CN103560500A - Energy-saving selecting method for grounding resistor of transformer substation grounding transformer - Google Patents

Abstract

The invention relates to an energy-saving selecting method for a grounding resistor of a transformer substation grounding transformer. The energy-saving selecting method includes the steps that step1, a resistor power loss model of a grounding transformer neutral point is built; step2, a primary resistance value of the grounding resistor is calculated; step3, a final resistance value of the grounding resistor is determined, and the 85% margin of the resistance value obtained through calculation in the step2 is taken as the finally determined resistance value of the grounding resistor. The relation between the resistance value of the transformer substation grounding transformer neutral point and power loss is analyzed, in this way, the resistor power loss mathematic model is built, and an optimum resistor selecting method is provided on the premise that zero-sequence protection sensitivity of a transformer substation grounding transformer is not changed, so that energy-saving operation of transformer substation equipment is achieved, and service life of the grounding equipment is prolonged.

Description

The energy-conservation choosing method of substation grounding transformer grounding resistance

Technical field

The invention belongs to Study on Power Grid Planning field, be applicable to the earth resistance energy-saving design of substation grounding transformer, be specifically related to a kind of energy-conservation choosing method of substation grounding transformer grounding resistance.

Background technology

The neutral grounding mode of electric power system is a global question; it is relevant with electric pressure, single-line to ground fault electric current, overvoltage level, protection configuration etc., and directly affects the insulation level of electrical network, the security of operation of the reliability of system power supply and continuity, main transformer and generator and to interference of communication line etc.In recent years along with China's urban distribution network development, the application of cable line is on the increase, the capacity current existing in system also constantly increases, according to the overvoltage protection of < < alternating-current electric device and insulation coordination DL/T620-1997 > > 3.1.4 bar code requirement, " when single phase ground fault capacitance current is larger, can adopt low resistance grounding mode, but should consider power supply reliability requirement, instantaneous voltage during fault, the impact of transient current on electric equipment, on the impact of communication and Protection Technology requires and local operating experience etc. ".Therefore, many areas all adopt Experiences, and conventionally selecting resistance value is the effective grounding that the earth resistance of 10 ohm is realized system.

But; in production real process, because three-phase operation voltage in electric power system exists degree of unbalance to a certain degree, therefore when normal operation; on earth resistance, also can flow through a certain amount of unsymmetrical current; thereby on earth resistance, produce power loss, cause resistive element heating, this configuration mode not only energy-saving effect is poor; when serious, even may damage electric equipment; therefore be necessary choose reasonable earth resistance, realize transformer station's energy-saving run, effectively protect equipment.

Summary of the invention

The present invention is directed to the neutral resistance operation thermal losses problem bigger than normal that the grounding transformer in China's electrical network isolated neutral system is drawn, a kind of energy-conservation choosing method of substation grounding transformer grounding resistance is provided.

The present invention solves its technical problem and takes following technical scheme to realize:

An energy-conservation choosing method for transformer grounding resistance, comprises that step is as follows:

The first step, sets up grounding transformer neutral resistor power loss model; By the constraints of the quantity of transformer station's cable outlet, grounding transformer current quick, grounding transformer overcurrent protection, neutral resistor zero-sequenceprotection, transformer capacity; by impedance matching principle, obtain grounding transformer neutral resistor power loss model:

$\left\{\begin{array}{c}P=u^2/r\\ i_c=100\mathrm{\&pi;}{C}_0{u}_n\mathrm{nl}/\sqrt{3}=181.3C_0{U}_N\mathrm{nl}\\ i_{\mathrm{dl}}^i>i_a+i_b+i_c>i_c\\ i_{\mathrm{dl}}^{\left(1\right)}=u_n/(r_k+{\mathrm{jx}}_k)\end{array}\right.$ Formula (one)

In above formula, u, r is respectively neutral point voltage and earth resistance, is the variable intercoupling; C ₀for unit length cable earth capacitance, u _nfor the rated operational voltage of cable, l is cable length, and n is cable outlet number, is constant;

Second step, earth resistance primary election value is calculated;

There is capacitance current i in transformer load _cfor benchmark, press unit cable capacitance current as base, utilize following formula to solve neutral resistance primary election value,

R _n+1=(u _n+ Δ i * r _n-1)/(i _min+ Δ i * (n-1)) formula (two)

In formula, r _nrepresent the n time iterative value of neutral resistor, n=1 ... m (cable returns number), Δ i represents the capacitance current that 1 telegram in reply cable wrap contains, i _minrepresent transformer transmission line circuit number hour capacitance current, initial value r ₁get 0 to u _n/ i _minbetween arbitrary value;

The 3rd step, earth resistance final value is determined;

According to the first step, in formula (), the third line and fourth line neutral point current allowed band, utilize zero-sequenceprotection sensitivity, gets second step, and the nargin of the earth resistance resistance 85% calculating in formula (two) is as the final determined value of earth resistance.

Advantage of the present invention and good effect are

1, the present invention is by analyzing the relation of substation grounding transformer neutral point resistance and power loss, set up small resistor power loss Mathematical Modeling, and under the prerequisite of zero-sequenceprotection sensitivity that does not change substation grounding transformer, propose optimal resistance choosing method, realized the energy-saving run of substation equipment;

2, the present invention can reduce the power loss of grounding through resistance, extends the useful life of grounding apparatus.

Accompanying drawing explanation

Fig. 1 is method step flow chart of the present invention.

Embodiment

Below in conjunction with accompanying drawing, the invention process is further described, following examples are descriptive, are not determinate, can not limit protection scope of the present invention with this.

An energy-conservation choosing method for transformer grounding resistance, as shown in Figure 1, comprises that step is as follows:

The first step, sets up grounding transformer neutral resistor power loss model; By the constraints of the quantity of transformer station's cable outlet, grounding transformer current quick, grounding transformer overcurrent protection, neutral resistor zero-sequenceprotection, transformer capacity; by impedance matching principle, obtain grounding transformer neutral resistor power loss model:

$\left\{\begin{array}{c}P=u^2/r\\ i_c=100\mathrm{\&pi;}{C}_0{u}_n\mathrm{nl}/\sqrt{3}=181.3C_0{U}_N\mathrm{nl}\\ i_{\mathrm{dl}}^i>i_a+i_b+i_c>i_c\\ i_{\mathrm{dl}}^{\left(1\right)}=u_n/(r_k+{\mathrm{jx}}_k)\end{array}\right.$ Formula (one)

In above formula, u, r is respectively neutral point voltage and earth resistance, is the variable intercoupling; C ₀for unit length cable earth capacitance, u _nfor the rated operational voltage of cable, l is cable length, and n is cable outlet number, is constant.

From formula (), can find out, want to realize neutral resistor power minimum, should reduce neutral point voltage as far as possible or increase neutral resistor, but, grounding transformer neutral resistor in real work can not be infinitely great, need to meet the sensitivity impact of ground connection zero-sequenceprotection, so earth resistance need to be chosen in certain interval;

Second step, earth resistance primary election value is calculated;

There is capacitance current i in transformer load _cfor benchmark, press unit cable capacitance current as base, increase gradually neutral point current, and consider the uncertainty of transformer lines quantity, utilize following formula to solve neutral point primary election resistance value,

R _n+1=(u _n+ Δ i * r _n-1)/(i _min+ Δ i * (n-1)) formula (two)

In formula, r _nrepresent the n time iterative value of neutral resistor, n=1 ... m (cable returns number), Δ i represents the capacitance current that 1 telegram in reply cable wrap contains, i _minrepresent transformer transmission line circuit number hour capacitance current, initial value r ₁desirable 0 to u _n/ i _minbetween arbitrary value;

The 3rd step, earth resistance final value is determined;

According to the third line in formula () and fourth line neutral point current allowed band; in conjunction with the earth resistance resistance calculating in formula (two); utilize zero-sequenceprotection sensitivity, choose the nargin of the earth resistance resistance 85% calculating in formula (two) as the final determined value of earth resistance.

Calculate and finish.

Illustrate the resistance value design that adopts this method to determine grounding transformer below:

According to < < conductor and electrical equipment, select the earth resistance in designing technique regulation > > (DL/T5222-2005) 18.2.6 to select computing formula:

$R_n=U_N/\left(\sqrt{3}{I}_d\right)$

Wherein, I _dfor selected single-phase-to-ground current, A.

The about 2.5km of average radius of electricity supply of somewhere 10kV electric pressure circuit, conventional 10kV cable model is 3*240mm ², transformer station builds three transformers conventionally, 10kV side design outlet 36 times.

(1) traditional approach is selected resistance:

If according to traditional approach, the small resistor general choice 600A of 10kV grounding transformer, the parameter of 10s,

$R_n=U_N/\left(\sqrt{3}{I}_d\right)=10\&times;{10}^3/(\sqrt{3}\&times;600)=9.623\&ap;10\mathrm{\&Omega;}.$

And the Energy Saving Algorithm proposing according to the present invention (2):

The first step, according to grounding transformer neutral resistor loss model, in conjunction with regional actual conditions, considers while supposing actual motion that a transformer transmission line circuit number 24 is back to 36 times, and cable outlet, utilizes formula (), and the capacitance current that calculates single-phase earthing is:

$i_{\max }=100\mathrm{\&pi;}{C}_0{U}_{N}l/\sqrt{3}=181.3C_0{U}_{N}l=2\&times;2.5\&times;36=180A$

$i_{\min }=100\mathrm{\&pi;}{C}_0{U}_{N}l/\sqrt{3}=181.3C_0{U}_{N}l=2\&times;2.5\&times;24=120A$

And the capacitance current of every cable is Δ i=5A.

Second step, earth resistance primary election value is calculated; Take the single-phase-to-ground current 180A that calculates as basis, get r ₁=1 ohm, according to formula (two), solve r _n:

$R_{\mathrm{ini}\min }=(U_N+5\&times;24)/(I_{\min }+60))=10\&times;{10}^3/\sqrt{3}/240=24.35\mathrm{\&Omega;}$

The 3rd step, earth resistance final value is determined;

Utilize zero-sequenceprotection sensitivity; conventionally in 100 amperes to 600 amperes intervals; choose the nargin of the earth resistance resistance 85% calculating in formula (two) as the final determined value of earth resistance; r=20.67 ohm; round rear r=21 ohm; the customization of now zero-sequenceprotection, at 500 amperes, meets zero-sequenceprotection sensitivity.

The energy saving comparison of (3) two kinds of resistance selection methods:

When main transformer moves, because 10kV side load may exist the situation of three-phase imbalance, thereby produce at low pressure neutral point the side-play amount that amplitude peak is 10%.According to conventional design, while selecting earth resistance, selection work electric current 600A, resistance value are 10 Europe, can produce the power loss of 36kW while normally moving on resistor.This programme is considered this part energy-conservation demand, in design, meeting under earth resistance defencive function prerequisite, suitably increases grounding resistance; reduce operating current; selection work electric current is that 300A, resistance value are the earth resistance in 20 Europe, and the power loss of this part element is down to 18kW, has reduced power consumption.By using the change of 3 ground connection, annual maximum can save power 473.04MW, and electricity price is calculated by 0.5 yuan/kWh, and annual realization saved 23.65 ten thousand yuan of maximum economic benefits.

Claims (1)

1. an energy-conservation choosing method for substation grounding transformer grounding resistance, is characterized in that comprising that step is as follows:

The first step, sets up grounding transformer neutral resistor power loss model; By the constraints of the quantity of transformer station's cable outlet, grounding transformer current quick, grounding transformer overcurrent protection, neutral resistor zero-sequenceprotection, transformer capacity; by impedance matching principle, obtain grounding transformer neutral resistor power loss model:

$\left\{\begin{array}{c}P=u^2/r\\ i_c=100\mathrm{\&pi;}{C}_0{u}_n\mathrm{nl}/\sqrt{3}=181.3C_0{U}_N\mathrm{nl}\\ i_{\mathrm{dl}}^i>i_a+i_b+i_c>i_c\\ i_{\mathrm{dl}}^{\left(1\right)}=u_n/(r_k+{\mathrm{jx}}_k)\end{array}\right.$

In above formula, u, r is respectively neutral point voltage and earth resistance, is the variable intercoupling; C ₀for unit length cable earth capacitance, u _nfor the rated operational voltage of cable, l is cable length, and n is cable outlet number, is constant;

Second step, earth resistance primary election value is calculated;

There is capacitance current i in transformer load _cfor benchmark, press unit cable capacitance current as base, utilize following formula to solve neutral resistance primary election value,

r _n+1=(u _n+Δi×r _n-1)/(i _min+Δi×（n-1))

In formula, r _nrepresent the n time iterative value of neutral resistor, n=1 ... m (cable returns number), Δ i represents the capacitance current that 1 telegram in reply cable wrap contains, i _minrepresent transformer transmission line circuit number hour capacitance current, initial value r ₁get 0 to u _n/ i _minbetween arbitrary value;

The 3rd step, earth resistance final value is determined;

According to first step neutral resistor power loss model neutral point current allowed band, utilize zero-sequenceprotection sensitivity, get the nargin of the earth resistance resistance 85% that second step calculates as the final determined value of earth resistance.

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