Clay core wall type dam stabilizing system based on electroosmosis pulse

Abstract

The utility model discloses a clay core wall type dam stabilizing system based on electroosmosis pulses. A core wall is arranged in a dam body of a clay core wall type dam; a plurality of pairs of electrodes are arranged between the core wall and the upstream face of the dam in the length direction of the dam; after electroosmosis pulses are applied to the electrodes, an anti-seepage electric field is formed between the core wall and the upstream face, so that an intangible anti-seepage wall is formed, water is prevented from leaking to the dam and the outer side of the dam, and the stability of the dam is facilitated. The stability of the dam is improved.

Description

Technical Field

[0001] The utility model relates to a clay core wall type dam stabilization system based on electroosmotic pulse. Background Art

[0002] A clay core dam is an earth-rock dam that uses a low-permeability clay mass at the center of the dam body as a seepage control device. This type of dam features a core wall or a sloping core wall for seepage control. The upstream and downstream dam shells support the core wall to maintain dam stability. Drainage prisms are installed at the downstream dam foot to protect the foot from scour. The drainage prisms also ensure that water seeping out of the dam is clear.

[0003] The key to the stability of this type of dam is to keep the core wall functioning properly.

[0004] A conventional clay core rockfill dam includes a dam foundation, a concrete cover slab, an anti-seepage curtain, a clay core, an upstream filter layer, an upstream transition layer, an upstream rockfill area, an upstream rock retaining wall, an upstream slag backfill area, a downstream filter layer, a downstream transition layer, a downstream rockfill area, a downstream rock retaining wall, a downstream slag backfill area, a horizontal cushion layer, a dam crest road, and a wave-breaking wall on the upstream side of the dam crest road. The clay core anti-seepage soil material quality requirements generally require a liquid limit of less than 40%, a plasticity index of 10-20, and a clay content of 15-40% to meet existing specifications.

[0005] To achieve the stability of clay core dams, it is not only necessary to optimize the design of the dam structure, but also necessary to comprehensively consider other aspects (such as suppressing seepage) to further enhance the stability of the dam.

[0006] Chinese patent publication number 217384618U discloses a flood embankment monitoring and anti-seepage system based on electroosmotic pulses. Positive and negative electrodes are inserted into the embankment to maintain the water content of the embankment within a certain range, preventing it from being too high or too low. This has a certain effect on solving the problem of high-water level flooding invading the rammed earth dam, causing dam failure or piping. However, due to the large distance between the positive and negative electrodes and the limited voltage used (generally not exceeding the safe voltage of 36V), this solution is not very effective in preventing water molecule leakage.

[0007] Therefore, it is necessary to design a new system and method for stabilizing clay core dams. Utility Model Content

[0008] The technical problem to be solved by the utility model is to provide a clay core wall type dam stabilization system based on electroosmotic pulses, which can realize the detection of the dam slope status and the implementation of active stabilization measures.

[0009] The technical solutions of the utility model are as follows:

[0010] A clay core dam stabilization system based on electroosmotic pulses, wherein a core wall is provided in the dam body of the clay core dam; multiple pairs of electrodes are arranged between the core wall and the water-facing surface of the dam along the length direction of the dam;

[0011] The dam is equipped with pulse generators. The system also includes a data acquisition terminal (MCU) for collecting current data flowing through each positive and negative electrode and feeding it back to a control center. The pulse generators emit electroosmotic pulses through electrodes inserted into the base of the dam. The system also includes a control center, which is connected to the N pulse generators via a CAN bus. The control center can be an industrial computer or a master control device based on a DSP or PLC, also known as a host.

[0012] After the pulse generator applies electroosmotic pulses to the electrodes, an anti-seepage electric field is formed between the core wall and the water-facing surface, thus forming an invisible anti-seepage wall, preventing water from leaking into the dam and outside the dam, which is beneficial to the stability of the dam.

[0013] Each pair of electrodes includes a positive rod and a negative rod, and the distance between the positive rod and the negative rod is within 2 meters (taking the electroosmotic pulse output voltage level of 36V and below as an example).

[0014] Multiple pairs of electrodes are divided into K groups; K is an integer, K≥3; each group of electrodes includes at least 3 pairs of electrodes; a pulse generator is used to implement group control on the K groups of electrodes (to avoid excessively long wiring and to facilitate zoning management and control).

[0015] Multiple electrodes are also arranged on the upstream slope.

[0016] The multiple electrodes are arranged as follows: the water-facing slope of the dam is divided into M rows and N columns of grid areas; M ≥ 3, N ≥ 3; at least one set of positive and negative electrodes is set in each grid area; the positive and negative electrodes are vertically inserted into the water-facing slope of the dam; the positive and negative electrodes are connected to a pulse generator; the pulse generator is controlled by the control center. The dam protection system also includes a data acquisition terminal (MCU data processing unit) for collecting current data flowing through each positive and negative electrode and feeding it back to the control center.

[0017] The length of the overlapping portion of the positive and negative electrodes in adjacent columns is L; L is 30-100 cm, preferably 50 cm.

[0018] The bottom ends of the positive and negative electrodes in each set of positive and negative electrodes are aligned;

[0019] Different rows of grid areas use different pulse voltage levels. Grid areas with greater depth (i.e., the number of rows or lines, counting from top to bottom) have higher pulse voltage levels than those with less depth. The higher the water pressure, the higher the voltage. The maximum voltage is no more than 36V, and the minimum is 12V. Intermediate voltages can be 24V, or other voltages, such as 16V.

[0020] The area of ​​the grid zone shall not exceed 50 square meters.

[0021] A clay core dam stabilization method based on electroosmotic pulses adopts the aforementioned clay core dam stabilization system to form an anti-seepage layer between the core wall and the water-facing slope of the dam, which can be called a reverse anti-seepage layer or an invisible anti-seepage wall to prevent excessive water from entering the dam body (keeping the water content of the dam body medium within a stable range), thereby ensuring the stability of the dam body.

[0022] A pulse generator is installed on the dam; the pulse generator is connected to the electrodes; in each electrode, the negative electrode is on the side close to the water body (the water-facing side), and the positive electrode is on the side away from the water body (the water-facing side);

[0023] The pulse output of each grid area is controlled in a timed sequence; for example, during time t1, only the first column of grid areas outputs pulses; during time t2, only the second column of grid areas outputs pulses; and during time t3, only the third column of grid areas outputs pulses. This controls the orderly movement of water within the dam body under the influence of electroosmotic forces, thereby ensuring a stable moisture content in the dam body and ensuring its safety. T1-t3 can be any value between 1 and 100 seconds.

[0024] Each pulse generating unit is connected to multiple positive electrodes and multiple negative electrodes. In the pulse generating unit, the MCU serves as the main control unit. The MCU controls the pulse generator through a pulse drive circuit to generate a pulse signal with a preset frequency, duty cycle, and voltage value. A first current sampling resistor is provided on the wire connecting the pulse generator to each positive electrode; a second current sampling resistor is provided on the wire connecting the pulse generator to each negative electrode. The voltage sampling signals generated by the first current sampling resistor and the second current sampling resistor respectively pass through their corresponding amplification circuits and A / D conversion circuits and then enter the MCU to complete data collection.

[0025] Different working units in different rows use different voltages. The pulse frequency is generally 4Hz, and the frequency range is:

[0026] 2-10Hz.

[0027] The system is usually activated in advance before a flood arrives.

[0028] The dam protection system also includes a bus, and a plurality of pulse generating units are mounted on the bus. The pulse generating units include a pulse generator for generating a pulse sequence and electrodes, and the electrodes include a positive electrode and a negative electrode. The electrodes are arranged on the dam slope.

[0029] The pulse sequence of each cycle consists of three parts: a positive pulse segment (positive voltage pulse), a negative pulse segment (negative voltage pulse) and a pause segment (zero voltage pulse); among them: the positive pulse prompts the cations and the water molecules bound to them to move from the anode side to the cathode side, which is opposite to the direction induced by the water gradient, preventing water from penetrating into the dam; the negative voltage pulse allows a certain amount of water to be controlled in the dam as an electroosmotic medium to avoid excessive drying of the dam body; the pause segment provides sufficient response time for the effects of the positive and negative pulses, allowing the system to reach a new equilibrium state.

[0030] The pulse generating unit applies electroosmotic pulses to electrodes arranged in the dam slope, so that the water content in the dam medium is stabilized, thereby keeping the dam body in an optimal stable state.

[0031] It also includes an IoT platform and a monitoring center. The monitoring center communicates with the IoT platform and is mounted on the bus. The monitoring center and IoT platform communicate via the MQTT mechanism. MQTT (Message Queuing Telemetry Transport) refers to message queue telemetry transport.

[0032] The bus is a CAN bus.

[0033] Each pulse generating unit is connected to a plurality of positive electrodes and a plurality of negative electrodes.

[0034] In the pulse generating unit, the MCU serves as the main control unit. The MCU controls the pulse generator through the pulse driving circuit to generate a pulse signal with a preset frequency, duty cycle and voltage value. A first current sampling resistor is provided on the wire connected to each positive electrode of the pulse generator; a second current sampling resistor is provided on the wire connected to each negative electrode of the pulse generator.

[0035] The voltage sampling signals generated on the first current sampling resistor and the second current sampling resistor respectively pass through their corresponding amplifying circuits and A / D conversion circuits and then enter the MCU to complete data collection.

[0036] MCU data conversion mainly converts the analog signal into binary format, and then digitally filters, classifies, stores, and encodes it into the CAN communication protocol format and sends it to the bus through the CAN controller.

[0037] An alarm is installed at the monitoring center or pulse generating unit.

[0038] The negative electrode is a negative electrode rod, and the positive electrode is a zinc tube positive electrode; the negative electrode net or negative electrode rod is laid along the slope surface where the dam contacts the water body; the zinc tube positive electrode is inserted into the structure of the dam (that is, the natural soil of the dam itself), and the pulse generator is laid on the dam.

[0039] The current data collected by the pulse generating unit at the dam site is used to determine the water content of the dam slope, thus realizing the status monitoring of the dam slope.

[0040] When the current exceeds a preset value, the duty cycle of the electroosmotic pulse increases to reduce the moisture content of the dam slope and achieve active stabilization. When the moisture content exceeds 20%, the positive pulse width increases by 5 milliseconds every six hours, while the negative pulse decreases by 2 milliseconds. This continues until the moisture content drops by 20%. At this point, the positive pulse width decreases by 5 milliseconds every six hours, while the negative pulse increases by 2 milliseconds, to maintain a stable moisture content. Electroosmotic pulse parameter settings range: positive pulse width 100-200ms, negative pulse width 5-150ms, and frequency 3 to 5Hz.

[0041] If the current is higher than the preset alarm value, the monitoring center or pulse generating unit will trigger an alarm, such as sound and light alarm, telephone alarm, etc.

[0042] The principle of electroosmotic pulse to stabilize the dam:

[0043] The pulse sequence consists of three parts: a positive pulse segment (positive voltage pulse), a negative pulse segment (negative voltage pulse), and a pause segment (zero voltage pulse). The positive pulse causes the cations and their bound water molecules to move from the anode side to the cathode side, in the opposite direction of the water gradient, preventing water from penetrating the dam. As the hydrated cations form a double layer along the capillary wall, polarization leads to a reduction in flow. The negative voltage pulse allows a certain amount of water to be controlled in the dam medium to avoid excessive drying of the dam body. Under the action of the electroosmotic pulse, a polarization effect is produced on the water molecules: hydrogen gathers into a polarized cathode, and hydroxyl groups gather into a polarized anode. The high-speed moving cations and anions floating in the capillary fluid between the double layers will reverse, and the anode will become the cathode and the cathode will become the anode.

[0044] The positive voltage pulse has the longest pulse time and the signal amplitude is usually between 12 V and 36 V DC. The use of a bipolar pulse waveform can prevent the dam medium from over-drying and losing its structural integrity.

[0045] One of the most critical aspects of this technology is the negative voltage pulse. This allows the moisture content within the dike medium to be controlled, preventing excessive drying and subsequent degradation of the electroosmotic medium. The anode is inserted into the structure, while the cathode is placed directly in the soil outside. The positive and negative pulses trigger chemical reactions during the electrolysis process. Meanwhile, a rest period (no voltage applied) allows the system to reach equilibrium.

[0046] Beneficial effects:

[0047] The clay core dam stabilization system based on electroosmotic pulse of the utility model has the following characteristics:

[0048] First, a pre-installed anti-seepage barrier based on a multi-electrode arrangement was installed on the waterfront. Due to the large span of the earth dam slope and the limited range of electroosmosis, multiple electrodes were required. By switching circuits, water seepage was controlled in a single direction, ensuring a stable water content in the dam. Multiple sets of corresponding positive and negative electrodes were buried along the waterfront slope of the dam, with their bases aligned and preferably within two meters of each other. Starting from the dam crest, the top of the next positive electrode should be approximately 50 centimeters away from the bottom of the next negative electrode, and so on all the way to the dam base. Along the lateral extension or natural course of the dam, the positive and negative electrode control areas were divided into independent groups, each no larger than 50 square meters. Based on the varying flood heights, different voltages were applied from the dam crest to the dam base to counteract varying water pressures. As the flood receded, the voltage could be gradually adjusted based on the varying water levels. The system was fully operational three months before the flood.

[0049] In addition, on the dam, anti-seepage facilities based on multiple pairs of electroosmotic electrodes are installed between the core wall and the water-facing surface to form a second anti-seepage barrier;

[0050] The utility model fully utilizes the basic principle of electroosmotic pulse, and monitors the moisture content and its changing trend in the clay core wall dam in real time through electric current. It can not only implement early warning, but also, by adjusting the pulse parameters, implement active prevention and control for the dam slope. It is low in cost and easy to deploy, and has significant economic benefits (cost advantages) and social benefits.

[0051] The core of this utility model is to set up a double-layer anti-seepage barrier (one is to use multiple electrodes to form a continuous electric field in the water-facing slope of the dam, thereby forming a continuous leakage blocking layer; the other is an anti-seepage electrode located inside the dam), which effectively prevents water molecules from leaking into the dam body, thereby achieving the goal of stabilizing the dam body. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 This is a schematic diagram of the layout of the clay core dam stabilization system based on electroosmotic pulses of the present invention (vertical cross-sectional view, without multiple electrodes on the water-facing surface);

[0053] Figure 2 This is a schematic diagram of the layout of the clay core dam stabilization system based on electroosmotic pulses of the present invention (top view, without multiple electrodes on the water-facing surface);

[0054] Figure 3 This is a schematic diagram of the layout of the clay core dam stabilization system based on electroosmotic pulses of the present invention (top view, with multiple electrodes arranged on the water-facing surface);

[0055] Figure 4 is a schematic diagram of electrode group arrangement;

[0056] Figure 5 It is the control circuit block diagram;

[0057] Figure 6 It is a schematic diagram of the arrangement of electrodes on the water-facing surface;

[0058] Figure 7 It is the electrical control block diagram;

[0059] Figure 8 Schematic diagram of the positive electrode rod structure (main cross-sectional view);

[0060] Figure 9 This is the overall block diagram of the electroosmotic pulse system;

[0061] Figure 10 Schematic diagram of data acquisition in the electroosmotic pulse system;

[0062] Figure 11 Schematic diagram of the pulse generating unit;

[0063] Figure 12 It is a pulse waveform diagram.

[0064] Explanation of numbers: 1-dam body, 2-core wall, 3-positive electrode, 4-anti-seepage electric field, 5-negative electrode, 6-copper core wire, 7-conductive PE layer, 8-conductive mortar, 9-zinc pipe, 10-pointed cone; 11-water-facing surface, 12-water body, 13-sub-control area, 13-multiple electrodes. DETAILED DESCRIPTION

[0065] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0066] Example 1: Figure 1 A clay-core dam stabilization system based on electroosmotic pulses is described. A clay-core dam has a core wall within its dam body. Multiple pairs of electrodes are positioned along the length of the dam, between the core wall and the water-facing surface. Applying electroosmotic pulses to the electrodes creates an anti-seepage electric field between the core wall and the water-facing surface. This field effectively inhibits water molecules from leaking through the dam body to the rear (backward) side, thereby stabilizing the dam. Each pair of electrodes consists of a positive and a negative rod, with the positive and negative rods spaced within two meters (assuming an electroosmotic pulse output voltage level of 36V or less).

[0067] like Figure 2 , multiple pairs of electrodes are divided into 3 groups; each group of electrodes includes 3 pairs of electrodes; a pulse generator is used to implement group control of the 3 groups of electrodes (to avoid long wiring and to facilitate zoning management and control.).

[0068] The system also includes a control center, multiple pulse generators, and multiple sets of positive and negative electrodes; (Multiple electrode layout refers to the layout of multiple sets of positive and negative electrodes in a gradient manner;)

[0069] Multiple electrodes are also arranged on the upstream slope, such as Figure 4 The water-facing slope of the dam is divided into 9 grid areas in 3 rows and 3 columns; 3 groups of positive and negative electrodes are set in each grid area; the positive and negative electrodes are vertically inserted in the water-facing slope of the dam; the positive and negative electrodes are connected to the pulse generator; and the pulse generator is controlled by the control center.

[0070] When the pulse voltage adopts a voltage level of 36V or below, the distance between the positive and negative poles in each group of positive and negative poles shall be within 2 meters.

[0071] The length of the overlapping portion of the positive and negative electrodes of adjacent columns is L; L is 50 cm.

[0072] The bottom ends of the positive and negative electrodes in each set of positive and negative electrodes are aligned.

[0073] Different rows of grid areas use different pulse voltage levels. The pulse voltage level of the grid area with a large depth (i.e. the number of rows or rows, counted from top to bottom) is higher than that of the grid area with a small depth. The higher the water pressure, the higher the voltage. The voltages of rows 1 to 3 are 12V, 24V and 36V respectively. The different voltage levels are determined by Figure 3 The first driving circuit, the second driving circuit and the third driving circuit are provided respectively.

[0074] The area of ​​the grid zone shall not exceed 50 square meters.

[0075] The pulse output of each grid area is controlled in a timed sequence; for example, during time t1, only the first column of grid areas outputs pulses, during time t2, only the second column of grid areas outputs pulses, and during time t3, only the third column of grid areas outputs pulses. T1 (or t2, t3) can be a value between 1 and 100 seconds. The time cycle is repeated, controlling the orderly movement of water within the dam body under the influence of electroosmotic forces. This ensures a stable moisture content in the dam body and ensures its safety.

[0076] Each pulse generating unit is connected to multiple positive electrodes and multiple negative electrodes. In the pulse generating unit, the MCU serves as the main control unit. The MCU controls the pulse generator through a pulse drive circuit to generate a pulse signal with a preset frequency, duty cycle, and voltage value. A first current sampling resistor is provided on the wire connecting the pulse generator to each positive electrode; a second current sampling resistor is provided on the wire connecting the pulse generator to each negative electrode. The voltage sampling signals generated by the first current sampling resistor and the second current sampling resistor respectively pass through their corresponding amplification circuits and A / D conversion circuits and then enter the MCU to complete data collection.

[0077] A clay core dam stabilization method based on electroosmotic pulses adopts the aforementioned dam protection system to implement active protection of the dam.

[0078] In this system, the pulse frequency is 4 Hz. The system is usually started in advance before the flood.

[0079] Furthermore, the monitoring center is communicatively connected to the plurality of pulse generating units;

[0080] Each pulse generating unit includes a pulse generator and a positive electrode and a negative electrode connected to the pulse generator, wherein the positive electrode and the negative electrode are both arranged on the clay core wall dam, and the pulse generating unit collects current data from the positive electrode and the negative electrode as a pulse generating unit; the pulse generator is used to generate electroosmotic pulses;

[0081] The monitoring center is used to collect the current data sampled by each pulse generating unit and process the data, thereby realizing the monitoring of the dam slope state and implementing active stability control of the dam slope based on the electroosmotic pulses.

[0082] It also includes an IoT platform, and the monitoring center communicates with the IoT platform via the MQTT (Message Queuing Telemetry Transport) mechanism.

[0083] The monitoring center is connected to multiple pulse generating units via CAN bus communication.

[0084] In the pulse generating unit, the MCU serves as the main control unit. The MCU controls the pulse generator through the pulse driving circuit to generate a pulse signal with a preset frequency, duty cycle and voltage value. A first current sampling resistor is provided on the wire connected to the positive electrode of the pulse generator; a second current sampling resistor is provided on the wire connected to the negative electrode of the pulse generator.

[0085] The voltage sampling signals generated on the first current sampling resistor and the second current sampling resistor respectively pass through their corresponding amplifying circuits and A / D conversion circuits and then enter the MCU to complete data collection.

[0086] MCU data conversion mainly converts the analog signal into binary format, and then digitally filters, classifies, stores, and encodes it into the CAN communication protocol format and sends it to the bus through the CAN controller.

[0087] An alarm is installed at the monitoring center or pulse generating unit.

[0088] The negative electrode is a negative electrode rod, and the positive electrode is a zinc tube positive electrode.

[0089] Specifically, the monitoring center uses a system screen, which is a touch screen with an embedded operating system. It is used to view the data status of various sites and the safety indicators of the dam. If necessary, relevant parameters can be set.

[0090] When the system is working, the current data collected by the pulse generating unit at the dam site is used to determine the water content of the dam slope, thereby realizing the status monitoring of the dam slope.

[0091] When the current is higher than the preset value, the duty cycle of the electroosmosis pulse is increased to reduce the water content of the dam slope and achieve active stabilization of the dam slope.

[0092] The specific control method is: when the moisture content exceeds 20%, the positive pulse width increases by 5 milliseconds every 6 hours, and the negative pulse decreases by 2 milliseconds, until the moisture content drops by 20%, the positive pulse width decreases by 5 milliseconds every 6 hours, and the negative pulse increases by 2 milliseconds to maintain the stability of the slope moisture content.

[0093] The electroosmotic pulse parameter setting range is: positive pulse width 100-200ms, negative pulse width 5-150ms, and frequency 3 to 5Hz.

[0094] If the current is higher than the preset alarm value, the monitoring center or pulse generating unit will trigger an alarm, such as sound and light alarm, telephone alarm, etc.

[0095] The structure of the rod-shaped electrode as the positive electrode is as follows Figure 4 As shown, the rod electrode's outer layer is constructed of a structurally strong zinc tube. This zinc tube is not only corrosion-resistant but also highly conductive. Through electroosmosis, it continuously provides cations, forming hydrated cations. The rod electrode's tapered tip facilitates easy penetration through soil and rock layers under applied pressure, facilitating burial within the embankment. Current transmission utilizes an inner copper wire, while the outer conductive PE layer conducts the positive current. The gap between the conductive PE and the zinc tube is filled with conductive mortar. This structure effectively ensures the strength of the far-end electroosmotic field, preventing attenuation. The conductive mortar filling ensures good contact between the conductive PE and the zinc tube. Heat shrink tubing can also be placed on the upper end of the rod electrode to prevent overflow of the conductive mortar.

[0096] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A clay core dam stabilization system based on electroosmotic pulse, characterized in that: A core wall is provided in the dam body of a clay core dam; multiple pairs of electrodes are provided along the length of the dam between the core wall and the water-facing surface of the dam; A pulse generator is installed on the dam; the system also includes a data acquisition terminal for collecting current data flowing through each positive and negative electrode and feeding it back to the control center.

2. The clay core dam stabilization system based on electroosmotic pulse according to claim 1, characterized in that: Each pair of electrodes includes a positive rod and a negative rod, and the distance between the positive rod and the negative rod is within 2 meters.

3. The clay core dam stabilization system based on electroosmotic pulse according to claim 1, characterized in that: The multiple pairs of electrodes are divided into K groups; K is an integer, K≥3; each group of electrodes includes at least 3 pairs of electrodes; a pulse generator is used to implement group control on the K groups of electrodes.

4. The clay core dam stabilization system based on electroosmotic pulse according to any one of claims 1 to 3, characterized in that: Multiple electrodes are also arranged on the upstream slope.

5. The clay core dam stabilization system based on electroosmotic pulse according to claim 4, characterized in that: The multiple electrodes are arranged in the following manner: the water-facing slope of the dam is divided into M rows and N columns of grid areas in a grid pattern; M ≥ 3, N ≥ 3; at least one set of positive and negative electrodes is set up in each grid area; the positive and negative electrodes are vertically inserted into the water-facing slope of the dam; the positive and negative electrodes are connected to a pulse generator; the pulse generator is controlled by a control center; the dam protection system also includes a data acquisition terminal for collecting current data flowing through each positive and negative electrode and feeding it back to the control center; The length of the overlapping part of the positive and negative electrodes of adjacent columns is L; The bottom ends of the positive and negative electrodes in each set of positive and negative electrodes are aligned; Different rows of grid areas use different pulse voltage levels. The pulse voltage level of the grid area with a larger depth is higher than that of the grid area with a smaller depth. The area of ​​the grid zone shall not exceed 50 square meters.

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