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IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 42, NO. 10, OCTOBER 2014
The Influence of L-Shaped Structure on Partial Discharge Radiated Electromagnetic Wave Propagation in GIS Xiaohua Wang, Tianhui Li, Dan Ding, and Mingzhe Rong
Abstract— To clarify the propagation process and improve the utilization of ultrahigh frequency (UHF) technique in partial discharge diagnosis, the propagation characteristics of electromagnetic wave in different directions in an L-shaped gas insulated switchgear tank are profoundly investigated in this paper. According to the property of electric field distribution and attenuation curves of the UHF signal, the influence of L-shaped structure is analyzed. Index Terms— Electromagnetic (EM) wave propagation, gas insulated switchgear (GIS), partial discharge (PD).
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LTRAHIGH frequency (UHF) method has been proved to be effective and applicable for partial discharge (PD) detection and on-line monitoring system in gas insulated switchgear (GIS). As the foundation of diagnosis and assessment of PD, the electromagnetic (EM) wave propagation mechanism in GIS, which will also be affected by some special structural elements, is crucial to be declared [1]–[3]. The detailed investigation concerning the EM wave component in different directions, as well as the influence of the special structure to it, has scarcely been performed in the previous research. Therefore, the EM wave propagation and the effect of L-shaped structure (LS) are examined in this paper. Based on a 252-kV GIS, an L-shaped GIS tank model is built including a reserved interface with metal cover. A protrusion defect on the HV conductor is set next to the left end of the tank as the discharge source, and a Gaussian pulse with peak value of 15 mA is used as the PD current pulse. The corresponding charge quantity is 5 pC, which agrees with the conventional sensitivity requirement of PD detection. The electric field distribution and attenuation curves of the peak to peak value (Vpp) and cumulative energy received by 10 probe couplers [2] are shown in Fig. 1, while the coordinate system and parameters of the tank are included.
Manuscript received November 1, 2013; revised August 16, 2014; accepted August 20, 2014. Date of publication September 5, 2014; date of current version October 21, 2014. This work was supported in part by the Program for New Century Excellent Talents in University and in part by the National High Technology Research and Development Program (863 Program) of China under Grant 2011AA05A121. (Corresponding author: Tianhui Li.) X. Wang, D. Ding, and M. Rong are with the State Key Laboratory of Electrical Insulation and Power Equipment, School of Electrical Engineering, Xi’an Jiaotong University, Xi’an 710049, China (e-mail: xhw@ mail.xjtu.edu.cn;
[email protected];
[email protected]). T. Li is with Hebei Electric Power Research Institute, Shijiazhuang 050021, China (e-mail:
[email protected]). Digital Object Identifier 10.1109/TPS.2014.2351583
In x direction as shown in Fig. 1(a), the E field component is fairly small and so are the Vpp and energy. After the EM wave being generated at 2 ns in the beginning, it reaches the LS and is reflected partly at 11.6 ns. Then, it continues to spread in the posterior part of the tank with insignificant change. The two attenuation curves are found to keep a consistent decreasing trend and the energy has a significant sudden drop when passing LS. As Fig. 1(b) shows, the strongest E field component appears in y direction. The generated EM wave at 2 ns and the reflection at 6.3 ns are much more obvious than before. What is different as well is that the E field intensity that propagates to the posterior part is relatively low at 11.6 ns, which leads to significant decline of both Vpp and energy. Meanwhile, the two curves that are about one order of magnitude larger than those in the other two directions maintain the same variation. The result in z direction shown in Fig. 1(c) is quite distinct. The generation of the E field component is always in longitudinal direction. In other words, it is the way that the TM mode built. Next, when the EM wave arrives at the corner and the reflection just begins at 6 ns, some intensive axial E field components have already been formed, which is earlier than the cases before. That is because that the LS can be regarded as a source of TM mode due to the discontinuity of wave impedance. For this reason, the E field intensity in the posterior part is strengthened at 11.6 ns. The two curves that rise first and then decrease ahead of LS are caused to increase conversely when passing LS, and then maintain at a certain level instead of getting reduced, which leads to the deviation in the latter parts. The above results indicate that LS has distinct effect on the EM wave propagation in different directions, and the influence on z direction is the greatest. When propagating through the L-shaped tank, the EM waves in both x and y directions get decreased generally because most high order TE modes are involved in the reflection and mode transformation [4]. While only the EM wave in z direction has a great rise. The whole trend of Energy−axial has also been changed significantly. It infers that LS is more conducive to transmit TM mode, so the axial signal is enhanced and its original attenuation rule is changed, too. In conclusion, this paper has clarified the propagation process and mechanism of EM wave in L-shaped tank. The presented results lay the foundation for rational use of UHF sensor and better implementation of PD detection.
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WANG et al.: INFLUENCE OF LS ON PD RADIATED EM WAVE PROPAGATION IN GIS
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Fig. 1. E field evolution during the propagation of EM wave and the attenuation curves of Vpp and cumulative energy (1 aJ = 1e − 18 J) in different directions. Time of the electric field distribution in axial section is 2, 6.3, and 11.6 ns (except for the second Ez as 6 ns). (a) x direction. (b) y direction. (c) z direction.
R EFERENCES [1] M. D. Judd and O. Farish, “FDTD simulation of UHF signals in GIS,” in Proc. 10th Int. Symp. High Voltage Engine, vol. 6. 1997, pp. 1–4. [2] T. Li, X. Wang, C. Zheng, D. Liu, and M. Rong, “Investigation on the placement effect of UHF sensor and propagation characteristics of PD-induced electromagnetic wave in GIS based on FDTD method,” IEEE Trans. Dielectr. Electr. Insul., vol. 21, no. 3, pp. 1015–1025, Jun. 2014.
[3] M. Hikita, S. Ohtsuka, J. Wada, S. Okabe, T. Hoshino, and S. Maruyama, “Propagation properties of PD-induced electromagnetic wave in 66 kV GIS model tank with L branch structure,” IEEE Trans. Dielectr. Electr. Insul., vol. 18, no. 5, pp. 1678–1685, Oct. 2011. [4] S. Okabe et al., “Simulation of propagation characteristics of higher order mode electromagnetic waves in GIS,” IEEE Trans. Dielectr. Electr. Insul., vol. 13, no. 4, pp. 855–861, Aug. 2006.
