CN104834819B - A kind of method for determining to draw outer earth mat optimal location - Google Patents

Abstract

The invention discloses a method for determining the optimal position of an external ground network, which is characterized in that: the unequal potential model of the main ground network and the external ground network is established, and the grounding resistance of the grounding system is obtained through calculation. A mathematical optimization model with the objective function of minimum grounding resistance of the grounding system and the length of the connecting line as a variable is established. The optimal connecting line length is obtained by using the genetic algorithm, so the optimal location of the ground network can be determined, so that the resistance reduction effect of the ground network can be achieved best while taking into account the economy.

Description

A Method of Determining the Optimum Position of the External Network

technical field

The invention discloses a method for determining the optimal length of a connection line of an external ground network, relates to the technical field of electric power system grounding, and is suitable for reducing grounding resistance by using an external ground network in the field of electric power engineering construction and determining the position of an external ground network.

Background technique

With the development of modern power grids in the direction of ultra-high voltage, large capacity, and long distances, the requirements for the safe and stable operation of power systems are getting higher and higher, so a good grounding system is required. In order to reduce the grounding resistance of the grounding system of the power substation and ensure the safe and reliable operation of the power system, auxiliary grounding measures are often used in engineering to reduce resistance.

Since the connection line itself has a certain impedance, the length of the connection line will affect the resistance reduction effect of the external ground network. When the external ground network is close to the main ground network, due to the large shielding effect, the resistance reduction effect of the external ground network is not obvious; The effect of reducing resistance is negligible, so determining the location of the ground network is of great significance for the effect of reducing resistance and economy.

Contents of the invention

In order to overcome the above-mentioned defects, the technical problem to be solved by the present invention is to provide a method for determining the optimal position of the external ground network, which can determine the optimal position of the external ground network, that is, the optimal length of the connecting line.

In order to achieve the above-mentioned technical purpose, the present invention is realized through the following technical solutions: a method for determining the optimal location of the connection line of the ground network for external introduction, the method includes the following steps:

The first step: establish the unequal potential model of the grounding system to obtain the grounding resistance of the grounding system;

Second step: set up with the grounding system grounding resistance minimum as objective function, the optimization model that connecting line length l is independent variable;

The third step: use the genetic algorithm to obtain the optimal length of the connection line, and obtain the minimum grounding resistance value of the grounding system.

In the first step, the grounding resistance of the grounding system of the unequal potential model is:

Among them: the self-resistance of the main ground network is recorded as R ₁₁ , the self-resistance of the external ground network is recorded as R ₂₂ , the resistance of the connection line is recorded as R _connection , and the mutual resistance between the main ground network and the external ground network is recorded as R ₁₂ .

In the second step, the following mathematical optimization model is established

Among them: l is the length of the connecting wire, R(l) is the grounding resistance of the grounding system.

The specific process of the third step is: encode the length of the connecting line with a real number, randomly generate a population of N individuals, use R(l) as the fitness function of the genetic algorithm, and calculate the fitness value of the individual in the population. And perform selection, crossover, and mutation operations on individuals in the population, the specific operations are as follows:

1. Selection: The selection operation selects excellent individuals from the old population with a certain probability to form a new population. The genetic algorithm selection operation adopts the roulette method, that is, individuals with high individual fitness have a high probability of being selected, so as to ensure excellent The individual remains.

2. Crossover: Since the individual is coded with real numbers, the crossover position is randomly selected according to a certain crossover probability.

3. Mutation: With a given mutation probability, randomly select the mutation position.

Then check whether the end condition is satisfied (whether the maximum number of iterations is reached), if it is satisfied, the optimal connection line length and the corresponding grounding resistance value will be obtained, if not, it will return to the selection operation.

In order to better illustrate the present invention, the main ground grid and the external ground grid have been replaced by two vertical ground electrodes respectively, and the vertical ground electrodes are connected by connecting lines.

The beneficial effect of the invention is that the resistance-reducing effect of the external ground net can be fully utilized to obtain the optimal placement position of the external ground net, and both economy and resistance-reduction effect are taken into consideration.

Description of drawings

Figure 1 is the unequal potential model of the grounding system;

Figure 2 is the unequal potential model under the vertical grounding electrode;

Figure 3 is the change curve of the length of the connecting line and the grounding resistance of the grounding system;

Figure 4 is a flow chart of the genetic algorithm.

detailed description

The technical solutions of the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. Among them, grounding electrode #1 and grounding electrode #2 are described by using vertical grounding electrodes. To enable those skilled in the art to better understand and implement the present invention, the examples given are not intended to limit the present invention.

Fig. 1 is the unequal potential model of the grounding system, which is composed of #1 main ground network and #2 external ground network and connecting lines; the voltage of the #1 main ground network is V ₁ , and the current flowing into the earth is I ₁ ; The voltage of the above-mentioned #2 lead-out ground network is V ₂ , and the current flowing into the ground is I ₂ ; the current of the connecting line is I ₂ .

Figure 2 is the unequal potential model under the vertical ground electrode, which is composed of vertical ground electrode #1, vertical ground electrode #2 and ground wire, taking #1 and #2 vertical ground electrodes located in uniform soil (resistivity ρ) as an example, From this model, the grounding resistance of the grounding system can be obtained.

---System grounding resistance

in: --- Vertical ground electrode #1 self-resistance

--- Vertical ground electrode #2 self-resistance

R _even = R ₀ l --- connecting wire resistance

--- Mutual resistance between #1 and #2 vertical ground electrodes

Where: ρ is the uniform soil resistivity, Ω·m

L ₁ is the length of the vertical ground electrode 1, m

L ₂ is the length of the vertical ground electrode 2, m

a is the radius of the vertical ground electrode, m

l is the length between ground electrodes, m

R ₀ is the unit resistance of the connecting wire, Ω/m

I is the grounding current of the grounding system, A

V ₁ is the vertical ground #1 voltage, V

I ₁ is the current flowing into the earth from the vertical ground electrode #1, A

I ₂ is the current flowing into the earth from the vertical ground electrode #2 current, A

Set the length of vertical ground electrodes #1 and #2 to be 40m, and the soil resistivity is 1000Ω·m. The radius of the vertical grounding electrode and the connection line is 0.1m, and the unit resistance of the connection line is 0.5Ω/km.

Figure 3 is the change curve of the grounding resistance of the grounding system as the length of the connecting line changes. It can be seen from the figure that there is an optimal length of the connecting line to minimize the grounding resistance of the grounding system. Therefore, the optimal value is obtained by genetic algorithm.

Figure 4 is a flowchart of the genetic algorithm. Through the optimization of the genetic algorithm, it is obtained that when the length of the connecting line is 2222.84m, the grounding resistance of the grounding system reaches the minimum value, and the minimum value is 13.30Ω. Simultaneously by CDEGS simulation, when the connecting line length is 2222.84m, its grounding resistance is 12.85Ω. The difference between the two is 3.3%, which shows the accuracy of the above grounding resistance calculation formula.

The above are only examples of the present invention, and do not limit the patent scope of the present invention. Any equivalent structure or equivalent process conversion made by using the description of the present invention and the contents of the accompanying drawings, or directly or indirectly used in other related technical fields, All are included in the scope of patent protection of the present invention in the same way.

Claims (1)

1. a kind of method that outer earth mat connecting line optimal location is drawn in determination, the method includes following steps：

The first step:Earthed system not equipotential model is set up, earthed system earth resistance is obtained；The not equipotential model connects Ground system earth resistance be：

Wherein：Main earth mat is designated as R from resistance₁₁, draw outer earth mat and be designated as R from resistance₂₂, connect line resistance and be designated as R_Even, main earth mat and draw other places Mutual resistance between net is designated as R₁₂；Main earth mat and drawing connected by connecting line between outer earth mat；

Earthed system is in equipotential model, main earth mat and draws outer earth mat and is respectively set as vertical grounding electrode #1, vertical grounding electrode # 2,

Wherein：

R_Even=R₀L--- connects line resistance

ρ is uniform soil resistivity, Ω m

L₁It is the length of vertical grounding electrode #1, m

L₂It is the length of vertical grounding electrode #2, m

A is vertical grounding electrode radius, m

L is the length between earthing pole, m

R₀It is connecting line unit resistance, Ω/m

I is earthed system earth current, A

V₁It is vertical grounding electrode #1 voltages, V

I₁It is the electric current that the earth is flowed into by vertical grounding electrode #1, A

I₂It is the electric current that the earth is flowed into by vertical grounding electrode #2 electric currents, A；

Second step:Set up with the minimum object function of earthed system earth resistance, connection line length is the mathematical optimization of independent variable Model；Set up following mathematic optimal model

$\left\{\begin{array}{c}minR\left(l\right)\\ l>0\end{array}\right.$

Wherein：L is connection line length；

R (l) is earthed system earth resistance,

3rd step:Using genetic algorithm, connecting line optimization length is obtained, and obtain the minimum grounding resistance of earthed system；Tool Body process is：Real coding is carried out to connection line length, the population of individuality is randomly generated, using R (l) as genetic algorithm Fitness function, is calculated the fitness value in population at individual；And the individuality in population is selected, is intersected, make a variation behaviour Make, then investigate whether meet termination condition, i.e., whether reach maximum iteration, such as meet if obtain it is optimal connect line length and Corresponding grounding resistance, is such as unsatisfactory for, then be back to genetic algorithm selection operation；Selection：Selection operation from old population with The excellent individuality of certain probability selection constitutes new population, and the genetic algorithm selection operation uses wheel disc bet method, i.e., individual Fitness individuality high, the probability chosen is big, so ensures that defect individual retains；Intersect：Because individuality is compiled using real number Code, i.e., according to certain crossover probability, randomly choose crossover location；Variation：Under given mutation probability, random selection becomes dystopy Put.