CN104201664A - Distributed grounding electrode design method for high-voltage direct-current transmission system - Google Patents

Abstract

A design method for a distributed ground electrode used in a HVDC transmission system, including step 1, initially selecting the scope of the new ground electrode according to the planning and land acquisition, and determining the optimal location of the new ground electrode through the global optimal position variation particle swarm optimization algorithm the best position; Step 2, determine the maximum potential rise of the sub-poles by the temperature rise of the grounding electrodes, and check the step potential; Step 3, connect all the grounding electrodes and the newly-built sub-poles through overhead lines; Step 4, establish distribution A unified model for the DC current distribution of the grounding pole and the AC grid; step five, predict the risk of DC bias in each transformer in the AC grid according to the solved DC current distribution in the AC grid; step six, predict the risk of DC bias Transformers, take measures to suppress or even eliminate the adverse effects of DC bias problems. The invention can reduce the risk of DC bias and can predict the degree of DC bias after completion, reducing the damage caused by DC bias.

Description

A Design Method for Distributed Grounding Electrode Used in HVDC Transmission System

technical field

The invention relates to the field of high-voltage direct current transmission engineering design, in particular to a design method for distributed grounding electrodes of a high-voltage direct current transmission system.

Background technique

At present, my country's receiving end converter stations are often located in economically developed areas, where the population density is high, the grid structure is huge and complex, and there are many underground metal facilities (such as oil and gas transmission and water supply pipelines, etc.), which makes the traditional conventional grounding electrode Under the design mode, the site selection of DC grounding electrode becomes more and more difficult. At the same time, with the massive operation of large-capacity UHV DC transmission projects, the problems of electromagnetic compatibility caused by the DC transmission ground current and the harmonics of the converter station have become more prominent, and the DC transmission ground current has a series of adverse effects on the environment and other systems. . However, the site selection of traditional converter stations mainly considers anti-fouling issues to prevent flashover, the impact of noise on the environment, transportation and installation of large equipment, and rarely considers the impact of DC transmission ground current on the AC grid.

The distributed DC grounding pole is composed of several sub-grounding poles (referred to as sub-poles) located in different regions in terms of geographical location. Electrically, it is a grounding system in which multiple sub-poles are electrically connected through feeder lines. The geographical wiring diagram of distributed grounding electrodes is shown in Figure 1. The use of distributed grounding poles can not only reduce the difficulty of DC pole site selection, but also reduce the impact of the DC system on the AC grid. The AC grid can achieve a good DC bias suppression effect without taking measures or only taking a small amount of suppression measures.

However, the site selection of traditional distributed grounding poles does not consider the degree of influence of the DC current into the ground on the AC grid, so that it is impossible to predict the risk of DC bias of each transformer in the AC grid, resulting in the inability to predict the risk of DC bias for transformers with a high risk of DC bias. Taking measures will lead to losses due to DC bias problems after the new grounding pole is put into operation.

Contents of the invention

The invention provides a design method for a distributed grounding pole used in a high-voltage direct current transmission system, which can consider the degree of influence of the direct current into the ground on the AC power grid when selecting a site, and then predict the DC bias of each transformer in the AC power grid after completion Therefore, measures can be taken in advance to reduce or eliminate the loss caused by the DC bias problem after the new grounding pole is put into operation.

A design method for a distributed grounding electrode used in a high-voltage direct current transmission system, comprising the following steps:

Step 1. Preliminarily select the scope of the new ground electrode according to the planning and land acquisition, and determine the best position of the new ground electrode through the global optimal position variation particle swarm optimization algorithm;

Step 2. Determine the maximum potential rise of the sub-pole by the temperature rise of the ground electrode, and check the step potential;

Step 3. Connect all ground electrodes and newly-built sub-poles through overhead lines to form a distributed ground electrode. The wiring method of the distributed ground electrode refers to the substation wiring method of the power system;

Step 4. Establish a unified model of the distributed grounding electrodes and the DC current distribution of the AC grid to evaluate the impact of the distributed grounding electrodes on the DC current distribution of the AC grid;

Step 5. According to the DC current distribution in the AC grid solved in the above steps, predict the risk of DC bias in each transformer in the AC grid;

Step 6: Take measures to suppress or even eliminate the adverse effects of DC bias problems for transformers that are predicted to have DC bias risks.

Among them, Step 1 is specifically:

a. Define the objective function, and take the minimum average value of the transformer magnetomotive force in the system, the minimum average neutral point current of the transformer or the minimum maximum neutral point current of the transformer as the objective function;

b. Initialize the position and velocity of the particles, and obtain the initial global optimal solution g*=min[f(p1),...,f(pn)], t=0, where p1,...,pn are initialization The n groups of solutions of are all two-dimensional vectors containing the abscissa and ordinate information of the solution, f(p1), ..., f(pn) are the objective function values corresponding to p1, ..., pn respectively; t is the optimal calculation The number of cycles, the initial position and velocity of the particles should be uniformly distributed throughout the valid range of the inversion parameters

${\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&eta;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&eta;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

In the formulas (1) and (2), x _max , y _max and x _min , y _min are the maximum and minimum values of the abscissa and ordinate of the new DC grounding electrode or substation respectively, and η _i is a random number between 0 and 1 number, the initial velocity of the particle is generally set to 0, that is

c. t=t+1, for all n _p particles, use the formula (3) to generate a new velocity vti, then update the particle position according to the formula (4), and calculate the objective function of each particle, and update each particle’s The optimal position x*i, and obtain the current global optimal solution g*;

${\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

In formula (1), pi and vi are the velocity and position of particle i respectively, θ is the inertia weight, its function is to maintain the inertia of particle motion, so that the algorithm has a tendency to expand the search space and has the ability to explore new areas, θ∈ [0.5,0.9], ε ₁ and ε ₂ are two 2-dimensional random vectors between 0 and 1; x⊙y=[xi*yi], α and β are acceleration coefficients;

d. If the objective function value no longer decreases or exceeds the number of iterations, then output the result, otherwise t=t+1, go to step c.

Beneficial effects of the present invention:

1. Determine the optimal site selection for the new DC grounding pole through the calculation of the global optimal position variation particle swarm optimization algorithm in the early stage, reduce the risk of DC bias and predict the degree of DC bias after completion, and reduce the damage caused by DC bias.

2. When selecting the site for the new grounding pole, predict the risk of DC bias in each transformer of the AC grid after completion, so that measures can be taken in advance to reduce or eliminate the loss caused by the DC bias problem after the new grounding pole is put into operation.

Description of drawings

Figure 1 is a schematic diagram of the wiring of the distributed grounding electrode system;

Fig. 2 is a schematic flow chart of the design method of the distributed ground electrode used in the HVDC power transmission system according to the present invention.

Detailed ways

The technical solutions in the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the present invention.

The invention provides a design method for a distributed grounding electrode used in a high-voltage direct current transmission system, which includes the following steps:

Step 1. Preliminarily select the scope of the new grounding electrode according to the planning and land acquisition, and determine the best position of the new grounding electrode through the global optimal position variation particle swarm optimization algorithm.

Specifically, Step 1 is as follows:

a. Define the objective function. The minimum average value of the transformer magnetomotive force in the system, the minimum average neutral point current of the transformer or the minimum maximum neutral point current of the transformer can be used as the objective function. The independent variable p=(x, y), represents the coordinates of the new DC grounding pole or substation.

b. Initialize the position and velocity of the particles, and obtain the initial global optimal solution g*=min[f(p1),...,f(pn)], t=0, where p1,...,pn are initialization The n groups of solutions of are all two-dimensional vectors containing the abscissa and ordinate information of the solution, f(p1), ..., f(pn) are the objective function values corresponding to p1, ..., pn respectively; t is the optimal calculation Cycles. The starting positions and velocities of the particles should be evenly distributed throughout the valid range of the inversion parameters

${\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&eta;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&eta;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

In the formulas (1) and (2), x _max , y _max and x _min , y _min are the maximum and minimum values of the abscissa and ordinate of the new DC grounding electrode or substation respectively, and η _i is a random number between 0 and 1 number. The initial velocity of particles is generally set to 0, that is,

c. t=t+1, for all n _p particles, use the formula (3) to generate a new velocity vti, then update the particle position according to the formula (4), and calculate the objective function of each particle, and update each particle’s The optimal position x*i, and obtain the current global optimal solution g*.

${\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

In formula (1), p _i and v _i are the velocity and position of particle i respectively, θ is the inertia weight, its function is to maintain the inertia of particle motion, so that the algorithm has the tendency to expand the search space and has the ability to explore new areas, θ∈[0.5,0.9], the present embodiment takes θ=0.7; ε ₁ and ε ₂ are random vectors between two 2-dimensional 0～1; x⊙y=[xi*yi], α and β are Acceleration coefficient, in general, α=β=2. In addition, vi may take any value, but in practice, the upper and lower limits of the speed should be set to prevent divergence, and the upper and lower limits of the speed are generally set according to the range of the element interval.

d. If the objective function value no longer decreases or exceeds the number of iterations, then output the result, otherwise t=t+1, go to step c.

The invention calculates and determines the optimal site selection of the new DC grounding pole through the global optimal position variation particle swarm optimization algorithm, which can reduce the risk of DC bias and predict the degree of DC bias after completion, reducing the damage caused by DC bias.

Step 2. Determine the maximum potential rise of the sub-pole by the temperature rise of the ground electrode, and check the step potential:

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; =</span>\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&lambda;\&rho;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; my</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

In the above formula (5), Ve is the potential rise (V) allowed by the grounding electrode, λ is the thermal conductivity of the soil (W/m/°C), ρ is the resistivity of the soil (Ω·m), and θ _c is The maximum earth temperature (°C) of the pole address of the grounding electrode, θ _my is the maximum temperature (°C) of the grounding electrode allowed by the design.

The step potential can be verified by the following formula Em:

E _m =7.42+0.0318ρ _s (6)

In formula (6), ρs is the surface earth resistivity.

Step 3: Connect all the grounding electrodes and newly-built sub-poles through overhead lines to form a distributed grounding electrode. The wiring method of the distributed grounding electrode can refer to the wiring method of multiple substations in the power system, as shown in Figure 1.

Step 4: Establish a unified model of the distributed grounding electrodes and the DC current distribution of the AC grid to evaluate the impact of the distributed grounding electrodes on the DC current distribution of the AC grid.

The node voltage equation of distributed grounding electrode and DC current distribution unified network of AC grid:

YU＝J (7)

In formula (7), Y is the node conductance array, U is the node voltage array, J is the node injection current vector, and their expressions are respectively

U=[U _A ; U _D ] (8)

$\mathrm{<span\; class="notranslate">\; Y</span>}<span\; class="notranslate">\; =</span>\left[\begin{array}{cc}{\mathrm{<span\; class="notranslate">\; Y</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& {\mathrm{<span\; class="notranslate">\; Y</span>}}_{\mathrm{<span\; class="notranslate">\; D.</span>}}\end{array}\right]<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 9</span>}<span\; class="notranslate">\; )</span>$

The definition of the current vector injected by the node is:

J＝H′GP (10)

In the above formula (10), H′GP is the equivalent current injection vector of all nodes in the unified network; H is the correlation matrix between substation nodes and all nodes, H′ is the transpose of H; P is the induced potential column vector of substation .

$\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; =</span>\left[\begin{array}{cc}{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& {\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; D.</span>}}\end{array}\right]<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 11</span>}<span\; class="notranslate">\; )</span>$

In the above formulas (8)-(11), the variables with the subscript A represent the variables of the AC power grid, and the variables with the subscript D represent the variables of the distributed grounding electrodes.

For ground conductance there are:

$\mathrm{<span\; class="notranslate">\; G</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>{\left[\begin{array}{cccc}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& <span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span>& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& {\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; D.</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& <span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span>\end{array}\right]}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 12</span>}<span\; class="notranslate">\; )</span>$

For the induced potential there are:

P=MI (13)

In formula (13), M represents the mutual resistance matrix of the large system composed of substations and sub-poles in the unified network, and I represents the column vector of the substation and sub-poles' ground current. The definition of ground current is:

I＝G(HU-P) (14)

Combining formulas (7), (11), (13) and (14) can complete the unified model for calculating the DC current distribution of the entire distributed grounding electrode and AC grid, and the final solution formula is as follows:

C=[YH′GM(R+M) ^-1 H]U (15)

By solving the equation of formula (15), the node voltage distribution of the unified model can be obtained, and then the DC current distribution of the entire power grid can be obtained.

Step 5: According to the DC current distribution in the AC grid obtained in the above step, the risk of DC bias magnetic field occurrence in each transformer in the AC grid is predicted. If the absolute values of the transformer neutral point currents monitored in the AC power grid are: A1, A2...An, for a single transformer, it can be based on the requirements of DL/T 437-2012 "High Voltage DC Grounding Electrode Technical Guidelines", or according to The neutral point DC current threshold I _λ is set according to local actual conditions. For transformers with neutral point current A _i >I _λ , it can be considered that there is a DC bias risk after the new grounding pole is put into operation.

Step 6. For the transformers that are predicted to have the risk of DC bias, add resistance and capacitance to the neutral point, or take DC blocking measures to suppress or even eliminate the adverse effects of DC bias problems.

Taking a certain DC pole in Hubei Province as an example, assuming that due to survey and land acquisition, the scope of the new DC grounding pole is limited to the area of (111.37,30.51), (111.50,30.51), (111.50,30.63), (111.37,30.63) In the new DC grounding pole, the current into the ground is 3000A, the grounding resistance is 0.2 ohms, and the buried depth is 3m. The method of the present invention is used to optimize the calculation of the grounding pole position. 2. The average neutral point current of the transformer within the 100km range is the smallest; 3. The maximum neutral point current of the transformer within the 100km range is the smallest; 4. The maximum DC magnetomotive force of the transformer within the 100km range is the smallest; 5. The 100km range The average neutral point current of the 500kV transformer in the system is the smallest; 6. The average neutral point current of the 220kV transformer in the system within 100km is the smallest; 7. The average DC magnetomotive force of the 500kV transformer in the system within 100km is the smallest; 8. Within the system within 100km The average DC magnetomotive force of the 220kV transformer is the smallest. The optimization effects of the eight cases are shown in Table 1.

Table 1 Optimal results of site selection for DC grounding electrodes

It can be seen from Table 1 that no matter which optimization objective function is chosen, the global optimal position mutation particle swarm optimization algorithm has achieved good application results. In practical applications, the objective function should be the minimum average DC magnetomotive force of transformers within the system within 100km.

Claims (2)

1. for a method for designing for the distributed earth electrode of HVDC (High Voltage Direct Current) transmission system, it is characterized in that comprising the steps:

Step 1, according to the scope of planning and the preliminary selected newly-built earth electrode of expropriation of land, determine the optimum position of newly-built earth electrode by global optimum's position Particle Swarm Optimization Algorithm;

Step 2, raise by the maximum potential of the true stator poles of earth electrode temperature rise, and verification step voltage;

Step 3, by overhead transmission line, all earth electrodes and the newly-built sub-utmost point are connected, form distributed earth electrode, the mode of connection of distributed earth electrode is carried out with reference to the bus arrangement mode of electric power system;

Step 4, set up the unified model that distributed earth electrode and AC network direct current distribute, impact AC network direct current being distributed to assess distributed earth electrode;

Step 5, distribute according to direct current in the AC network solving in above-mentioned steps, the risk of each transformer generation D.C. magnetic biasing in prediction AC network;

Step 6, to there is the transformer of D.C. magnetic biasing risk in prediction, the adverse effect that D.C. magnetic biasing problem is brought of taking measures to suppress even to eliminate.

2. the method for designing of the distributed earth electrode for HVDC (High Voltage Direct Current) transmission system as claimed in claim 1, is characterized in that step 1 is specially:

A, objective definition function, in system, the maximum neutral point current minimum of transformer magnetomotive force mean value minimum, the average neutral point current minimum of transformer or transformer is as target function;

The position of b, initialization particle and speed, and obtain initial globally optimal solution g*=min[f (p1), ..., f (pn)], t=0, wherein p1 ..., pn is that initialized n group is separated, be the abscissa that comprises solution and the bivector of ordinate information, f (p1) ..., f (pn) is p1, the target function value that pn difference is corresponding, t optimizes the cycle-index of calculating, and the original position of particle and speed should be evenly distributed among effective codomain of whole inverted parameters

$x_i^{t=0}=x_{\min }+{\mathrm{\&eta;}}_i(x_{\max }-x_{\min })---\left(1\right)$

$y_i^{t=0}=y_{\min }+{\mathrm{\&eta;}}_i(y_{\max }-y_{\min })---\left(2\right)$

In formula (1), (2), x _max, y _maxand x _min, y _minbe respectively maximum and the minimum value of newly-built direct current grounding pole or transformer station's horizontal stroke, ordinate, η _ibe the random number between 0～1, the starting velocity of particle is made as 0,

C, t=t+1, to all n _pindividual particle, uses formula (3) to produce new speed v t _i, then press formula (4) and upgrade particle position, and calculate the target function of each particle, upgrade the optimal location x*i of each particle, and obtain current globally optimal solution g*;

$p_i^{t+1}{=p}_i^t+v_i^{t+1}---\left(4\right)$

In formula (1), p _iand v _ibe respectively speed and the position of particle i, θ is inertia weight, and its effect is the inertia that keeps Particles Moving, makes algorithm have the trend in expanded search space and has the ability to explore new region, θ ∈ [0.5,0.9], ε ₁and ε ₂be two 2 dimension 0～1 between random vector; X ⊙ y=[xi*yi], α and β are accelerator coefficient;

If d target function value no longer reduces or exceeds iterations, Output rusults, otherwise t=t+1, proceed to step c.