Method for detecting a source of ground potential rise around a buried metal pipeline
Patent Information
- Authority / Receiving Office
- KR · KR
- Patent Type
- Applications
- Current Assignee / Owner
- 이현창
- Filing Date
- 2026-07-30
- Publication Date
- 2026-08-05
Smart Images
Figure PAT00001_ABST
Abstract
Description
Technology Field
[0001] Gas pipes, metal pipes, water pipes, heat pipes, corrosion, inspection, cathodic protection Background Technology
[0002] Since 2021, the Korea Electro-technical Code (KEC) has been fully applied following a two-year grace period after being incorporated into law under Article 67 of the Electric Power Business Act in 2018.
[0003] Despite being an unavoidable measure for the introduction of international standards (IEC) and the smooth development and field operation of new and renewable energy, the individual grounding method by type, which has been used for over 50 years as shown in [Figure 1], has been abolished and changed to using separate or common grounding between high and low voltage facilities and integrated grounding with protection facilities as shown in [Table 1].
[0004] Name Justice Neutral wire multiple grounding It refers to a system grounding method in which the neutral wire of a power system is connected to the ground in multiple ways, and the neutral point of a transformer is connected to that neutral wire. isolated grounding A method of grounding by separating the grounding electrodes of high-voltage, extra-high-voltage, and low-voltage electrical facilities. common ground A method of grounding the grounding electrodes of high-voltage, extra-high-voltage, and low-voltage electrical facilities in common. Integrated grounding A method of grounding by sharing grounding electrodes for electrical equipment grounding facilities, building lightning protection facilities, electronic and telecommunications facilities, etc.
[0005] In particular, while high and low voltage neutral lines have been common grounded in overhead power distribution, as shown in [Fig. 2], low voltage neutral lines in underground power distribution have been operated ungrounded. However, with the legal application of the KEC regulations, as shown in [Table 1], multiple grounding (TNC) of the underground low voltage neutral line must be implemented, and integrated grounding involving common grounding of high and low voltages and equipotential bonding with the building must also be carried out. In this application, "grounding" may include the neutral line multiple grounding, common grounding, and integrated grounding as described in [Table 1], which have been modified in accordance with the Korean Electrical Equipment Regulations (KEC). Accordingly, in the event of a fault in an underground high-voltage line, the fault current previously returned to the substation through the underground high-voltage sheath line; however, now the fault current can also flow through the low-voltage neutral line, thereby suppressing the Earth Potential Rise (EPR) and maintaining contact and step voltages below the specified values, thereby ensuring safety.
[0006] However, while there is an advantage in suppressing the rise in ground potential by relying on the low-voltage neutral line for the effect of dispersing high-voltage line fault current, as shown in [Figure 3], a disadvantage occurs in that the high-voltage fault current flows through the low-voltage neutral line grounding, expanding the area of interference for the rise in ground potential.
[0007] In addition, as shown in [Fig. 4], the low-voltage lines are not connected 1:1 exclusively for customers, but in actual field operations, they are configured 1:N, with one low-voltage supply line supplying power to multiple customer facilities.
[0008] As shown in [Fig. 4], when the neutral line of a low-voltage line is ungrounded, the leakage current or residual current flowing through the line can be measured at the power source (transformer) to detect and address the leakage current. However, as shown in [Fig. 5], when the neutral line is commonly multi-grounded, the leakage current does not return to the power source (transformer) but returns to a nearby grounded neutral line, making it impossible for the power source to detect it. This problem results in a blind spot in protection.
[0009] [Fig. 5] shows that when undergrounding of power lines increases in urban areas, power line fault currents or instantaneous non-linear currents caused by train operation can cause interference to metal pipes located at a distance that have not previously been affected by grounding, due to the rise in ground potential.
[0010] [Figure 6] shows the status of the rapidly increasing number of renewable energy power generation businesses. As they have increased exponentially, there are approximately 80,000 small-scale power sources scattered across the country, including both members and non-members, and this will also cause the rise in ground potential through grounding.
[0011] [Figure 7] shows an example of a cathode protection system configuration to prevent corrosion of underground buried metal bodies. Gas pipe protection is primarily protected by coating the outer surface of the gas pipe in contact with the ground to prevent contact with the electrolyte (earth) and thus protect against oxidation. Secondary protection is provided by applying a (+) DC current to a sacrificial anode and a (-) DC current to the gas pipe to be protected, so that even if the coating of the primary protection means fails, the electrolyte in contact with the gas pipe maintains alkalinity.
[0012] [Fig. 8] shows a CIPS (Closed Interval Potential Survey) method in which, in such a cathode protection environment, a current interrupter that changes the current into a pulse form is inserted in the middle of a wire supplying (-) current to the pipe, one wire is connected to a test point with a reference electrode buried underground, and the other wire is connected to a battery cell in contact with the ground surface, and then the potential is measured while moving along the buried metal pipe path to determine whether there is a coating defect, which is a primary protection means.
[0013] In addition, other methods include DCVG and ACVG inspection methods, which measure the potential difference between two locations on the ground surface along the buried path without connecting wires, similar to CIPS.
[0014] In this way, the metal body with a defective coating, which is a primary protective measure, comes into direct contact with the surrounding electrolyte, the soil, but if there is a cathodic protection system, which is a secondary protective measure, the progression of corrosion can be delayed.
[0015] However, the cathode protection function, such as [Fig. 7], which maintains (-) polarity by alternating positive and negative poles to provide corrosion protection, may not function properly, and corrosion may continue to occur.
[0016] In addition, in places where the same (-) polarity cannot be maintained due to commercial power interference, diagnostics such as DCVG (DC Voltage Gradient) or CIPS (Closed Interval Pulse Survey) as shown in [Fig. 8] become impossible.
[0017] [Fig. 9] shows a gas pipeline inspector contacting the ground to measure the voltage drop (IR) gradient between the gas pipeline and the soil to locate areas with coating defects, and a heat pipeline inspector moving along the pipeline burial route in a vehicle to measure areas of ground temperature rise using a thermal imaging camera to locate areas with heat pipeline abnormalities.
[0018] When inspecting gas pipelines, it takes a long time to measure ground potential by walking along the pipelines one by one. When inspecting heat pipelines, if the ground temperature rises above ambient temperature to the point where it can be detected by a thermal imaging camera, it may be impossible to perform effective preventive inspections if the corrosion is detected only when it has already progressed significantly.
[0019] Furthermore, as shown in [Fig. 10], electrical fires account for more than 50% of all domestic fire incidents (excluding negligence), and given that the number of incidents increases by more than double during the rainy season in August compared to normal times, it would not be unreasonable to argue that even if a protection blind spot occurs after neutral wire grounding, the cause of potential rise is not eliminated and persists, and that the insulation resistance decreases due to the rainy season, which can lead to the occurrence of an ignition source.
[0020] Accordingly, due to the recent expansion of areas susceptible to interference from rising ground potential following changes in grounding, interference sources such as ground potential rise caused by leakage currents are not being properly eliminated. Consequently, it is necessary to establish countermeasures against corrosion of buried metal structures and electrical fires during the rainy season caused by interference with commercial power. The problem to be solved
[0021] Development of a method for early detection of buried metal corrosion and building fires caused by commercial power interference (influence). means of solving the problem
[0022] First, the severity of commercial power interference in buried metal bodies is evaluated. Then, the source causing the interference is identified and removed at points exceeding the threshold. Subsequently, a DC exploration power source is connected to the cathode protection conductor of the metal pipe to locate and repair defective piping, thereby eliminating the source of failure. Additionally, leakage sources located in protection blind spots within the building are identified and removed by measuring high-voltage insulation resistance diagonally when they are not in contact with the electrolyte, thus preventing electrical fires during the rainy season. Effects of the invention
[0023] It has the advantage of accurately identifying the source of fire within a building and corrosion of buried metal bodies caused by commercial power influences (interference), such as power line induction. Brief explanation of the drawing
[0024] [Fig. 1] is a partial explanation of the Korean Electrical Installation Regulations, which have been enacted into law and enforced since 2011. [Fig. 2] illustrates interference when the high and low voltage neutral lines are grounded together. [Fig. 3] explains the comparison between the ideal and actual configurations of a low-pressure network. [Fig. 4] illustrates the occurrence of a protection blind spot when the neutral line is multi-grounded in an actual low-voltage network configuration. [Fig. 5] explains the cause of the long-distance expansion of non-linear current interference zones due to the increase in undergrounding of power lines. [Fig. 6] shows the status of power generation operators, which have been rapidly increasing recently. [Fig. 7] shows an example of cathode protection for preventing corrosion of metal pipes. [Fig. 8] shows the configuration of an inspection facility for identifying the location of coating defects in metal pipes. [Fig. 9] shows the inspection of coating defects on metal pipes. [Figure 10] shows the statistics on the share of electrical fires and their increase during the rainy season. [Fig. 11] is a vertical drawing showing the burial depth for each type of underground utility as stipulated by the Seoul Metropolitan City Ordinance. [Fig. 12] is a plan view determining the location of underground buried structures as determined by the Ministry of Land, Infrastructure and Transport. [Fig. 13] shows gas and electrical piping and meters installed in close proximity. [Fig. 14] illustrates the phenomenon where the ground potential continuously rises when a short circuit occurs in a protection blind spot. [Fig. 15] illustrates another form of blind spot in protection. [Fig. 16] illustrates the phenomenon of commercial power entering and exiting (a1, a2) through buried metal bodies. [Fig. 17] shows an example of a device for evaluating the severity of commercial power interference in buried metal bodies. [Fig. 18] illustrates the ground potential measuring section of a device for evaluating the severity of commercial power interference of buried metal bodies. [Fig. 19] illustrates the measurement data collection unit of a device for evaluating the severity of commercial power interference of buried metal bodies. [Fig. 20] shows an example of a diagnostic path setting for a device that evaluates the severity of commercial power interference in buried metal bodies. [Fig. 21] is a flowchart for identifying the source location using a device that evaluates the severity of commercial power interference of buried metal bodies in a path set as in [Fig. 20]. [Fig. 22] is a flowchart of the process for locating defective primary protective means (coating) on metal piping after removing the source, using a device that evaluates the severity of commercial power interference on buried metal bodies. [Fig. 23] is a flowchart of the process for finding the source of a commercial power interference using a device that evaluates the severity of commercial power interference of buried metal bodies in an area where periodic commercial power interference occurs. [Fig. 24] is a flowchart of fire prevention operations for identifying the location of commercial power interference sources in blind spots of protection within a building. Specific details for implementing the invention
[0025] [Figure 11] shows the depth of burial facilities for each type of underground burial facility as stipulated by the Seoul Metropolitan City Ordinance. It can be seen that, unlike power lines which are installed at the top of the underground burial facilities, city gas pipes are installed at the bottom. Power was initially supplied using overhead facilities, but recently the method was changed to underground burial, so they are placed at the top closest to the surface. Conversely, city gas has been installed underground since the initial installation and is installed at the deepest point, maintaining a vertical distance between the two facilities.
[0026] [Fig. 12] shows the burial locations of underground facilities horizontally below the road surface as determined by the Ministry of Land, Infrastructure and Transport. It can be seen that gas pipes and electrical pipes are installed adjacent to each other underground near the sidewalk.
[0027] As shown above, although there appears to be a vertical separation distance between the electrical equipment and the gas or heat pipes, it can be seen that they are installed in the closest proximity in the horizontal direction.
[0028] In addition, low-pressure gas pipes supplied to households use PE (Polyethylene) pipes in the underground buried sections to prevent corrosion, but metal pipes are used above ground and within households and are installed together near power lines as shown in [Fig. 13].
[0029] [Fig. 14] illustrates a case where, when a power line fault occurs in a protection blind spot during neutral multi-grounding, the signal returns to a nearby neutral multi-grounding (PEN) point, and because the power source does not recognize this, the fault is not cleared and persists, resulting in a rise in ground potential caused by the commercial power supply.
[0030] [Fig. 15] illustrates another case of a protection blind spot. Specifically, the point of supply between the power company and the customer is the connection point at the eaves of the building. In reality, inspecting the area beyond this point would require disconnecting the commercial power supplied by the power company from the transformer; however, since this is practically difficult, the Korea Electrical Safety Corporation periodically measures insulation resistance starting from the meter to check for faults. Furthermore, when meters are installed outdoors for the convenience of recent meter readings, the area from the meter to the distribution box containing the breaker is not protected, leading to instances where electrical leakage is left unaddressed.
[0031] While this is not a problem when power lines are installed overhead, as underground power facilities increase due to the recent promotion of undergrounding, devices and methods must be devised to identify the possibility of corrosion and electrical fires in metal pipes, such as gas, water supply, and heat pipes, installed in areas where the ground potential has been raised by power facilities. However, in this application, the metal pipes (metal pipes) are not limited to the three uses (gas, water supply, and heat pipes) mentioned above, and may include "buried metal bodies" that may suffer corrosion damage by causing an influence (interference) to prevent commercial power leaked into the ground due to faulty facilities of electric or railway operators from maintaining (-) polarity.
[0032] In metal conduits that run parallel to or intersect power lines, an induced current is generated in the metal conduit in proportion to the current flowing through the power line, and an induced voltage is generated by this current. However, in high-voltage lines, the induction of high voltage due to electrostatic coupling can be ignored because there is a sheath line grounded on the outer surface.
[0033] If a non-linear large current is generated due to a fault or other factors in a power line near a metal conduit as shown in [Fig. 5], an induced current of a certain magnitude or larger flows through the metal conduit, and the high voltage generated by the high resistance between the inside of the metal conduit and the ground when it is ungrounded selects the place with the weakest insulation stress among the coated outer surfaces, destroys the local insulation, and the current returns.
[0034] Metal pipes with such defective coating come into direct contact with the surrounding electrolyte, soil, but if there is a cathodic protection system, the progression of corrosion can be delayed.
[0035] However, if commercial power induced from the power line flows through the inflow point a1 and outflow point a2 of [Fig. 16], which are locations with defective coating, the cathode protection equipment [Fig. 7], which maintains the negative polarity of the metal body to prevent corrosion, may be interfered with and unable to function properly, leading to continuous corrosion.
[0036] In the present application, “commercial power interference” may include cases where a commercial power supply malfunction (failure) leaks into the ground and interferes with the secondary protection means, such as a negative protection device, preventing the metal body from maintaining (-) polarity, thereby causing corrosion of the metal body to proceed at the primary fault location.
[0037] In addition, in places where the metal body cannot maintain the same (-) polarity due to such commercial power interference, diagnostics such as DCVG (DC Voltage Gradient) or CIPS (Closed Interval Pulse Survey) as shown in [Fig. 8] become impossible.
[0038] Accordingly, when commercial power induced from power lines flows through buried metal bodies, a diagnostic method different from [Fig. 8] must be devised.
[0039] As described above, at locations where non-linear commercial power induced from power lines flows in (a1) or out (a2) through insulation (coating) defects on the outer surface of the metal body, a rise in ground potential due to commercial power occurs on the ground surface.
[0040] Utilizing this principle, a vehicle equipped with a device for evaluating the severity of commercial power interference of buried metal bodies, such as [Fig. 17], moves along the road surface of the area where the rapid pipeline is buried and uses wheel electrodes to identify the location of the rise in ground potential caused by the commercial power.
[0041] However, unlike previous technology which allows driving on a wide road surface without any restrictions, measurement data may differ depending on the lane position even when moving along the same path. Therefore, a camera is used to maintain a specific lane on the road surface, or a laser distance measuring device is used to maintain a constant distance from the road center line or the curb, and the distance is managed and recorded so that during the next movement, the same lane, center line, or curb distance is maintained while moving and measuring, making it possible to compare with previous data.
[0042] A previous driving data-based guide device can be used to record and manage ground potential data for each driving route recorded in this way, and to ensure that the ground potential is measured at the same location during the next diagnosis, by utilizing previous driving lane information and maintaining the same location and keeping it within a certain distance using the previous driving data as a reference point.
[0043] [Fig. 18] illustrates a ground potential measuring device in a device for evaluating the severity of commercial power interference in buried metal bodies. It records ground potential measurements input from multiple wheel electrodes and transmits the measurement data via wireless communication to a recording, mapping, and alarm device located inside the vehicle, depending on the travel speed. Additionally, a vibration meter may be added to measure the water level of a water tank and to correct errors in the wheel electrode measurements.
[0044] [Fig. 19] illustrates a recording and mapping alarm device installed inside a vehicle. The measurement data collection unit combines ground potential measurement information acquired from wheel electrodes via wireless communication with GNSS reception information to generate ground potential information by location and shares the results with the vehicle operation record unit and data management unit.
[0045] The vehicle operation information logbook acquires image information from cameras to manage and record lane maintenance information, obtains driving information such as lane changes and turns, and travel times to major landmarks (intersections, steering elements), and also exchanges vehicle operation information (start, end, and temporary stop), direction changes, lane changes, and speed information from within the vehicle, compares and corrects it with the image information, and shares the results with the data management department.
[0046] The driving guide unit informs the driver to maintain a certain distance using the driving information in the recent vehicle driving information record as a reference point when driving the same section next time, so that the ground potential value can be measured at the same location as the previous data's reference point.
[0047] The Data Management Department compares and corrects the location-specific ground potential information provided by the Measurement Data Collection Department and the vehicle operation information provided by the Vehicle Operation Information Recording Department, and provides the results to the User Interface Department.
[0048] The User Interface section displays data provided by the Data Management section in a map format on the screen and also enables tracking, management, and analysis by allowing the user to know the location when an alarm value occurs.
[0049] [Fig. 20] shows an example of a diagnostic path to locate the source of interference in metal pipes using a device that evaluates the severity of commercial power interference in buried metal bodies. Since ground potential differences may occur depending on the location of the road, the ground potential rise location detection device is designed so that wheel electrodes can cover one lane, and it moves along that lane. At the end of the measurement, it turns around to measure the same lane in the opposite direction and repeats the measurement until the end.
[0050] [Fig. 21] describes the procedure for evaluating the severity of commercial power interference of buried metal bodies and finding the source of the alarm at the location where the threshold value is exceeded. The ground potential measuring device of the commercial power interference severity evaluation device for buried metal bodies is set, and starting from the lane position of the road to be driven, the ground potential input through the wheel electrode is continuously measured to identify the point of maximum ground potential rise by measuring in the same sequence as in [Fig. 20].
[0051] This shows a case where an alarm is triggered at a wheel electrode location where the threshold value of commercial power interference severity is 50mV or higher and maintained for 3 cycles or more.
[0052] [Fig. 22] moves to the maximum point (Vmax) among the commercial power interference severity alarm occurrence locations detected by the device evaluating the commercial power interference severity of buried metal bodies, searches for a location of ground potential equal to or greater than Vmax in an area where vehicles cannot enter, and conducts a commercial power interference source location investigation centered on that location.
[0053] After conducting the above investigation into the source of commercial power interference and isolating it, remove Vmax, and in the absence of commercial power interference, apply a DC exploration voltage to the buried metal body or the cathode protection conductor connected to ground to identify the location of the primary protection failure of the buried metal body.
[0054] [Fig. 23] describes a method for locating defective buried metal bodies in areas where commercial power interference occurs periodically, such as during the operation of electric trains by railway operators.
[0055] The direction of an interference source that matches the aforementioned commercial power interference cycle is identified by measuring the surrounding neutral line ground PEN voltage, and the commercial power interference source is located near that position. After verifying whether the commercial power interference operating time (cycle), for example, the operating time in the case of an electric train, matches the rising cycle of Vmax or Vpen, if they match, the off-time of the interference source is identified or a temporary off-time is discussed. When the voltage such as Vmax is removed upon the shutdown of the commercial power interference source, a DC exploration voltage is applied to the cathode protection equipment as shown in [Fig. 22] to locate the defective buried metal body.
[0056] [Fig. 24] explains the procedure for preventing fires caused by a commercial power interference source located in a blind spot of protection inside a building when commercial power interference occurs near the building. As shown in [Fig. 22], if the maximum commercial power interference potential is detected at the building boundary around Vmax, a live line investigation is conducted to identify the source of commercial power interference inside the building. If the source of interference is not found inside the building, the insulation resistance of the equipment located within the blind spot of protection is measured in consultation with the power company to determine if there is a defect. If necessary, even if the primary protection means is defective, the electrolyte in contact with the power line inside the building may remain insulated during the dry season, unlike when it is buried underground, so it may be necessary to inspect it during the rainy season.
[0057] After completing the process of removing the commercial power interference source, verify that Vmax has been removed from the previous interference location when the commercial power is restored, and then finish the work. Explanation of the symbols
[0058] Cathode Protection, CIPS (Closed Interval Potential Survey), commercial power source, primary protection (coating), secondary protection (cathode protection), interference
Claims
Claim 1 A method for identifying a source of rising ground potential in an area where a buried metal pipe is buried, comprising: a step of moving a first mobile ground potential exploration device equipped with a plurality of wheel electrodes in contact with the ground surface along a first investigation path corresponding to the burial path of the buried metal pipe, while measuring the AC commercial power ground potential at each location to identify the spatial maximum point of ground potential rise Vmax and the location of said Vmax on said first investigation path; a step of moving a second mobile ground potential exploration device to the location of said identified Vmax, and then moving it along a second investigation path starting from the location of said Vmax while measuring the ground potential Vs at each location of said second investigation path; and a step of using Vmax identified in said first investigation path as a comparison standard for the ground potential Vs at each location measured in said second investigation path to identify the location where a ground potential Vs equal to or greater than said Vmax is measured. A method for detecting a source of rising ground potential in a buried metal pipe investigation area, characterized by including the step of conducting a leakage current investigation of power facilities centered on a location where a ground potential Vs equal to or greater than the above Vmax is measured, and identifying a source of rising ground potential affecting the area where the above buried metal pipe is buried. Claim 2 A method for detecting a source of rising ground potential in a buried metal pipe investigation area, characterized in that, in claim 1, the first mobile ground potential exploration device is a vehicle-type ground potential measuring device that moves along a lane of a road corresponding to the burial path of the buried metal pipe, the second mobile ground potential exploration device is a cart-type mobile ground potential exploration device, the first investigation path includes a lane of a road corresponding to the burial path of the buried metal pipe, and the second investigation path includes a path extending from the position of Vmax identified in the lane of the road toward the sidewalk or toward the center line of the road. Claim 3 A method for detecting a source of rising ground potential in a buried metal pipe investigation area, further comprising: a step of isolating a source of ground potential identified around a location where a ground potential Vs equal to or greater than Vmax is measured in the second investigation path by the power facility leakage investigation; and a step of, after isolating the source of ground potential, confirming whether the maximum point of ground potential rise Vmax spatially identified in the first investigation path before isolating the source of ground potential has been removed. Claim 4 A method for detecting a source of rising ground potential in a buried metal pipe survey area according to claim 1, further comprising: a step of generating ground potential information by combining location-specific AC commercial power ground potential measurement information obtained from a plurality of wheel electrodes of the first mobile ground potential survey device with location information indicating the location where the measurement information was obtained; a step of recording the location information of Vmax and the location where a ground potential alarm occurred in the location-specific ground potential information; a step of recording driving path information including lane information and driving information when the first mobile ground potential survey device moves along the first survey path; a step of displaying the location-specific ground potential information in a map form by correlating the location of Vmax and the location where the ground potential alarm occurred; and a step of guiding the first mobile ground potential survey device to move again along a survey path corresponding to the location where the location-specific ground potential was measured in the previous survey, based on the recorded lane information and driving path information, when the area where the buried metal pipe is buried is surveyed again. Claim 5 In claim 2, the internal resistance of the first mobile ground potential exploration device is 1 MΩ, and the first mobile ground potential exploration device is set with a first alarm voltage of 50 mV AC and a maintenance condition in which the state in which the AC commercial power ground potential at each location exceeds the first alarm voltage continues for at least 3 cycles of the commercial power supply, the first mobile ground potential exploration device moves along the first investigation path at a speed of 20 km / h or less, and generates a ground potential alarm at a location where the AC commercial power ground potential at each location exceeds the first alarm voltage and satisfies the maintenance condition, and identifies the Vmax among the AC commercial power ground potentials measured at a plurality of spatial locations where the ground potential alarm occurred, the internal resistance of the second mobile ground potential exploration device is 1 MΩ, and the second alarm voltage of 500 mV AC is set on the second mobile ground potential exploration device, and at each location of the second investigation path A method for detecting a source of rising ground potential in a buried metal pipe investigation area, characterized by comparing the ground potential Vs at each location with Vmax identified in the first investigation path when the ground potential Vs is greater than or equal to the second alarm voltage. Claim 6 A method for identifying the source of periodic ground potential fluctuations in an area where buried metal pipes are installed, comprising: a step of measuring the ground potential at each location while moving a mobile ground potential exploration device equipped with multiple wheel electrodes in contact with the ground surface along an investigation path corresponding to the installation path of the buried metal pipes, and identifying the location of Vmax, a point of maximum spatial ground potential rise that fluctuates periodically among multiple locations on the investigation path; a step of measuring the voltage Vpen at a neutral wire grounding PEN located near the location of the spatially identified Vmax, and identifying the direction of the source of a large current associated with the periodic ground potential fluctuations based on the measurement result of Vpen; a step of selecting the source of a large current located in the identified direction as a candidate source; and a step of confirming whether there is a match by comparing the operating time or runtime of the candidate source with the rise period of Vmax or Vpen. A method for detecting a source of periodic ground potential rise in a buried metal pipe investigation area using a maximum point of ground potential rise and neutral line grounding voltage, characterized by including the step of identifying a source of high current related to the periodic ground potential fluctuation among the candidate sources by utilizing the direction identified based on the measurement result of the above Vpen and the above matching. Claim 7 A method for detecting a source of periodic ground potential rise in a buried metal pipe investigation area, further comprising: a step of determining the idle time of a high current source identified as a source associated with periodic ground potential fluctuations or temporarily stopping the operation of the high current source by confirming that the high current source is located in a direction identified based on the measurement result of the Vpen and that the operating time or run time matches the rise cycle of the Vmax or the Vpen; and a step of confirming whether the Vmax spatially identified on the investigation path was removed before the idle time or stoppage while the high current source is idle or its operation is stopped. Claim 8 A method for detecting a source of periodic ground potential rise in a buried metal pipe investigation area, wherein, in claim 6, the source of the high current includes an electric train or a high current generating device, the electric train or the high current generating device located in a direction identified based on the measurement result of the Vpen is selected as a candidate source, and the operating time of the electric train or the operating time of the high current generating device is compared with the rise cycle of the Vmax or the Vpen. Claim 9 A method for investigating a source of periodic ground potential rise in a buried metal pipe survey area, wherein, in claim 6, the step of measuring ground potential by location comprises: measuring the ground potential by location while moving a vehicle-type ground potential measuring device, which is a mobile ground potential exploration device, along a lane of a road corresponding to the burial path of the buried metal pipe; generating ground potential information by location by combining ground potential measurement information measured by the vehicle-type ground potential measuring device with location information indicating the location where the ground potential measurement information was acquired; and identifying a spatial Vmax that fluctuates periodically and the location of said Vmax among a plurality of ground potentials by measurement location included in the ground potential information by location. Claim 10 A method for detecting a source of rising ground potential in a buried metal pipe survey area, characterized in that, in claim 1 or claim 6, an underground power line is buried at a depth closer to the surface than the buried metal pipe, the neutral line of the underground power line is grounded to the ground at a plurality of points, the grounding of a high-voltage or extra-high-voltage electrical facility and the grounding of a low-voltage electrical facility in a power system including the underground power line are connected in common, at least a portion of the fault current or leakage current of the underground power line does not return directly to the power source but returns through a nearby grounded neutral line, and the maximum point of rising ground potential Vmax is used to detect a source of rising ground potential related to the return path of the fault current or leakage current through the grounded neutral line.