CN110188319B  Method for calculating number of grounding points of TNC grounding system based on multiobjective optimization  Google Patents
Method for calculating number of grounding points of TNC grounding system based on multiobjective optimization Download PDFInfo
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 CN110188319B CN110188319B CN201910467715.0A CN201910467715A CN110188319B CN 110188319 B CN110188319 B CN 110188319B CN 201910467715 A CN201910467715 A CN 201910467715A CN 110188319 B CN110188319 B CN 110188319B
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Abstract
The invention discloses a method for calculating the number of grounding points of a TNC grounding system based on multiobjective optimization, which aims at the grounding configuration of the TNC grounding system, provides a multiobjective optimization model which simultaneously meets the requirements of the number of grounding points with the lowest contact voltage, the largest possible fault phase zerosequence current and the lowest grounding cost under the condition of considering the uniform distribution of the grounding points, and further calculates the number of the grounding configurations by utilizing a given solving model. The calculation method provided by the invention gives the optimal number of the grounding electrodes of the TNC grounding system on the basis of the comprehensive consideration of the goals of lowest contact voltage, highest fault phase zerosequence current and lowest grounding cost, and is convenient for field personnel to reasonably select the number of the grounding electrodes of the TNC grounding system.
Description
Technical Field
The invention relates to the field of electrical systems, in particular to a method for calculating the number of grounding points of a TNC grounding system based on multiobjective optimization.
Background
The lowvoltage distribution network is a terminal system for supplying power to thousands of households and also relates to a power supply system which has the widest scope and can cause damage to user equipment and personal casualty accidents. Because the grounding selection is improper or the personnel or equipment accidents caused by improper handling after the grounding fault occurs in the lowvoltage system, the deep analysis and the solution of the groundingrelated problem of the lowvoltage system have very important significance.
The grounding types of the lowvoltage system are mainly three, namely a TN system, a TT system and an IT system. Wherein TN can be divided into TNC, TNCS and TNS systems according to the configuration mode of working neutral wire (N) and protective neutral wire (PE) ^{[1]} 。
In the middle of the 20 th century, the grounding mode of the soviet union lowvoltage distribution system basically adopts a TNC system. Although the TNC system can save one PE wire compared with the TNS system, when the PEN wire is broken, because the overcurrent protection can not be operated, the leakage equipment has very high contact voltage for a long time, which is easy to cause electric shock hazard. In recent years, foreign countries have also studied the possible damage of lowvoltage networks with residual current protectors installed, and document [2] mentions that when a fault occurs after a leakage protector is installed, the device still generates a contact voltage.
While adopting TNS system abroad ^{[3]} Also for TNC systemsThe improvement is that after entering the building, a TNCS system is adopted, and in order to reduce the contact voltage when the PEN line is broken, the PEN line is repeatedly grounded at the entrance of the building. The united states has adopted a repeatedly grounded TNCS system. Such a repeatedground TNCS system, also referred to as a multipoint protection grounding system, is now more and more commonly used in the uk for new building power supply. Documents [4 to 6]The application of a TNCS system in recent years abroad is introduced, and although the TNCS system can effectively reduce the contact voltage generated when the PEN wire is broken, the investment of one conducting wire needs to be increased, and the cost is increased.
In order to meet the IEC standard and to increase the electrical safety, at the end of the last 90 s.a.russia proposed to change the lowvoltage distribution network before 1995 from a TNC system to a TNS system, but with millions of kilometers of wires and cables, and therefore suggested to modify the soviet union code, the TNC system had to be repeatedly earthed at the user access, whether it was supplied by an overhead line or a cable line ^{[7]} . When the potential of the protective conductor is not close to the ground potential as much as possible in large buildings such as highrise buildings and the like, the underground conductor which is connected with the total equipotential in the building can be used as a repeated grounding body ^{[8]} The electrical safety level of the repeatedly grounded TNC system is not inferior to that of the TNS system, so the repeatedly grounded TNC system is generally adopted abroad ^{[9]} However, the IEC standard does not clearly specify the grounding resistance value and grounding position of the repetitive grounding, and there is still a lack of research on the rational arrangement of the repetitive grounding for safety and economy.
In China, because the poor power supply and utilization equipment in the 70 s and the backward management level cause the accidents of personal electric shock and casualty to happen, the national protection of lowvoltage lines is to firstly popularize and use the voltage type protector in rural areas ^{[10]} The protector is suitable for the operation mode that the neutral point of a distribution transformer is not grounded, so that the rural lowvoltage power grid is changed into the operation mode that the neutral point of the lowvoltage side is grounded through high resistance from the end of 70 to the beginning of 80 years, namely an IT system indicated by rural lowvoltage power technical code. Documents [11 to 13]Some applications of IT systems are presented.
Over the years of operation, neutral ungrounded systemsCannot limit high voltage to ground caused by some reason of lowvoltage network, such as induced overvoltage caused by lightning strike, operation overvoltage, erection of highlow voltage lines on same pole, etc ^{[14]} . In the neutral point highresistance grounding system, the phase line grounding voltage is increased to the line voltage due to the leakage of one phase line to the ground, the voltage of the zero line to the ground is measured in maintenance, and the phenomenon that one phase line has no voltage to the ground ^{[15]} . Although the voltagetype protector plays a small role in protecting the electric shock casualty accidents at that time, the voltagetype protector is rapidly replaced by the currenttype protector in the 80 s due to the defects of low commissioning rate, poor protection reliability, incapability of installing shunt protection, power grid operation and the like ^{[1617]} 。
It can be seen from the above that the operation mode of the lowvoltage power grid in China is changed in 80 s to adapt to the operation requirement of the leakage protector ^{[18]} . At present, after rural power grid engineering transformation, most electric power facilities reach a certain level, the health condition of rural power supply facilities is not lower than that of a city, and a grounding mode of a TNC system can be adopted as in the urban power grid.
The TNC system has the advantages that the PEN line has the functions of the PE line and the N line, one conducting wire can be saved, and meanwhile, overcurrent protection can be used as insulation fault protection of electric equipment. The fault current can form a loop through a person touching the leakage equipment and the working ground of the transformer if the system has a ground short circuit fault, thereby causing direct use threat to the human body.
In order to solve the above problem, the main solution at present is to repeatedly ground. From the present research situation, most of the articles mention and analyze the role and importance of the repeated grounding ^{[1921]} Reference [22]]The approximate location of repeated grounding and resistance values are given, document [23]]Demonstrating the importance of repeated grounding and equipotential bonding combinations for reducing faulty contact voltages [24]It is proposed that in order to ensure that the safety voltage is below 50V during fault, the resistance value of the repeated grounding should not be simply set to 10 Ω, but the article only analyzes whether the repeated grounding is effective by using an equivalent circuit, and does not give a specific repeated grounding position and resistance value. Document [25]]Analyze the lowvoltage distribution network systemThe limitation of grounding and zerocrossing protection in the system proposes a solution of repeated grounding, but does not propose a specific solution. Therefore, repeated grounding configuration research of grounding patterns of the TNC system is started, but a specific optimization configuration scheme is not mentioned yet. That is, the main disadvantage of the prior art is that it is not possible to provide the optimal number of grounding points based on the multiple objectives of simultaneously keeping the contact voltage as low as possible, the zerosequence current of the fault phase as large as possible, and the grounding cost as low as possible, and therefore, how many grounding points? This is entirely empirical or heuristic in practice and does not give quantitative analysis and comparison.
Disclosure of Invention
The invention aims to provide a method for calculating the number of grounding points of a TNC grounding system based on multiobjective optimization.
The technical scheme adopted by the invention is as follows:
the method for calculating the number of grounding points of the TNC grounding system based on multiobjective optimization comprises the following steps:
step 1, constructing a multiobjective optimization model for calculating the number of grounding points of the TNC grounding system;
step 11, constructing an objective function, wherein a specific formula is as follows:
minf(n)＝[f _{1} (n),f _{2} (n),f _{3} (n)] (1)
wherein f is _{1} (n) is the total grounding cost of the TNC grounding system; f. of _{2} (n) is the reciprocal of a fault phase zero sequence current modulus value when a singlephase earth fault occurs in the TNC grounding system; f. of _{3} (n) is the device contact voltage;
step 12, constructing a multiobjective optimization model based on constraint conditions: a multiobjective optimization model for calculating the grounding point number of the TNC grounding system is constructed based on equality constraint and inequality constraint conditions of the TNC grounding system, and the method comprises the following specific steps:
wherein f is _{1} (n) is total of TNC grounding systemThe cost of grounding; f. of _{2} (n) is the reciprocal of a fault phase zero sequence current modulus value when a singlephase earth fault occurs in the TNC grounding system; f. of _{3} (n) is the device contact voltage; h (n) represents a mapping relation, U, which is satisfied when the power grid complies with kirchhoff law constraints _{safe} Indicating a safety voltage, I, specified for the TNC grounded system _{set} The action setting value of zero sequence protection on the line in the TNC grounding system is represented;
step 2, obtaining the optimal grounding number based on the multiobjective optimization model;
step 21, constructing an unconstrained weighting function based on the multiobjective optimization model, wherein the formula is as follows:
wherein, mu _{1} ，μ _{2} ，μ _{3} As weighting coefficients, α, β, λ _{k} Are penalty coefficients, N is the total number of the equation represented by h (N) =0 in the formula (6), h _{k} (n) is the kth element of the h (n) vector;
and 22, solving the optimal grounding number n based on the weighting function of the formula (7).
Further, in step 11 f _{1} (n) is expressed as the following equation:
f _{1} (n)＝cn (2)
n is the number of grounding points at the TNC grounding system, and the n grounding points are uniformly distributed; c is the comprehensive investment of each set of grounding device.
Further, in step 11 f _{2} (n) is expressed as the following formula:
f _{2} (n)＝1/I _{0} (3)
wherein, I _{0} Indicating fault phase zero sequence current phasor when singlephase earth fault occurs in TNC grounding systemA modulus value of (d);
further, in step 11 f _{3} (n) is expressed as the following formula：
f _{3} (n)＝U _{T} (4)
Further, in the step 22, the optimal grounding number n is solved by adopting a particle swarm optimization algorithm based on the weighting function of the formula (7).
By adopting the technical scheme, aiming at the TNC grounding system, the optimization function for calculating the number of grounding points with the lowest contact voltage, the largest fault phase zerosequence current and the lowest grounding cost is simultaneously met, and the grounding configuration number is further calculated by utilizing a given solving model. The calculation method provided by the invention gives the optimal number of the grounding electrodes of the TNC grounding system on the basis of the comprehensive consideration of the goals of lowest contact voltage, highest fault phase zerosequence current and lowest grounding cost, and is convenient for field personnel to reasonably select the number of the grounding electrodes of the TNC system.
Drawings
The invention is described in further detail below with reference to the accompanying drawings and the detailed description;
FIG. 1 is a schematic diagram of a typical distribution network TNC grounding system;
FIG. 2 is a flow diagram of the method for calculating the number of grounding points of the TNC grounding system based on multiobjective optimization.
Detailed Description
Interpretation of terms:
an IT grounding system: the power supply neutral point is not grounded or grounded through high impedance, and the exposed conductive part of the load side electric equipment is directly grounded through respective protective zero line and is mutually independent from the grounding of the power supply side.
TT grounding system: the power supply neutral is connected directly to ground, while the exposed conductive portion of the load side electrical device is connected to a grounding system on a separate grounding device independent of the power system grounding point.
TN grounding system: the neutral point of the power supply is grounded, a neutral line is led out, and the exposed conductive part of the electrical equipment is directly connected with the neutral line.
TNC grounding System: and the working neutral wire N and the protection neutral wire PE are integrated into a grounding system.
TNS ground system: a grounding system in which the working neutral wire N and the protection neutral wire PE are separated.
TNCS grounding system: the protection zero line (PE) and the working zero line (N) of the trunk line part of the whole system are integrated, and the protection zero line (PE) and the working zero line (N) of the branch line part are separated grounding systems.
The invention mainly aims at a typical distribution network TNC grounding system shown in figure 1, and optimally configures the number of grounding poles according to an optimization method. In figure 1 f indicates a singlephase earth fault in one phase,for the zero sequence current flowing through the fault phase,contact voltage of the user equipment housing.
As shown in FIG. 2, the invention discloses a method for calculating the number of grounding points of a TNC grounding system based on multiobjective optimization,
step 1, constructing a multiobjective optimization model for calculating the number of grounding points of the TNC grounding system;
step 11, constructing an objective function, wherein a specific formula is as follows:
minf(n)＝[f _{1} (n),f _{2} (n),f _{3} (n)] (1)
wherein f is _{1} (n) is the total grounding cost of the TNC grounding system; f. of _{2} (n) is the reciprocal of a fault phase zero sequence current modulus when a singlephase earth fault occurs in the TNC grounding system; f. of _{3} (n) is the device contact voltage;
further, in step 11 f _{1} (n) is expressed as the following formula:
f _{1} (n)＝cn (2)
n is the number of grounding points of the TNC grounding system, and the n grounding points are uniformly distributed; c is the comprehensive investment of each set of grounding device.
Further, in the TNC grounding system shown in FIG. 1, when a singlephase ground fault occurs, the phase current is failed due to the faultModulus value of _{0} Is a function of n, so 1/I _{0} Also a function of n, i.e. f in step 11 _{2} (n) is expressed as the following equation:
f _{2} (n)＝1/I _{0} (3)
wherein, I _{0} Indicating fault phase zero sequence current phasor when singlephase earth fault occurs in TNC grounding systemA modulus value of (d);
further, in the TNC grounding system shown in FIG. 1, when a singlephase ground fault occurs, the equipment contacts the voltageIs also a function of n, then f in step 11 _{3} (n) is expressed as the following formula:
f _{3} (n)＝U _{T} (4)
Step 12, constructing a multiobjective optimization model based on constraint conditions: the method comprises the following steps of constructing a multiobjective optimization model for calculating the number of grounding points of the TNC grounding system based on equality constraints and inequality constraints of the TNC grounding system, and specifically comprising the following steps:
wherein f is _{1} (n) is the total grounding cost of the TNC grounding system; f. of _{2} (n) is the reciprocal of a fault phase zero sequence current modulus when a singlephase earth fault occurs in the TNC grounding system; f. of _{3} (n) is a mapping relation which is satisfied when the equipment contact voltage h (n) represents the power grid obeys kirchhoff's law constraint, U _{safe} Indicating the safety voltage, I, prescribed by the TNC grounding system _{set} The action setting value of zero sequence protection on a circuit in the TNC grounding system is represented;
specifically, the derivation process of the constraint conditionbased multiobjective optimization model is as follows:
considering that when the grounding point is configured, the total grounding cost is as small as possible, the contact voltage of the equipment is as small as possible, and the fault phase current modulus I is simultaneously enabled _{0} As large as possible to ensure the zero sequence protection can operate smoothly, therefore, when configuring the grounding point, the objective function shown in formula (1) should be considered comprehensively:
minf(n)＝[f _{1} (n),f _{2} (n),f _{3} (n)] (1)
for the typical TNC grounding system shown in fig. 1, when a singlephase ground fault occurs, the system should also satisfy the following constraint relationship:
in the formula (5), x is a voltage vector and a current vector in the system, is a state variable of the system and is a function of n; g (x) =0 represents the circuit constraint relationship that the power grid should follow kirchhoff's law after the singlephase earth fault occurs, and since x is a function of n, g (x) =0 can be further expressed as g (x) = h (n) =0. In the formula (5), U _{safe} Represents the safety voltage, I, prescribed for TNC earthed systems _{set} The method is an action setting value of zero sequence protection on a line in the TNC grounding system.
By combining formula (1) and formula (5), the optimization model shown in formula (6) can be formed.
Wherein f is _{1} (n) is the total grounding cost of the TNC grounding system; f. of _{2} (n) is singlephase connection of TNC grounding systemThe reciprocal of the fault phase zero sequence current modulus at the time of ground fault; f. of _{3} (n) is the device contact voltage; h (n) represents a mapping relation, U, satisfied when the power grid complies with kirchhoff's law constraint _{safe} Indicating the safety voltage, I, prescribed by the TNC grounding system _{set} The action setting value of zero sequence protection on a circuit in the TNC grounding system is represented;
step 2, obtaining the optimal grounding quantity based on the multiobjective optimization model;
step 21, constructing an unconstrained weighting function based on the multiobjective optimization model, and modifying the objective function shown in the formula (6) into each objective weighted sum shown in the formula (7) in an unconstrained form, wherein the specific formula is as follows:
wherein u is _{1} 、u _{2} And u _{3} Are all weighting coefficients, α, β, λ _{k} Are penalty coefficients, N is the total number of the equation represented by h (N) =0 in the formula (6), h _{k} (n) is the kth element of the h (n) vector;
and 22, solving the optimal grounding number n based on the weighting function of the formula (7). Specifically, in this step, the existing mature algorithm may be selected to solve the formula (7), and as a feasible implementation, the particle swarm optimization algorithm is adopted to solve the weighting function of the formula (7) in step 22 to obtain the optimal ground number n.
The specific calculation process of the present invention is described below with respect to a specific embodiment:
taking the system shown in fig. 1 as an example, for simplicity, the resistance R on the horizontal ground in the actual grid is taken into account _{1} Relatively small, this example takes R approximately _{1} =0, the equivalent resistance to the earth system as seen from point O is R, according to fig. 1 _{O} ＝n×R _{2} Wherein R is _{2} Is the ground resistance of each ground electrode.
In this example, the system to the left of the bus B is assumed to be an infinite power system, i.e. the second transient supply potentialWhen short circuit occurs, the impedance is zero, and the impedance formed by winding resistance and leakage reactance of transformer is Z _{T} And the equivalent ground impedance of the parallel device is Z _{D} And mutual inductance between the effective conductive part of the device and the housing is jX _{M} 。
According to fig. 1, assuming that the cost of laying each grounding electrode is C, and n grounding electrodes are laid in total, according to the above steps, the following steps can be obtained: f. of _{1} (n)＝cn。
In fig. 1, when a singlephase ground fault occurs at point f, the equivalent positive sequence impedance viewed from point f is:
Z _{1∑} ＝(Z _{T} +Z _{L(1)} )//Z _{D} +Z′ _{L(1)} (e1)
z in the formula (e 1) _{L(1)} 、Z′ _{L(1)} Are positive sequence impedances of the supply lines, the former to the left of the device in fig. 1 and the latter to the right of the device in fig. 1.
The equivalent negative sequence impedance as seen from point f is:
Z _{1∑} ＝(Z _{T} +Z _{L(2)} )//Z _{D} +Z′ _{L(2)} (e2)
z in the formula (e 2) _{L(2)} 、Z′ _{L(2)} Are positive sequence impedances of the supply lines, the former to the left of the device in fig. 1 and the latter to the right of the device in fig. 1.
The equivalent zerosequence impedance seen from point f is:
Z _{0∑} ＝(Z _{T} +Z _{L(0)} +3nR _{2} )//Z _{D} +Z′ _{L(0)} (e3)
when a singlephase earth fault occurs at point f, the constraint that the corresponding circuit in fig. 1 should satisfy according to kirchhoff's law is as follows:
in the formula (e 4), the reaction mixture,positive, negative and zero sequence voltages of respective fault points The positive sequence current, the negative sequence current and the zero sequence current flowing through the fault point respectively, and the six quantities form a state vector x of the system, namely:
the abbreviation is written for equation (e 4) as:
g(x)＝0 (e6)
given the parameters of the system, it can be seen from the previous analysis that Z is a factor _{0∑} Is a function of n, so x in equation (e 6) is necessarily a function of n, and therefore equation (e 6) can be written in the abbreviated form shown in equation (e 7):
h(n)＝0 (e7)
the result shown in formula (e 8) can be obtained from formula (4) and FIG. 1.
By the formula (e 8)Taking the reciprocal after taking the modulus value to further obtain f _{2} (n)＝1/I _{0} 。
The results shown in formula (e 9) can be obtained from formula (e 8).
From the above, a multiobjective optimization model for calculating the number of grounding points of the system shown in FIG. 1 can be written, in this example, U _{safe} Is taken as 36V _{set} When 0.1A is taken, the model shown by the formula (e 10) can be obtained.
Next, this example will solve the model given by equation (e 10) in the form of equation (7) described in the aforementioned application. The weighting factor for each term in equation (7) can be given based on the importance of each term, in this case μ _{1} Is taken as 0.2, mu _{2} And mu _{3} Are all taken to be 0.4, in order to guarantee constraint, in this example α, β, λ _{k} Take larger values, all taken as 100.
Next, the model shown in formula (7) is solved by using the basic particle swarm optimization. The basic form of iteration is shown as equation (e 11).
In the formula (e 11), the reaction mixture,is the position of the particle i at the k iteration;the speed of the kth iteration of the particle i is generally required to be satisfiedP _{best·i} Is the optimal solution experienced by the particle i itself; g _{best} An optimal solution experienced for the entire population of particles; w is the coefficient of inertia, in this example decreasing in a linear manner from 0.9 to 0.1; c. C _{1} 、c _{2} For the acceleration constant, the value is taken to be 2 in this example; r is _{1} 、r _{2} Is [0,1]Random numbers are uniformly distributed in the interval. In a specific iteration, x is taken as the number n of the grounding electrodes to be solved in this example.
In this example, the parameters R in FIG. 1 _{2} Taken as 5 omega, Z _{T} Is taken as 0.02+j0.3 omega, Z _{D} Is taken as 0.4+ j1 omega, jX _{M} Taken as 0.2 omega, Z _{L(1)} Is taken as 0.6 j0.8 omega, Z _{L(2)} Is taken as 0.6 j0.8 omega, Z _{L(0)} Taken as 0.8+j2.4 omega, Z' _{L(1)} Taken as 0.3+ j0.4 omega, Z' _{L(2)} Taken as 0.3+ j0.4 omega, Z' _{L(0)} Take as 0.4+ j1.2 omega. And (4) iteratively calculating according to the formula (e 11) by using the programmed program, wherein the calculation result of the number n of the grounding electrodes is 11, namely the target shown in the formula (e 10) is achieved, and 11 grounding electrodes are needed in total.
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Claims (5)
1. The method for calculating the number of grounding points of the TNC grounding system based on multiobjective optimization is characterized by comprising the following steps: which comprises the following steps:
step 1, constructing a multiobjective optimization model for calculating the number of grounding points of the TNC grounding system;
step 11, constructing an objective function, wherein a specific formula is as follows:
minf(n)＝[f _{1} (n),f _{2} (n),f _{3} (n)] (1)
wherein f is _{1} (n) is the total grounding cost of the TNC grounding system; f. of _{2} (n) is the reciprocal of a fault phase zero sequence current modulus value when a singlephase earth fault occurs in the TNC grounding system; f. of _{3} (n) is the device contact voltage; n is the number of grounding points at the TNC grounding system, and the n grounding points are uniformly distributed;
f _{1} (n) is expressed as the following formula：
f _{1} (n)＝cn (2)
Wherein, c is the comprehensive investment of each set of grounding device;
f _{2} (n) is expressed as the following formula:
f _{2} (n)＝1/I _{0} (3)
wherein, I _{0} Indicating fault phase zero sequence current phasor when singlephase earth fault occurs in TNC grounding systemA modulus value of (d);
f _{3} (n) is expressed as the following equation:
f _{3} (n)＝U _{T} (4)
step 12, constructing a multiobjective optimization model based on constraint conditions: the method comprises the following steps of constructing a multiobjective optimization model for calculating the number of grounding points of the TNC grounding system based on equality constraints and inequality constraints of the TNC grounding system, and specifically comprising the following steps:
wherein h (n) represents a mapping relation which is satisfied when the power grid complies with kirchhoff law constraints, and U _{safe} Indicating the safety voltage, I, prescribed by the TNC grounding system _{set} The action setting value of zero sequence protection on the line in the TNC grounding system is represented;
step 2, calculating and obtaining the optimal grounding number based on the multiobjective optimization model;
step 21, constructing an unconstrained weighting function based on the multiobjective optimization model, wherein the formula is as follows:
wherein, mu _{1} 、μ _{2} And mu _{3} Are all weighting coefficients, α, β, λ _{k} N is the total number of the equation represented by h (N) =0 in the formula (6), h is a penalty coefficient _{k} (n) is the kth element of the h (n) vector;
and 22, solving the optimal grounding number n based on the weighting function of the formula (7).
2. The method for calculating the number of grounding points of the TNC grounding system based on multiobjective optimization according to claim 1, wherein: mu in step 21 _{1} Is taken to be 0.2 mu _{2} And mu _{3} Are all taken as 0.4; alpha, beta, lambda _{k} Are all taken as 100.
3. The method for calculating the number of grounding points of the TNC grounding system based on multiobjective optimization according to claim 1, wherein: and 22, solving the optimal grounding number n by adopting a particle swarm optimization algorithm based on the weighting function of the formula (7).
4. The method for calculating the grounding point number of the TNC grounding system based on multiobjective optimization according to claim 3, wherein: the iteration basic form of the particle swarm optimization algorithm is as follows:
wherein the content of the first and second substances,the iteration position of the particle i at the kth time is taken;the iteration speed of the particle i at the k time is satisfied P _{best·i} Is the optimal solution experienced by the particle i itself; g is a radical of formula _{best} An optimal solution experienced for the entire population of particles; w is an inertia coefficient which decreases in a linear manner from 0.9 to 0.1; c. C _{1} 、c _{2} Is an acceleration constant, r _{1} 、r _{2} Is [0,1]And uniformly distributing random numbers in the interval, and taking x as the number n of the grounding electrodes to be solved during iteration.
5. The method for calculating the number of grounding points of the TNC grounding system based on multiobjective optimization according to claim 4, wherein: c. C _{1} 、c _{2} The values of (c) were all taken to be 2.
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