JP5426415B2 - Electric corrosion prevention system and electric corrosion prevention method for buried metal pipeline - Google Patents

Description

  The present invention relates to a system and method for preventing galvanic corrosion of embedded metal pipelines.

  A current that flows from the rail to the ground during the operation of a DC electric railway vehicle (referred to as a rail leakage current) may flow into the metal pipeline buried under the rail of the DC electric railway vehicle. If it flows through the pipeline and flows to the ground at a place where the ground resistance is low, galvanic corrosion will occur there. The definition of electrolytic corrosion here is “a phenomenon in which metal bodies corrode due to electrolysis when current flows out from underground metal bodies” (explained by the Ministry of Land, Infrastructure, Transport and Tourism, Railway Bureau (Refer to “Electrical Edition”). One of the methods for preventing the DC stray current corrosion due to the leakage of the rail leakage current is a selective drainage method. The buried metal pipeline mentioned here includes a gas pipeline, a water pipe, an oil pipeline, a communication wiring protection pipe, and the like. Here, description will be made on the assumption that cathode protection is performed.

  In the selective drainage method, the rail-to-ground potential R / S (the potential of the pipeline P with respect to the reference electrode installed on the ground) of the buried metal pipeline (hereinafter simply referred to as the pipeline) P When the potential of the rail R with respect to the reference electrode installed on the ground is more negative, the pipeline P and the rail R (or the lead-in wire from the rail to the substation) are electrically connected via the selective drain. In this method, the current flowing through the pipeline P is returned directly to the rail R through the electric wire without directly flowing out to the ground (see Non-Patent Document 1).

  The selective drainage method uses the phenomenon that current is sucked up into the rail R in the vicinity of the substation, etc., and the pipeline P and the rail R are connected by electric wires by selecting the location where such a phenomenon occurs. By connecting and allowing only the current from the pipeline P to the rail R via the electric wire, the current is not discharged from the pipeline P to the ground.

The Institute of Electrical Engineers, Electrochemical Corrosion Prevention Research Committee, “New edition of Electric Corrosion / Soil Corrosion Handbook” published by the Institute of Electrical Engineers, May 1977, p. 239

  In recent years, most of the DC electric railway vehicles in the city center are of a regenerative braking system from the viewpoint of improving the efficiency of electric power energy. In this method, since the regenerative vehicle plays the same role as the substation, the rail ground potential R / S takes a negative value at the position where the regenerative vehicle passes, and the pipe ground potential P / S of the pipeline in the vicinity of the position is on the positive side. The value will cause a risk of electrolytic corrosion in the pipeline.

  FIG. 1 is an explanatory diagram for explaining the risk of electrolytic corrosion of a pipeline caused by the above-described regenerative vehicle. When a DC electric railway regenerative vehicle is in regenerative braking, a regenerative current is supplied to the powering vehicle via a train line as shown in FIG. 5A, and a resistance consumption type or an inverter type as shown in FIG. In some cases, a regenerative current is supplied to a substation having a regenerative power processing apparatus via a train line. Here, in any case, it is assumed that the pipeline P is cathodic protected by an external power source cathodic anticorrosion system (a cathodic anticorrosive current is supplied), and a selective drain is installed near the substation. As shown in FIGS. 6A and 6B, the pipe-to-ground potential P / S of the pipeline P buried near the passing point due to the passage of the regenerative vehicle shifts to the plus side, thereby causing the pipeline. The electric current flowing into P flows out from the vicinity of the passing point of the regenerative vehicle to the ground, and an electric corrosion risk is generated. In the case of (b) in the figure, since the rail ground potential R / S of the substation becomes a positive value, the selective drain connected to the negative pole rail of the substation does not operate, so it flows into the pipeline P. The rail leakage current flows out from the coating defect to the ground, resulting in an electric corrosion risk. The white arrow in the figure indicates the current flowing into the rail R or the pipeline P, and the black arrow indicates the current flowing out from the rail R or the pipeline P to the ground.

  In this way, the risk of electrolytic corrosion caused by the rail-to-ground potential R / S taking a negative value by the regenerative vehicle and the pipe-to-ground potential P / S of the pipeline P in the vicinity of the position taking a positive value is selectively discharged. If the effect of the regenerative vehicle is large, the rail R and the pipeline P are not necessarily close to each other, so the selective drainage is connected to the rail R and the pipeline P. May be difficult. In addition, unlike a fixed facility such as a substation, the regenerative vehicle moves, so there is a problem that it is difficult to set an appropriate installation location of the selective drain. Furthermore, since one end side of the selective drainage device is connected to the rail at a place where the vehicle is frequently operated, there is a problem that it is difficult to perform the installation work and maintenance of the selective drainage device.

  On the other hand, when the electric corrosion risk due to the regenerative vehicle is to be avoided by increasing the cathodic protection level of the anticorrosion section, the portion where the pipe-to-ground potential P / S is shifted to the plus side by the regenerative vehicle is a part of the pipeline P. In addition, since the influence is exerted only when the regenerative vehicle passes, if the cathodic protection level of the entire anticorrosion section is increased, there is a possibility that over-corrosion protection may occur in the absence of the regenerative vehicle. Further, when another buried metal body exists around the pipeline P, there is a problem that the risk of electrolytic corrosion occurs in the other buried metal body due to interference.

  Further, the pipeline P having the risk of electric corrosion due to the regenerative vehicle as described above may be subjected to AC induction caused by the transmission current of the high-voltage AC transmission line or the passage of the AC electric railway. In such a case, the electric corrosion risk of the pipeline P is further increased by alternating current induction, but as a countermeasure in this case, simply installing an additional selective exhauster or installing a forced exhauster is an alternating current. There is a problem that the electric corrosion risk due to induction cannot be eliminated and a separate AC induction reduction measure is required, which requires a large construction cost.

  If the effect of the regenerative vehicle on the pipeline P is left unattended, the pipe-to-ground potential P / S shifts to the positive side at the affected area of the pipeline P, increasing the risk of electric corrosion, and excessive rail leakage current. Therefore, the exhaust current of the existing selective exhaust device increases, which causes the risk of electrolytic corrosion in other buried metal bodies existing around the pipeline P. It will also do.

  This invention makes it an example of a subject to cope with such a problem. In other words, avoiding the risk of electrolytic corrosion of pipelines due to the effects of regenerative vehicles without increasing the number of selective drains and increasing the level of cathodic protection, in other words, the risk of electrolytic corrosion of pipelines due to the effects of regenerative vehicles. Avoiding over-corrosion of the pipeline and interference with other buried metal objects around the pipeline, and the pipeline affected by the regenerative vehicle is connected to the transmission current of the high-voltage AC transmission line When receiving AC induction caused by the passage of railways, it is possible to avoid the risk of electrolytic corrosion due to the effects of regenerative vehicles, including the effects of AC induction, without taking measures to reduce AC induction that requires a large construction cost, pipe For the line, it is possible to avoid the effects of regenerative vehicles, which are locally and for a limited time, with the minimum necessary current flow, and the flow of the existing selective drain It does not increase the flow, etc. It is an object of the present invention.

  In order to achieve such an object, an electrolytic corrosion prevention system and an electrolytic corrosion prevention method for a buried metal pipeline according to the present invention include at least the configurations according to the following independent claims.

  An electric corrosion prevention system for a buried metal pipeline affected by a regenerative vehicle in a DC electric railway, wherein an electric wire is connected to the buried metal pipeline where the pipe-to-ground potential shifts to the positive side due to the effect of the regenerative vehicle. And a grounding electrode that shows a ground potential with a negative value from the anticorrosion potential of the buried metal pipeline, and a backflow preventer connected between the wires, the backflow preventer comprising the buried metal The direction of current flowing from the pipeline toward the ground electrode is a forward direction, and the pipe ground potential of the buried metal pipeline is a negative potential with respect to the anticorrosion potential and a positive potential with respect to the ground potential of the ground electrode. An electric corrosion prevention system for a buried metal pipeline, characterized by comprising a diode having an operating characteristic.

  A method for preventing galvanic corrosion of a buried metal pipeline affected by a regenerative vehicle in a direct current electric railway, wherein the location of the buried metal pipeline where the pipe-to-ground potential shifts to the plus side due to the effect of the regenerative vehicle is The ground electrode is identified by measuring the ground potential or predicted from the operation status of the regenerative vehicle, and the ground electrode showing the ground potential having a negative value from the anticorrosion potential of the buried metal pipeline is connected to the identified location via the electric wire. In addition, a backflow preventer is connected between the electric wires, and a voltage-current characteristic of a diode provided in the backflow preventer is set such that a current direction flowing from the buried metal pipeline toward the ground electrode is a forward direction, and the buried metal The pipeline ground potential is a negative potential with respect to the anticorrosion potential, and operates with a positive potential with respect to the ground potential of the ground electrode. Uni electrolytic corrosion prevention method of a buried metal pipeline and setting.

  According to the above-described feature of the present invention, a location where the pipe-to-ground potential shifts to the positive side is specified with respect to the buried metal pipeline affected by the regenerative vehicle, and the buried metal pipe is connected to the location via the backflow preventer. Since the earth electrode that shows a ground potential with a negative value from the anticorrosion potential of the line is connected, the current flows from the buried metal pipeline itself to the ground even if it is affected by the regenerative vehicle due to the current flowing from the ground electrode to the ground. This eliminates the risk of electrical corrosion of buried metal pipelines.

  The current leakage from the earth electrode to the ground can avoid the risk of pipeline corrosion due to the effect of the regenerative vehicle without adding a selective drain or increasing the level of cathodic protection. It is possible to avoid the risk of electrolytic corrosion of the pipeline due to the influence of the above by avoiding over-corrosion prevention of the pipeline and interference with other buried metal bodies existing around the pipeline.

  In addition, when the pipeline affected by the regenerative vehicle receives AC induction due to the transmission current of the high-voltage AC transmission line or the passage of the AC electric railway, the ground electrode connected to the buried metal pipeline is AC Since the induction reduction effect is also shown, the risk of electrolytic corrosion due to the influence of the regenerative vehicle including the influence of the AC induction can be avoided without taking an AC induction reduction measure that requires a large construction cost.

  In addition, current flows out from the earth electrode to the ground only when the buried metal pipeline is affected by the regenerative vehicle, so the effect of the regenerative vehicle on the pipeline for a limited time is limited. It can be avoided with the minimum necessary current outflow. As a result, the risk of electrolytic corrosion due to the influence of the regenerative vehicle can be avoided without causing interference with other buried metal bodies around the buried metal pipeline.

  When the rail leakage current etc. flows excessively into the buried metal pipeline, the current outflow action by the earth electrode works, so the drain current of the existing selective drainer installed near the substation of the DC electric railway is increased. I will not let you. As a result, the problem of interference caused by an increase in the exhaust current can be avoided.

It is explanatory drawing explaining the electric corrosion risk of the pipeline by a regeneration vehicle. FIG. 6A shows a case where a DC electric railway regenerative vehicle sends a regenerative current to a powering vehicle via a train line during regenerative braking, and FIG. In the case of regenerative braking, a case where a regenerative current is passed through a train line to a substation having a resistance consumption type or inverter type regenerative power processing device is shown. BRIEF DESCRIPTION OF THE DRAWINGS It is explanatory drawing explaining the electrolytic corrosion prevention system or the electrolytic corrosion prevention method of the buried metal pipeline which concerns on one Embodiment of this invention, The same figure (a) shows the system configuration including the laying environment of a buried metal pipeline FIG. 2B shows a system configuration for executing the operation check of the system. It is explanatory drawing which showed the specific structural example of the backflow preventer in the electric corrosion prevention system which concerns on embodiment of this invention. It is explanatory drawing explaining the operation example of the electric corrosion prevention system which concerns on embodiment of this invention.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 2 is an explanatory view for explaining an electrolytic corrosion prevention system or an electrolytic corrosion prevention method for a buried metal pipeline according to an embodiment of the present invention, and FIG. 2 (a) includes the laying environment of the buried metal pipeline. The system configuration is shown, and FIG. 5B shows the system configuration for executing the system operation check.

  In the embodiment described below, the pipeline P is described by taking a steel pipeline provided with a bituminous coating as an example, but the embodiment of the present invention is not particularly limited thereto. The pipeline P is subjected to cathodic protection by an external power supply system or the like, and the cathodic protection current is supplied to the pipeline P in the anticorrosion section. For example, the cathodic protection current output by the external power supply system is such that the pipe-to-ground potential P / S of the pipeline P at nighttime when the DC electric railway does not travel passes the anticorrosion potential in order to prevent the pipeline P from over-corrosion. The value to be controlled.

  And the pipeline P is embed | buried in the position which receives the influence of a regenerative vehicle. In a regenerative braking type DC electric railway vehicle, a current generated on a braking vehicle (regenerative vehicle) among vehicles traveling on the rail R is regenerated through a train line to a powering vehicle (powering vehicle). To improve the efficiency of electric power energy. Further, in the vicinity of the substation of the DC electric railway, a selective drain (or forced drain) is connected between the pipeline P and the rail R, and the rail leakage that frequently flows into the pipeline P is connected. The current is returned to the rail R.

  The pipeline P under such an environment may be further subjected to AC induction. When the pipeline P is laid along a high-voltage AC power transmission line or an AC electric railway, it receives AC induction caused by the transmission current of the high-voltage AC power transmission line or the passage of the AC electric railway. When the pipeline P receives AC induction, the potential change due to AC induction is superimposed on the pipe-to-ground potential P / S of the pipeline P shifted to the plus side as shown in FIG. Will be further increased.

  Under such circumstances, the electric corrosion prevention system for the buried metal pipeline according to the embodiment of the present invention is affected by the regenerative vehicle, and as shown in FIGS. 1A and 1B, the pipe ground potential P / The earth electrode 1 is connected to the place of the pipeline P where S shifts to the plus side via the electric wire 2, and the backflow preventer 3 is connected between the electrodes 2.

The ground electrode 1 is a metal electrode that shows a ground potential (potential with respect to the ground S) that is a negative value from the anticorrosive potential of the pipeline P (for example, -1200 mV _CSE (saturated copper sulfate electrode standard)). For the pipeline P, a magnesium (Mg) electrode having a ground potential of about -1300 mV _CSE is used.

  The backflow preventer 3 has a function of preventing current flowing from the ground electrode 1 from flowing into the pipeline P, and the pipe ground potential P / S of the pipeline P is on the positive side of the ground potential of the ground electrode 1. Even if a slight potential difference is set in this case, the current flows from the pipeline P toward the ground electrode 1. The main function of such a backflow preventer 3 is that the direction of current flowing from the pipeline P toward the ground electrode 1 is the forward direction, and the pipe-to-ground potential P / S of the pipeline P is a negative potential from the anticorrosion potential. This is achieved by a diode having a voltage-current characteristic that operates at a potential that is more positive than the ground potential of the ground electrode 1. In addition, the diode has a voltage-current characteristic in which the reverse current is zero until a sufficient reverse voltage in order to prevent a current from flowing from the ground electrode 1 in the direction of the pipeline P (referred to as a reverse direction). There is a need.

Here, the anticorrosion potential is a reference potential necessary for stopping electrolytic corrosion of the pipeline by cathodic protection. For example, in the case of a steel pipeline, the anticorrosion potential is -1200 mV _CSE .

  The electric corrosion prevention method using the electric corrosion prevention system according to the embodiment of the present invention will be described. First, the pipeline P in which the pipe-to-ground potential P / S is shifted to the positive side due to the influence of the regenerative vehicle. The location is specified by measuring the tube-to-ground potential P / S or by predicting the operation status of the regenerative vehicle. The tube-to-ground potential P / S is measured in a terminal box that is installed along the pipeline P at a predetermined interval (generally 250 m in the case of a gas pipeline) under a situation where rail leakage current is significant (for example, in the case of rain ) To measure a predetermined time in the passing time zone of the regenerative vehicle. In general, since regenerative braking is often performed at a curved portion of the rail R or in front of a station, it is possible to predict and specify a location affected by the regenerative vehicle from such an operation situation.

  Then, the ground electrode 1 is connected to the specified pipeline P via the electric wire 2, and the backflow preventer 3 is connected between the electric wires 2. The voltage-current characteristics of the diode provided in the backflow preventer 3 are set as described above.

The operating state of the electric corrosion prevention system according to the embodiment of the present invention can be confirmed by the system configuration of FIG. A voltmeter 11 is connected to the pipeline P in an electric wire to which an installed verification electrode (for example, saturated copper sulfate electrode) 10 is connected, and a pipe-to-ground potential P / S (V _CSE ) based on a saturated copper sulfate electrode is measured Is done. An ammeter 12 is connected to the electric wire 2 connecting the ground electrode (Mg electrode) 1 and the pipeline P, and the outflow current MgI (A) flowing through the electric wire 2 is measured. It is possible to evaluate whether or not the risk of electrolytic corrosion due to the influence of the regenerative vehicle has been eliminated by the measured value of the tube-to-ground potential P / S (V _CSE ). In the measurement of the outflow current MgI (A), normal operation confirmation and life prediction of the ground electrode can be made by the MgI _DC which is a DC component, and the AC induction reduction effect can be evaluated by the MgI _AC which is an AC component.

  The functions of the electric corrosion prevention system and the electric corrosion prevention method according to the embodiment of the present invention will be described. As shown in FIG. 1, when the pipe-to-ground potential P / S of the pipeline P in the vicinity of the regenerative vehicle becomes a positive value, and this value becomes a positive value than the anticorrosion potential, this point is moved from the pipeline P to the ground. Since current flows out, the risk of electrical corrosion increases. In this situation, when the electrolytic corrosion prevention system according to the embodiment of the present invention is equipped, when the pipe-to-ground potential P / S of the pipeline P is shifted to the plus side, the pipeline P → the ground electrode 1 → the ground S Current does not flow out directly from the pipeline P itself to the ground, and the risk of electrolytic corrosion of the pipeline P is eliminated. At this time, as the ground potential of the ground electrode 1 is a value on the negative side of the tube ground potential P / S, the effect of preventing galvanic corrosion increases. Therefore, a metal material exhibiting such ground potential is selected as the ground electrode 1. The An Mg electrode can be used for the steel pipeline P.

  Since the rail leakage current frequently flows into the pipeline P in the daytime when the DC electric railway is operated and not affected by the regenerative vehicle, the pipe-to-ground potential P / S of the pipeline P is There are many times when the value is on the minus side of the potential. At this time, an electromotive force that tries to flow a current from the earth electrode 1 to the pipeline P works, but if this current is allowed, if there is a coating defect near the current inflow point, the corrosion risk of that part is high. The trouble that becomes. In addition, when the inflow current flows through the selective drain, it induces the inflow of stray current such as rail leakage current into the ground electrode 1, and the exhaust current increases to increase the risk of interference with other embedded metal bodies. It will be. In order to avoid this, it is necessary to prevent the current flowing from the ground electrode 1 to the pipeline P, and the installation of the backflow preventer 3 described above is indispensable.

  Furthermore, the electric corrosion prevention system according to the embodiment of the present invention can be expected to reduce the AC induction by connecting the ground electrode 1 to the pipeline P. Generally, as a measure to reduce AC induction in high electrical resistance coating (plastic coating) pipelines, Mg electrodes, which are dispersed ground electrodes, are connected to the pipeline to reduce the pipeline AC induction voltage. However, as described above, when the ground electrode and the pipeline are connected without the backflow preventer 3 under the influence of the circuit vehicle, various problems due to the current flowing from the ground electrode to the pipeline occur. In the system according to the embodiment of the present invention, by providing the backflow preventer 3, the AC induction reduction effect is reduced as compared with the case where the ground electrode is directly connected to the pipeline, but the moderate AC induction reduction effect is exhibited. However, the risk of electric corrosion under the influence of regenerative vehicles is avoided.

  FIG. 3 is an explanatory diagram showing a specific configuration example of the backflow preventer in the electrolytic corrosion prevention system according to the embodiment of the present invention. Specifically, the backflow preventer 3 includes a diode 30 connected in series to the electric wire 2, a fuse (current interrupting means) 31 connected in series to the diode 30, a coil 32 connected in series to the diode 30, a diode 30 includes a power supply protector 33 connected in parallel to 30 and a varistor 34 connected in parallel to the diode 30. The coil 32, the power protector 33, and the varistor 34 are connected to a circuit in the backflow preventer 3 as a lightning surge shielding element.

  As described above, the voltage-current characteristic required for the diode 30 is that, as described above, in order to prevent the current from flowing from the ground electrode 1 to the pipeline P, the reverse current is increased to a sufficient reverse voltage. What can be made zero, and for one thing, when the pipe-to-ground potential P of the pipeline P is shifted to the positive side, a rising characteristic (operation characteristic) that allows an appropriate amount of current to flow from the pipeline P to the ground electrode 1 It is in having.

  The rise characteristics will be described in more detail. The diode 30 operates before reaching the anticorrosion potential of the pipeline P when the pipe ground potential P / S of the pipeline P is shifted to the positive side of the ground potential of the ground electrode 1. It has a rising characteristic that begins to start. As a result, before the pipe-to-ground potential P / S of the pipeline P reaches the anticorrosion potential, a current flows from the pipeline P toward the ground electrode 1 and the current flows out from the ground current 1 to the ground S. Since the pipe ground potential P / S is lowered, it is possible to prevent the pipe ground potential P / S from reaching the anticorrosion potential. Further, even if the connection location of the ground current 1 is not strictly specified, the current is discharged from the ground electrode 1 to the ground S until the tube-to-ground potential P / S reaches the anticorrosion potential, thereby avoiding the risk of electrolytic corrosion. Can do.

  As for the diode 30, when the pipe ground potential P / S of the pipeline P is a value on the plus side of the ground electrode 1 and is a minus side of the anticorrosion potential, the pipeline P passes the cathodic protection standard in that state. Therefore, a voltage-current characteristic is required such that the current flowing through the pipeline P → the ground electrode 1 → the ground S is relatively small. According to such a voltage-current characteristic, the influence of the regenerative vehicle on the pipeline P that is locally and for a limited time is avoided with the minimum necessary current outflow, and the interference risk of other buried metal bodies is a problem. It can be suppressed to a range that does not exist. If the pipe ground potential P / S is on the positive side of the anticorrosion potential, the pipeline P → the ground electrode 1 → the ground S increases as the difference between the pipe ground potential P / S and the anticorrosion potential increases. The voltage-current characteristic is required so that the current flowing through the capacitor increases. According to such voltage-current characteristics, the generated electric corrosion risk can be quickly eliminated.

As the diode 30 having such voltage-current characteristics, a Schottky barrier diode is suitable. As an example, the anode / cathode voltage (forward voltage V _F) operates the diode 30 is about 40mV or more, the anode / cathode voltage (forward voltage V _F) of about 100mV to about 0.3mA about order direction current I _F flows, the anode / cathode voltage (forward voltage V _F) the voltage a forward current flows I _F of about 2.1mA to about 150 mV - suitable those having a current characteristic. As the voltage-current characteristic of the reverse voltage, a voltage having a characteristic that hardly causes a reverse current to flow even if the reverse voltage is as high as about −60V is suitable.

When using a diode 30 of such properties, when the ground potential of the ground electrode 1 and about -1300MV _CSE, the pipe ground potential P / S is a small amount of current from the ground electrode 1 operates diode 30 is in -1260MV _CSE When the tube-to-ground potential P / S is on the minus side of the anticorrosion potential of -1200 mV _CSE , the current flows out to about 0.3 mV. If the pipe-to-ground potential P / S exceeds the anticorrosion potential and shifts to the plus side to about −1150 mV _CSE , the outflow current MgI is greatly increased in accordance with the difference from the anticorrosion potential to a value exceeding 2 mA. To do.

On the other hand, the fuse 31 that is connected in series to the diode 30 and serves as a current interrupting means has a function of interrupting the excess current when an excess current flows through the diode 30 continuously. If, when the diode 30 is forward current I be flowed _F pipe ground potential P / S operating becomes situations where shifted toward the negative side, the Schottky barrier diode is somewhat anode / cathode voltage ( When the forward voltage V _F ) increases, a current flows in a state close to no resistance. If the outflow current MgI increases in such a state, the risk of interference with other buried metal bodies increases. In order to avoid this, the backflow preventer 3 has a built-in fuse 31 so that the connection between the pipeline P and the ground electrode 1 is cut off when excessive current flows continuously through the diode 30. Yes. As an example, the fuse 31 is a slow blow type in which the rated current is set to a value at which the tube-to-ground potential P / S is blown at a positive value than −1.0 V _CSE and has a long fusing time to withstand instantaneous lightning current. Yes.

  FIG. 4 is an explanatory diagram for explaining an operation example of the electric corrosion prevention system according to the embodiment of the present invention, showing the operation of the system when the pipe-to-ground potential P / S of the pipeline P is shifted to the plus side. Yes. When the pipe ground potential P / S of the pipeline P is on the negative side of the ground potential (Mg ground potential) of the ground electrode P (range I in the figure), the ground electrode 1 is shown by the reverse voltage-current characteristics in the diode 30. The outflow current MgI from is maintained almost zero. Further, even if the pipe ground potential P / S of the pipeline P is shifted to the plus side from the Mg ground potential, if the forward current rising potential of the set diode 30 is minus side (range II in the figure), Again, the outflow current MgI from the ground electrode 1 is maintained almost zero.

  When the pipe-to-ground potential P / S of the pipeline P shifts to the plus side from the forward rising potential of the diode 30 (range III in the figure), the forward operation of the diode 30 (Schottky barrier diode) is started. The outflow current MgI from the ground electrode 1 begins to flow.

  At this time, since the forward rising potential of the diode 30 is set to the minus side of the anticorrosion potential, the outflow current MgI from the ground electrode 1 is reduced before the pipe-to-ground potential P / S of the pipeline P reaches the anticorrosion potential. The flow starts, and the pipe-to-ground potential P / S of the pipeline P is suppressed from shifting to the plus side. Therefore, in normal system operation, the pipe-to-ground potential P / S is illustrated even when the pipe-to-ground potential P / S of the pipeline P is shifted to the plus side due to the influence of the regenerative vehicle. It will stop in the range of III, and it can prevent beforehand that the pipe ground potential P / S exceeds the anticorrosion potential.

  And the fact that the pipe-to-ground potential P / S is in the range of III in the figure means that the anticorrosion state of the pipeline P is in a good state that passes the anticorrosion management standard. The outflow current MgI may be the minimum necessary, and the outflow current MgI is kept small by the voltage-current characteristics of the diode 30. As a result, when the pipe-to-ground potential P / S of the pipeline P remains within the range of FIG. III, the outflow current MgI is suppressed to a small value, so that there is no problem of risk of interference with other buried metal bodies.

  On the other hand, when the pipe-to-ground potential P / S of the pipeline P is shifted to the plus side from the anticorrosion potential due to a metal touch with another embedded metal body (in the range of IV in the drawing), in the voltage-current characteristics of the diode 30 Since a predetermined potential difference is provided between the forward current rising potential and the anticorrosion potential, a sufficiently large forward current flows when the tube-to-ground potential P / S is on the positive side of the anticorrosion potential. As a result, the outflow current MgI from the ground electrode 1 is increased so as to avoid a state in which the risk of electrolytic corrosion increases. If the pipe-to-ground potential P / S of the pipeline P does not shift to the negative side even when the outflow current MgI continues to be large, the backflow preventer 3 of the backflow preventer 3 is used to avoid excessive flow of the outflow current MgI. The fuse 31 functions to disconnect the connection between the pipeline P and the ground electrode 1.

  As described above, according to the electrolytic corrosion prevention system and the electrolytic corrosion prevention method for the buried metal pipeline according to the embodiment of the present invention, the risk of electrolytic corrosion of the pipeline P due to the effect of the regenerative vehicle is increased by adding a selective drainage device. Without having to increase the cathodic protection level. That is, the risk of electrolytic corrosion of the pipeline P due to the influence of the regenerative vehicle can be avoided by avoiding over-corrosion prevention of the pipeline P and interference with other buried metal bodies existing around the pipeline P. When the pipeline P affected by the regenerative vehicle receives AC induction due to the transmission current of the high-voltage AC transmission line or the passage of the AC electric railway, without taking measures to reduce AC induction that requires a large construction cost In addition, the risk of electrolytic corrosion due to the effect of the regenerative vehicle can be avoided including the effect of alternating current induction. Since the influence of the regenerative vehicle exerted on the pipeline P locally and for a limited time can be avoided with the minimum necessary current outflow, the interference risk of other embedded metal bodies can be suppressed to a range where there is no problem. Even if the rail leakage current frequently flows into the pipeline P, it can be dealt with by the outflow of current from the ground electrode 1, so that the exhaust current of the existing selective exhaust device is not increased.

1: Earth electrode (Mg electrode),
2: Electric wire,
3: Backflow preventer,
30: Diode,
31: fuse (current interruption means),
32: Coil (lightning surge shielding element),
33: A power protector (lightning surge shielding element),
34: Varistor (lightning surge shielding element),
P: Pipeline,
R: Rail,
S: Earth

Claims (10)

An electric corrosion prevention system for buried metal pipelines affected by regenerative vehicles in DC electric railways,
An earth connected to the buried metal pipeline where the pipe ground potential shifts to the plus side under the influence of the regenerative vehicle via an electric wire and showing a ground potential of a minus value from the anticorrosion potential of the buried metal pipeline. An electrode and a backflow preventer connected between the wires,
The backflow preventer has a forward direction as a direction of current flowing from the buried metal pipeline toward the ground electrode, and a pipe-to-ground potential of the buried metal pipeline is a negative potential from the anticorrosion potential, and the ground electrode An electric corrosion prevention system for a buried metal pipeline, comprising a diode having a voltage-current characteristic that operates at a potential on the plus side of the ground potential.   2. The electrolytic corrosion prevention system for a buried metal pipeline according to claim 1, wherein the buried metal pipeline is a steel pipeline, and the ground electrode is a magnesium (Mg) electrode. 3. The reverse current preventer according to claim 1, wherein the reverse current preventer is connected in series with the diode in order to cut off the excess current when excess current continuously flows through the diode. Electric corrosion prevention system for buried metal pipelines. 4. The electrolytic corrosion prevention system for an embedded metal pipeline according to claim 3 , wherein the backflow preventer is connected to a lightning surge shielding element in series or in parallel with the diode . In the vicinity of the substation in the DC electric railway, a selective drain or a forced drain is connected between the buried metal pipeline and the rail of the DC electric railway, and the buried metal pipeline 5. The cathodic protection system for buried metal pipelines according to any one of claims 1 to 4, wherein cathodic protection is applied . The electric corrosion prevention system for an embedded metal pipeline according to any one of claims 1 to 5, wherein the embedded metal pipeline is subjected to alternating current induction . An electric corrosion prevention method for buried metal pipelines affected by regenerative vehicles in a DC electric railway,
Identify the location of the buried metal pipeline where the tube-to-ground potential shifts to the plus side under the influence of the regenerative vehicle by measuring the tube-to-ground potential or predicting from the operation status of the regenerative vehicle,
While connecting the ground electrode showing the ground potential of the negative side value than the anticorrosive potential of the buried metal pipeline through the electric wire to the specified location, and connecting a backflow preventer between the electric wires,
The voltage-current characteristic of the diode provided in the backflow preventer is such that the direction of current flowing from the buried metal pipeline toward the ground electrode is the forward direction, and the tube-to-ground potential of the buried metal pipeline is on the minus side of the anticorrosion potential. A method for preventing galvanic corrosion of a buried metal pipeline, wherein the electric corrosion is set so as to operate at a potential which is a positive potential with respect to a ground potential of the ground electrode. The method for preventing electrolytic corrosion of a buried metal pipeline according to claim 7, wherein the buried metal pipeline is a steel pipeline, and the ground electrode is a magnesium (Mg) electrode . In the vicinity of the substation in the DC electric railway, a selective drain or a forced drain is connected between the buried metal pipeline and the rail of the DC electric railway, and the buried metal pipeline The method of preventing corrosion of buried metal pipelines according to claim 7 or 8 , wherein cathodic protection is applied . The method for preventing electrolytic corrosion of a buried metal pipeline according to any one of claims 7 to 9, wherein the buried metal pipeline is subjected to alternating current induction .

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