Evaluation Of Insulation Condition Research Articles

Comparison of Effects of Partial Discharge Echo in Various High-Voltage Insulation Systems

In this article, an extension of a conventional partial discharge (PD) approach called partial discharge echo (PDE), which is applied to different classes of electrical insulation systems of power devices, is presented. Currently, high-voltage (HV) electrical insulation is attributed not only to transmission and distribution grids but also to the industrial environment and emerging segments such as transportation electrification, i.e., electric vehicles, more-electric aircraft, and propulsion in maritime vehicles. This novel PDE methodology extends the conventional and established PD-based assessment, which is perceived to be one of the crucial indicators of HV electrical insulation integrity. PD echo may provide additional insight into the surface conditions and charge transport phenomena in a non-invasive way. It offers new diagnostic attributes that expand the evaluation of insulation conditions that are not possible by conventional PD measurements. The effects of partial discharge echo in various segments of insulation systems (such as cross-linked polyethylene [XLPE] power cable sections that contain defects and a twisted-pair helical coil that represents motor-winding insulation) are shown in this paper. The aim is to demonstrate the echo response on representative electrical insulating materials; for example, polyethylene, insulating paper, and Nomex. Comparisons of the PD echo decay times among various insulation systems are depicted, reflecting dielectric surface phenomena. The presented approach offers extended quantitative assessments of the conditions of HV electrical insulation, including its detection, measurement methodology, and interpretation.

The Applicability of Very Low Frequency Diagnostic Testing in the Evaluation of Thermally Aged Stator Coil

In this study, stator coils were aged under thermal stress and changes in insulation condition with the aging cycles were evaluated using diagnostic tests. Diagnostic tests such as partial discharge measurement and tan delta and capacitance measurements were performed at 50 Hz, 1 Hz and 0.1 Hz (very low frequency). The results obtained from this study demonstrate the possibility of evaluating the signs of thermal aging in a stator insulation system with very low frequency tests. Partial discharge parameters like peak apparent charge magnitude and integrated charge per cycle along with tan delta and capacitance tip-up values were used to evaluate the stator insulation condition. Diagnostic test results showed an identical trend with aging cycles at all the chosen test frequency, i.e. 50 Hz, 1 Hz and 0.1 Hz, which indicates that testing at 0.1 Hz is suitable for insulation condition evaluation. Further, the tip-up values have shown distinct variations, especially at 0.1 Hz indicating significant thermal degradation in a stator coil.

Fast Detection Method on Water Tree Aging of MV Cable Based on Nonsinusoidal Response Measurement

A MV power cable will exhibit nonlinear impedance when dendritic defects appear. To solve the long time-consuming measurement of pure sinusoidal excitation and realize rapid and accurate evaluation of insulation conditions, a measurement and evaluation method based on nonsinusoidal excitation is proposed in this paper. Firstly, a nonsinusoidal excitation test system is established, which can obtain the high voltage dielectric response in the frequency range of 0.01 Hz–1 kHz. For parameterizing dielectric response characteristics of MV XLPE insulation under nonsinusoidal excitation, a Hammerstein-Wiener model is proposed to realize system parameter identification under non sinusoidal excitation with different aging degrees of water tree. The time-domain current response waveform based on the H-W model is more accurate than the traditional linear model, and the resulting fitting degree of the frequency-domain dielectric loss factor curve between the calculated H-W model and the measured curve was higher than 95%. The results show that the rotation and distortion of the u-i hysteresis ellipse under nonsinusoidal excitation can be used to diagnose the insulation defects of XLPE MV cables. The response model and its detection method proposed in this paper can improve the efficiency and accuracy of the field tests of cable insulation.

Insulation condition assessment of cable intermediate joint based topsis method with variable weight

In order to monitor the insulation deterioration of cable intermediate joint in real time, a new insulation condition evaluation method based on improved TOPSIS with variable weight is proposed. Firstly, the evaluation indicators are extracted from online monitoring signal. Next, the subjective and objective weights are combined to obtain the constant weights. Also, considering that the weights of each index may change under extreme deterioration, the variable weight theory is introduced to optimize the constant weights. Secondly, the conventional TOPSIS method is improved by adding intermediate joints with extremely good insulation and extremely severe insulation deterioration as positive and negative reference points. Finally, the proximity between the cable joint and the positive reference point are calculated, and the insulation status of cable intermediate joint is evaluated according to the interval of proximity. The case analysis shows that the improved TOPSIS method with variable weight is more accurately than the traditional TOPSIS method in assessing the insulation condition of cable intermediate joint.

Evaluation of Non-Uniform Thermal Aging of XLPE Cable Based on Modified Debye Model

The polarization/depolarization curve (PDC), which contains abundant insulation information, is widely used to evaluate the insulation condition of the cross-linked polyethylene (XLPE) cables. However, the insulation condition assessing the result of the XLPE cables is usually inaccurate using the PDC technology because the parameters of the current Debye model are determined in a uniform aging hypothesis, instead of a real non-uniform situation. To solve this problem, the modified Debye model considering the real non-uniform situation is proposed, and the effectiveness of the modified model is proved by the comparison of the PDC test results with non-uniform and uniform aging materials. It is found that the parameters of the extended Debye model tend to overestimate the cable insulation performance, while the characteristic parameters obtained by the modified Debye model better reflect the real situation of cable non-uniform aging. Result analysis shows that the proposed method has better accuracy in the insulation condition evaluation of cables.

Temperature Segment Compensation Method of Dissipation Factor for Insulation Diagnosis in Converter Transformer Bushing

Temperature compensation occupies a significant function in the insulation condition evaluation of converter transformer bushings based on the Frequency Domain Spectroscopy (FDS), which could influence the accuracy of its insulation diagnosis. In order to accurately obtain the variation law of FDS at different temperature, a Resin Impregnated Paper (RIP) insulation bushing for converter transformer was designed by the equivalence of maximum electric field, coaxial cylinder structure and RIP materials. The increment law of dielectric parameters both dissipation factor and capacitance at wideband frequency (1mHz ~ 10kHz) was measured for a quality RIP insulation samples at the temperature from 30°C to 100°C. 1) Under the uniform temperature, it was found that the value of dissipation factor was rising with the frequency from 10 Hz to 0.001Hz, while the tendency was reversed at the frequency from 100Hz to10kHz. 2) The minimum value of tan <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\delta $ </tex-math></inline-formula> from 0.001Hz to 10kHz could be driven to higher frequency moving (10Hz to 10kHz) by the action of temperature rising 30°C to 100°C.3) The effect of temperature on the lower frequency 0.001Hz ~ 1Hz tan <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\delta $ </tex-math></inline-formula> of RIP insulation closely conformed to the index law of Arrhenius equation, while it was in accordance with the linear decrease at higher frequency 1kHz ~ 10kHz. The effect of temperature on dissipation factor could be eliminated by curve segment shifting based the experiment equation, which it at 0.001Hz dissipation factor could be eliminated by curve shifting based the index equation originated Arrhenius equation. The method is beneficial to eliminate the influence of temperature on the dielectric spectroscopy test results, and then to eliminate the influence of temperature on the dielectric spectroscopy diagnosis of RIP bushings.

Multi-feature Fusion and Damage Identification of Large Generator Stator Insulation Based on Lamb Wave Detection and SVM Method.

Due to the merits of Lamb wave to Structural Health Monitoring (SHM) of composite, the Lamb wave-based damage detection and identification technology show a potential solution for the insulation condition evaluation of large generator stator. This was performed in order to overcome the problem that it is difficult to effectively identify the stator insulation damage the using single feature of Lamb wave. In this paper, a damage identification method of stator insulation based on Lamb wave multi-feature fusion is presented. Firstly, the different damage features were extracted from time domain, frequency domain, and fractal dimension of lamb wave signals, respectively. The features of Lamb wave signals were extracted by Hilbert transform (HT), power spectral density (PSD), fast Fourier transform (FFT), and wavelet fractal dimension (WFD). Then, a machine learning method based on support vector machine (SVM) was used to fuse and reconstruct the multi-features of Lamb wave and furtherly identify damage type of stator insulation. Finally, the effect of typical stator insulation damage identification is verified by simulation and experiment.

A Noise Reduction Based Wavelet Denoising System for Partial Discharge Signal

Partial Discharge (PD) checking is a standout amongst the best technique for insulation condition evaluation of HV power system. PD releases inside a power transformer energize electromagnetic transients that can be identified utilizing sensors working in the ultra-high frequency band. Despite, on-line PD estimations are influenced by elevated amounts of electromagnetic interference that makes delicate PD identification exceptionally troublesome. In our proposed research present an approach which can reduce the noise level. Increase the quality of the PD signal. Here using an approximation logic which can reduce the complexity in terms of time and able to improve the quality. The proposed Double DWT able to get batter result as compares to existing PD techniques.

Fault Diagnosis and Condition Division Criterion of DC Gas Insulating Equipment Based on SF6 Partial Discharge Decomposition Characteristics

SF6 decomposition characteristics directly reflect the generation, development, and evolution of internal faults in gas-insulated equipment (GIE). However, establishing the DC-GIE internal insulation condition comprehensive division criterion and fault diagnosis method based on SF6 decomposition characteristics remains unsolved. Therefore, partial discharge (PD) and SF6 decomposition characteristics of typical insulation defects from initial discharge to the breakdown process are discussed in this paper. The average discharge magnitude in a second $Q_{\text {sec}}$ is selected as an electrical feature to characterize the PD condition, and the PD state is divided into three levels, namely, mild PD, medium PD, and severe PD. SF6 decomposition experiments are conducted under different PD conditions of each defect, and the SF6 decomposition characteristics under different failure conditions are obtained. On this basis, we construct five feature sets of 36 characteristic quantities for GIE PD fault diagnosis and analyze the validity. A minimum-redundancy-maximum-relevance-based feature selection algorithm is used to optimize the characteristic quantities, and an optimal feature set is selected, i.e., {C(SO2)/C(T), C(SOF2)/C(CT), C(SO2F2)/C(ST)}. The characteristic quantities of SF6 decomposition component, which characterizes PD condition, are reconstructed, and the component characteristic criterion of PD condition division is proposed. Thus, a decision tree evaluation model for the PD condition of the typical insulation defect inside DC-GIE is constructed. This paper lays a foundation for the insulation condition evaluation and fault diagnosis of DC-GIE.

Insulation performance evaluation of HV AC/DC XLPE cables by 0.1 Hz tan δ test on circumferentially peeled samples

The XLPE insulations of three 110 kV AC cables with different manufacturers and operation histories and two 160 kV DC cables before and after the one-year prequalification test are studied in this paper. Slice samples are taken from different radial locations of the cable insulation layers by a circumferential peeling method and measurements of discharge current, dielectric spectrum and VLF loss angle tangent are carried out on the inner, middle and outer insulation parts respectively. It is found that for AC cables under test, the older the cable is, the more slowly the discharge current decays, and the greater the performances of three parts differ. As for the dielectric spectrums, tan δ decreases when the frequency increases from 0.05 to 1,000 Hz, and a longer service life causes a larger amplitude of variation. Besides, the three insulation parts give similar values of tan δ at 50 Hz, while those at 0.1 Hz differ from each other, especially for cables long-term service-aged. A characteristic parameter defined as the ratio of tan δ under 0.1 Hz to 50 Hz is proposed for the purpose of insulation condition evaluation, and its value becomes larger as the result of site operation for AC cables and long-term test for DC cables. VLF tan δ are measured under four levels of the 0.1 Hz voltage, and a normalization processing is performed by using outer part as the reference for AC cables and middle part for DC ones. The deterioration degree of material property can be reflected by not only the voltage stability of tan δ value, but also the performance difference among different parts of a cable insulation body. The electrical and thermal stresses, either from the site operation or from laboratory tests, can result in a decreased voltage stability and an increased performance difference. Since above conclusions are applicable to the XLPE insulation under AC operation and DC test, the preliminary work of this paper can be considered as a good start for the exploration of using VLF tan δ to assess the insulation condition of HV AC and DC cables.

Evaluation of electrical insulation in three-phase induction motors and classification of failures using neural networks

This paper presents a study for the evaluation of the electrical insulation of the stator of three-phase induction motors (IM) and the classification of the failure mechanism using an approach based on computational intelligence tools (CIT). A brief review showing the main parameters for the evaluation of insulation condition and testing of IMs is presented, as well as the promising use of CITs for fault diagnosis of industrial equipment, including motors. This paper proposes a new methodology for evaluation and classification of insulation conditions with the aid of K-means clustering and of a classifier based on ANNs (artificial neural networks).

A new mathematical model of moisture equilibrium in mineral and vegetable oil-paper insulation

Moisture equilibrium characteristics of oil-paper insulation systems are important for insulation condition evaluation of oil-filled transformers. This paper presents moisture equilibrium curves of mineral and vegetable oil-paper insulation systems obtained by both direct and indirect methods. A new mathematical model is proposed to determine moisture content in oil-paper insulation systems. Experiments on moisture equilibrium in oil-paper insulation systems are conducted. The results estimated through the mathematical model agree with experimental results. The moisture equilibrium curves between vegetable and mineral oil-paper insulation systems are presented and compared. The moisture content in the vegetable oil-impregnated paper is significantly smaller than that in the mineral oil-impregnated paper, when both types of insulating oils have the same moisture content.

Digital algorithm based on orthogonal decomposition for measurement of dielectric loss factor

As one of the most important technical indexes for the evaluation of insulation condition, the dielectric loss factor is necessary in preventive experiments and online monitoring of insulation of high-voltage apparatuses in an electric power system. First, the definition of the dielectric loss factor and the impact of the harmonic voltage on that was discussed. Secondly, the voltage and the leakage current were defined as vectors in normed linear space. By using the characteristic of an orthogonal vector in the inner product space, the leakage current signal was decomposed to active and reactive components that were orthogonal. Subsequently, a novel digital algorithm of the dielectric loss factor measurement, which was defined as the ratio of norms of the active current to the reactive current, was proposed. At last, the proposed algorithm was simulated under several conditions such as harmonic voltage and voltage frequency fluctuation. In addition, the proposed algorithm was tested on two electric power capacitors. Both simulation and experiment results were provided and show that the proposed algorithm is simpler and less sensitive to influence factors than the Fourier analysis method.

절연파괴시험법을 이용한 3.3[kV] 유도전동기의 절연물 열화특성 분석

본 논문은 유도전동기 고정자권선의 절연물에 대하여 비파괴 및 파괴시험을 실시하여 절연물의 비파괴특성과 내전압강도와의 상호관계를 비교, 평가, 분석함으로써, 향후 전동기의 절연상태 평가시 수명 및 절연진단의 신뢰성을 도모하고자 제안하였다. 본 논문에서는 비파괴시험과 파괴시험과의 상관관계를 평가하기위하여 비파괴시험으로 설연저항시험, 성극지수시험, 유전정접시험, 부분방전시험을 실시하였으며, 파괴시험은 60[㎸] AC 내전압를 이용하여 실시하였다. 또한 장기간 사용된 전동기 권선의 절연물에 대한 연구결과로부터 기존 선진국의 진단방법 및 판정기준이 국내에서 제작된 전동기에 대한 절연특성 평가 및 분석에도 타당함을 증명하였으며, 향후 본 논문에서 제시한 자료들은 유사조건의 산업현장에서 운용중인 유도전동기의 수명 및 상태 평가를 위한 기초자료로 유용하게 사용될 수 있으리라 기대된다.