摘要: 為探討脈沖方波電壓頻率對局部放電特性的影響,基于超高頻(UHF)檢測方法和IEEE 488.2傳輸協(xié)議,構(gòu)建了寬頻、高速數(shù)據(jù)采集局部放電測試系統(tǒng).利用該系統(tǒng),研究了變頻電機耐電暈漆包線的局部放電脈沖幅值、相位和時頻特性.研究結(jié)果表明:頻率200 Hz以上的高頻脈沖電壓使空間電荷擴散效應(yīng)減小,增大了局部放電初始電子產(chǎn)生的概率,使得局部放電瞬時電壓降低,出現(xiàn)幅值小于200 mV的局部放電脈沖.在高頻脈沖電壓下,當局部放電發(fā)生在電壓上升時段時,快速變化的電壓幅值將改變局部放電特性,使得局部放電脈沖在1~2 GHz高頻能量的比重增大.因此,根據(jù)相關(guān)標準檢測變頻電機局部放電時,為易于激發(fā)絕緣薄弱點處局部放電,宜采用頻率低于200 Hz的低頻脈沖方波電壓,且局部放電超高頻傳感器在1.2 GHz及以上頻率處應(yīng)具有較好的增益特性,并采用500 MHz的高通濾波器,以提高測試系統(tǒng)的信噪比.
關(guān)鍵詞: 變頻電機;局部放電;脈沖方波電壓;超高頻;時頻分析;數(shù)據(jù)采集
中圖分類號: TM344.6文獻標志碼: AInfluence of Frequency of Impulsive Square Wave Voltage on
可見,在快速上升的脈沖電壓下,放電發(fā)生在脈沖上升時間時,放電過程中的電壓變化會改變局部放電脈沖特性[1012],這可能是導(dǎo)致局部放電高頻能量成分增加的原因.4測試電源頻率選取及傳感器設(shè)計基于以上試驗結(jié)果及機理分析,在較高頻率的脈沖電壓下,由于初始電子更易產(chǎn)生,導(dǎo)致放電延遲減小,局部放電脈沖距離電源干擾脈沖(脈沖方波電源逆變產(chǎn)生的干擾[4,9])時間間隔較短(見圖2(b)),因此可能導(dǎo)致電源干擾和局部放電脈沖的疊加.此時如果不采取合適的濾波策略,局部放電信號將被淹沒在電源干擾中,給放電測試帶來一定困難.
值得指出的是,當脈沖頻率繼續(xù)增加時,電壓極性翻轉(zhuǎn)后放電處電壓雖超過了起始放電電壓,但在下次電壓極性反轉(zhuǎn)時可能沒有初始電子產(chǎn)生,此時局部放電就不會在每個周期出現(xiàn),需要更高的外部激發(fā)電壓以增大初始電子產(chǎn)生概率,因此,在實際測試中可能得到比低頻脈沖電壓偏小的PDIV和RPDIV測試結(jié)果.
由于高電源頻率導(dǎo)致局部放電高頻能量增加,且電源干擾和局部放電時間間隔減小,為提高信噪比,必須設(shè)計高頻響應(yīng)較好的超高頻傳感器,配合后端高通濾波器,才能提取到局部放電,從而得到較為準確的PDIV和RPDIV測試結(jié)果.
綜上所述,在變頻電機局部放電檢測中,為確保局部放電初始電子產(chǎn)生,激發(fā)絕緣缺陷或薄弱點的局部放電,應(yīng)優(yōu)先考慮采用低頻(如<200 Hz)脈沖電壓,以促使相對高幅值的局部放電發(fā)生在脈沖電源干擾之后,從而提高測試靈敏度.在進行較高頻率下的局部放電測試時,應(yīng)提高超高頻傳感器的高頻響應(yīng)性能,從而有效提取出局部放電脈沖.5結(jié)論通過所設(shè)計的檢測系統(tǒng)及對不同頻率下的單點接觸試樣局部放電測試,可得到以下結(jié)論:
(1) 根據(jù)IEC標準進行變頻電機的局部放電測試時,應(yīng)根據(jù)電源干擾脈沖和局部放電的頻域能量特性,選取合適超高頻傳感器和濾波方案,從而提高信噪比.本研究中,局部放電能量主要集中在1.2 GHz處,采用500 MHz高通濾波器可有效抑制陡脈沖電源下的干擾.
(2) 脈沖電源頻率對放電相位和幅值具有較大影響,高頻下初始電子產(chǎn)生概率的增加使得放電延遲減小并導(dǎo)致放電時的瞬時激發(fā)電壓降低,促使較低幅值的局部放電脈沖產(chǎn)生.
(3) 在脈沖電壓下的變頻電機局部放電檢測中,為確保激發(fā)絕緣缺陷或薄弱點的局部放電,應(yīng)優(yōu)先考慮采用較低頻率的脈沖電壓.
當在高頻電壓下測試時,應(yīng)提高超高頻傳感器的高頻(>1.2 GHz)響應(yīng)性能,并結(jié)合高通濾波模塊,才可有效從強電源干擾中提取局部放電信號.
參考文獻:
[1]CAVALLINI A, FABIANI D, MONTANARI G C. Power electronics and electrical insulation systemspart 1:phenomenlogy overview[J]. IEEE Electrical Insulation Magazine, 2010, 26(3): 715.
[2]KAUFHOLD M, BORNER G, EBERHARDT M, et al.Failure mechanism of the interturn insulation of low voltage electric machines fed by pulsecontrolled inverters[J]. IEEE Electrical Insulation Magazine, 1996, 12(5): 916.
[3]YIN Weijun. Failure mechanism of winding insulation in inverterfed motors[J]. IEEE Electrical Insulation Magazine, 1997, 13(6): 1823.
[4]TOZZI M, CAVALLINI A, MONTANARI G C. Monitoring offline and online PD under impulsive voltage on induction motorspart 1:standard procedure[J]. IEEE Electrical Insulation Magazine, 2010, 26(4): 1626.
[5]CAVALLINI A, LINDELL E, MONTANARI G C. Offline PD testing of converterfed wirewound motors: when IEC TS 600341841 may fail[J]. IEEE Transaction on Dielectrics and Electrical Insulation, 2010, 17(5): 13851395.
(下轉(zhuǎn)第270頁)[6]FORSSEN C, EDIN H. Partial discharges in a cavity at variable A[J]. IEEE Transaction on Dielectrics and Electrical Insulation, 2008, 15(6): 10611069.
[7]CAVALLINI A, MONTANARI G C. Effect of supply voltage frequency on testing of insulation system[J]. IEEE Transactions on Dielectrics and Electrical Insulation, 2006, 13(1): 111121.
[8]HAZLEEI A, CHEN G, LEVWIN P L. Partial discharge behavior within a spherical cavity in a solid dielectric material as a function of frequency and amplitude of the applied voltage[J]. IEEE Transaction on Dielectrics and Electrical Insulation, 2011, 18(2): 432443.
[9]LINDELL E, BENGTSSON T, BLENNOW J, et al. Influence of rise time on partial discharge extinction voltage at semisquare voltage waveforms[J]. IEEE Transaction on Dielectrics and Electrical Insulation, 2010, 17(1): 141148.
[10]HAMMARSTROM T, BENGTSSON T, BLENNOW J, et al. Evidence for changing PD properties at short voltage rise times[J]. IEEE Transaction on Dielectrics and Electrical Insulation, 2011, 18(5): 16861692.
[11]WU Kai, PAN Cheng, GAO Minggang, et al. Effects of rising rate of square voltage on PD characteristics in aging process[C]∥International Conference on Condition Monitoring and Diagnosis. Tokyo: [s.n.], 2010: 573576.
[12]CAVALLINI A, LINDELL E, MONTANARI G C, et al. Inception of partial discharge under repetitive square voltages: effect of voltage waveform and repetition rate on PDIV and RPDIV[C]∥Annual Report Conference on Electrical Insulation and Dielectric Phenomena. West Lafayette: [s.n.], 2010: 14.
[13]FABIANI D, CAVALLINI A, MONTANARI G C. A UHF technique for advanced PD measurements on inverterfed motors[J]. IEEE Transactions on Power Electronics, 2008, 23(5): 25462556.
[14]LUTZ N. A generalized approach to partial discharge modeling[J]. IEEE Transaction on Dielectrics and Electrical Insulation, 1995, 2(4): 729743.
[15]GUTFLEISCH F, NIEMEYER L. Measurement and simulation of PD in epoxy voids[J]. IEEE Transaction on Dielectrics and Electrical Insulation, 1995, 2(5): 510528.
[16]KIMURK K, OKADA S, HIKITA M. Electromagnetic wave in GHz region of PD pulses under short rise time repetitive voltage impulses[C]//International Symposium on Electrical Insulating Materials. Yokkaichi: [s.n.], 2008: 633636.
[17]KEN K, SOJIRO U, TAKAHIRO, et al. PDIV characteristics of twistedpair of magnet wires with repetitive impulse voltage[J]. IEEE Transactions on Dielectrics and Electrical Insulation, 2007, 14(3): 744750.
(中文編輯:唐晴英文編輯:付國彬)刪a.表明,高頻下局部放電延遲時間縮短,使得局部放電激發(fā)電壓降低,從而產(chǎn)生低幅值的局部放電脈沖.通過不同頻率下局部放電頻域分析,發(fā)現(xiàn)高頻電壓下的局部放電在高頻范圍內(nèi)(1.6 GHz)具有較高能量成分周凱,吳廣寧,何景彥,等. 脈沖電壓下局部放電信號的提取和統(tǒng)計[J]. 西南交通大學學報,2008,43(03): 320325.
ZHOU Kai, WU Guangning, HE Jingyan, et al. Extraction and counting of partial discharges under pulse voltage[J]. Journal of Southwest Jiaotong University, 2008, 43(03): 320325.