Advanced Technology of Electrical Engineering and Energy (1., SO17 1BJ)

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1 Advanced Technology of Electrical Engineering and Energy Vol. 25, No. 3 July 2006 XLPE 1,2, 1, 1, G CHEN 3 (1., ; 2., ; 3., SO17 1BJ) : (XLPE) Hz, XLPE 250Hz 500Hz, : XLPE ; ; ; ; : TM247 : A : (2006) (PE) XLPE [5,8 ] D W Kitchin 1958, PE, [9,10 ] 100Hz, XLPE [1 ] [4,5 ],, ( [4 ], 250Hz) ( 500Hz) XLPE [1 3 ],, XLPE [6,7 ] XLPE XLPE : : (19642),, ; (19632), Π ; (19542),,

2 3 4,, XLPE 5mm, 2 50Hz, Fig. 2 Propagation characteristics of electrical trees at 50Hz 5 1 m, 3 1 m V Hz ( 250 Hz) XLPE,,,,, 1152 ( 250Hz) :, 1 (a) ;, 1 (b) ;, ( 1 (c) ) 2 ( ) : Fig. 3 Electrical trees at high frequency , ( 500 Hz) XLPE ( 500Hz) ( 3) 500Hz 1000Hz 2000Hz Hz 4 Fig. 1 Structure of electrical trees at 50Hz Fig. 4 Propagation velocity of electrical trees at high frequency

3 3 : XLPE 35 4 ( 5a) ; (2) 1, 1,, ;, 1 Tab. 1 Initiation and the propagation characteristics, of electrical trees at Hz Πmin Hz 500Hz 1000Hz 2000Hz Πmin Πs 25 Πmin Πmin 4 Πmin Πs 5 Πmin , ( 1), ( 3),, 5 6,, 100nm mm, 5 6, Fig. 5 Spherical crystal effect on trees in low frequency, : (1),, - ( 5b) ; (3),,, ( 5c) 6,,, ( 6) (a) ; (b) ; (c) (a) needlepoint lies in gap of spherocrystals (b) a branch of branch2like trees propagating into spherocrystal (c) needlepoint just penetrate into inside of big spherocrystal

4 3 6 6 Fig. 6 Structure of electrical tree at high frequency [ 5 ] (Zheng Xiaoquan), G Chen, A E Davies. XLPE 5 ( Types of electrical trees and influence factors in XLPE cable insulation) [J ]. XLPE (Adv. Tech. of Elec. Eng. & Energy),,2003, 22(4) : [ 6 ] Y Zhao, A S Vaughan, J V Champion, et al. The structure of electrical trees in semi2crystalline polymers [ A ]. Proc. : IEE 8th Conf. Materials, Measurements and Applications ; [ C]. Edinburgh, UK, ,, [ 7 ] Yuanxiang Zhou, Xiaoguang Luo, Ping Yan, et al. Influence ; of morphology on tree growth in polyethylene [ A ]. ISEIM 2001 [ C]. Himeji, Japan, [ 8 ] X Zheng, G Chen, A E Davies, et al. The influence of survival mechanical stress and voltage frequency on electrical tree in XLPE [ A ]. IEEE 2002 CEIDP [ C ]. Cancun, Mexico, [ 9 ] Suwarno, Y Suzioki, T Mizutani, et al. Effects of frequency, and applied voltage on electrical treeing discharges [ A ]. ICSD 95 [ C]. Leicester, England, [ 10 ] L Cisse, G Teyssedre, D Mary, et al. Influence of (References) : frequency, electrode material and superimposed DC on AC [ 1 ] A Hadid, C Laurent. An experimental technique to study electroluminescence in polymer films [J ]. IEEE Trans. on space charge injection in polymeric materials under AC Dielectrics and Electrical Insulation, 2002, 9(1) : voltage [J ]. IEEE Trans. on Electrical Insulation, 1992, 27 [11 ],, (Liu Jiaqi, Mou Lei, Jia Lei, et (6) : al. ). XLPE [ 2 ] Y F F Ho, G Chen, A E Davies, et al. Measurement of ( Influence of brass mantle on transient input characteristic of space charge in XLPE insulation under 50 Hz AC electric stresses using the LIPP method [ J ]. IEEE Trans. on Dielectrics andelectrical Insulation, 2002, 9(3) : [ 3 ] R Patsch, M Hoof. The influence of space charge and gas pressure during electrical tree initiation and growth [ A ]. Proc. 4th International Conf. on Properties and Applications of Dielectric Materials [ C]. Brisbane, Australia, [ 4 ] (Zheng Xiaoquan), G Chen, A E Davie. XLPE (Study on growing stages of electrical tree XLPE) [J ]. (Adv. Tech. of Elec. Eng. & Energy), 2003, 22 (3) : XLPE cable windings) [J ]. (Adv. Tech. of Elec. Eng. & Energy), 2005, 24(2) : Influence of frequency of voltage applied on the propagation characteristics of electrical trees in XLPE cable insulation XIE An2sheng 1,2, LI Sheng2tao 1, ZHENG Xiao2quan 1,G CHEN 3 (1. State Key Laboratory of Electrical Insulation and Power Equipment, Xi an Jiaotong University, Xi an , China ; 2. Environment Science and Engineering College, Chang University, Xi an , China ; 3. University of Southampton, Southampton SO17 1BJ, UK) Abstract : In this paper the structures and propagation characteristics of electrical trees under high voltage of Hz ( 72, cont. on p. 72)

5 7 2 [ 8 ] Han Ju Cha, Enjeti, P N. A new ride2through approach for matrix converter fed adjustable speed drives [ A ]. 37th IAS Annual Meeting [ C]. Pittsburgh, USA, [ 9 ] (Song Wenxiang, Chen Guocheng). SVPWM ( Study on SVPWM method for three2level neutral2point2clamped (NPC) inverter) [J ]. (Adv. Tech. of Elec. Eng. & Energy), 2004, 23(4) : [10 ],,, ( Zhang Haitao, Zhao Zhengming, Yuan Liqiang, et al. ). Lipeil, et al. ). ( Simulation and (Analysis on matrix converter operation in abnormal experimental analysis of short2circuit braking for 32level inverter2motor systems) [J ]. (Proc. of the CSEE), 2004, 24(8) : [11 ] ( Gao Jingde, Wang Xiangheng, Li Fahai). (AC machines and the related systems analysis) [M]. : (Beijing : Tsinghua Univ. Press), [12 ] (Li Fahai, Zhu Dongqi). ( Electromechanics) [ M]. : (Beijing : Science Press), [13 ] (Sun Kai, Zhou Daning, Huang conditions) [J ]. (Adv. Tech. of Elec. Eng. & Energy), 2004, 23(2) : A ne w control strategy of power loss ride through in MV inverters ZHANG Hai2tao, ZHAO Zheng2ming, YUAN Li2qiang, QIAN Jue, LU Ting (State Key Lab. of Control and Simulation of Power System and Generation Equipment ; Depart. of Elec. Eng. and Applied Electronic Technology, Tsinghua University, Beijing , China) Abstract : The voltage sag or instant power loss often happens in power supply system in medium voltage (MV) inverterπs working environment. Frequent start MV inverter2motor system causes great harm to the normal production. As the most important function of MV inverters, a new control strategy of power loss ride through ( PLRT) is investigated. Based on the brake of quickly reducing output frequency, the PLRT maintains the DC link voltage in a proper range. The principle, process and function design of PLRT are developed in this paper. The test results in a 55kW 32level inverter show that this PLRT is an efficient and feasible key to the instant power loss. Key words : MV inverter ; power loss ride through ; ASD system ( 36, cont. from p. 36) in the cross2linked polyethylene ( XLPE) cable insulation samples are studied. It is found that there are three kinds of electrical trees, the branch2like tree, mixed tree combining branch with jungle, and pure jungle2like trees, that will appeared in the sample when frequency is less than 250Hz due to non2uniform crystallization and micro2defects concentrated in XLPE cable insulation. Only one kind of electrical tree, the dense branch2like trees, will be developed when frequency is equal to or higher than 500Hz. The propagation mechanisms of these kinds of electrical trees are mainly decided by crystalline state of the dielectric and the frequency of voltage applied. The structures and propagation characteristics of electrical trees is closely related to aggregation state of material in low frequency, and is nothing to do with the aggregation state of material at high frequency. The propagation law of electrical trees in XLPE cable insulation at high frequency is similar as in epoxy resin and PMMA. The propagation characteristics of electrical trees not only depends upon the crystal2boundary and microspore in amorphous interface, but also depends upon the impurity concentration and the relative position between electrode tip and sphere2crystals or amorphous region in low frequency. Because the processes of injection and elicitation charge from and to dielectric by electrode are more violent at high frequency than at low frequency, it can form relatively uniform dielectric weak region at the front of needle electrode, so the initiation and propagation law of electrical trees at high frequency is similar each other. Key words : XLPE ; electrical trees ; frequency ; structure ; propagation

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