Detection of incipient defects in cables by partial discharge signal analysis (original) (raw)
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Challenges of partial discharge diagnostics of low-voltage cables
Journal of Electrostatics, 2013
Partial discharge measurement is one of the most important diagnostic methods to detect local faults in insulation systems. Detection of local faults in low-voltage cables would be attractive for condition assessment of power plant secondary cables. The construction of low-voltage cables is different from the medium and high voltage ones, preventing the direct application of the already developed models and methods. An analysis of partial discharge detection and evaluation methods for low-voltage cable diagnostics are given in this paper. Some laboratory measurement results are also presented and the identified issues are described in this paper.
Practical issues of partial discharge testing of low-voltage cables
2011 Electrical Insulation Conference (EIC)., 2011
ABSTRACT Demand for low voltage cable diagnostics, arising from lifetime extension programs of power plants, grows recently. This paper reports on investigations of the authors with partial discharge testing of low voltage control, measurement and signal cables. The construction of low voltage cables differs in many ways from the middle voltage and high voltage cables, on which partial discharge diagnostics has been widely investigated and highly developed. The lack of semiconducting layers makes them less lossy on higher frequencies than MV and HV ones. These results in a different behavior of the propagation of PD induced impulses. Besides, without smoothing layers, these cables are not necessarily PD free at their test voltage. Due to the issues mentioned above, the bandwidth and impulse resolution of the measuring equipment were addressed as well as the discrimination between discharge impulses formed in the insulation bulk and on the conductor surfaces. Measurements were carried out on single and multiple conductor cables by equipments with different bandwidth. The results of the investigation are presented and discussed in this paper. Keywords-low-voltage cables, partial discharges, cable diagnostics
Detection of Partial Discharges and its Effect on Solid Insulation used in High Voltage Cable
— Most of the high voltage (HV) power equipment is made up with solid insulation like paper insulation, glass insulation, epoxy insulation etc. The oldest kind of insulating material among all insulation, the paper insulation is used in cable and nowadays the Cross linked Polyethylene (XLPE) is commonly used for cable insulation. The presence of impurities in the insulation system is one of the root causes of insulation failure as they are form a weak zone inside the healthy insulation system. Therefore, early identification of degradation process like formation of electrical tree structures inside such solid electrical insulation due to high voltage tress during its operating life is utmost requirement to prevent the electrical power equipment from a sudden and complete insulation failure. To study the growth mechanism of electrical tree structure inside the insulation with different applied high voltage a commonly used insulating material like XLPE insulation in HV power cable are consider for this present work. This work also describes the ageing process by conducting the partial discharge (PD) test on the same insulating materials. Finally, the effect of PD on insulation i.e., formation of electrical tree structure on solid insulation was observed by using Scanning Electron Microscope (SEM) and analyzed.
On-line Partial Discharge Detection in Cables - 1997
This paper describes a11 on-line partial discharge (PD) detection technique in power cables. The technique uses a digital spectrum anal?/zer with a high-frequency preampl(fier and several types of highfrequency inductive sensors. In extruded and inipregnated power cables, the PD detection IS nrade in the VHF range. The suitability and the sensitivity of the VfIF technique were checked agoinst two other conventionnl PD detecting methods (Pulse Phase Annlyzer and Fast Digital Scope) by performing PD n~ea.surenrents i n EPR-insulated cable under laboratory-coiitrollerl concli tioiis. The sui to b i li ty an cl semci tivi ty of the VHkmethod were as good CIS the two conventionnl PD de te cti 011 171 e th o CIS. The VHF method then wns u.secl to conduct on-.cite PD nrea.surenrent.s in se\)eral power cables. These nreasurements were conclucted while the cables were in .service. Special care wns given to distinguish between external electroningnetic noise and electronragnetic signals produced by the PD activities inside the cnhle insulation.
Condition Monitoring of Medium Voltage Electrical Cables by Means of Partial Discharge Measurements
SAIEE Africa Research Journal, 2014
The purpose of this paper is to discuss condition monitoring (CM) of medium voltage electrical cables by means of partial discharge (PD) measurements. Electrical cables are exposed to a variety of operational and environmental stressors. The stressors will lead to the degradation of the cable's insulation material and ultimately to cable failure. The premature failure of cables can cause blackouts and will have a significant effect on the safety of such a network. It is therefore crucial to constantly monitor the condition of electrical cables. The first part of this paper is focussed on fundamental theory concepts regarding CM of electrical cables as well as PD. The derivation of mathematical models for the simulation of PD is also discussed. The simulation of discharge activity is due to a single void within the insulation material of medium voltage cross-linked polyethylene (XLPE) cables. The simulations were performed in the MATLAB ® Simulink ® environment, in order to investigate the effects of a variety of parameters on the characteristics of the PD signal. A nonintrusive CM technique was designed for the detection of PD activity within cables. The CM technique was used to measure and analyse practical PD data. Two MATLAB ® programs were designed to analyse the PD data in both the time-domain and frequency-domain.
2013
The purpose of this paper is to investigate the effect of PD (partial discharge) activity within medium voltage XLPE (cross-linked polyethylene) cables. The effect of partial discharge was studied by means of a number of simulations. The simulations were based on the well-known three capacitor model for partial discharge. An equivalent circuit was derived for partial discharge due to a single void in the insulation material of a power cable. The results obtained from the simulations will form the basis of the design proses of a non-intrusive condition monitoring technique. The technique is based on the classification of discharge activity according to five levels of PD. Future work will include the improvement of the simulation model by investigating the high frequency model of a power cable as well as the statistical nature of PD activity. This will improve the accuracy of the simulation results when compared to actual measurements. The work discussed in this paper will be used to ...
22nd International Conference and Exhibition on Electricity Distribution (CIRED 2013), 2013
The paper focuses on the new possibilities of managing a key element of the power supply system: the power cable network. The possibilities are created by the technical condition assessment of power cables based on partial discharge diagnosis at damping (self-extinguishing) AC voltage. Both cable manufacturers and their users pursue to obtain a high technical reliability of the power network. Modern IT and measurement systems make it possible to acquire data enabling a better assessment of the line technical condition. Undoubtedly, among the new data sources there is also diagnostics based on partial discharge (PD) measurement (PD inception voltage, PD extinguishing voltage, the PD apparent charge value for different voltage levels, PD intensity, PD distribution as a function of cable length). Providing a unique data set which describes an insulation technical condition of particular line elements, such a diagnostics creates an opportunity to change the current method of power cable network management to a new more effective one, both technically and economically. Measurements of partial discharges in MV cable network were carried out in one of the distribution companies in Poland in the years 2005-2010. They were intended to develop an optimal method for the use of partial discharges diagnosis in the assessment of technical condition of power cables. The main area of research covered MV cable lines of a total length of 590 km.. The studies on power cables provided a group of measurements for Paper Insulated Lead Covered power cables (PILC). From all the measurements there were selected 18 cases where a cable failure was recorded and the measurements of partial discharges were carried out both before the failure and immediately after the repair of the failure. Basing on the carried research work and analysis it has been found that: Basic parameters indicating the risk of the failure are: reduced PD inception voltage and the occurrence of increased PD intensity in a power cable. The study shows that, the lower the PD inception voltage, the higher the percentage of cable sections of an increased PD intensity. Consequently, a greater number of cable sections which can be included to the group of increased risk of failure. No correlation between the increase of PD value and increasing probability of the failure occurrence has been found..
2017 IEEE 21st International Conference on Pulsed Power (PPC), 2017
The breakdown of insulation in cables while in service can cause considerable damage to equipment and the accessories to which they are connected. PD in cables arises due to the overstressing of cable insulation resulting from electric field enhancement caused by imperfections in cable core and screen. The nature and magnitude of PD activity depends upon the type of defect, aging, environmental factors, applied voltage and cable loading. Reduction in system voltage can potentially reduce PD, which will correspondingly extend the service life of the cable. Currently, industry voltage statutory requirements permit ±6% tolerance setting on nominal voltage on distribution networks. This ±6% voltage reduction on may have little or an adverse effect on PD magnitude depending on the nature of defect present in the cable. Hence there is a clear requirement to predetermine the PD inception voltage in cables through laboratory experiments to understand the significance of voltage reduction. This means to verify the effect of voltage reduction on extinguishing or minimizing PD activity in cables. In this paper, range of voltages at which PD incepts termed as partial discharge inception voltage(PDIV) is measured using a test cell containing different types of electrode configuration having different spacing. PDIV measured using the test cell is verified by conducting partial discharge testing in paper insulated lead covered (PILC) and cross-linked poly ethylene(XLPE) cables. It has been found that PDIV measured using the test cell and cable are in good agreement.