operating voltages.

НАДЁЖНОСТЬ ИЗОЛЯЦИИ СТАТОРНЫХ ОБМОТОК ЧАСТОТНО-УПРАВЛЯЕМЫХ ЭЛЕКТРОДВИГАТЕЛЕЙ

Relevance Widespread use of semiconductor frequency converters is due to the significant advantages of this technology: smoothness and accuracy of controlling the speed and torque of the electric motor, smooth start and stop; increased energy efficiency; the possibility of remote monitoring, etc. The accumulated operational experience has shown an increased failure rate of stator winding insulation of asynchronous motors operating with pulsed power. The presence of high-frequency overvoltages in the inverter signal can lead to the appearance of partial discharges even in the low-voltage motors windings. It’s leading to accelerated degradation of electrical insulation and premature breakdown. Over the past three decades, a significant amount of information has been accumulated in the technical literature: high-frequency transient models have been created; partialdischarge and corona-resistant test methods have been developed; the most important voltage parameters determining the intensity of insulation aging have been determined; regulatory documentation for testing and selection of insulation systems have been developed. Analysis and systematization of existing results are necessary to determine the directions of further research in the subject. Аim of research Identification of new solutions and trends of insulation reliability windings of lowvoltage electric machines when powered by modulated voltage. Research methods Bibliographic analysis, methods of statistical data processing. Results Analysis of the most relevant works on the reliability of low-voltage winding insulation systems in frequency electric drive systems is carried out, a bibliographic list of these works is given. The main results concerning the overvoltages simulation, insulation testing methods, studying the aging mechanisms of winding polymer insulation with pulsed power supply, determining the characteristics of emerging discharges are shown. The ways of further development aimed at modeling overvoltages, taking into account high-frequency effects, increasing the volume of experiments to estimate the insulation lifetime, studying the conditions for the occurrence of partial discharges, creating a common approach to insulation testing are determined.

The measurement and modeling of partial discharges in solid fossil fuels

The paper is devoted to the study of the characteristics of partial discharges in solid fossil fuels. The appearance of partial discharges in solid fuels occurs at very low voltages, which are not typical for most dielectrics. The activity of partial discharges leads to the onset of rock breakdown. The characteristics of partial discharges in the oil shale of the Huadan deposit (China), presented in the work, indicate the voltage value at which partial discharges arise and breakdown occurs, and also show how these characteristics depend on voltage. We attempted to explain the low value of the voltage of partial discharges in solid fuels, as well as to substantiate the possibility of using partial discharge characteristics to predict the breakdown of the interelectrode space for use in the technology of in-situ heating and the pyrolysis of solid fuels. Keywords: Oil shale, subterranean conversion, field distribution simulation, apparent chage measurement.

Измерение и моделирование частичных разрядов в твердых топливах

The paper is devoted to the study of the characteristics of partial discharges in solid fossil fuels. The appearance of partial discharges in solid fuels occurs at very low voltages, which are not typical for most dielectrics. The activity of partial discharges leads to the onset of rock breakdown. The characteristics of partial discharges in the oil shale of the Huadan deposit (China), presented in the work, indicate the voltage value at which partial discharges arise and breakdown occurs, and also show how these characteristics depend on voltage. We attempted to explain the low value of the voltage of partial discharges in solid fuels, as well as to substantiate the possibility of using partial discharge characteristics to predict the breakdown of the interelectrode space for use in the technology of in-situ heating and the pyrolysis of solid fuels.

Development and modeling of LED indicator of high voltage insulator status

The article discusses a non-contact method for monitoring the state of high-voltage insulation. The principle of operation of circuits of devices built using various electronic components is described. The results of modeling the operation of the device in the software complex of finite element modeling COMSOL Multiphysics are presented. The modeling was carried out by constructing and analyzing three-dimensional models of insulators of the LK70/35 and LK 70/110 brands with indicators installed on them. The presented method of insulation control will allow, during visual inspection of overhead lines, to additionally receive information about the change in the electric field and the appearance of partial discharges in the insulation. The main results of this article are the determination of the parameters and requirements for the electronic components of the considered circuits of indicators of the state of high-voltage insulators.

ACOUSTIC EMISSION TESTING OF POWER TRANSFORMERS INSULATION

Testing results of power transformers insulation for the presence of insulation defects, accompanied by the partial discharges occurrence, by means of the acoustic emission method are presented in this article. In particular, the testing of two power transformers with different lifetime was carried out. One transformer was defect-free and one with a willing insulation defect. Based on the testing results, the features of acoustic emission data for power transformers in the presence of partial discharges are found. High sensitivity of acoustic emission method for acoustic wave registration from partial discharges is shown in the article. A method for filtering of noise hits and extraction of hits from partial discharges is proposed. This method is based on excretion of acoustic emission hits from partial discharges out of total number of hits by means of periodicity of their registration, which is synchronized with power supply frequency on the first step. On the next step based on acoustic emission parameters of hits excretion on the previous step, filtration was carried out. The location of the insulation defect which led to the appearance of partial discharges was determined based on the volume location algorithm, by means of acoustic emission method. The insulation defect was confirmed by verification.

Thermal diagnostics of oil-filled equipment under operating voltage

The article justifies the need for technical diagnostics of high-voltage insulation of electrical equipment under operating voltage. The thermal imaging monitoring method of equipment condition is considered in the document. It is shown that by means of rejection criterion (tgMEAS-tgPLANT) defects in an initial stage of development come to light. The efficiency of control of high-voltage paper-oil insulation under operating voltage has been experimentally proved. The analysis of the causes of damage to high-voltage bushings and current transformers of 500 kV, based on which it was revealed that local defects are characteristic, the development of which leads to either thermal breakdown or the appearance of partial discharges and electrical breakdown of the main insulation. Thermal imaging diagnostics of such equipment as, for example, high-voltage bushings, coupling capacitors and current transformers makes it possible to detect almost all possible defects in insulation and measure their insulation characteristics. The efficiency of thermal imaging monitoring of the state of electrical equipment under operating voltage is shown. The calculated tg values from thermal imaging measurements are more accurate, since the results of measurements with a thermal imager are not affected by electromagnetic interference.It has been concluded that it is possible to abandon several traditional methods of testing with shutdown and without electrical equipment.

Contribution to the analysis of PWM inverter parameters influence on the partial discharge inception voltage

The work presented in this paper deals with the influence of pulse width modulation (PWM) power supply parameters on the partial discharge inception voltage (PDIV). For a given system supplied using PWM, the behavior of partial discharges may be different from a classical AC or DC power supply configuration. An experimental study was conducted in order to observe changes in PDIV levels with respect to PWM parameters such as duty cycle, switching frequency and voltage rise time. Measurements were done on a simple twisted pair of enameled wires, placed inside a climatic chamber for control of the environmental conditions. The experimental results show that the PDIV depends mainly on the waveform of the voltage oscillations; a voltage oscillation with a low frequency would favor the appearance of partial discharges (PD) because the probability of the presence of an initiatory electron to initiate the discharge is higher. Moreover, the waveform shape depends mainly on the rise time of the voltage and the length of the power cable. A parameter that also has a significant effect is the duty cycle; a low duty cycle in unipolar power is favorable for the appearance of PD.

Nonlinear characteristics of leakage current for flashover monitoring of ice-covered suspension insulators

This paper investigates nonlinear characteristics of leakage current (LC) for analyzing and monitoring AC flashover performance of ice-covered suspension insulators. The experiments were carried out in a cold climate room of CIGELE Laboratories according to the methods recommended by IEEE Std. 1783/2009. The maximum withstand voltage (V MW = 81 kV rms ) and minimum flashover voltage (V MF = 84 kV rms ) were obtained to reflect electrical performance of suspension insulators under a most dangerous ice type. The ice accretion process, the length, width and number of icicles associated with the appearance of partial discharges were observed and discussed to present the final formation of a relatively uniform ice layer and vertical icicles along the insulator string. This ice-covered insulator string was characterized by air gaps on the grounded-side shed space and complete ice bridging of the other shed spaces, which have significant influence on the development of arcing discharges leading to flashover. Nonlinear characteristics of LC were analyzed by using a recurrent plot (RP) technique, which graphically gives nonlinear variations of LC on RP maps as well as nonlinear indicators for quantitative prediction of the flashover. The obtained results reveal that dynamic behavior (initiation, propagation, extinguishment and re-ignition) of arcing discharges on ice-covered suspension insulators can be visually reflected by the texture transition of RP maps of LC, which correlate with different stages during the flashover process. The quantitative indicators including a recurrence rate (RR) value lower than 0.24 and a deterministic (DET) value lower than 0.965 are proposed as the predictive values to indicate the highest probability of flashover occurrence. The results obtained will be helpful to predict most hazards of ice-covered outdoor insulators; this is one of monitoring methods based on LC characteristic analysis.

Diagnosis of EPDM's aging by electrical trees

This paper is aimed at the characteristics of treeing phenomena developing in EPDM (Ethylene Propylene Diene Monomer) in a point – plane electrode arrangement and the resulting damages when subjected to ageing AC voltage. It reports mainly on the measurements of the partial discharge inception voltage (PDIV) and partial discharges (PDs) accompanying the evolution of tree structures, the dissipation factor (tgδ) and capacitor (Cx) of insulation as well as the chemical analyses that are Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) to identify the changes in the morphology and microstructure of damaged polymer. The obtained results evidence the fact that the tree formation is linked to the appearance of partial discharges which are promoted by off-gases forwards to the material microstructure modification.

Physico-chemical diagnosis of EPDM electrical aging by tree phenomenon

This paper presents a physico-chemical experimental study of treeing structures expanding in EPDM (Ethylene Propylene Diene Monomer) in a point - plane electrode geometry. Accelerated electrical degradation tests, under alternating 50 Hz electrical field, were realised on this polymer to initiate trees and to follow their propagation (i.e. the tree length) by measuring the partial discharges (PDs) occurring within this insulating material. A chemical analysis by Scanning Electron Microscopy (SEM) and by Infrared spectroscopy (IR) are undertaken to determine the damaged polymer microstructures and changes in its morphology. The chemical groups existing in this material and the changes due to its degradation under electrical field have been identified by Infrared spectroscopy. The microstructure modification of this material, by breaking chemical bonds and splitting molecular chains, explains the formation of tree channels, and accompanying off-gases that promote the appearance of partial discharges and develop the defect. This process is related to the amplitude and the duration of the electrical field which governs the tree forms and which depends on the diameter of the channels and their internal texture revealed by SEM analysis.

Paper - Oil Insulation - New Definition of Damage

Results obtained in paper insulation tests have led to a new definition of the damage as D = K (Vn t)a, when the appearance of partial discharges with 25 pC of apparent charge is used aa a failure criteration. It is suggested that the proposed expression for damage can be generalized to the aging of soild insulators if the criterion of total failur of specimens is adopted.