KR20220128965A - Method for surveying the laying path of mv underground cable using current impulse signal - Google Patents

Abstract

The present invention has a function capable of detecting a phase difference between voltages and currents in a receiver and recognizes a phase difference, a level, and the like in a transformer, to which a transmitter is connected, before leaving for route survey to be used during route survey in a location at a distance from the transmitter for having an advantage of surveying a high-voltage and low-voltage line without visiting all the way to an end part of the low-voltage line when the transformer transmits a high current impulse signal for survey.

Description

How to explore the high-voltage cable buried path

The present disclosure relates to a power line buried path exploration method. In particular, it is a disclosure of a method for stably exploring a high-voltage line by proposing a method for minimizing the mutual signal influence in a place where a low-voltage line and a high-voltage line are mixed.

As shown in [Fig. 1], the common distribution network usually has two voltage networks based on the transformer. Among them, a network with a high voltage is called a high voltage network, and a network with a lower voltage is called a low voltage network.

In order to explore the buried path and connection configuration of the low voltage line constituting the low voltage network, connect the transmitter to one point of the low voltage line to be explored and generate a current pulse signal. will flow

When a current impulse signal with a nonlinear characteristic flows through a low voltage line to distinguish it from the general load current, the receiver receives the magnetic field signal emitted from the surroundings, removes the general load component, but detects only the current impulse signal with non-linear characteristics, such as a buried path, etc. will explore

However, in recent years, a technique for exploring the composition of a high-voltage network rather than a low-voltage network is attracting attention. Like the low-voltage network exploration method above, you can connect the transmitter to one point of the high-voltage line to be explored and generate a current impulse signal to conduct the exploration. Otherwise, if you want to connect by removing insulation, you have to remove insulation with a diagonal wire, so the advantage of live wire exploration technology is lost. In addition, in manufacturing the transmitter, the device becomes larger in order to have a high-voltage insulation distance, the development of a switching device with the voltage of the high-voltage network is delayed, and it is expensive, so it is difficult to commercialize it for reasons such as economic feasibility. Therefore, it becomes unrealistic to connect and explore the transmitter after removing the insulation of the connection each time.

Fortunately, the withstand voltage characteristics of voltage-driven wide bandgap switch devices using SiC or GaN have recently been improved, allowing semiconductor switches to control the current flow by switching on/off the current flow of several hundred to several kA at a low voltage network voltage. became

It is possible to modify the existing transmitter to increase the current capacity by using a wide bandgap semiconductor switch element with increased current capacity as described above.

Accordingly, as in [Fig. 2], instead of a transmitter that can be connected to a high-voltage network, a transmitter is connected to a low-voltage network to generate a large current, and the current is converted into a high-voltage current through a transformer and flows through the high-voltage line.

However, it was discovered that when a large current impulse current occurs, the probe signal flows through the surrounding power line and the magnetic field signal is detected.

In particular, it is difficult to classify magnetic field signals and search for probe current impulse signals simultaneously in high-voltage lines as well as in low-voltage lines.

When a current impulse signal is generated by connecting the transmitter to the secondary terminal of the transformer of the public distribution network, the transformer converts it into high-voltage network current and flows through the high-voltage line, the receiver detects the magnetic field signal and explores the high-voltage line

become

When a probe current signal is generated from the load side of the low-voltage line, the current impulse current flows through the low-voltage line and the high-voltage line and cannot be distinguished. It is connected to generate a current impulse signal and probes a high-voltage line.

However, when a large current pulse is generated, the current supplied is not only supplied from the high-voltage power supply through the primary winding of the transformer, but some of the charged current of the low-voltage line connected to the secondary is reversed, and a magnetic field signal is also generated in the low-voltage line.

Accordingly, when a probe current signal is generated from the power supply side of a low-voltage line during high-voltage line exploration, it is necessary to develop a technology that can effectively probe a high-voltage line by developing a method for classifying the magnetic field signal generated by the current flowing in the low-voltage line.

When a high-current impulse signal for exploration occurs, a voltage drop occurs at the low-voltage end, and current is generated in the high-voltage line and the low-voltage line.

However, the current flow direction is based on the transformer, and the current bar to block the polarity of the current flowing at the same time. By comparing the characteristics of the waveforms flowing through the high voltage line and the low voltage line, a device that analyzes them can be added to the receiver so that the investigator can distinguish the probe current pulse It is possible to trace the low-voltage and high-voltage lines flowing through it, and to compare the two voltages to determine it.

It is possible to determine whether a high-voltage line and a low-voltage line are buried at the same time, trace the line connection, and analyze the waveform in a place where the wire cannot be seen to determine whether it is a low-voltage or high-voltage line. The high-voltage line that supplies power and the low-voltage line that receives power can be identified at the same time. In particular, it has the advantage of tracking the low voltage line even when the probe current pulse cannot be injected because the load side connection point of the power line cannot be found, such as an idle line cut in the middle.

1 illustrates the direction of current flow when a current impulse signal is generated at the load side of a low voltage line connected to a general polarization transformer.
2 is a configuration in which a large current pulse transmitter is installed on the power supply side of the low voltage line to reduce the influence of the low voltage line.
3 is a view showing a high current pulse transmitter connected to a secondary terminal of a transformer in the same configuration as in FIG.
4 is a configuration for simulating the load effect when a current pulse is generated.
5 is a waveform comparing the power-side current A1 and the load-side current A2 when a current pulse is generated in the simulation test configuration as in FIG. 4 .
6 is an enlarged waveform of FIG.
7 shows voltage fluctuations when a current impulse signal is generated in a real system.
8 shows the power supply side and the load side current when a current impulse signal is generated in the real system.
9 illustrates the reverse current flow direction due to voltage drop in the same configuration as in FIG. 2
10 is a waveform comparison of impulse currents generated from high-voltage lines and low-voltage lines;
11 illustrates an example of an actual high-voltage system for distribution.
12 is a view showing an area to be explored in FIG. 11;
13 shows the work sequence for the exploration area.
14 illustrates the operation of the probe current signal generator connection transformer.
15 is a result of detecting a probe signal from a high-voltage line terminal in the FIG. 14 transformer.
Fig. 16 is a waveform view of the power-side transformer and switchgear measured with respect to the transformer (load) of Fig. 14;
Fig. 17 shows the work sequence for identifying the buried path after identifying the device (transformer, switchgear) connection configuration
18 shows the change of the waveform according to the direction of exploration when figuring out the buried path on the ground.

The example of the present application describes the case of using the public distribution network of the Republic of Korea as an example, and as shown in FIG. 1 , the public distribution network has two constant voltage networks, a high voltage network and a low voltage network, and the two networks are transformed into a transformer. are connected by magnetic field coupling. The primary winding of the transformer is connected to the high voltage network and the voltage is 22,900V, and the secondary winding is connected to the low voltage network and the voltage is 380V. Accordingly, the transformer ratio turns ratio is 60:1, and the polarized winding with the same phase of the primary and secondary voltages is standard.

If a transmitter is connected to one point of the low-voltage line as in [Fig. 1] to explore the high-voltage line and a current pulse signal is generated, the current impulse signal for exploration flows through the low-voltage line and the transformer to the high-voltage line, making it difficult to distinguish during exploration work.

In order to solve this problem, in the previous technology, the high-voltage line was probed by generating a current impulse signal by directly connecting it to the secondary terminal of the transformer without going through the low-voltage line as shown in FIG. 2 .

[Figure 3] shows the voltage and current waveforms when a transmitter with a large current impulse signal generation capacity of several hundred A is connected (connection point) to one point of a low voltage line as in [Figure 1], especially depending on the presence or absence of a load connected in parallel to the transmitter connection point The test configuration for observing the change of

[Fig. 4] is a waveform comparing the power-side current (A1) and the load-side current (A2) with the voltage (V) when the transmitter generates a current impulse signal when operating (connecting) or not (disconnecting) the parallel-connected heater load at the connection point. is showing

That is, it can be seen that when a current impulse signal is generated when there is no load, the load-side current A2 shows a minute change.

The underground cable used in the actual public distribution network has a structure that must have a line capacity component because of its high voltage density compared to the cable cross-sectional area.

In the test configuration of {FIG. 3], when a heater is connected through a 2 m long lead wire, the change of current is shown in [Fig. 4] and [Fig. It can be reasonably expected that the capacitive components of underground cables with a length of ~ several km may be affected or affected by the occurrence of current pulses.

In addition, the voltage drop V drop occurs at the time when the current pulse is generated, and the power supply voltage V continues to maintain the low voltage once lowered until the current ends. That is, it can be seen that when a large current is supplied through a low voltage line, a voltage drop occurs due to the line impedance, and thus the magnitude of the current impulse signal is limited by the low voltage.

[Fig. 6] shows a voltage waveform when a current impulse signal is generated by directly connecting a transmitter to a transformer without going through a low voltage line as in [Fig. 2]. Unlike the voltage waveform shown in Fig. 4 above, an instantaneous voltage drop occurs for a short moment, but immediately returns to the normal voltage and thereafter, the voltage drop does not occur. However, it can be seen that the voltage fluctuation occurs again when the switch is turned off, resulting in a surge voltage much higher than the normal voltage.

That is, when a current impulse signal is generated by directly connecting a transmitter to a transformer, there is no voltage drop due to line loss, so a large current pulse signal can be generated, but a momentary voltage fluctuation occurs severely when the switch is on/off.

[Fig. 7] shows the current supplied when the impulse current flow starts by turning on the semiconductor switch of the transmitter. [Fig. 7a] shows the flow of current in the direction of the transformer winding, which is the power source side of the transmitter connection point, compared with the voltage waveform, and [Fig. 7b] shows the flow of current in the load direction of the low voltage line, which is the load side of the transmitter connection point, compared with the voltage waveform. have. The current flow polarity of the two waveforms is opposite, and it can be seen that the current flowing in from the load side of the low voltage line in [Fig. 7b] is small, but moves faster in the direction of the transmitter than the current supplied from the transformer winding

[Fig. 8] shows that when the transmitter is directly connected to the transformer and generates a current impulse signal as shown in [Fig. 7], all current signals are generated in the direction of the transmitter, but the movement speed is higher than the voltage charged in the low voltage line is higher than the voltage supplied by the transformer. It can be seen that it is sent back faster and fed to the transmitter.

And similarly to the generation of a current impulse signal by connecting the transmitter at the load side connection point of the low voltage line as in [Fig. 1], even if the current impulse is generated by connecting the transmitter as in [Fig. 2] without going through the low voltage line, the low voltage line Current flow is occurring. Also, both current flow directions are towards the transformer (transformer input direction), so the polarity is opposite.

However, if it is difficult to install the transmitter as in [Fig. 1] in a place where access to the load installation site of the low-voltage line is restricted by using this phenomenon inversely, or where there is a disconnection in the middle due to the occurrence of a short circuit in the low-voltage line, as shown in [Fig. A current pulse is generated by connecting a transmitter to a power source, and a path can be traced by detecting a magnetic field signal generated when the charging current of the low voltage line moves.

In addition, when grasping the rough route of the low-voltage line, it is possible to explore the schematic burial location or connection configuration without visiting the low-voltage line load (customer equipment) every day.

[Fig. 9] compares the magnitude of the current pulse signal generated almost simultaneously in the high-voltage cable and the low-voltage cable. [Fig. 9a] shows a magnetic field signal received around a high-voltage cable compared with a voltage waveform, and [Fig. 9b] is a comparison of a voltage waveform with a magnetic field signal received around a low-voltage cable. That is, the current flowing in the high-voltage cable reduces the current impulse signal generated in the low-voltage network as much as the transformation ratio, but the current flowing in the low-voltage cable has no conversion loss, so it can be seen that the magnitude is more than twice that of the magnetic field signal detected in the high-voltage cable.

[Fig. 10] is an enlarged view of the received magnetic field signal waveform of [Fig. 9]. As described above, it can be seen that the signal detected from the high-voltage line is much smaller than the signal from the low-voltage line. For reference, the current flowing in the low voltage line is attenuated by 1/60 due to the transformer ratio and flows through the high voltage line. That is, 1A high-voltage line current is 60A low-voltage line current. For this reason, the magnetic field signal generated from the low-voltage line has a much larger amplitude than the magnetic field signal from the high-voltage line.

[Fig. 11] shows the magnetic field signals emitted from the high-voltage line and the low-voltage line at the same location where the low-voltage line and the high-voltage line are installed in the same path and compared with the voltage waveform. In [Fig. 11a], it can be seen that the low-voltage line current flows slightly ahead of the high-voltage line current. In [Fig. 11b], the polarities of the current impulse signals flowing through the low-voltage line and the high-voltage line are opposite, and the rising rate (di/dt) is faster in the low-voltage line. can be reconfirmed that

[Fig. 12] shows a configuration example of an underground high-voltage network. There are two switchgear (SW1, SW2) on both sides, and terminal 3 of switch 2 (SW2), which is one of them, is closed (Normal Close) to supply the high voltage network voltage to three series-connected transformers (TR3, TR2, TR1). supply power with Terminal 2 of switch 1 (SW1) is normally open so that power can be supplied in case of emergency without supplying power.

Accordingly, the high-voltage power is supplied to SW2 terminal 3 -> TR3 HB-> TR3 HA-> TR2 HB-> TR2 HA-> TR1 HB, and TR1 HA->SW1 terminal 2 is pressurized, but no current flows. For reference, M between the 3rd terminal of SW2 and the HB terminal of TR3 indicates a manhole.

Previously, the power was tracked by grasping the polarity (current flow direction) of the magnetic field signal. If it is assumed that the high-voltage line exploration target is switch 2 (SW2) and transformer 3 (TR3), the section highlighted by the dotted line should be explored.

[Fig. 14] explains how to determine the current flow direction (polarity) when generating a current impulse by connecting the transmitter to the load-side connection point of the low-voltage line as in [Fig. 1]

That is, when the transmitter is connected to the low-voltage line connected to the L1 terminal, the current of the low-voltage line connected to L1 is in the direction out of the transformer as shown in [Fig. 21], so it has a negative polarity. Since current flows into terminal HB, it has a (+) polarity, and the high-voltage line and low-voltage line have opposite polarities.

In addition, as shown in [Fig. 18], the high-voltage terminal HA is on the load side of the high-voltage line rather than the transmitter installation point TR3, so no current is generated.

In this way, the polarity of the current flowing in HA, HB, and L1 was different or not detected, so the paths of the high-voltage line and the low-voltage line could be clearly traced.

Of course, as described in [Fig. 11] to [Fig. 13] above, the speed (di/dt) or current size of the current flowing in the high-voltage line and the low-voltage line is added to the polarity comparison as shown in the drawing, and the characteristics of the waveform are compared. can improve accuracy

[Fig. 15] explains the direction of current flow when the transmitter has a connection point to the transformer and generates a current impulse signal as in [Fig. 8]. As the low voltage power supply is external (line charging power), an instantaneous current flows in the L1 direction of the transformer, and the current in the high voltage line flows in the same direction as the current from SW2 to HB.

In such a place, it is possible to distinguish high-voltage lines and low-voltage lines by comparing other characteristics as in [Fig. 11] to [Fig. 13], which are not polarized. If they are buried in the same direction or high and low voltage power lines are buried in the same common area at the same time, there may be a problem that they cannot be clearly distinguished from the ground with a distance.

[Fig. 16] shows that when the high-voltage line section from the transformer (TR) 3 to the switchgear 2 is to be explored, the transmitter is moved to the load side of the high-voltage line, not the transformer belonging to the probe, and installed in a transformer other than the exploration section.

As described above, the transmitter was connected to the transformer (TR) 3, the starting point of the exploration target, and the high-voltage line was probed. will be needed

In other words, by installing the transmitter in transformer (TR)2 or transformer (TR)1, not in the area to be explored, the voltage of the low-voltage network in the area to be explored is not affected, so that unnecessary low-voltage line current flow does not occur, so only the desired high-voltage line exploration becomes possible

If it is necessary to explore the high-voltage line from Transformer (TR) 1 to Switchgear 1, which is the no-load section in the section to be explored, change the load from switch 2 to switch 1, then take measures so that the power is supplied from switch 1, and now reverse the transformer. If the transmitter is connected and probed in transformer 2 or 3 on the load side of 1, as described above, only high-voltage lines can be probed without the influence of low-voltage lines.

Underground power line burial path exploration should be able to accurately detect magnetic field signals and determine polarity without being affected by other noise signals on the ground with a distance from the underground power line. Accordingly, in order to minimize the effect of the transmitter, 1. Steps to identify the device connection configuration from the transmitter installation point, which is the high voltage final load, to the high voltage final power source (tracing the connection part (connection terminal) of the high voltage line from the final load to the final power source), 2. Transmitter A method of exploring a buried path on the ground is presented by moving from a place far away from (i.e., final power) to the direction of the final load where the transmitter is located.

Accordingly, the work sequence is largely divided into two steps: the step of grasping the final power source within the exploration target by grasping the high-voltage line connection part (connection terminal), and the step of recognizing the burial route by moving in the direction of the transmitter in the reverse direction.

To further subdivide this, the step of identifying the final power source is (1) the step of connecting the transmitter to a transformer located on the load side of the high-voltage network more than the transformer of the section to be explored, (2) the high-voltage line of nearby high-voltage equipment (transformers, switchgear, etc.) Detecting the probe signal transmitted by the transmitter at the connection part (elbow) (3) Continuing to detect the signal up to the connection terminal (elbow) of the final power source (switch) within the probe to identify the system that supplies power to the transmitter connection point;

The step of identifying the buried path on the ground from the final power source position to the transmitter position (or the location of the device to be explored) is (4) installing a reverse current limiter in the section to be explored (for example, between transformer 3 and switchgear 2). Step (5) It moves along the path and if there is a structure such as a manhole, goes inside and traces the high-voltage line, (6) moves along the path and finds the buried path to the device where the transmitter is installed (or the final load-end device to be explored) may include the steps of

In addition, when searching for a buried path, a probe signal is transmitted on one of the three-phase power lines, and during exploration, it may be affected by the buried position of the power line (depth and direction of the ground for each phase of the power line). change and explore.

[FIG. 17] explains the contents of the operation in the transformer (eg, transformer 2) to which the transmitter is to be installed. Since it is a device that instantaneously generates a large current, check whether the transformer is abnormal by conducting a basic investigation including voltage and appearance. If it is determined that there is no abnormality, connect the transmitter and turn on and set the receiver BT that can display the waveform information by receiving the magnetic field signal. When the transmitter generates a current pulse, the high-voltage cable connector (elbow)-elbow does not include the sheath wire, and the cable-cable includes the sheath wire and current flows (refer to the magnetic field signal when searching for a path) Waveforms, etc. are analyzed and saved

[Fig. 18] shows the waveforms received from the high-voltage line elbow terminals HA and HB in the transformer in which the transmitter is installed as in [Fig. 17]. That is, it can be seen that the high voltage power supply of the corresponding transformer is connected to HB.

In this way, the transmitter generates a current impulse signal at low voltage, passes through the transformer, stores the waveform information detected at the high voltage connector (elbow) and the cable, and moves to the next device (switchgear or transformer).

[Fig. 19] is a waveform obtained by measuring a signal at the high-voltage line connection terminal (elbow) in the transformer 3, which is the power-side device, in the transformer to which the transmitter is connected. You can see that HA is connected to the load side transformer and HB is connected to the power side.

[Fig. 20] shows the operation sequence for the exploration of the buried path of the high-voltage line between both ends of the device to be explored after determining the final power source within the exploration section by grasping the device connection terminal (elbow). It is recommended to follow the buried path in the direction of power->load, which is far from the transmitter, and follow the path, but that does not mean that it cannot be searched while moving in the reverse direction of load->power.

[Fig. 21] is an example of a magnetic field signal waveform detected on the ground during path exploration. Depending on the direction of the magnetic field sensor coil, the direction of the load or power supply side can be detected.

[Fig. 22] shows a Rogowski coil-type magnetic field sensor used to detect a probe current signal from a high-voltage terminal (elbow) inside the device and a magnetic field sensor in which a plurality of ferrite coils are connected in parallel to explore a buried path on the ground. have.

When exploring the high-voltage terminals inside the device, a loop ring-type Rogowski-type magnetic field sensor that is not affected by the surrounding magnetic field is used to track and identify the high-voltage line power. explore At this time, if the signal is weak due to the influence of the burial depth or other signals, the magnetic field reception sensitivity can be improved by intensively stacking a plurality of ferrite magnetic field sensors and connecting the outputs in parallel.

As above, if the current impulse signal generator is installed on a transformer located on the load side more than the high-voltage line to be probed, the influence of the low-voltage line can be minimized. However, it will be possible to find more effective and accurate high-voltage cable exploration by understanding the buried path of high-voltage cables connecting the identified devices.

Claims (3)

A method for constructing a high-voltage network connection of a public power distribution network and exploring the burial route,
identifying the final load transformer in the high-voltage network section to be explored;
having a transmitter connection point to the transformer;
connecting a transmitter to the connection point;
Receiving the current signal waveform transmitted by the transmitter to determine the power-side connection terminal;
Steps to determine the final power device terminal by identifying the connection terminal on the next power device:
Moving from the final power source to the transmitter installation site and determining the burial path;
High-voltage cable buried path exploration method comprising the in claim 1 above
High-voltage cable buried path exploration method, characterized in that the step of setting the connection point of the transmitter to a high-voltage network load transformer other than the exploration target can be added In claim 1,
High-voltage cable buried path exploration method, characterized in that the installation of a reverse current suppressor can be added to the sheath of the high-voltage cable connected between the two devices

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