The observation of neutral current of 500 kV power line and the - PowerPoint PPT Presentation

The observation of neutral current of 500 kV power line and the application to the monitoring of the underground electrical conductivity Makoto HARADA (Earthquake Prediction Research Center, Tokai University) Jun IZUTSU* (Earth Watch – Safety Net Research Center, Chubu University) Tomiichi UETAKE, Takeshi TERAYAMA (Tokyo Electric Power Co., Inc.) Toshiyasu NAGAO (Earthquake Prediction Research Center, Tokai University) EMSEV-DEMETER Joint Workshop, Romania, 2008/09/09

Telluric current measurement Conventional telluric current measurement V 2 V 1 Telluric Current • We use two electrodes and voltmeter. • The potential difference is measured. We measure the telluric currents by using already existing electric power line system. EMSEV-DEMETER Joint Workshop, Romania, 2008/09/09

Super High Voltage Electric Substation 1 2 3 In each wire, 3 phase alternating current flow. 120 degree Three Phase Alternating Current The electric power is usually transmitted by 3 Phase 3 Wire Alternating Current. EMSEV-DEMETER Joint Workshop, Romania, 2008/09/09

Neutral Point The ends of three wires are connected to each other. Neutral Line Neutral point is connected to the earth directly . In the neutral line, no current flows theoretically because the sum of three phases is zero. EMSEV-DEMETER Joint Workshop, Romania, 2008/09/09

Telluric Current If there are electromagnetic anomalies, V 1 is not equal to V 2 . Neutral Point Neutral Point (DC range) grounded grounded Electromagnetic V 2 V 1 Anomalies The potential difference V 1 - V 2 generates the telluric current. This current in the earth may be measured by the ammeter A (DC range). Neutral Current This method has been used to measure GIC (Geomagnetically Induced Current). EMSEV-DEMETER Joint Workshop, Romania, 2008/09/09

Observation Area We choose some electrical substations in the high earthquake activity area. Observed during Observed since 2002 1998 to 2003 Western Japan Eastern Japan Reinan Higashi Yamanashi Shin Hadano Minami Kyoto ShinFuji Inagawa EMSEV-DEMETER Joint Workshop, Romania, 2008/09/09

Magnetic Storm Neutral currents and geomagnetic components (Kakioka) during the large magnetic storm Fluctuation range is at most 10A. EMSEV-DEMETER Joint Workshop, Romania, 2008/09/09

Anomalous neutral current Sep. 1999 – Mar. 2003 Reinan Analogue record in Inagawa electrical substation (Sep. 21 – Sep. 23, 1999) 1999/09/22 M3.0 over 30A 24A Inagawa 9/21 9/22 9/22 9/22 Minami 18:00 00:00 06:00 12:00 Kyoto Kp index 2- 2- 3+ 3+ 4- 2 2 2 3 Earthquake (M3.0) 19:17 Sep. 22, 1999 geomagnetic storm 9/22 9/23 9/23 9/23 9/23 18:00 00:00 06:00 12:00 18:00 3- 5 4- 6 8 6+ 6 3 However, there are many earthquakes larger than this earthquake. Large fluctuation cannot be explained by GIC. No other anomalous current has been observed. EMSEV-DEMETER Joint Workshop, Romania, 2008/09/09

Quantitative analysis The observed neutral current at ST0 ( I ST0 ), can be considered as the superposition of current which flows between 2 sets of substations ( I ST0 = I 01 + I 02 ) . We consider that induced We consider that induced neutral current are generated neutral current are generated from the geomagnetic from the geomagnetic I 01 variations, of which variation variations, of which variation are perpendicular to the are perpendicular to the direction of 2 substations. direction of 2 substations. I 02 EMSEV-DEMETER Joint Workshop, Romania, 2008/09/09

Transfer Function H 1 Relationship between neutral current H 3 I 01 and geomagnetic changes I 02 ω = ω ⋅ ω + ω ⋅ ω I ST ( ) TF 1 ( ) H ( ) TF 2 ( ) H ( ) 0 1 3 0 ω ： Neutral current observed at ST0 I ( ) ST 1 ω ： component 1 of geomagnetic field (Kakioka) H ( ) 3 ω ： component 3 of geomagnetic field (Kakioka) H ( ) 1 ω 2 ω ： Transfer Function Coefficients TF ( ), TF ( ) We calculated TF1 and TF2 using observed data. RRRMT (Robust Remote Reference MT) algorithm (Chave et al., 1987) EMSEV-DEMETER Joint Workshop, Romania, 2008/09/09

Transfer functions at Shin-Fuji ω = ω ⋅ ω + ω ⋅ ω I ST ( ) TF 1 ( ) H ( ) TF 2 ( ) H ( ) 0 1 3 Higashi Shin Yamanashi Shin-fuji & Higashi- Yamanashi Tama Shin Hadano Shin Fuji Shin-fuji & Shin-hadano EMSEV-DEMETER Joint Workshop, Romania, 2008/09/09

Transfer functions at Shin-Hadano ω = ω ⋅ ω + ω ⋅ ω I ST ( ) TF 1 ( ) H ( ) TF 2 ( ) H ( ) 0 1 3 Higashi Shin Yamanashi Shin-Hadano & Shin-Fuji Tama Shin Hadano Shin Fuji Shin-Hadano & Shin-Tama EMSEV-DEMETER Joint Workshop, Romania, 2008/09/09

Telluric current measurement in Atsugi We have observed telluric currents at Atsugi by conventional method. Conventional Method Ch.1, Ch.3 are used in this study Data Logger SES-96 Sampling rate 10sec. Configuration of observation points Configuration of electrodes EMSEV-DEMETER Joint Workshop, Romania, 2008/09/09

MT parameters at Atsugi Apparent resistivity phase EMSEV-DEMETER Joint Workshop, Romania, 2008/09/09

Compare to MT method MT method ω ω ω ω ⎛ ⎞ ⎛ ⎞ ⎛ ⎞ E ( ) Z ( ) Z ( ) H ( ) ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ x = xx xy ⋅ x ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ ω ω ω ω E ( ) Z ( ) Z ( ) H ( ) ⎝ ⎠ ⎝ ⎠ ⎝ ⎠ y yx yy y , apparent resistivity phase ( ( ) ) ⎛ ω ⎞ 2 ω ( ) Im Z 1 E ( ) φ ω = − ⎜ ⎟ tan 1 ρ ω = ⎜ ) ⎟ ( ( ) ( ) ω ⎝ ⎠ μ ω ω Re Z a H ( ) 0 Transfer Function ω = ω ⋅ ω + ω ⋅ ω I ST ( ) TF 1 ( ) H ( ) TF 2 ( ) H ( ) 0 1 3 “pseudo-” apparent resistivity “pseudo-” phase ⎛ ω ⎞ 2 ω I ( ) I ( ) 1 φ ω = − ⎜ ⎟ ω = ⋅ 1 ST 0 ST 0 s ( ) tan ⎜ ⎟ Rs ( ) factor ω μ ω ω ⎝ ⎠ H ( ) H ( ) 0 EMSEV-DEMETER Joint Workshop, Romania, 2008/09/09

“Pseudo-” apparent resistivity and phase Higashi at Shin-Hadano Shin Yamanashi Tama Apparent resistivity at Atsugi Shin-Hadano & Shin-Fuji Shin Hadano Shin Apparent resistivity Phase Fuji Shin-Hadano & Shin-Tama Apparent resistivity Phase EMSEV-DEMETER Joint Workshop, Romania, 2008/09/09

Time Variation of “Pseudo-” apparent resistivity and phase at Shin-Hadano ○： Oct.& Aug., 2003 factor = 100 ●： Nov.,2004 Shin-Hadano & Shin-Tama Apparent resistivity phase change of resistivity ? EMSEV-DEMETER Joint Workshop, Romania, 2008/09/09

Conclusion We observed telluric current between substations by using the power line system. We observed the anomalous neutral current before and after an earthquake in 1999. However, We have never observed such anomalous neutral current after that. We calculate the transfer function between a neutral current and geomagnetic changes. The coefficients of this transfer function have the information of the underground conductivity. Comparing with the result by MT method, we can estimate monitor the change of the under ground conductivity. EMSEV-DEMETER Joint Workshop, Romania, 2008/09/09