| 1. |
- Yuan, Chao, et al.
(författare)
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Dielectric Response Characterization of In-service Aged Sheds of (U) HVDC Silicone Rubber Composite Insulators
- 2016
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Ingår i: IEEE Transactions on Dielectrics and Electrical Insulation. - 1558-4135 .- 1070-9878. ; 23:3, s. 1418-1426
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Tidskriftsartikel (refereegranskat)abstract
- Investigations of bulk dielectric properties of specimens extracted from in-service aged and aged UHVDC composite insulator sheds are reported in this paper. The program of the study included measurements of DC conductivity and complex permittivity at frequency range 10-4 – 103 Hz at various temperatures in dry and wet (water immersion) conditions. The obtained results are analyzed by considering a combination of relations describing various dielectric relaxation modes in dielectrics, included three Cole-Cole types of responses and a hopping process. The hopping has the strongest impact on the responses in the whole frequency range. Two of the Cole- Cole responses appearing in the low frequency range are attributed to Maxwell- Wagner-Sillars relaxations at macroscopic and mesoscopic levels; first one representing interfacial polarization at the border between specimen and air gap in the electrode arrangement, while the second one is attributed to the charge relaxation at filler boundaries and internal cavities in the polymeric materials. The third Cole-Cole process, active at higher frequencies, is considered as a sign of polymer degradation, as it shifts with the ageing to higher frequencies.Based on the results of this study, it is claimed that dielectric response measurements on specimens of in-service aged composite insulator sheds can provide useful information on the degree of material degradation. In addition, a water immersion test in combination with such measurements may be a good way to enhancing the observed changes.
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| 2. |
- Yuan, Chao, et al.
(författare)
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Space charge behavior in silicone rubber from in-service aged HVDC composite insulators
- 2019
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Ingår i: IEEE Transactions on Dielectrics and Electrical Insulation. - 1558-4135 .- 1070-9878. ; 26:3, s. 843-850
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Tidskriftsartikel (refereegranskat)abstract
- Space charge behavior in sheds removed from service aged 500 and 800 kV HVDC silicone rubber insulators and compared to a stored reference insulator is reported in this paper. The aim of this investigation is to evaluate the material aging. The investigations are made under electric field of ±20 kV/mm at room temperature using pulsed electro-acoustic technique. Based on the results, the electric field distribution and mobility of charge carriers, considering the contributions of de-trapping process from both shallow and deep traps, are deduced. It is concluded that space charge concentration in the aged material increases compared to that in the reference material and the dynamics of the charge decay changes. The understanding of this behavior provides a means of possibility assessing insulator material aging.
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| 3. |
- Yuan, Chengyin, et al.
(författare)
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Surface Potential Decay on Material Samples Taken From In-service Aged HVDC Silicone Rubber Composite
- 2017
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Ingår i: IEEE Transactions on Dielectrics and Electrical Insulation. - : Institute of Electrical and Electronics Engineers (IEEE). - 1558-4135 .- 1070-9878. ; 24:1, s. 592-600
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Tidskriftsartikel (refereegranskat)abstract
- Surface potential decay characteristics of specimens extracted from in-service aged and reference HVDC composite insulator sheds are reported and analyzed in this paper. In the experiments, surfaces of the insulator samples were charged by dc corona and the decay was recorded utilizing a non-contact technique. In addition, surface and bulk conductivities of the specimens were determined and used for analyzing by means of computer simulations their impact on the potential distribution profiles and its decay. Based on the performed experiments, trap density distributions, mobility of charge carriers and field dependent bulk conductivities are deduced for the investigated samples with the aim to evaluate the ageing severity.
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| 4. |
- Yuan, Chao, et al.
(författare)
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Ultrasonic phased array detection of internal deffects in composite insulators
- 2016
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Ingår i: IEEE Transactions on Dielectrics and Electrical Insulation. - 1558-4135 .- 1070-9878. ; 23:1, s. 525-531
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Tidskriftsartikel (refereegranskat)abstract
- To reduce the risk imposed by use of defected composite insulators on the operation of power grids, this paper introduces a nondestructive ultrasonic phased array (UPA) technique that allows effectively test such insulators. The method offers a great potential by reducing inspection time as well as allowing for analyzing components characterized by a complex geometry. The UPA inspection system utilizes an open-ended rectangular waveguide sensor, operating at frequency of 2.5 MHz. The system is simple, safe and relatively inexpensive. In this work, samples of silicone rubber composite insulators with various types of detects are studied and the obtained results show that void defects in the bulk of the insulator housing are easiest to be detected. Holes under insulator sheds can also be detected by the edge of scanning range. For the defects near the core-shed interface, the detection becomes possible by comparisons with sample without defects.
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