CN113656996B - Submarine cable rapid discharge strategy optimization method and grounding grid risk control method - Google Patents
Submarine cable rapid discharge strategy optimization method and grounding grid risk control method Download PDFInfo
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Abstract
The invention discloses a submarine cable rapid discharge strategy optimization method, which is characterized in that a submarine cable discharge loop equivalent circuit model is established, and a discharge strategy in a multi-resistor series discharge process of a cable terminal is optimized according to current and power limiting conditions of a discharge resistor; the invention also discloses a grounding grid risk control method, which optimizes the design scheme of the grounding grid by establishing a calculation model of the step voltage and the electrostatic field of the submarine cable terminal site and according to the step voltage and the electrostatic field distribution model; the invention takes into account the two limiting conditions of the maximum allowable current and the maximum allowable power of the discharge resistor, ensures the optimized discharge strategy, can obtain the fastest discharge speed on the premise of ensuring the safe operation of the discharge resistor, properly reduces the grid spacing of the grounding grid around the submarine cable, and effectively reduces the grounding grid material and the installation cost while ensuring that the field step voltage is lower than the human body safety voltage.
Description
Technical Field
The invention belongs to the field of cable terminal engineering, and particularly relates to a submarine cable rapid discharge strategy optimization method and a grounding grid risk control method.
Background
The DC cable can store a large amount of charges after long-term operation or DC withstand voltage test, so that the cable terminal can maintain higher terminal voltage for a longer time after power failure, and the subsequent treatment process of power failure maintenance or test can not be safely carried out. It is therefore desirable to rapidly discharge it to reduce the time for power outage repairs or post-test treatments. The cable terminal discharging resistor is formed by connecting multiple sections of resistors in series, and a plurality of sections of resistors are gradually shorted in the discharging process so as to accelerate the discharging speed. In the discharging process, the discharging resistor is limited by self-limiting conditions and surrounding site safety conditions, so that a quick discharging strategy and risk control method for the submarine cable are needed, and the safety and risk controllability of the discharging process of the submarine cable terminal are monitored.
Disclosure of Invention
The invention aims to: in order to make up for the lack of technical means for monitoring the safety and risk controllability of the submarine cable terminal discharging process in the prior art, the invention provides a submarine cable rapid discharging strategy optimization method and a grounding grid risk control method, which can be used in the engineering fields of power failure overhaul or withstand voltage test of a cable terminal and the like and are suitable for the rapid discharging problem of long-distance high-voltage direct current submarine cables.
The technical scheme is as follows: the submarine cable rapid discharge strategy optimization method comprises the following steps:
step 1: establishing an equivalent circuit model of a submarine cable discharge loop:
step 2: judging whether m-1 is equal to 1, if so, stopping iteration, otherwise, executing the step 3;
step 3: changing the resistance connected into the discharging loop from m sections to (m-1) sections, calculating the current and power at the moment n based on the equivalent circuit model of the discharging loop of the submarine cable, and judging whether the current at the moment n exceeds the maximum allowable current I max And whether the power at time n exceeds the product of the maximum allowable power of a single section and the number of resistance sections connected to the discharge loop, if the current at time n does not exceed the maximum allowable current I max And the power at the moment n does not exceed the product of the maximum allowable power of a single section and the number of resistance sections connected into the discharge loop, executing the step 4; if the current at time n exceedsExcessive maximum allowable current I max Or the power at the moment n exceeds the product of the maximum allowable power of a single section and the number of resistance sections connected into the discharge loop, executing the step 5;
step 4: recording the number m of discharge resistor segments connected to submarine cable at time n n = (m-1), while n=n+1, m=m-1, step 2 is performed;
step 5: maintaining the number m of the discharge resistor connected to the discharge loop unchanged, i.e. the number m of the discharge resistor connected to the submarine cable at time n n =m, n=n+1, step 2 is performed.
Further, the submarine cable discharging circuit equivalent circuit model is expressed as:
wherein U (t) represents a function of the change of the voltage of the submarine cable terminal to the ground with time during discharging, U 0 The method is characterized in that the voltage to ground of the submarine cable terminal at the initial moment of discharging is calculated, t is time, m is the node number of the resistor connected to the discharging loop, C is the capacitance value of the submarine cable equivalent to one capacitor, and R is the resistance value of each node of the resistor connected to the discharging loop.
Further, the calculating the current and the power at the time n based on the submarine cable discharging loop equivalent circuit model specifically comprises the following steps:
discretizing the time scale of the discharging process according to the equivalent circuit model of the submarine cable discharging loop, wherein the nth discrete moment is t n Let n Δt, where Δt is the time step, n=0 is the initial time, and the discretization of the discharge resistance current over time is expressed as:
the discretization expression of the power change of the discharge resistor along with time is as follows:
wherein I is n 、P n Respectively representing the current and the power of the submarine cable terminal at the nth moment in the discharging process, m n The number of discharge resistor nodes connected into the submarine cable at the nth moment is represented;
according to the formulas (4) and (5), the current and power at the time n are calculated.
The invention also discloses a submarine cable grounding grid risk control method, which comprises the steps of discharging the submarine cable by adopting the submarine cable rapid discharging strategy optimization method, optimizing the design scheme of the grounding grid according to the maximum ground voltage in the whole discharging process and the distribution rule of the field step voltage and the electrostatic field when accidental ground discharge occurs.
Further, the method comprises the following steps:
s100: the value of the potential at the discharge point to ground is set to the maximum voltage to ground that occurs during the whole discharge strategy optimization process.
S200: calculating field intensity distribution of the submarine cable terminal when the submarine cable terminal is grounded without a grounding network;
s300: comparing the field intensity distribution calculated in S200 with the critical field intensity to obtain the minimum transverse density d of the grounding grid required by each position in the grounding field of the submarine cable terminal x.max Minimum longitudinal density d y.max ；
S400: on the basis of S300, the peripheral length of the grounding discharge point is l E Width d of square inner grid of (2) E Lateral width d of other area grid x Longitudinal width d of other area grid y Combining, and screening the size of the grounding grid conforming to the step voltage limit;
s500: selecting the grounding grid size with the lowest manufacturing cost from the grounding grid sizes conforming to the step voltage limit, and taking the grounding grid size as an optimal scheme;
s600: according to the optimal scheme in S500, a corresponding grounding grid is buried in the submarine cable terminal on siteBurying a ground discharge point in a ground net with a width d E Is within a square grid of (c).
Further, in the step S100, the calculation method of the maximum ground voltage of the submarine cable terminal in the whole optimization process of the discharging strategy is as follows:
the discretization of the change of the voltage to ground of the submarine cable terminal along with time is expressed as follows:
in U n Representing the ground voltage of the submarine cable terminal at the nth moment in the discharging process;
the ground voltage U at each time calculated according to the formula (10) 0 、U 1 、U 2 …U n Comparing the ground voltages at all times to obtain the maximum ground voltage U of the submarine cable terminal in the whole discharging strategy optimization process m ：
U m ＝max{U 0 ,U 1 ,U 2 ,…U n } (11)。
Further, the step S200 specifically includes the following steps:
orthogonal grid subdivision is used for the submarine cable terminal grounding field to obtain a series of discrete points and the electric potential of each discrete point is calculated;
calculating to obtain the step voltage between any two points of the submarine cable terminal site based on the electric potential of each discrete point;
and calculating the field electrostatic field intensity of the submarine cable terminal based on the electric potential of each discrete point.
Further, the calculating to obtain the electric potential of each discrete point specifically includes:
the potential distribution in the submarine cable terminal grounding field accords with the poisson equation, and the potential of each discrete point is calculated by applying a finite difference method.
Further, S300 specifically includes the following steps:
s301: taking a ground discharge point as a circle center, selecting a radius standard as a minimum value in all radiuses which meet the requirement that the circle can enclose all areas with the electric field intensity exceeding the critical field intensity; the area inside the circle is a dangerous area, and the area outside the circle is a safety range;
s302: the field grounding grid is a metal grid formed by a plurality of longitudinal and transverse metal strips, and the number of the transverse metal strips and the longitudinal metal strips of the grounding grid is increased one by one to reduce the range of a dangerous area until the radius of the dangerous area meets the requirement; obtaining the lowest density d of the grounding grid according to the number of the metal strips of the grounding grid and the length and width of the ground at the moment x.max D y.max 。
Further, the step S400 specifically includes the following steps:
s401: the length of the surrounding edge of the grounding discharge point is l E Number n of square inner bars E Number of longitudinal steel bars n in other areas of the field VO And the number of transverse steel bars n in other areas of the field HO The method comprises the following steps of:
at the selection of the grid width d E 、d x And d y When n should be ensured E 、n VO And n HO Is an integer, and d x Should not be greater than d x.max ，d y Should not be greater than d y.max ；
S402: the side length around the grounding discharge point is l E Width d of square inner grid of (2) E Lateral width d of other area grid x Longitudinal width d of other area grid y Combining, and screening out the grounding grid meeting the step voltage limitSize.
The beneficial effects are that: compared with the prior art, the invention has the following advantages:
(1) The discharge strategy of the invention takes into account two limiting conditions of the maximum allowable current and the maximum allowable power of the discharge resistor, ensures the optimized discharge strategy, and can obtain the fastest discharge speed on the premise of ensuring the safe operation of the discharge resistor;
(2) According to the grounding grid risk control method, the grounding grid spacing around the submarine cable is properly reduced, so that the on-site step voltage is ensured to be lower than the human body safety voltage, and the grounding grid material and the installation cost are effectively reduced.
Drawings
FIG. 1 is a schematic diagram of an equivalent circuit of a submarine cable discharge circuit;
FIG. 2 is a flowchart of a subsea cable quick discharge strategy optimization;
FIG. 3 is a schematic diagram of the positions of a ground grid and a discharge point to ground;
FIG. 4 is a schematic diagram of a spatial orthogonal meshing step size;
FIG. 5 is a schematic diagram of the number of grids of the ground grid;
fig. 6 is a flow chart for ground grid design optimization.
Detailed Description
The technical scheme of the invention is further described with reference to the accompanying drawings and the embodiments.
According to the submarine cable rapid discharge strategy optimization method, the change rule of the discharge resistor current and the power in the discharge process is researched by establishing the submarine cable discharge loop equivalent circuit model, the expression of the change rule of the discharge resistor current and the power in the discharge process is discretized, and the discharge strategy in the multi-resistor series discharge process of the cable terminal is optimized according to the current and the power limiting conditions of the discharge resistor; according to the method, the submarine cable is discharged by adopting a submarine cable rapid discharging strategy optimization method, and according to the maximum ground voltage in the whole discharging process, a calculation model of the field step voltage and the electrostatic field of the submarine cable terminal is built, so that the distribution rule of the field step voltage and the electrostatic field when accidental ground discharging occurs is obtained, and the design scheme of the grounding grid is optimized.
The above process will now be described in detail.
The length of the discharged submarine cable is l, and the capacitance per unit length is C 0 The submarine cable is equivalent to a capacitor, the capacitance value of the capacitor is C, the resistance of an access discharge loop is m sections, the resistance value of each section is R, the total resistance value is mR, as shown in fig. 1, the submarine cable discharge loop equivalent circuit model is a first-order RC zero input response loop model, the discharge time constant is tau= mRC, and the cable terminal voltage to ground follows the first-order RC zero input response, and the specific form is as follows:
wherein U (t) represents a function of the change of the voltage of the submarine cable terminal to the ground with time during discharging, U 0 The voltage to ground of the cable terminal at the initial moment of discharge is set, and t is time.
According to the equivalent first-order RC zero input response loop, the change of the discharge resistance current along with time in the discharge process is derived and can be expressed as:
according to the equivalent first-order RC zero input response loop, the change of the discharge resistance power along with time in the discharge process is derived and can be expressed as:
because a plurality of resistors are required to be short-circuited in the discharging process, the discharging speed is increased, and the number m of the resistor connected into the discharging loop can be changed, the formula (2) and the formula (3) cannot be directly used, and the time scale of the discharging process is required to be discretized.
The discretization adopts a time step delta t, then the nthAt discrete time t n N Δt, and specifies an initial time n=0.
The discretized expression of the change of the discharge resistance current with time is:
the discretization expression of the power change of the discharge resistor along with time is as follows:
wherein Δt represents the time step taken by discretization, subscript n represents the nth time, I n 、P n Respectively representing the current and the power of the submarine cable terminal at the nth moment in the discharging process, m n The number of discharge resistance sections of the access submarine cable at the nth time is shown.
The current limiting conditions of the discharge resistor are as follows: the current I (t) of the discharge resistor during discharge must not exceed the maximum allowable current I max 。
The power limiting conditions of the discharge resistor are: the power P (t) of the discharge resistor during discharge must not exceed the product mP of the maximum allowable power of a single section and the number of resistance sections connected to the discharge loop max 。
As shown in fig. 2, the discharge strategy in the process of optimizing the multi-resistor series discharge of the cable terminal is as follows: changing the resistance connected into the discharge loop from m section to (m-1) section at each iteration moment, calculating the current and the power at the moment by using the formula (4) and the formula (5), comparing the current and the power with the limiting conditions, and taking the moment as the moment of shorting a section of resistance if the current and the power are under the limiting conditions at the moment; if the current or power is above the limiting condition, the number of resistance sections connected into the discharge loop at the moment is kept unchanged. The method is iterated until only one resistance node is left in the connected discharge loop.
According to the maximum ground voltage in the whole discharge strategy optimization process, the embodiment provides a submarine cable grounding grid risk control method, and the design scheme of the grounding grid is optimized according to the distribution rule of field step voltage and electrostatic field when accidental ground discharge occurs.
The process of optimizing the design scheme of the grounding grid is as follows: firstly, calculating field intensity distribution when the high-voltage electrode is grounded in the absence of a net: comparing calculated field intensity with critical field intensity, designing the minimum density of the grounding grid required by each position of the safety area and the field, and according to the actual three grid widths d E 、d x 、d y And then selecting a different d E 、d x 、d y The combination is performed to verify the effect of the ground grid at this grid width on the field step voltage. Given maximum permissible value U of step voltage max And screening out the type of the grounding grid conforming to the step voltage limit. The control method will now be described in detail.
As shown in fig. 3, the submarine cable terminal is embedded with a grounding grid in the field, and the ground discharge point is located in a certain grid of the grounding grid. Based on a finite difference method, the distribution rule of the field step voltage and the electrostatic field is calculated under the condition of accidental discharge to the ground in the discharge process, and the design scheme of the grounding grid is optimized based on the distribution rule of the field step voltage and the electrostatic field.
Firstly, establishing a finite difference method calculation model of the step voltage and the electrostatic field of a submarine cable terminal site:
the potential distribution in the field, which conforms to poisson's equation, is expressed as:
in the method, in the process of the invention,representing the potential.
Orthogonal meshing is used for the field to obtain a series of discrete points, and the meshing step length is shown in fig. 4. For the (i, j, k) th discrete point therein, the finite difference method form of formula (6) is:
the finite difference method is used to calculate the potential of each discrete point, with the help of certain boundary conditions.
(1) Infinity boundary condition:
(2) The discharge point potential to ground is known as:
in the method, in the process of the invention,representing the potential at the point of discharge to ground.
Maximum ground voltage U appearing at submarine cable terminal in optimizing process of numerically rounding whole discharge strategy m The calculation method is as follows:
the discretization of the change of the voltage to ground of the submarine cable terminal along with time is expressed as follows:
in the method, in the process of the invention,U n the ground voltage of the submarine cable terminal at the nth time during the discharging process is shown. The ground voltage U at each time calculated according to the formula (10) 0 、U 1 、U 2 …U n Comparing the ground voltages at all times to obtain the maximum ground voltage U of the submarine cable terminal in the whole discharging strategy optimization process m ：
U m ＝max{U 0 ,U 1 ,U 2 ,…U n } (11)
(3) Different medium current density continuous conditions:
in gamma 1 、γ 2 Representing the conductivity of the two media respectively,representing the component of the potential gradient of the interface of the two media along the normal direction of the interface.
(4) Suspension potential conductor boundary conditions:
such boundary conditions are represented by formulae (13) and (14).
Equation (13) represents a conductor occupying n discrete points, the potentials of which are equal everywhere, beingIs a to-be-calculated quantity); equation (14) is the gaussian theorem, meaning that the sum of the normal components of the potential gradients (electric field strengths) at each point on the conductor boundary is 0.
After solving the potential of each discrete point in the field, calculating the step voltage between any two points in the field:
the field intensity of the electrostatic field in the field is:
where "grad" denotes a gradient.
An approximate gradient method is:
wherein,representing a unit component along the X, Y, Z axis.
The submarine cable terminal is buried underground in the field, the grounding grid is a metal grid formed by conductors, as shown in figure 5, and the transverse length of the field is l x A longitudinal length of l y The grounding grid is a metal grid formed by a plurality of steel bars, has a limiting effect on the diffusion of potential distribution around accidental discharge points, and enables the step voltage of most areas of the site to be maintained at a lower level.
Taking a ground discharge point as a circle center, selecting a radius standard as a minimum value in all radiuses which meet the requirement that the circle can enclose all areas with the electric field intensity exceeding the critical field intensity; the area inside the circle is a dangerous area, and the area outside the circle is a safety range; the number of the transverse metal strips and the longitudinal metal strips of the grounding grid is increased one by one to reduce the range of the dangerous area until the radius of the dangerous area meets the requirement; obtaining the lowest density d of the grounding grid according to the number of the metal strips of the grounding grid and the length and width of the ground at the moment x.max D y.max 。
The peripheral length of the discharge point to the ground is l E Is different from the grid density of other areas of the field. The peripheral length of the discharge point to the ground is l E Is d in the width of the square inner grid E The transverse width of the grid of other areas of the field is d x A longitudinal width d y . Therefore, the peripheral length of the discharge point to the ground is l E Number n of square inner bars E Number of longitudinal steel bars n in other areas of the field VO And the number of transverse steel bars n in other areas of the field HO The method comprises the following steps of:
n should be guaranteed when selecting the grid width E 、n VO And n HO Is an integer, and d x Should not be greater than d x.max ，d y Should not be greater than d y . max
Number of longitudinal steel bars of grounding grid n V Number of transverse bars n H The method comprises the following steps of:
the grounding grid with the lowest manufacturing cost is selected from the grounding grid types meeting the step voltage limit to be used as an optimal scheme, so that the field step voltage is ensured to be lower than the human body safety voltage, and meanwhile, the grounding grid material and the installation cost are effectively reduced.
Let the unit cost of the grounding grid steel bar be c, then the cost of the whole grounding grid is:
C＝c(n V l y +n H l x ) (23)。
Claims (7)
1. a submarine cable rapid discharge strategy optimization method is characterized by comprising the following steps of: the method comprises the following steps:
step 1: establishing an equivalent circuit model of a submarine cable discharge loop:
step 2: judging whether m-1 is equal to 1, if so, stopping iteration, otherwise, executing the step 3;
step 3: changing the resistance connected into the discharging loop from m sections to (m-1) sections, calculating the current and power at the moment n based on the equivalent circuit model of the discharging loop of the submarine cable, and judging whether the current at the moment n exceeds the maximum allowable current I max And whether the power at time n exceeds the product of the maximum allowable power of a single section and the number of resistance sections connected to the discharge loop, if the current at time n does not exceed the maximum allowable current I max And the power at the moment n does not exceed the product of the maximum allowable power of a single section and the number of resistance sections connected into the discharge loop, executing the step 4; if the current at time n exceeds the maximum allowable current I max Or the power at the moment n exceeds the product of the maximum allowable power of a single section and the number of resistance sections connected into the discharge loop, executing the step 5;
step 4: recording the number m of discharge resistor segments connected to submarine cable at time n n = (m-1), while n=n+1, m=m-1, step 2 is performed;
step 5: maintaining the number m of the discharge resistor connected to the discharge loop unchanged, i.e. the number m of the discharge resistor connected to the submarine cable at time n n =m, n=n+1, step 2 is performed;
the submarine cable discharge loop equivalent circuit model is expressed as:
wherein U (t) represents a function of the change of the voltage of the submarine cable terminal to the ground with time during discharging, U 0 The method comprises the steps that ground voltage of a submarine cable terminal at the initial moment of discharging is calculated, t is time, m is the number of nodes of resistors connected into a discharging loop, C is the capacitance value of a capacitor equivalent to the submarine cable, and R is the resistance value of each node of resistor connected into the discharging loop;
based on the submarine cable discharging loop equivalent circuit model, calculating the current and power at the moment n specifically comprises the following steps:
discretizing the time scale of the discharging process according to the equivalent circuit model of the submarine cable discharging loop, wherein the nth discrete moment is t n Let n Δt, where Δt is the time step, n=0 is the initial time, and the discretization of the discharge resistance current over time is expressed as:
U n-1 representing the ground voltage of the submarine cable terminal at the n-1 time in the discharging process;
the discretization expression of the power change of the discharge resistor along with time is as follows:
wherein I is n 、P n Respectively representing the current and the power of the submarine cable terminal at the nth moment in the discharging process, m n The number of discharge resistor nodes connected into the submarine cable at the nth moment is represented;
according to the formulas (4) and (5), the current and power at the time n are calculated.
2. A submarine cable grounding grid risk control method is characterized by comprising the following steps of: the submarine cable is discharged by adopting the submarine cable rapid discharging strategy optimization method as claimed in claim 1, and the design scheme of the grounding grid is optimized according to the distribution rule of field step voltage and electrostatic field when accidental ground discharge occurs according to the maximum ground voltage in the whole discharging process, and the method comprises the following steps:
s100: setting the value of the potential of the discharge point to the ground to the maximum voltage to the ground U occurring in the whole discharge process m ；
S200: based on maximum voltage to ground U m Calculating field intensity distribution of the submarine cable terminal when the submarine cable terminal is grounded without a grounding network;
s300: comparing the field intensity distribution calculated in S200 with the critical field intensity to obtain the minimum transverse density d of the grounding grid required by each position in the grounding field of the submarine cable terminal x.max Minimum longitudinal density d y.max ；
S400: on the basis of S300, the peripheral length of the grounding discharge point is l E Width d of square inner grid of (2) E Lateral width d of other area grid x Longitudinal width d of other area grid y Combining, and screening the size of the grounding grid conforming to the step voltage limit;
s500: selecting the grounding grid size with the lowest manufacturing cost from the grounding grid sizes conforming to the step voltage limit, and taking the grounding grid size as an optimal scheme;
s600: according to the optimal scheme in S500, a corresponding grounding grid is buried in the submarine cable terminal on site, and a grounding discharge point is buried in the grounding grid with the width of d E Is within a square grid of (c).
3. A submarine cable grounding grid risk control method according to claim 2, characterized by: in the step S100, the maximum voltage to ground occurring in the whole discharging process is calculated by the following steps:
the discretization of the change of the voltage to ground of the submarine cable terminal along with time is expressed as follows:
in U n Representing the ground voltage of the submarine cable terminal at the nth moment in the discharging process;
the ground voltage U at each time calculated according to the formula (10) 0 、U 1 、U 2 ...U n Comparing the ground voltages at all times to obtain the maximum ground voltage U in the whole discharging process m ：
U m ＝max{U 0 ，U 1 ，U 2 ，...U n } (11)。
4. A submarine cable grounding grid risk control method according to claim 2, characterized by: the step S200 specifically includes the following steps:
orthogonal grid subdivision is used for the submarine cable terminal grounding field to obtain a series of discrete points and the electric potential of each discrete point is calculated;
calculating to obtain the step voltage between any two points of the submarine cable terminal site based on the electric potential of each discrete point;
and calculating the field electrostatic field intensity of the submarine cable terminal based on the electric potential of each discrete point.
5. The submarine cable grounding grid risk control method according to claim 4, wherein: the electric potential of each discrete point is calculated, and the method specifically comprises the following steps:
the potential distribution in the submarine cable terminal grounding field accords with the poisson equation, and the potential of each discrete point is calculated by applying a finite difference method.
6. A submarine cable grounding grid risk control method according to claim 2, characterized by: the step S300 specifically includes the following steps:
s301: taking a ground discharge point as a circle center, selecting a radius standard as a minimum value in all radiuses which meet the requirement that the circle can enclose all areas with the electric field intensity exceeding the critical field intensity; the area inside the circle is a dangerous area, and the area outside the circle is a safety range;
s302: the grounding grid of the submarine cable terminal grounding site consists of a plurality of longitudinal and transverse metal strips, and the range of a dangerous area is reduced by increasing the number of the transverse metal strips and the longitudinal metal strips of the grounding grid one by one until the radius of the dangerous area meets the requirement; obtaining the lowest density d of the grounding grid according to the number of the metal strips of the grounding grid and the length and width of the grounding field of the submarine cable terminal x.max D y.max 。
7. A submarine cable grounding grid risk control method according to claim 2, characterized by: the step S400 specifically includes the following steps:
s401: the length of the surrounding edge of the grounding discharge point is l E Number n of square inner bars E Number n of longitudinal steel bars in other areas of submarine cable terminal grounding field VO And the number n of transverse steel bars in other areas of the submarine cable terminal grounding field HO The method comprises the following steps of:
at the selection of the grid width d E 、d x And d y When n should be ensured E 、n VO And n HO Is an integer, and d x Should not be greater than d x.max ，d y Should not be greater than d y.max ；l x The transverse length of the ground field is l for the submarine cable terminal y Grounding the submarine cable terminal to a ground site longitudinal length;
s402: the side length around the grounding discharge point is l E Width d of square inner grid of (2) E Lateral width d of other area grid x Longitudinal width d of other area grid y Combining, and screening the size of the grounding grid meeting the step voltage limit.
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