Partial Discharge In Power Cables Research Articles

Review on Detection and Analysis of Partial Discharge along Power Cables

Partial discharge (PD) detection and analysis plays a crucial role for acceptance testing and condition monitoring of power cables. Various aspects are related to PD in power cables from theory to practice. This paper first summarizes the PD mechanism and models used for PD analysis in power cables. Afterwards, PD detection is addressed in the aspects of off-line test, on-line test, and sensors. PD analysis is discussed in detail. Specifically, related quantities and algorithms for PD analysis are outlined. PD characteristics with affecting factors, e.g., dielectric type, load, and applied voltage are discussed. Experience on PD development trend with measurements in field is analyzed. Based on the comprehensive review, challenges of PD detection and analysis along a power cable are proposed.

Effect of magnetic field on partial discharge parameters in power cables and on the breakdown characteristics of impregnated paper insulation

This article demonstrates that parameters of partial discharges in power cables and impregnated paper insulation breakdown characteristics vary in presence of grid-frequency alternating magnetic field. Experimental and theoretical demonstrations confirm that magnetic field affects the probability of partial discharges in air cavities inside inhomogeneous insulation. Based on the developed method, the impact of magnetic field on breakdown probability and on Weibull distribution parameters that approximate experimental breakdown voltage data is estimated. The differences in chemical and structural properties of the breakdown area in electrical and electromagnetic fields are determined using scanning electron microscopy and energy dispersive spectroscopy.

Charge concept in partial discharge in power cables

Present paper discusses Partial Discharge (PD) occurrence and its relevant parameters in power cables. A spherical void in the insulation of a power cable is assumed as the origin of PD. To study PD in power cables, a model based on the three capacitor type is proposed, and the associated circuit elements for the spherical void and different layers of the cable are obtained with closed form solutions. In the procedure of deriving parameters of the model, a defect column is selected with a particular geometry which its boundaries are in the direction of the electric field. The results for PD magnitude and current pulse are acquired from the proposed model, along with Finite Element Method (FEM) simulations. Both methods show matching results but in contrast with the dipole model. FEM simulations are accomplished in 3D, on account of spherical geometry of the void. Other simulation results achieved from FEM and the model are as well included.

From the editors' desk

The first article in this issue is "Special Requirements of High Frequency Current Transformers in the On-Line Detection of Partial Discharges in Power Cables," by Yang Xu, Xiao Gu, Bin Liu, and Baojun Hui of the State Key Laboratory of Electrical Insulation and Power Equipment, Xi'an Jiaotong University, Xi'an, China; Zhigang Ren of the Beijing Electric Power Research Institute, Beijing, China; and Shaoxin Meng of the China Electrical Power Research Institute, Wuhan, China. The article discusses some special requirements of high frequency current transformers and the instrumentation in the on-line detection of partial discharge (PD) in cables. Four types of defects representing typical situations in the field were created in a 110-kV cable and joint for PD detection. Based on the frequency analysis of the PD signals, the upper frequency of a measuring instrument needs to be higher than 40 MHz and the lower frequency no less than 500 kHz. The lower frequency limit is recommended to avoid power line interference. Provided that the high frequency current transformer satisfies the bandwidth requirement, a high transfer impedance is preferred. A sensitivity better than 100 pC is expected in on-site PD detection and in high noise environments. The article compares eight PD measuring instruments based on high frequency current transformer detection with respect to lower and upper limit frequencies, sensitivity, PD pattern recognition functions, and PD signal attenuation. Among the existing functions, the PD pattern recognition function needs to be improved for on-line cable tests. In addition, the article concludes that there still is a need for an on-line calibration method based on high frequency current transformer sensors.

Special requirements of high frequency current transformers in the on-line detection of partial discharges in power cables

The insulation condition of power cables is closely associated with partial discharge (PD) [1]. Early signs of cable insulation failure such as from electrical treeing are revealed by PD detection [2], and insulation failure will eventually lead to breakdown [3]–[5]. For AC cross-linked polyethylene (XLPE) cables, online PD detection is used to determine potential defects in the cable, and high frequency current transformers (HFCT) are most commonly applied for convenient and noninvasive detection. Conventional PD measuring techniques have been specified in IEC 60270 [6], and cable factory tests are based on this method. When PD detection is conducted on cables in service, some special issues such as noise reduction and dynamic range have to be dealt with [7]. Complex electromagnetic interferences and noise may significantly affect detection results by reducing the detection sensitivity [8]. Some high frequency components of PD signals cannot be covered by the detection bandwidth of a measuring instrument because the upper limit frequency is not high enough [9]. One more challenge is that a long cable can cause significant attenuation of PD signals [10]–[12], which will decrease the signal amplitudes to be detected. Therefore, the PD measuring instruments for on-line detection for cables have to satisfy some additional requirements.

Quantitative Analysis of Rogowski CT Frequency Characteristics

Partial discharges in power cables will generate small currents with low frequencies in the ground cords. In cable PD online monitoring systems, CTs are usually used to obtain such PD signals. In this paper, by derivations based on theories of wave propagation, the frequency characteristics of Rogowski CTs (RCTs) and the effects of transformer parameters (size, core material, etc.) on its pass band B, sensitivity H(jω0), the lower cutoff frequency fL is acquired. The feasibility of such derivations is verified by experiments. By conducting comparative experiments, the effect of the use of screening box and the way of coil winding on the performance of a current transformer is acquired. A feasible plan to improve the frequency characteristics of CTs is presented, in order to acquire more stable gain and better anti-interference ability within their pass band.

Design of Broadband Planar Spiral Antenna for Partial Discharge in Cable

The detection of partial discharge in power cables is an effective method to diagnosis early fault of XLPE cable . When partial discharge occurs, it emits abundant frequency component in ultra-high frequency (UHF) band, and broadband planar spiral antenna is an effective sensor to detect UHF partial discharge signals. High frequency electromagnetic simulation software Ansoft HFSS is used to simulate and analysis planar Equiangular spiral antenna and Archimedean spiral antenna. The simulation results show that the two kinds of antennas work effectively in 400 MHZ ~ 1 GHZ frequency band and are high sensitivity and superior performance. Because of with smaller size and larger gain, the Archimedean spiral antenna is used to detect UHF signals of partial discharge in XLPE cable.

Advanced signal processing and modeling for partial discharge diagnosis on mixed power cable systems

Power cable grids have been growing enormously over the years; due to their aging, there is a strong need for Partial Discharge (PD) measurement techniques in order to identify incorrectly installed or damaged cable joints or cavities in cross-linked polyethylene (XLPE) insulated and paper-insulated lead-covered (PILC) cables. Mixed power cable systems consist of a mixture of interconnected cables of various types. The Time Domain Reflectometry (TDR) is a standard technique for the location of PD in power cables. However, the localization process on-the-field is impeded by various interferences and noise. Additionally, propagation velocities of PD pulses traveling on the line differ depending on the cable type (XLPE or PILC cables), which leads to significant location errors. This paper provides automatable signal processing tools for increasing the detection ratio as well as location accuracy in the field of mixed cable systems. A mixed cable system model provides the possibility of analyzing PD data of even complex cable interconnections.

Comprehensive 3‐capacitors model for partial discharge in power cables

PurposeThe paper proposes and presents a comprehensive and integrated circuit model for investigating the behaviour of partial discharges occurring in voids inside the solid insulations of medium and high voltage cables.Design/methodology/approachThe model is based on the well‐known three capacitors model, which is remarkably improved to handle physical parameters such as cavity size, position, shape and pressure, environmental parameters such as cable temperature, in addition to operational parameters such as the contributions of the avalanche of free electrons inside the cavity through considering stochastic time delays.FindingsA complete, flexible and reliable model for partial discharges in voids inside the solid insulation of medium and high voltage cables is presented whose output agrees with experimental reported results.Research limitations/implicationsThe proposed model deals only with single voids, and the semiconductor layers in the insulation of cables are not considered.Practical implicationsThe model can be used in different physical, environmental and operational conditions in order to investigate the characteristics of partial discharge signals to be used as the bases for partial discharge detection and classification in power cables.Originality/valueThis paper presents a novel comprehensive and integrated circuit model with controlling functions to propose the behaviour of partial discharge occurring in voids inside the solid insulation of power cables. The model provides the contribution of geometrical parameters of the void, and operational conditions such as cable temperature and source frequency in partial discharge analysis.

Phase Difference Method for Two-end Partial Discharge Locating System of Power Cables

A method to locate partial discharges in power cables is presented in this article. The method is based on the phase difference between the first arriving waves of a partial discharge pulse at the cable terminals. The phase difference as a function of frequency is obtained using the cross-Fourier spectral density function. The partial discharge location can be determined from the slope of the unwrapped phase difference. The performance of the method is tested using the electromagnetic transient program on a 20 kV, 2-km underground cable, which takes into account the frequency-dependent parameters. The statistical results indicate high location accuracy.

Auto-detection of partial discharges in power cables by discrete wavelet transform

One of the serious problems that can occur in power XLPE cables is destruction of insulator. The best and conventional way to prevent this is ascertaining partial corona discharges occurring at small voids in organic insulators. However, there are some difficulties in detecting those partial discharges due to the existence of external noise in detected data, whose patterns are hardly identified at a glance. For this reason, there have been a number of researches into detecting partial discharges by employing a neural network (NN) system, which is widely known as a system for pattern recognition. We have been developing an NN system for auto-detection of partial discharges, and have input numerical data of the waveform itself and obtained appropriate performance. In this paper, we employed the discrete wavelet transform (DWT) to acquire more detailed transformed data in order to use them in the NN system. Employing the DWT, we were able to express the waveform data in time–frequency space, and achieved effective detection of partial discharges by the NN system. We present herein the results using DWT analysis for partial discharges and noise signals which we obtained. Moreover, we present results out of the NN system which dealt with those transformed data. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 152(1): 24–30, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10315

Auto-Detection of Partial Discharges in Power Cables by Descrete Wavelet Transform

Auto-Detection of Partial Discharges in Power Cables by Descrete Wavelet Transform

Estimating the location of partial discharges in cables

There are several techniques that can be used to estimate the location of partial discharges in cables, however, certain technical obstacles need to be overcome before acceptance of this type of testing becomes widespread. A review of the theory of signal propagation in power cables is presented along with its relation to partial discharge site location. Fundamental limitations affect the detectability and location accuracy of partial discharges in power cables. The sources of these errors are discussed along with methods that minimize their effects. The advantages and disadvantages of alternative methods for locating partial discharge sites are presented along with a calibration method that improves the accuracy of these methods.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>