An Approach of the Continuous Electrical State Monitoring by Using the Ground Wire of Neutral Point at Extra-high Voltage Substations

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1 Bull. Earthq. Res. Inst. Univ. Tokyo Vol. 2-,**2 pp.,0/,1, +, - -, +, - * An Approach of the Continuous Electrical State Monitoring by Using the Ground Wire of Neutral Point at Extra-high Voltage Substations A Preliminary Report +, - -, Jun Izutsu, Makoto Harada, Takeshi Terayama, Tomiichi Uetake and Toshiyasu Nagao * +, - Earth Watch - Safety Net Research Center, Chubu University Earthquake Prediction Research Center, Tokai University Tokyo Electric Power Co., Inc. Abstract We propose a new monitoring system by using the neutral current of transformers at substations of an electric power company named neutral current monitoring. It means that we have been measuring the telluric field by using the power line system in order to monitor the electromagnetic state of the underground over an extended time period. The principle of this system is as follow: the neutral points of the transformers in the substations are grounded to the earth and power lines connect them. If the neutral points of the transformers correspond to the grounded electrodes and the power line between substations corresponds to the electric wire between the electrodes, we can observe the telluric field and change of the electromagnetic structure of the underground between substations by measuring the current which flows at the neutral point of the transformer to some extent. We found that the neutral current is a# ected by various factors such as the geomagnetic changes and artificial noises like as the conventional telluric field observations. We would be able to investigate the underground electric conductivities near the substations by calculated response function between geomagnetic field data and neutral current data. Key words: neutral current of transformers, telluric field observation, geomagnetic variation + * nagao@scc.u-tokai.ac.jp 265

2 +*,* Fig. +. The conceptual figure of the measurement of the current by the power line system., +, +,* km+* km Uyeshima,,**1 +, Fig. + Fig GIC Geomag- netic Induced Current : Albertson et al., +31., Lundby et,, al., +32/ Boteler et al.,

3 3 0** Al- len et al., , /** kv Fig.,. The distribution map of substations, the Atsugi telluric field observation station, and hypocenters from /** kv,**, to,** ,*** ,, * km Fig., -* A +,**,,**1 +*,***,1/ kv, Hz GPS Fig.,,**-,**-, NTT +. -,. km. /,**, -,**-,**- Izutsu et al.,,**

4 Fig. -. The fluctuation of neutral currents and geomagnetic components observed at the Kakioka geomagnetic observatory during the large magnetic storm from Nov., 3 to Nov. ++,,**.. Fig. -,**. ++ * ,***. Fig. /,**,,**1 JR Fig..,**/ 2,,,2,. JR 2,/ ++,. +, 2 0,. - JR M, O+ 268

5 Fig... The figure shows the daily variations of the neutral current observed at the Higashi Yamanashi substation from Aug.,, to,2,,**/. The open rectangular on Aug.,, shows DC-driven train stopped due to Typhoon No. ++. Fig. /. The change of the neutral current at the Shin-Hadano substation and the temperature at the Ebina AMEDAS observatory from,**, to,**1. JR 0 JR Fig. 0,** * ch *+: +.2 m + m; ch *-: +-+ m + m; ch *3: ch*+ ch*- +.2 m,* m; ch +* : ch+- ch m,* m; ch ++ :.3 m + m /* m; ch +-:.3 m + m /* m ; ch +0 : -.-* m.2 m -* m 269

6 Fig. 0. The neutral currents at each substation and the electric potential di# erences at Atsugi station observed from June +,,**- to June -*,,**-. The geomagnetic variation at Kakioka, the temperature and rain fall at Atsugi station are also shown. Tanbo et al.,,**, 1 Harada et al.,**. Fig. 1 TF+ I w w TF+ w TF, w Hxw Hyw TF, w 3/ IwTF+ w H wtf, w H w x y,** TF+ w TF, w +***, 270

7 2,**2 ++ +, 0** m : LS--/* + Hz *. 1 :.* m.* m : Fig. 2 +,, Fig. 1. Calculated inter-station transfer functions between the Shin-Hadano neutral current data and the Kakikoka magnetic data. 3,**, MT MT Fig. 2. An example of the temporal observation near the Shin-Fuji substation on December,,,**2. 271

8 EMC-*- -,-./.3. Izutsu, J., T. Ochi, T. Uetake and T. Mutakamihigashi, The relationship between the current through the transformer neutral point and natural phenomena, IEEJ Transactions on Fundamentals and Materials, +,0-A, No..,,--,-1,,**0. Lundby, S., B.E. Chapel, D.H. Boteler, T. Watanabe, and R.E. Horita, +32/, Occurrence Frequency of Geomagnetically Induced Currents : A Case Study on a B.C. Hydro /** kv Power Line, Journal of Geomagnetism and Geoelectricity, -1, +* ,***. :,*,--,.,.,**-, EMC-*- -,, Albertson, V.D., J.M. Thorson Jr. and S.A. Miske Jr., +31.,,**- The E# ects of Geomagnetic Storms on Electrical Power Systems, IEEE Transactions on Power Apparatus and + EMC- Systems, PAS-3-, No.., +*-+ +*.. *--1-1., Allen, J., L. Frank, H. Saver, and P. Reif, +323, E# ects of the Tanbo, T., Nagao, T. and Sakai, H.,,**,, Geoelectromagnetic March +323 Solar Activity, EOS, 1*, No..0, study using the leak current from railroad as a signal. Boteler, D.H., R. J. Pirjola and H. Nevanlinna, +332, The Application to Ohtawa Station, Gifu Prefecture, Ja- E # ects of Geomagnetic Disturbances on Electrical Sys- pan 12, Ser. B, tems at the Earth s Surface, Advances in Space Research,,**-,,, No. +, +1,1. Harada, M., Hattori, K. and Isezaki, N.: Transfer Function EMC-* Approach to Signal Discrimination of ULF Geomagnetic Uyeshima, M.,,**1, EM Monitoring of Crustal Processes In- Data, Phys. Chem. Earth,,3, pp..*3.+1,,**.. cluding the Use of the Network-MT Observations, Surv.,*** Geophys,,2, +33,-1, DOI +*. +**1 /s+*1+,-**1-3*,--x. HV-** -/,/ , GIC,. No. 1.-*,**-.--. Received June,.,,**2 Accepted February, 272