Design of a Flexible Rogowski Coil with Active Integrator Applied in Lightning Current Collection

Transcription

1 2016 International Conference on Lightning Protection (ICLP), Etoril, Portugal Deign of a Flexible Rogowki Coil with Active Integrator Applied in Lightning Current Collection Yang Jun #1, Guiting Li #2, Huping Liu #3, Guohua Yang #4,Gong Ling #5 R&D Department, Sichuan Zhongguang Lightning Protection Techniologie Co.,LTD.19 Tianyu Road, Wet Park, Chengdu Hi-Tech Zone, Chengdu, Sichuan, P.R.China 1 yangj@zhongguang.com 2 liuhp@zhongguang.com Abtract Rogowki coil ha been applied widely in the field of lightning current meaurement, becaue it ha good linearity, no aturation phenomenon, a well a the electrical iolation between the primary ide and econdary ide. Thi paper mainly introduce three kind of Rogowki coil applied in lightning current collection, and alo analyze and compare them with experiment. We can elect the appropriate coil according to the different occaion, cot and intallation form. Thi paper focue on the application and deign of flexible Rogowki coil with active integrator which i ued in lightning current collection. The experimental reult indicate that the active integrator ha good linearity and waveform retoration, epecially better integral effect on the frequencie from hundred Hz to hundred khz. Keyword Rogowki coil Active integrator Lightning Current Collection Linearity Waveform retoration I. INTRODUCTION In recent year, electronic current tranformer baed on Rogowki coil ha wider application propect than conventional electromagnetic current tranformer. It advantage include large dynamic range, wide frequency repone and trong reitance to electromagnetic interference. It unique tructure avoid the problem of temperature and vibration that exit in the pure optical ening head. Electronic current tranformer baed on Rogowki coil i the future direction of current tranformer, which can adapt to development trend of digitalization and automation of electric meaurement and relay protection. Rogowki coil i an effective tool to meaure the trong impule current becaue of it advantage of high preciion, good tability, trong antiinterference capability, wide dynamic range and mall ize. It can meaure the current of tranformer, GIS, circuit breaker and PASS witch. Rogowki coil i alo widely applie to the meaurement of high power pule technology. The reearch of rigid and flexible tranducer baed on Rogowki coil ha become hot at preent. Thi paper analyze and compare the rigid Rogowki coil, flexible Rogowki coil with ordinary RC paive integrator and flexible Rogowki coil with active integrator, repectively. The reearche and problem in development of three kind of coil are mainly illutrated by the experimental waveform. In thi paper, the experimental waveform are obtained from 8/20µ impule current generator, digital ocillocope, PEARSON current monitor, 8/20µ compatible 10/350µ impule current device. II. INTRODUCE OF LIGHTNING CURRENT Lightning i a trong dicharge phenomenon between the thundercloud or between a thundercloud and the earth formed in evere convection weather. It ha high impule current, high temperature, violent hock wave and trong electromagnetic radiation, which can damage the building, tranmiion line, outdoor equipment and reult in caualty of the human and animal. Lightning ha characteritic uch a high voltage, large current, intantaneity and long ditance. Lightning current i a non-periodic tranient current that uually oon roe to the peak and low to fall. The impule wave ue a combination of two value T1/T2 to illutrate. T1 i front time from 10% up to 90% of peak value. T2 i the time to half value on the tail of impule current. Thee time ue µ a the unit marked with T1/T2. The tandard of IEC and GB tipulate the lightning teting waveform uch a 8/20µ, 10/350µ(current wave), 10/700µ and 1.2/50µ(voltage wave). For example, in 1.2/50µ impule voltage, front time i 1.2µ, the time to half value i 50µ; in 8/20µ impule current, front time i 8µ, the time to half value i 20µ; in 10/350µ impule current, front time i 10µ, the time to half value i 350µ. Fig.1 i 8/20µ impule current waveform. Fig.1 8/20µ impule current waveform Lightning effect are divided into direct-lightning and lightning electromagnetic pule (LEMP). Direct-lightning i characterized by 10/350µ. LEMP i characterized by 8/20µ. Thi provide a practical waveform verification bai for u to deign and tet the coil.

2 III. COMPARISON OF THREE KINDS OF ROGOWSKI COIL Three kind of Rogowki coil are mentioned in thi paper, they are rigid Rogowki coil, flexible Rogowki coil with paive integrator and flexible Rogowki coil with active integrator. Rigid Rogowki coil ue magnetic material a keleton to wind. Magnetic material with high magnetic conductivity i eay to atify the elf-integral condition, o thi coil ue the form of elf-integral to retore the waveform. Rigid coil i electromagnetic tructure. But it ha a large volume and heavy weight, in particular, it magnetic core i eay to generate magnetic aturation when a fault happen on the line. It i hard to realize the meaurement of wide range current. On the intallation, the heavy rigid tranducer with magnetic core can t fall or hake, and eay to be influenced by outide environment. It i not convenient to diaemble and intallation, thu it application i limited. The reult of experimental waveform i hown in figure 2, CH1 i the waveform of PEARSON current monitor (1000 time), CH2 i the waveform of elf-made rigid coil. -50kA 10/350µ waveform: +30kA 8/20µ waveform: Fig.2 Experimental waveform of rigid Rogowki coil +60kA 8/20µ waveform: -30kA 10/350µ waveform: Flexible tranducer i a new current tranducer baed on the Rogowki principle. It ha uch advantage a light weight, oft and pliable, complete iolation between the primary and econdary ide, convenience to intall and diaemble, large teting range (10A up to 1000kA), wide dynamic range, low cot, good linearity, no magnetic aturation. According to the different integral method, it i divided into paive integrator and active integrator. Flexible Rogowki coil with paive integrator i winded in the non-magnetic material keleton a ame a the flexible Rogowki coil with active integrator, but they are different in integral method. Rogowki coil with paive integrator adopt RC paive integrator with imple circuit tructure. It can t imultaneouly obtain the higher enitivity and lower limit. Under the ame enitivity condition, it can t lower the low frequency limit of integrator. Only when the integral time contant RC T (ignal period), it can obtain approximate integral effect, but with low output preciion and mall output amplitude, and it i advere to improve the S/N ratio. The bandwih of flexible Rogowki coil with paive integrator i not wide enough, it i not effective to tranmit the tranient current ignal and eay to generate the waveform ditortion at low frequency. The reult of teting waveform i hown in figure 3, CH1 i the waveform of PEARSON current monitor (100 time), CH2 i the waveform of flexible Rogowki coil with paive integrator. +10kA 8/20µ waveform:

3 -10kA 10/350µ waveform: Type Rigid Rogowki coil Flexible Rogowki coil with paive integrator Flexible Rogowki coil with active integrator Integral form Self-integral conventional RC integral active integral Intallation method Down lead mut be diaembled requirement for intallation poition requirement for intallation poition Range of frequency 200Hz~ 4MHz 1kHz~ 4MHz 200Hz~ 6MHz Magnetic aturation Ye Fig.3 Teting waveform of flexible Rogowki coil with paive integrator From the figure above we can ee, flexible Rogowki coil with paive integrator i not good to retore the waveform of 8/20µ and 10/350µ, the time to return to zero i prolonged, and it caue the 10/350µ waveform ditortion more eriouly. But compared with the rigid Rogowki coil, flexible Rogowki coil with paive integrator i portable and flexible, and ha the advantage of light weight, low cot and not being prone to magnetic aturation. However it i not better than rigid Rogowki coil in preciion. Conidering the advantage-diadvantage and application environment of exiting Rogowki coil, we deign a flexible Rogowki coil with active integrator. Flexible Rogowki coil with active integrator ue high performance operational amplifier to make up the analog integrator. When working at low frequency, paive integrator can t collect uch weak output ignal from coil(le than mv). However, active integrator can apply to collect the low frequency ignal. The operational amplifier ha advantage of high input impedance, high open-loop gain, virtual-hort and virtual-cutoff, which can effectively guarantee the higher integral preciion. The higher bandwih and preciion provided by active integral method can effectively retore the meaured current waveform. The comparion of three kind of Rogowki coil i hown in table 1. TABLE I Comparion of three kind of Rogowki coil IV. THE DESIGN OF FLEXIBLE ROGOWSKI COIL WITH ACTIVE INTEGRATOR APPLIED IN LIGHTNING CURRENT COLLECTION The working principle of flexible Rogowki coil with active integrator decribed in thi paper i: differential ignal of lightning current i obtained when tranmiion line pae through the flexible Rogowki coil of traveling-wave enor, which i reverted to the current ignal by integrator. Active integrator need to be adapted to pecific parameter of Rogowki coil, and the enitivity of coil relate to the integral parameter of active integrator, which can be adjuted according to the relationhip between the integral parameter and the coil. The output of Rogowki coil i the differential ignal of the lightning current. Fig.4 i an equivalent circuit diagram of Rogowki coil, ignoring the effect of the coil ditributed capacitor. Fig.4 equivalent circuit In fig.4, L i the elf-inductance of Rogowki coil, M i the mutual-inductance of Rogowki coil, R i the internal reitance of Rogowki coil, I i the meaured current, i i the current of Rogowki coil, u i i the induced electromotive force, R i the ampling reitance, u i the ampling voltage. According to the equivalent circuit of Rogowki coil, we have:

4 di ui M (1) di ui L ( R R ) i (2) di When L ( R R ) i, implify a: ui I ( R RS ) / M R (3) The condition of Rogowki coil worked at exterior di integrator i L ( R R ) i, that i the terminating ampling reitance R >> R,and R L, where i the frequency of input ignal. Becaue of the little internal reitance R of Rogowki coil, active integrator only need the condition of R L. From equation 3 we have: a differential relationhip exit between meaured current I and ampling voltage u i, that i, Rogowki coil and the ampling reitance R are ubtantially a differentiation element and an integrator i needed to integrate the voltageu i, which can revert the output ignal to the meaured current. The original lightning current ignal can be retored by integrator. Fig.5 i the baic circuit of active integrator that conit of reitance R, capacitor C and OPA operational element. The principle of integrator i: from the virtual-hort and virtual-cutoff principle of negative feedback circuit in operational amplifier, we have: i ui / R, uo uc 1/ C ic That i the current through the reitor integrated on the capacitorc. The preciion of active integrator i baed on the virtual-hort and virtual-cutoff feature, the inverting input of operational amplifier ha virtual-hort feature: i u / R, that enure the accurate charging current of the capacitor, which i an important reaon that active integrator ha higher preciion than paive one. By contrat, the charging current of capacitor with paive integrator will decreae with increaing voltage of capacitor, which can reduce the integral preciion. i Fig.5 Baic circuit of active integrator In the deign of flexible Rogowki coil baed on active integrator, the experimental circuit of practical active integrator i hown in fig.6. Fig.6 The experimental circuit of practical active integrator Flexible Rogowki coil baed on active integrator adopt flexible Rogowki coil with low cot and high performance a enory package. Flexible Rogowki coil i made of flexible keleton and enamelled wire, which i required to wound evenly baed on one winding in the proce of winding. Therefore, flexible Rogowki coil i not only to reduce the cot, but alo to improve the ampling frequency, to eliminate aturation phenomenon and to increae reliability. Moreover, traveling-wave enor of different amplitude can realize large range lightning current meaurement o a to improve the poitioning accuracy, reliability of device, and bandwih limit. In fig.6, R1 i ampling reitance, R2 i integral reitance, C 2 i integral capacitor, R 3 i dicharge reitance ued to table the low frequency gain and retrain the output drift of operational amplifier which lead the output aturation of operational amplifier. U 1 i high performance operational amplifier, C 1 i a mall capacitor of pf grade that i ued to filter the high-frequency noie of coil, D1 i tranient voltage uppreor that i ued to protect the operational amplifier from lightning-triking damage, R4 i balance reitance of operational amplifier that i ued to reduce the offet voltage from the output caued by the bia current of operational amplifier, P1 i connecting ocket of coil. The working principle i: P 1 connect the flexible Rogowki coil and reitance R 1, when meeting the condition of R1 Rt, R1 L ( R t i inner reitance of coil, i upper-limit of operating frequency), the coil work a an exterior integrator. The coil induce by the meaured current and output the differential ignal of voltage that i proportional to the meaured current, the differential ignal of voltage i retored to the voltage ignal proportional to the meaured current through the integrator which conit of R 2 C 2 U 1.

5 The lower limit of active integrator i determined by the contant of integral time: f L 1 2 R C 2 2 ; the upper limit i determined by the lew-rate of operational amplifier: f H SR, SR i lew-rate, Vom 2 V om i the amplitude of output ignal. The bandwih of active integrator i: BW f f. H L The performance of operational amplifier, integral reitance and integral capacitor could influence the actual performance of integrator. Epecially the performance of operational amplifier and integral capacitor decide the bandwih frequency of integrator. Integral capacitor need the ditributed inductance a mall a poible, which can influence the bandwih of upper limit frequency of integrator and caue the wave ditortion. The capacity of integral capacitance and leakage reitance are choen to be a big a poible without impacting the ditributed inductance, which can reduce the impact of capacitor dicharge on the preciion. Operational amplifier i required of the following particular propertie: high gain bandwih, high lew-rate, high inputimpedance, low bia current and low offet voltage, otherwie it can impact the bandwih of upper limit frequency of integrator. In order to validate the ample preciion of thi coil, the tet platform i etablihed hown in fig.7. The impule lightning current generator generate 8/20µ and 10/350µ tandard current waveform with different amplitude and polarity. The tandard current tranducer and ocillocope contitute the tandard collection circuit. The collection device get the preciion of ample ytem by comparing the waveform of ample and tandard circuit. The output current of impule lightning current generator i preet in turn a: 1kA, 2kA, 10kA and 25kA, the poitive impule dicharge tet and the negative impule dicharge tet are carried out each time, and then we can read the tet data from the digital torage ocillocope repectively. Fig.7 Wiring diagram of current monitoring Uing the tet data to calculate the monitor error according to the following formula, the reult need to meet: In formula: amplitude error; Im0 Im 1 100% Im0 I m0 I m1 amplitude reading of digital torage ocillocope amplitude of ample The tet reult of 8/20µ waveform are hown in table2. The tet reult of 10/350µ waveform are hown in table3. TABLE2 Impule current (8/20μ) The teting reult of 8/20µ waveform Standard current monitor (0.2kA/V) value(v) Flexible coil with active integrator(v) Monitoring error (%) +1kA kA kA kA kA kA kA kA TABLE 3 The teting reult of 10/350µ waveform Impule current (10/350μ) Standard current monitor (0.5kA/V) Value(V) Flexible coil with active integrator(v) Monitoring error (%) +1kA kA kA kA kA kA kA kA Fig 7 i a waveform diagram between the tandard and the ample which are from impule output current (8/20µ) preet a +1kA, +10kA, -2kA and -20kA. Fig 8 i a waveform diagram between the tandard and the ample which are from impule output current (10/350µ) preet a +2kA +25kA -2kA -10kA. Waveform of +1kA:

6 Waveform of +10kA: Waveform of +25kA: Waveform of -2kA: Waveform of -1kA: Waveform of -20kA: Waveform of -10kA: Fig 7 Standard waveform and ample waveform of current Fig 8 Standard waveform and ample waveform of current Waveform of +2kA:

7 V. CONCLUSION A kind of flexible Rogowki coil with active integrator mentioned in thi paper, realize the lightning current collection of 8/20µ and 10/350µ with good linearity. It can collect the lower frequency ignal of 10/350µ and higher frequency ignal of 8/20µ with high preciion. Thi kind of Rogowki coil reolve the problem of low preciion of conventional Rogowki coil with paive integrator, expand the bandwih, eay to intall and provide good retoration of waveform. But there i till much room for improvement. The circuit board i placed near the lightning cabling without any meaure in electromagnetic hielding and electromagnetic compatibility (EMC), waveform burr i induced by high frequency noie of lightning. For example, the wave front of 8/20µ ha many burr due to the ring ignal generated by the high-frequency component caued by the harp variation of input ignal, affecting the moothne of waveform. Thi problem can be olved by deigning a low pa filter in the future. [1] Wang Hao, Qingjie Jiao Tet Technology Reearch for Rogowki Coil, Equipment for electronic product manufacturing. 129 [2] Ray W F. Rogow k i t randucer fo r meauring large magnitude ho rt durat ion pule. IEE Sympo ium on pule pow er, London, U K, 2000, (23) : 164 [3] Luo Chengmu 1 Reearch on Pule Current Meauring Coil and CAD Deign 1 Journal of Tinghua Univerity (Science and Technology) 1995, 35 (4): 22 [4] Li Haiyan 1 Development of Nanoecond Rogowki Coil[Mater Thei]1 Xi an: Xi an Jiaotong Univerity, 1988 [5] Zou Jiyan 1 Simulation Calculation and Experiment Reearch of Rogowki Coil Meauring Current 1 Tranaction of China Electrotechnical Society 2001, 16 (1) : 81 [6] Li Weibo Mao Chengxiong Lu JimingOnline Meauring Technique for vel Magnetic potentiometer [J1.Senor Technology,2001,20(11): ] [7] Fang Zhi Zhao ZhongyuanQiuYuchangHigh Frequency Characteritic Analyi for Rogowki CoilEJ3.High Voltage Technology (8): 17-18, 21 [8] Jin Yongtao Liu HuijinXiongLinglingFrequency Characteritic Analyi and Band Broadening Method for Rogowki Coil [J] Electronic Logging and Intrument, 2003,40(9): [9] Zhang Mingming Zhang Yan Li HongbinIntegrator Technology of Rogowki Coil Current Tranformer [EJ] High Voltage Technology 2004, 30(9):13-16 [10] Li Weibo Mao Chengxiong Lu JimingReearch on the Influence of RogowkiCoil Structure and Electromagnetic Parameter on ItPerformance [J]. High-voltage Electrical apparatu 2004, 40(2): [11] Qiao E AnZuopingLuoChengmuRogowki Coil Applied in Hybrid Optoelectronic CurrentTtranformer [J]. Tranformer (5): [12] Peng Li Reearch on 10kV/35kV Electronic Voltage/Current Tranformer Mater Thei of Huazhong Univerity of Science and Technology [13] Zhang Renyu Chen Changyu Wang ChangchangHigh Voltage Experimental Technology Tinghua Univerity Pre [14] Dai Jianhua Li KaichengSuper-current MeaurementBaed on Rogowki High Voltage Project Vol.28.1 Jan.2002 [15] Luo SunanTianChaobo Zhao XicaiPerformance Analyi for Current Tranformer of Hollow Coil Proceeding of the Chinee Society for Electrical Engineering Vol.24.3 Mar.2004 [16] Jin Yongtao Liu HuijinXiongLinglingFrequency Characteritic Analyi and Band Broadening Method for Rogowki Coil Electronic Logging and Intrument Vol.24.3 Mar.2004 [17] Fang Zhi Zhao ZhongyuanQiuyumin Li ShuangHigh Frequency Characteritic for Rogowki CoilHigh Voltage Technology Vol.28.8 Apr [18] Wang Hao Jiao QingjieReearch on Teting Technique of Rogowki Coil Equipment for Electronic Indutry VoL.71.4 Oct.2005 [19] Ward D A,Exon J La T.Uing RogowkiCoil for Tranient Current Meaurement[J].IEEE cience and Engineering Journal,1993, 2(3): [20] QiaoHuiUU Hui-jinWANG QufengThe Reearch of Optical Current Tranducer Baed on RogowkiCoil[J].Relay,2002,30(7): [21] TianZhaobo,Su Nan J le,luo Su nan,et a1.rogowkicoil Electronic Current Tranducer Applied to Protection and Monitoring of GIS[J].Electric Power,2003,36(10)l [22] WANG Xin xin,han Min,WANG Xiang heng,et a1.study of the Core Saturation In a RogowkiCoil[J].Tranaction of China Electrotechnieal Society,1994,7(2):34 38.