A monitoring method for the corrosion of tower grounding body and a remaining life assessment system

Abstract

The present invention proposes a monitoring method and remaining life evaluation system for the amount of corrosion of the pole tower grounding body, monitors the stray current entering the ground of the pole tower, and simultaneously implements the monitoring of the electric field in the ground. The background electric field in the ground is decoupled through the monitoring data of the current entering the ground of the pole tower grounding body and the electric field in the ground. From the perspective of the factors affecting the corrosion of the pole tower grounding body, a calculation method for the amount of corrosion caused by the current entering the ground and the electric field in the ground is proposed, and a remaining life calculation formula for flat steel and round steel conductors is proposed. The present invention effectively improves the timeliness of the monitoring of the amount of corrosion of the pole tower grounding body, overcomes the defects of the traditional grounding resistance measurement method, and provides a basic technical guarantee for the safe operation of the transmission line.

Description

Technical Field

[0001] The invention belongs to the field of electric power facility maintenance technology, and relates to a method for obtaining the corrosion amount of a tower grounding body. Background Art

[0002] The tower grounding body is a grid composed of interconnected metal structures located underground under the transmission line tower, which is used for safety protection and lightning protection. The grounding body is made of steel plates and steel pipes, some of which are galvanized. It is inevitable that they will be gradually corroded. It is necessary to detect the amount of corrosion and compare it according to the requirements of relevant standards to confirm whether it needs to be replaced. The causes of grounding body corrosion include pH value, moisture content, salt content, etc. The correlation between a single factor and the amount of corrosion is not strong, and the amount of corrosion cannot be well calculated. Stray current - refers to the abnormal current component found outside the design path, and the stray current of the low-frequency component with a frequency less than 5Hz. Among them, stray current with an amplitude greater than 0 flowing into the grounding body will cause electrolytic corrosion of the grounding body, while negative current is considered not to cause electrolytic corrosion of the grounding body. Ground electric field / background electric field - refers to the background electric field component that appears in the earth. In reality, it may be caused by factors such as geological environment and external interference, causing electrolytic corrosion at the anode position of the grounding body. During operation, the grounding bodies of transmission line towers are subject to the effects of unbalanced ground current, stray current of DC transmission projects, and the background electric field of the earth, which can easily cause electrolytic corrosion of metals. Once a breakpoint occurs in the line grounding body due to corrosion, the grounding performance will be greatly reduced, seriously endangering the safe operation of the transmission line. Since the tower grounding bodies are buried in the ground all year round, the corrosion status cannot be judged by non-excavation means. In addition, there are a large number of towers and the terrain environment in the area is harsh, so it is not possible to conduct large-scale excavation inspections on site.

[0003] Since it is currently impossible to directly monitor and evaluate the amount of corrosion on the line tower grounding body, it is often necessary to measure the line tower grounding resistance every 4 to 6 years on site to detect whether the tower grounding system meets the operating requirements. However, the sensitivity of the grounding resistance to the corrosion integrity and remaining life of the tower is low, so it is impossible to evaluate the amount of corrosion and remaining life of the grounding system. In addition, the tower grounding resistance measurement cycle is too long, resulting in poor timeliness of the measurement results, which poses a hidden danger to the safe operation of the transmission line. Summary of the invention

[0004] The invention aims to propose a method for monitoring the corrosion of a tower grounding body, obtain the relationship between the low-frequency stray current and the low-frequency electric field component in the ground and the corrosion amount, and propose a monitoring scheme.

[0005] Another object of the present invention is to provide a tower grounding body remaining life assessment system, which obtains the tower grounding body remaining life through measured ground current data and corrected geoelectric field background data.

[0006] The technical solution of the present invention is: a method for monitoring the corrosion amount of a tower grounding body, the first step is to measure the stray current entering the ground at the tower foot, and summarize the total stray current entering the ground on the tower grounding body I ( t ), filter the total stray current entering the ground and remove the AC unbalanced current entering the ground;

[0007] Step 2: Measure the electric field data in the ground. Measure the potential difference with a rectangular coordinate distance of 10 meters from point O to obtain the electric field components in the X and Y directions. Filter the electric field data in the ground to obtain the 0-5 Hz range component.

[0008] Step 3: Implement the correction of the ground electric field, separate the ground background electric field and the ground current electric field in the ground electric field, and obtain the ground background electric field E x0 ( t )and E y0 ( t );

[0009] Step 4, calculation of stray current corrosion:

[0010] On the branch road L j Stray current I s ( j,t k ) average corrosion depth h ( j ) is calculated by Faraday's electrolysis formula:

[0011] ,in, k For time t Number, time t k = k Δ T , Δ T is the time step of stray current measurement, D j For branch L j The cross-sectional perimeter of F A function is a positive function if and only if x >0 hours F ( x )= x ,otherwise F ( x )=0;

[0012] Step 5: Calculation of the amount of corrosion due to the background electric field in the ground:

[0013] Background electric field vector in the ground for: , calculate the projection positions of the starting and ending points of all grounding conductor branches on the background electric field lines in the ground, and let the grounding conductor branches L j The projection positions of the starting point and the end point of the ground on the background electric field line are e j1 and e j2 , take the maximum projection position of all conductor branches e jmax and minimum value e jmin , the electrochemical center potential coordinates of the ground body are e 0= e jmax + e jmin ;

[0014] Get all positive and negative grounding branches: If the starting and ending points of the branch cross the projected position e 0, then press e The 0 position divides the conductor branch into a positive part and a negative part;

[0015] If the starting and ending points of the branch are at the projected position e 0, the branch is positive;

[0016] If the starting and ending points of the branch are at the projected position e If it is below 0, the branch is negative;

[0017] Forming a positive branch collection L pi}, i = 1, 2, …, N ;

[0018] Forming a negative branch collection { L mi}, i = 1, 2, …, K ;

[0019] Calculate the amount of corrosion caused by the background electric field in the ground: Take out all the positive branches { L pi}, forming a ground conductor branch L pi The conductor pointing vector for: , ( x i1 , y i1 , z i1 )and(x i2 , y i2 , z i2 ) is the conductor set L i The two endpoints of

[0020] Calculation of ground conductor branches L pi Projection length on the field lines of the background electric field in the ground P ( i ):

[0021] ,

[0022] In the positive branch L pi The average daily corrosion depth caused by the background electric field in the ground h e ( i ):

[0023] , ρ is the equivalent earth resistivity;

[0024] Step 6, synthetic corrosion amount:

[0025] The stray current corrosion amount and the background electric field corrosion amount in the ground are superimposed:

[0026] The average corrosion depth of the positive electrode branch is H pi}, i = 1, 2, …, N ;

[0027] The average corrosion depth of the negative electrode branch is H mi}, i = 1, 2, …, K ;

[0028] The maximum daily average corrosion depth of the positive branch H pmax .

[0029] Preferably, the method for measuring the stray current entering the ground at the foot of the tower in step 1 is: installing open flexible stray current sensors at the four feet of the tower, which are respectively I 1( t ), I 2( t ), I 3( t ), I 4( t), , filtering obtains the current component in the range of 0 to 5 Hz.

[0030] Preferably, in step 2, the three-electrode method is used to measure the ground electric field data. Three platinum electrodes X, Y, and O are buried at a depth of 40 cm in the ground where the grounding body is located. The lines connecting X and O and the lines connecting Y and O form a vertical angle. The lengths between X and O and between Y and O are both 10 m. The measured value of the ground electric field is , ,in, E x ( t )and E y ( t ) are the electric field components in the X and Y directions, Δ x and Δ y are the potential differences between XO and YO respectively.

[0031] Preferably, in step 4, Δ T Select 0.1s.

[0032] A tower grounding body remaining life assessment system, wherein the input device inputs the aforementioned measurement data, and a processor with a computer program for implementing the calculation is used to execute the aforementioned method to calculate the maximum daily average corrosion depth. H pmax , calculate the remaining life of the grounding body based on 50% of the remaining cross-sectional area: For flat steel, take the cross-sectional width as w , the remaining life of the grounding body T d for For round steel, the cross-sectional radius is r , the remaining life of the ground conductor T d for .

[0033] The beneficial effects of the present invention: It solves the defect that the traditional on-site ground resistance detection method cannot evaluate the life of the grounding body, and greatly improves the timeliness of corrosion monitoring. A decoupling and correction method for the background electric field in the ground with respect to the external ground current is proposed, which effectively avoids the interference of stray current on the background electric field in the ground, and provides an effective means for solving the corrosion amount of the ground current and the corrosion amount of the natural background electric field. The comprehensive corrosion amount and remaining life of the grounding grid are evaluated by the measured ground current data and the corrected ground electric field background data, which improves the timeliness of corrosion monitoring and provides a basic method support for the development of subsequent monitoring systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the arrangement scheme of the flexible stray current sensor of the method of the present invention;

[0035] Figure 2 It is a schematic diagram of the method for measuring the electric field in the ground according to the present invention;

[0036] Figure 3 is a schematic diagram of the positions of the conductor segments of the method of the present invention;

[0037] Figure 4 It is a schematic diagram of the positions of the conductor branches and the observation points of the method of the present invention;

[0038] Figure 5 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0039] A monitoring method and life assessment system for the corrosion of a tower grounding body, the flow chart of the scheme is as follows: Figure 5 shown.

[0040] Specific technical solutions:

[0041] Step 1: Implement the monitoring of stray current from towers entering the ground:

[0042] Install open flexible stray current sensors at the four tower feet of the line tower (the installation scheme diagram is shown in the figure). Figure 1 As shown in the figure), the ground current on the four tower feet is obtained synchronously, and then the total ground stray current on the tower grounding body is obtained by summing up. I ( t );

[0043] Total stray current into the ground I ( t ) is calculated as: The ground stray current monitoring data may show AC unbalanced ground current, so it is necessary to remove the influence of this part of the AC unbalanced ground current component and filter the total ground stray current through a low-pass filter with a cutoff frequency of 5Hz to obtain the current component in the range of 0~5Hz.

[0044] Step 2: Monitor the ground electric field while monitoring the stray current entering the ground:

[0045] The three-electrode measurement method is used to monitor the electric field in the ground. The schematic diagram is shown in the figure. Figure 2 As shown;

[0046] The principle of measuring the electric field in the ground is to bury three platinum electrodes X, Y, and O at a depth of 40 cm in the ground. The length between X and O, and between Y and O are both 10 meters, and the line connecting X and O, and the line connecting Y and O form a vertical angle. The measured value of the electric field in the ground is , , in, E x ( t )andE y ( t ) are the electric field components in the X and Y directions, Δ x and Δ y are the potential differences between XO and YO respectively;

[0047] The ground electric field data is filtered through a low-pass filter with a cutoff frequency of 5 Hz to obtain the 0-5 Hz range component.

[0048] Step 3: Implement the correction of the geoelectric field to obtain the background electric field in the ground:

[0049] The electric field in the ground is generated by the superposition of the background electric field in the ground and the current entering the ground:

[0050] , in, E x0 ( t )and E y0 ( t ) are the background electric field components in the X and Y directions, E x1 ( t )and E y1 ( t ) are the electric field components of the ground current generated by the stray current of the tower grounding body, Δ x1 and Δ y1 are the potential differences between XO and YO generated by the ground current;

[0051] The ground current data is known, Δ x1 and Δ y1 The solution can be obtained by the following steps:

[0052] 3.1 Collect the data of the conductor segment of the grounding body and obtain M Straight conductor branch data { L 1, L 2, … L i , L j …, L M}.

[0053] 3.2 Conductor segment mutual impedance decoupling:

[0054] In the earth, L i and L j See the schematic diagram of the conductor segment location where the straight line grounding conductor branch data is located. Figure 3 .

[0055] make i ≠ j , L i and L j Mutual resistance of conductor segments R ( i , j )for:

[0056] ,in, R ( i,j ) is the conductor segment L i and L j The mutual resistance, dist function is the distance function, for L j Mirror image, ρ is the equivalent earth resistivity.

[0057] make i = j , L i Self-resistance R ( i, i )for:

[0058] ,

[0059] in, s is the equivalent radius of the grounding conductor, for L i Mirror image,

[0060] 3.3 Solution of ground current distribution relationship:

[0061] M A square array of straight conductor branches R , let the column vector of the ground current of the branch conductor be I s , the potential rise column vector formed by the tower grounding body V ( t )for: , the above formula includes V ( t )and I s common M +1 undetermined quantity and undetermined earth resistivity parameter ρ , but there are only M equations, so we need to add two equations. First, add the current conservation equation:

[0062] Secondly, measure the grounding resistance of the tower grounding body R g equal: ,

[0063] Combining the above formulas, we finally get ρ , V ( t )and I s .

[0064] 3.4 Correction of geoelectric field measurement data:

[0065] The ground potential caused by the stray current entering the ground is calculated using the point matching moment method. The calculation formula is as follows:

[0066] ,in, p is the location of the ground electric field monitoring point (X, Y, O).

[0067] make( x i1 , y i1 , z i1 )and( x i2 , y i2 , z i2 ) is a conductor L i The two endpoints (schematic diagram as shown Figure 4 In the ground potential formula The analytical expression is as follows:

[0068] , in: , , , ( x p , y p , z p ) is the observation point p The position of a, b , c is an intermediate variable,

[0069] The ground potential formula The analytical expression is as follows:

[0070] , in: , , a. e , f is an intermediate variable,

[0071] Calculate the background electric field in the ground, substitute the position data of points X, Y, and O into the ground potential calculation formula of the stray current entering the ground in step 3.4 to solve the potential formed by the stray current entering the ground U ( X ), U ( Y ), U ( O ), further substituting into the electric field formula in the ground: , , in, E x0 ( t )and E y0 ( t ) are: , ,

[0072] At this point, the calibration of the ground electric field measurement data has been completed, and the true ground background electric field has been obtained. E x0 ( t )and E y0 ( t ).

[0073] Step 4, calculation of stray current corrosion:

[0074] On the branch road L j Stray current I s ( j,t k ) average corrosion depth h ( j ) is calculated by Faraday's electrolysis formula:

[0075] , in, k For time t Number, time t k = k Δ T , Δ T is the time step of stray current measurement, D j For branch L j The cross-sectional perimeter of . T Preferably 0.1s, F A function is a positive function if and only if x >0 hours F ( x )= x ,otherwise F( x )=0.

[0076] Step 5: Calculation of the amount of corrosion due to the background electric field in the ground:

[0077] 5.1 Formation of the background electric field vector in the ground: ;

[0078] 5.2 Calculate the projection positions of the starting and ending points of all grounding conductor branches on the background electric field lines in the ground. L j The projection positions of the starting point and the end point of the ground on the background electric field line are e j1 and e j2 , take the maximum projection position of all conductor branches e jmax and minimum value e jmin , the electrochemical center potential coordinates of the ground body are e 0= e jmax + e jmin ;

[0079] 5.3 Obtain all positive and negative grounding branches:

[0080] If the starting point and end point of the branch cross the projection position e 0, then press e 0 position divides the conductor branch into a positive part and a negative part. Specifically, for the ground conductor branch L j , e The 0 position corresponds to ( x j0 , y j0 , z j0 );like e j1 > e 0, the positive electrode is ( x j1 , y j1 , z j1 ) -( x j0 , y j0 , z j0 ), the negative electrode is ( x j2 , y j2 ,z j2 ) -( x j0 , y j0 , z j0 );like e j1 < e 0, the positive electrode is ( x j2 , y j2 , z j2 ) -( x j0 , y j0 , z j0 ), the negative electrode is ( x j1 , y j1 , z j1 ) -( x j0 , y j0 , z j0 ).

[0081] If the starting and ending points of the branch are at the projected position e 0, the branch is positive.

[0082] If the starting and ending points of the branch are at the projected position e 0, the branch is negative.

[0083] Forming a positive branch assembly { L pi}, i = 1, 2, …, N .

[0084] Forming a negative branch collection { L mi}, i = 1, 2, …, K .

[0085] 5.4 Calculation of the amount of corrosion caused by the background electric field in the ground.

[0086] Remove all positive branches { L pi}, forming a ground conductor branch L pi The conductor pointing vector is: ,

[0087] Calculation of ground conductor branches L pi Projection length on the field lines of the background electric field in the ground P ( i ):

[0088] ,

[0089] In the positive branch L pi The average daily corrosion depth caused by the background electric field in the ground h e ( i ) is calculated by the following formula:

[0090] ,

[0091] Step 6, synthetic corrosion amount:

[0092] The stray current corrosion amount and the background electric field corrosion amount in the ground are superimposed:

[0093] The average corrosion depth of the positive electrode branch is H pi}, i = 1, 2, …, N .

[0094] The average corrosion depth of the negative electrode branch is H mi}, i = 1, 2, …, K .

[0095] The maximum daily average corrosion depth of the positive branch H pmax .

[0096] Step 7, calculation of remaining life:

[0097] Analyze the remaining life of the grounding conductor based on 50% of the remaining cross-sectional area:

[0098] For flat steel, the cross-sectional width is w , the remaining life of the grounding conductor T d for ;

[0099] For round steel, the cross-sectional radius is r , the remaining life of the grounding conductor T d for ,

[0100] The experimental data of the effect of this method are compared with the data measured by the weight loss method:

[0101] Table 1 Error rate between the weight loss method and the data of this method

[0102]

[0103] Table 1 shows that the flat steel and round steel were subjected to corrosion tests, and the corrosion degree was tested by the weight loss method and the method of the present invention respectively. The error rate of the obtained data compared with the weight loss method was basically within 5%, which basically conforms to the actual corrosion situation.

[0104] In order to quickly obtain the results of the above method, a tower grounding body remaining life assessment system is designed, which includes an input device, a memory, and a processor. The memory stores a computer program, and the processor calls the program to process the data input by the input device. The input device inputs the aforementioned measurement data, and the processor executes the above method. The hardware structures of the input device, the memory, and the processor are all existing technologies.

Claims

1. A method for monitoring the corrosion of a tower grounding body, characterized in that: Step 1: Measure the stray current entering the ground at the foot of the tower and summarize the total stray current entering the ground on the tower grounding body. I ( t ), filter the total stray current entering the ground and remove the AC unbalanced current entering the ground; Step 2: Measure the electric field data in the ground. Measure the potential difference with a rectangular coordinate distance of 10 meters from point O to obtain the electric field components in the X and Y directions. Filter the electric field data in the ground to obtain the 0-5 Hz range component. Step 3: Implement the correction of the ground electric field, separate the ground background electric field and the ground current electric field in the ground electric field, and obtain the ground background electric field E x0 ( t )and E y0 ( t ); Step 4, calculation of stray current corrosion: On the branch road L j Stray current I s ( j,t k ) average corrosion depth h ( j ) is calculated by Faraday's electrolysis formula: ,in, k For time t Number, time t k = k Δ T , Δ T is the time step of stray current measurement, D j For branch L j The cross-sectional perimeter of F The function is a positive function if and only if x >0 hours F ( x )= x ,otherwise F ( x )=0; Step 5: Calculation of the amount of corrosion due to the background electric field in the ground: Background electric field vector in the ground for: ,in, E x0 ( t )and E y0 ( t ) are the background electric field components in the X and Y directions respectively; Calculate the projection positions of the starting and ending points of all grounding conductor branches on the background electric field lines in the ground, and let the grounding conductor branches L j The projection positions of the starting point and the end point of the ground on the background electric field line are e j1 and e j2 , take the maximum projection position of all conductor branches e jmax and minimum value e jmin , the electrochemical center potential coordinates of the ground body are e 0= e jmax + e jmin ; Get all positive and negative grounding branches: If the starting and ending points of the branch cross the projected position e 0, then press e The 0 position divides the conductor branch into a positive part and a negative part; If the starting and ending points of the branch are at the projected position e 0, the branch is positive; If the starting and ending points of the branch are at the projected position e 0, the branch is negative; Forming a positive branch collection L pi }, i = 1, 2, …, N ; Forming a negative branch collection { L mi }, i = 1, 2, …, K ; Calculate the amount of corrosion caused by the background electric field in the ground: Take out all the positive branches { L pi }, forming a ground conductor branch L pi The conductor pointing vector for: , ( x i1 , y i1 , z i1 )and( x i2 , y i2 , z i2 ) is the conductor set L i The two endpoints of Calculation of ground conductor branches L pi Projection length on the field lines of the background electric field in the ground P ( i ): ； In the positive branch L pi The average daily corrosion depth caused by the background electric field in the ground h e ( i ): , ρ is the equivalent earth resistivity; Step 6, synthetic corrosion amount: The stray current corrosion amount and the background electric field corrosion amount in the ground are superimposed: The average corrosion depth of the positive electrode branch is H pi }, i = 1, 2, …, N ; The average corrosion depth of the negative electrode branch is H mi }, i = 1, 2, …, K ; The maximum daily average corrosion depth of the positive branch H pmax .

2. The method for monitoring the corrosion amount of a tower grounding body according to claim 1, characterized in that: The first step is to measure the stray current entering the ground at the foot of the tower: install open flexible stray current sensors at the four feet of the tower, which are I 1( t ), I 2( t ), I 3( t ), I 4( t ), , filtering obtains the current component in the range of 0 to 5 Hz.

3. The method for monitoring the corrosion amount of a tower grounding body according to claim 1, characterized in that: Step 2: Use the three-electrode method to measure the ground electric field data. Three platinum electrodes X, Y, and O are buried at a depth of 40 cm in the ground where the grounding body is located. The lines connecting X and O and Y and O form a vertical angle. The length between X and O and between Y and O is 10 m. The measured value of the ground electric field is , ,in, E x ( t )and E y ( t ) are the electric field components in the X and Y directions, Δ x and Δ y are the potential differences between XO and YO respectively.

4. The method for monitoring the corrosion amount of a tower grounding body according to claim 1, characterized in that: Step 4 Δ T Select 0.1s.

5. A tower grounding body residual life assessment system, characterized in that The input device inputs the measurement data of claim 1, and the processor with a computer program for implementing the calculation executes the method of claim 1 to calculate the maximum daily average corrosion depth. H pmax , calculate the remaining life of the grounding body based on 50% of the remaining cross-sectional area: For flat steel, take the cross-sectional width as w , the remaining life of the grounding body T d for For round steel, the cross-sectional radius is r , the remaining life of the ground conductor T d for .

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