Insulation Of High Voltage Equipment Research Articles

An indicator of a defect in a high-voltage insulating structure

To monitor the insulation of high-voltage equipment, different kinds of devices, including in situ ones, are used. This paper considers the possibility of using optical indicators—light emitters mounted on the insulation structure of high-voltage lines and substations—as such devices. The principle of operation of an optical indicator is as follows. The electric field distribution over an insulation structure changes with breakage of the integrity of its separate parts; when the potential difference at a damaged section decreases, the voltage at the undamaged part correspondingly increases. A faulty condition of the insulating structure can be determined using the light intensity of an indicator installed in the section of the insulating structure or pylon, since the luminance depends on the voltage drop across its terminals. Experiments showed that such insulation failure can visually be determined without using any additional devices, for example, during routine inspections. It is shown that it is possible to produce indicators that are easy to manufacture and do not require any additional maintenance.

Acoustic emission from DC pre-treeing discharge processes in silicone elastomer

Partial discharge in polymeric insulation of high voltage equipment causes cumulative damage that progressively deteriorates the insulation, leading to eventual failure. The electrical detection of related discharge current pulses may be challenged by electromagnetic interference from the environment. In such situations the detection of acoustic emission from partial discharge can greatly enhance its detectability, especially when electromagnetically immune fiber-optic acoustic sensors are used. During experiments involving such fiber-optic sensors that were specifically designed for the detection of partial discharge in elastomeric insulation, an unexpected type of acoustic emission was observed in silicone elastomer specimens with tip-plate electrode configurations and under DC electrical stress. We present and discuss experimental results that indicate space charge injection and subsequent spontaneous dynamical processes as the source of the detected acoustic emission. We use sensitive conventional partial discharge measurement instrumentation to show that the apparent acoustic efficiency of the processes leading to the observed acoustic emission is very high. Acoustic emission triggered by discharge events with individual apparent charge values of only a few femtocoulombs could be detected.

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.

Support Vector Machine-based Denoising Technique for Removal of White Noise in Partial Discharge Signal

—Partial discharge (PD) measurement has emerged as a dominant investigative tool for condition monitoring of insulation in high voltage equipment. In general, PD signals are severely polluted by several noises like white noise, random noise, discrete spectral interferences (DSI). The challenge lies with removing these noises from PD signal effectively by preserving the signal features. In this article, support vector machine (SVM) based denoising technique has been proposed for the removal of white noise from PD signal. The proposed SVM technique retains the edge of the original signal efficiently and also pseudo Gibbs phenomenon does not exist with SVM technique. In order to evaluate the effectiveness of the proposed method, artificially simulated PD signal mixed with white noise and the measured PD readings are considered. For the purpose of comparison, other denoising techniques such as fast Fourier transform (FFT), discrete wavelet transform (DWT), and translation invariant wavelet transform (TIWT) are also considered. The results reveal that, SVM based denoising technique shows better performance in terms of higher signal to noise ratio, signal reconstruction error ratio, cross correlation coefficient and reduction in noise level, mean square error, and waveform distortion.

Partial Discharge Signal Denoising using Adaptive Translation Invariant Wavelet Transform-Online Measurement

Partial discharge (PD) measurements have emerged as a dominant investigative tool for condition monitoring of insulation in high voltage equipment. But the major problem behind them the PD signal is severely polluted by several noises like White noise, Random noise, Discrete Spectral Interferences (DSI) and the challenge lies with removing these noise from the onsite PD data effectively which leads to preserving the signal for feature extraction. Accordingly the paper is mainly classified into two parts. In first part the PD signal is artificially simulated and mixed with white noise. In second part the PD is measured then it is subjected to the proposed denoising techniques namely Translation Invariant Wavelet Transform (TIWT). The proposed TIWT method remains the edge of the original signal efficiently. Additionally TIWT based denoising is used to suppress Pseudo Gibbs phenomenon. In this paper an attempt has been made to review the methodology of denoising the PD signals and shows that the proposed denoising method results are better when compared to other wavelet-based approaches like Fast Fourier Transform (FFT), Discrete Wavelet Transform (DWT), by evaluating five different parameters like, Signal to noise ratio, Cross-correlation coefficient, Pulse amplitude distortion, Mean square error, Reduction in noise level.

PD Characteristics in Transformer Oil under AC Condition

Partial discharge (PD) detection is a technique widely used for high voltage equipment insulation condition assessment. The metal protrusion is a situation that often appear in transformer. Metal protrusion will cause the electric field concentration and lead to partial discharge. In this paper, PD characteristics in transformer oils are examined under AC conditions, using a needle-to-plane electrode system. The PD activity in transformer oil is confirmed as appearing in pulse burst form and the PD number and amplitude will increase with the applied voltage increase. The PRPD pattern display behavior typical of corona PD in oil.

Detection and wavelet analysis of acoustic emission signal from partial discharge captured by multimode optical fiber and piezoelectric sensors in insulation oil

High-voltage transformer is the most critical and expensive component in a power system network in order to ensure the stability of the system. Partial discharge (PD) detection is a technique widely used for high voltage equipment insulation condition monitoring and assessment. In this paper, the characteristics of two acoustic sensors multimode fiber optical (FO) and piezoelectric (PZT) sensor have been successfully explored and monitor the condition of high voltage equipment insulation. Both the sensors were placed in an oil tank in which optical breakdown was produced by neodymium-doped yttrium aluminum garnet (Nd:YAG) laser (1064 nm) device. The optical signal of light source was linked by a photodetector which was also connected with multimode fiber (MMF) by means of a fiber optical adapter. The data obtained by both sensors were then analyzed in time and frequency domain. Key words: Fiber optical sensor, piezoelectric sensor, acoustic emission, optical breakdown, partial discharge, wavelet analysis.

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.

Acoustic data of cross linked polyethylene (XLPE) and cured liquid silicone rubber (LSR) by means of ultrasonic and low frequency DMTA

Partial discharges may cause damage to electrical insulation of high voltage equipment. They initiate elastic waves in the insulating material, e.g. in the stress cone of an outdoor termination. Localisation of the origin of such elastic waves can help to predict serious damaging processes in the electrical insulation. In order to measure and evaluate the wave propagation effects in typical multilayered elastomeric structures, knowledge of the material properties is required. The propagating velocity and the attenuation of longitudinal waves are important parameters. Values for these quantities found in the literature were not appropriate. Therefore, for cross-linked polyethylene (XLPE) and cured liquid silicone rubber (LSR), the longitudinal wave velocity and the attenuation were evaluated in the temperature interval from -20°C to 50°C and in the frequency range from 200 kHz to 600 kHz using a two-sample ultrasound technique. The loss factor was determined from these measured quantities. Additionally, low frequency Dynamic Mechanical Thermal Analysis (DMTA) was applied to investigate LSR and XLPE in a temperature interval between -100 and 50°C and to check qualitatively the ultrasound data.

Data mining on partial discharge signals of power transformer's defect models

SUMMARY Partial discharge (PD) is a common phenomenon that occurs in the insulation of high-voltage equipment, such as transformers, and has a damaging effect on the insulation. If data mining techniques are used to extract special specifications and features for different types of PDs in power transformers or other power equipment, one can diagnose the insulation condition of such equipment by its continuous online monitoring. These diagnosis results can be used to develop precise preventive measures and maintenance procedures. This maintenance would cost less and can be carried out in a shorter time. Consequently, the lifetime expectancy of the transformers will be improved. In this article, experimental models are developed to simulate some of the PD types that can occur in a power transformer. Using these models, some of the features that can differentiate those PD types are extracted through texture analysis. Two classification algorithms are used for the separation of PD sources, decision tree and k-nearest neighbors algorithm. It is anticipated that these models can help us to identify the type of PD fault in a transformer when the required PD measured data are available. Copyright © 2012 John Wiley & Sons, Ltd.

Design of the System for Online Monitoring Dielectric Loss

For knowing the dielectric loss of high-voltage capacitive electrical equipment timely and mastering the electrical insulation of high voltage equipment effectively to ensure the reliable operation of these voltage equipments, an online monitoring system is designed in this paper based on the practical project. The system is made up of two parts including lower computer and upper computer. Using the microcontroller C8051F023 as the core of the lower computer and adopting an improved zero-crossing comparison method, the measurement of dielectric loss is realized and the data are sent to upper computer by wireless way. SQL2000 is used in the upper computer for data management, which can be real-time displayed, inquired and printed in report forms. At present, this monitoring system has successfully applied in the Houqiao 330 kV transformer substation in Ningxia. The operating results show that the system can meet well the online monitoring demand of the high voltage capacitive electrical equipment.

Substation monitoring by acoustic emission techniques

The deterioration of oil–paper insulation in high voltage equipment is a matter of continuous concern. The degradation typically occurs under normal operating conditions although insulation failure may be accelerated under certain in-service conditions, such as switching and lightning impulses, overvoltages and moisture ingress. For this reason, only continuous monitoring can provide the necessary field data to better understand in-service insulation behaviour, particularly insulation degradation, thus preventing catastrophic damage to property and risk to human life. Based on the promising results obtained previously from an acoustic emission (AE) portable detection system an AE substation monitoring system has been developed. This has been operational in a 33 kV primary substation for eighteen months and detailed data have been collected and downloaded to a computer from a remote site on a daily basis. The analysed results have indicated that a specific cable box in the substation is a source of heavy discharge activity and a recommendation has been made to the Regional Electricity Company that a high-voltage test be carried out on the suspected switchgear for further investigation.

Space charge measurements on impregnated paper: a review of the PEA method and a discussion of results

In electrical insulation in high voltage equipment being serviced under dc stress, space charge is often present. This change greatly influences the electrical field. Quantitative knowledge about the presence of space charge is therefore needed. This paper describes the quest for useful measurement principles. One measurement principle, the Pulsed Electroacoustic method, will be described extensively. The method of calibration and the importance of knowledge about the frequency response of the system are described. The results of space charge measurements on impregnated paper samples are presented and discussed, along with a model that predicts the observations fairly well.

Partial discharge. VII. Practical techniques for measuring PD in operating equipment

For pt.VI see ibid., vol.7, no.3, p.9 (1991) Online partial-discharge (PD) tests for monitoring the condition of the solid dielectric insulation in high-voltage equipment are discussed. Sources of external electrical noise are identified, as are attributes of PD and noise that are helpful in drawing distinctions between them. Methods for distinguishing between PD and noise are described. They are based on pattern recognition, time and frequency domain characteristics, or pulse time-of-flight analysis. Several online PD measuring systems for rotating machines, substation equipment, and high-voltage cables are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Discussion on “Electrical discharges in air-gaps facing solid insulation in high-voltage equipment” before the South Midland Centre, at Birmingham, 2nd November, 1953

Discussion on “Electrical discharges in air-gaps facing solid insulation in high-voltage equipment” before the South Midland Centre, at Birmingham, 2nd November, 1953

Electrical discharges in air-gaps facing solid insulation in high-voltage equipment

Electrical discharges in air-gaps facing solid insulation in high-voltage equipment

Electric discharges in air-gaps facing solid insulation in high-voltage equipment

The performance of high-voltage alternators under conditions of over-voltage is materially improved by the application of an insulating sheathing to exposed parts of the bare earthed metal. The authors first derive the physical explanation for this observation from experiments using auto-photographic recording methods. These experiments are then expanded to cover other phenomena observed with discharges between insulated electrodes and lead to problems of discharges in voids. In particular, two hitherto unexplained phenomena are considered: the increase of discharge current with rising voltage, and the origin of the long discharge-free range in the decaying part of alternating voltages. Both these observations can be explained by the loss of some of the surface charges left from earlier discharges due to local reversals of the electric field. Some of the explanations of the probable mechanism by which charges are lost must still be considered as tentative, and more experimental evidence will be needed for a complete clarification of the processes involved. The results give some information on the effect of harmonics on internal discharges, which have been observed to lead to accelerated ageing of dielectrics.