CN103577633A - Method for simulating and inhibiting direct-current magnetic biases of transformers based on earth potential rise - Google Patents

Abstract

The invention discloses a method for simulating and inhibiting direct-current magnetic biases of transformers based on earth potential rise. The method comprises the following steps: calculating earth potentials of earth points of transformers according to distribution of direct-current earth electrode potentials; building an electromagnetic transient model of an alternating-current and direct-current system in simulation software; simulating the influence of earth current of a direct-current transmission project on transformer excitation branches by rising the earth potentials of the earth points of the transformers; analyzing and judging the degree of influence on the alternating-current and direct-current system by detecting harmonic components in alternating-current bus voltage and current and transmission power of the direct-current transmission project, and selecting proper transformer direct-current magnetic bias inhibition measures according to simulation judgment results to inhibit the direct-current magnetic biases of the transformers. According to the method, the actual influence of the direct-current magnetic biases of the plurality of transformers with different types and parameters in the same transformer substation/convertor substation under the same earth potential can be effectively simulated, the direct-current magnetic bias inhibition measures are correctly selected, and the running safety of the transformer substation and a power grid is improved.

Description

A kind of transformer DC magnetic bias simulation and inhibition method raising based on earth potential

Technical field

The invention belongs to transformer DC magnetic bias field, relate to a kind of transformer DC magnetic bias simulation and inhibition method raising based on earth potential.

Background technology

When DC transmission engineering one pole ground return circuit is moved, than being easier to cause AC transformer and converter power transformer generation DC magnetic bias phenomena.With reference to figure 1, when transformer station and current conversion station site and DC transmission system earthing pole are nearer, under the DC transmission system one pole ground return circuit method of operation, larger earth current makes certain DC current flow through transformer neutral point or Transformer Winding, cause DC magnetic biasing, cause that transformer core is saturated, make it work in the nonlinear area of core sataration curve, as shown in Figure 2, transformer magnetizing current is distorted in half wave cycles, and produce a large amount of low-order harmonics (especially even-order harmonic), make transformer become a harmonic source of ac and dc systems.

Transformer station and current conversion station merge while building, and exchange main-transformer and converter power transformer all nearer apart from direct current grounding pole, and DC magnetic biasing very easily occurs transformer.When exchanging main-transformer and converter power transformer and all DC magnetic biasing occurs, its impact on ac and dc systems has been amplified in the each harmonic coupling that it produces respectively to a certain extent.If do not take certain braking measure, may affect the stable transfer of the normal operation of transformer and DC transmission engineering power, the stable operation of entail dangers to ac and dc systems and the safety of electrical network when serious.Recent year has a large amount of high voltage direct current transmission projects to build up to put into operation, and wherein, most DC transmission engineering adopt AC Substation and DC converter station to adopt the mode of building that merges.Its transformer DC magnetic bias is more obvious on ac and dc systems impact, so ，Dui transformer station is when build with current conversion station merging, the analysis and research significant of transformer DC magnetic bias.

At present, the main method of research transformer DC magnetic bias is that the neutral point at transformer injects certain DC current and comes analog stream to cross the DC component of transformer, and the method is used for studying the situations of single transformer or the identical transformers connected in parallel operation of many model parameters.When transformer station and current conversion station merge while building, different transformers are under same earth point condition, although transformer grounding point earth potential is consistent, the electric current that flows through each transformer neutral point is also not quite identical.Therefore, the magnetic bias degree of each transformer is also not quite identical, cannot each transformer actual influence of correct response DC magnetic bias phenomena, and can not take correct braking measure to suppress, jeopardize the stable operation of transformer station and ac and dc systems and the safety of electrical network.

Summary of the invention

The object of the invention is to overcome the defect of prior art, a kind of transformer DC magnetic bias simulation and inhibition method raising based on earth potential is provided, especially different model parameter is used the simulation of transformer DC magnetic bias phenomenon and the inhibition method of same earth point, has fully demonstrated earth point earth potential and has changed the impact of power transformer and suppress.

For achieving the above object, by the following technical solutions:

Transformer DC magnetic bias simulation and an inhibition method that earth potential raises, comprise the following steps:

1), according to the earthy distribution of direct current grounding pole, try to achieve each transformer grounding point earth potential;

2) in simulation software, build ac and dc systems electro-magnetic transient model, comprise electro-magnetic transient model and the straight-flow system control model of single-phase high voltage autotransformer and transformer;

3) by each transformer grounding point earth potential that raises, carry out the impact of analog DC power transmission engineering earth current on static exciter branch road;

4), by detecting harmonic components and the DC transmission engineering through-put power in ac bus voltage and current, analyze and judge the influence degree to ac and dc systems;

5), according to the judged result of step 4), select transformer DC magnetic bias braking measure to suppress the DC magnetic bias phenomena that each transformer occurs.

While building ac and dc systems electro-magnetic transient model described step 2), first, set up electromagnetism saturation curve and the transformer correlation properties of range transformer, then, build based on this electro-magnetic transient model of range transformer.

In described step 3), according to the electro-magnetic transient model of each transformer, on each transformer grounding point, add a controlled voltage source and change each transformer neutral point earth point earth potential, the impact on static exciter branch road on electric current for analog DC earthing pole.

In described step 4), by detecting ac bus each harmonic containing ratio and total percent harmonic distortion and the fluctuation of DC transmission engineering through-put power, judge the impact of transformer bias degree on ac and dc systems;

The computing formula of each harmonic containing ratio and total percent harmonic distortion is as the formula (1):

$\left\{\begin{array}{c}{\mathrm{THD}}_V=(\sqrt{\underset{n-2}{\overset{N}{\mathrm{\Σ}}}{V}_n^2}/V_1)\×100\%\\ {\mathrm{HR}}_{\mathrm{Vn}}=(V_n/V_1)\×100\%\end{array}\right.---\left(1\right)$

Vn in formula, V1 is respectively the effective value of nth harmonic voltage and fundamental voltage;

$P_d\left(t\right)=U_{\mathrm{dc}}{I}_{\mathrm{dc}}+\underset{k=1}{\overset{n}{\mathrm{\Σ}}}\left[\begin{array}{c}{P}_k+P_{1k}\sin (\mathrm{k\ωt}+{\mathrm{\β}}_k)\\ +P_{2k}\cos (2\mathrm{k\ωt}+{\mathrm{\α}}_k)\end{array}\right]---\left(2\right)$

DC transmission engineering transmit power calculation formula as the formula (2), P in formula _d(t) represent power relation, U over time _dc, I _dcrepresent DC voltage and the steady state value of electric current after Fourier transform; P _k, P _1k, P _2kthe power swing amplitude that represents respectively steady state value, power that the power that caused by k subharmonic changes the k time and 2k time; α _kthe phase differential that represents k direct current harmonic voltage and k direct current harmonic current, β _kthe initial phase that represents k power swing.

In described step 5), selectable transformer DC magnetic bias braking measure has: at transformer neutral point serial capacitors, neutral point crosstalk resistance or inverse injection electric current, suppress transformer DC magnetic bias.

The present invention by building ac and dc systems electro-magnetic transient model in simulation software, by each transformer grounding point earth potential analog DC power transmission engineering earth current impact on static exciter branch road that raises, fully demonstrate earth point earth potential and changed the impact on power transformer, compare with former studies method, this research method can embody and reflect different DC magnetic biasing degree and the impact on ac and dc systems separately when earth potential changes of each transformer.Can effectively simulate in same transformer station/current conversion station, the transformer of many different models and parameter is in identical earthy situation, actual influence to ac and dc systems while there is DC magnetic biasing, according to simulation judged result, select suitable transformer DC magnetic bias braking measure to suppress the DC magnetic bias phenomena that each transformer occurs, solve in prior art in same transformer station/current conversion station, the transformer of many different models and parameter cannot selecting properly DC magnetic biasing braking measure problem, and transformer station and safe operation of electric network are provided.

Accompanying drawing explanation

Fig. 1 is the direct current AC network schematic diagram of flowing through in ground;

Fig. 2 is transformer generation DC magnetic biasing schematic diagram;

Fig. 3 is transformer saturation characteristics figure;

Fig. 4 is that actual DC power transmission engineering (one pole) transformer station/current conversion station merges the schematic diagram of building a station;

Fig. 5 is actual DC engineering one pole transmission each harmonic power profile;

Tu6Wei transformer station/current conversion station merges while building a station current potential schematic diagram equivalently.

Embodiment

Below in conjunction with the drawings and specific embodiments, the present invention is specifically described:

Transformer DC magnetic bias simulation and an inhibition method that earth potential raises, comprise the following steps:

1. for the relatively concentrated Ac/dc Power Systems of DC transmission engineering; According to the earthy distribution of direct current grounding pole, try to achieve the main grounded screen of each transformer station/current conversion station (being each transformer grounding point) earth potential.

2. in transformer station and current conversion station, may use the transformer of different model different parameters, the earth point earth potential of each transformer is consistent; But the electric current that the neutral point of each transformer flows through is also inconsistent.

First in ， simulation software, set up electromagnetism saturation curve and the transformer correlation properties of range transformer, and build based on this electro-magnetic transient model of range transformer.

3. the electro-magnetic transient model of the range transformer of building according to the one or two step, needs in conjunction with actual DC power transmission engineering, be applied to (spy) high voltage direct current transmission project electro-magnetic transient model Zhong， transformer station and current conversion station and merge while building the main transformer of transformer station/current conversion station and configuration thereof as shown in Figure 4.Ru Tu6Wei transformer station/current conversion station merges while building a station current potential schematic diagram equivalently, add the earth potential that a controlled voltage source changes its transformer (comprise and exchange main-transformer and converter power transformer) neutral ground point exchanging on the earth point of main-transformer and DC converter transformer, for the impact of analog DC earthing pole Dui Gai transformer station/current conversion station.

4. by detecting ac bus each harmonic containing ratio and total percent harmonic distortion and the fluctuation of DC transmission engineering through-put power, judge the impact of transformer bias degree on ac and dc systems.The computing formula of each harmonic containing ratio and total percent harmonic distortion is as the formula (1):

$\left\{\begin{array}{c}{\mathrm{THD}}_V=(\sqrt{\underset{n-2}{\overset{N}{\mathrm{\Σ}}}{V}_n^2}/V_1)\×100\%\\ {\mathrm{HR}}_{\mathrm{Vn}}=(V_n/V_1)\×100\%\end{array}\right.---\left(1\right)$

Vn in formula, V1 is respectively the effective value of nth harmonic voltage and fundamental voltage.

$P_d\left(t\right)=U_{\mathrm{dc}}{I}_{\mathrm{dc}}+\underset{k=1}{\overset{n}{\mathrm{\Σ}}}\left[\begin{array}{c}{P}_k+P_{1k}\sin (\mathrm{k\ωt}+{\mathrm{\β}}_k)\\ +P_{2k}\cos (2\mathrm{k\ωt}+{\mathrm{\α}}_k)\end{array}\right]---\left(2\right)$

In addition, can by observing the fluctuation of DC transmission engineering one pole through-put power, analyze the impact of transformer DC magnetic biasing in various degree on DC transmission system, as the formula (2), Pd in formula (t) represents that relation, Udc, Idc represent DC voltage and the electric current steady state value after Fourier transform to power over time to its main formulas for calculating; Pk, P1k, P2k represent respectively the power swing amplitude of steady state value, power that the power that caused by k subharmonic changes the k time and 2k time; α k represents the phase differential of k direct current harmonic voltage and k direct current harmonic current, and β k represents the initial phase (can try to achieve by harmonic voltage and harmonic current) of k power swing.

5. according to the judged result of step 4, select transformer DC magnetic bias braking measure to suppress the DC magnetic bias phenomena that each transformer occurs; Selectable transformer DC magnetic bias braking measure has: at transformer neutral point serial capacitors, neutral point crosstalk resistance or inverse injection electric current, suppress transformer DC magnetic bias.

Below in conjunction with specific embodiment, the inventive method specifically:

The Practical Project that uses certain 750kV transformer station and ± 500kV current conversion station to merge to build a station is as embodiment, and the high side voltage grade that exchanges main-transformer is that 750kV, medium voltage side electric pressure are that 330kV, low-pressure side electric pressure are 66kV.

DC transmission engineering adopts bipolar 12 pulse conversion valve groups, and rectification side adopts determine current control mode, and inversion side adopts determines voltage, surely closes angle of rupture control.Converter power transformer adopts three-phase double winding, and is furnished with loaded automatic voltage-regulating, and its range of regulation is :+25/-5 shelves (span is 1.25%).The saturation characteristic of converter power transformer is to form continuous flex point curve by knee voltage, hollow reactance and three parameters of exciting current.Knee voltage, hollow reactance and exciting current (perunit value) are respectively 1.25,0.32 and 1.0%; Exchange main-transformer and adopt UMEC(Unified Magnetic Equivalent Circuit) adopt saturation characteristic that V-I curve carrys out indication transformer as shown in Figure 3, the saturation characteristics that exchanges main-transformer and converter power transformer is BH curve, in the present embodiment, its equivalence is converted to V-I family curve.

All adopt equivalent method by its equivalence beyond AC system Zhong Chu transformer station current conversion station major part, in Fig. 5,750kV top-cross flows equivalent systematic parameter (perunit value) and is: E=1.0118; R+jX=0.0077+j0.0026; The 330kV side equivalent systematic parameter of the interchange except straight-flow system (perunit value) is: E=1.0167; R+jX=0.0053+j0.0041, rectification side current conversion station is connected with 330kV side bus.AC Substation and current conversion station merge to be built, and as shown in Figure 4, each transformer grounding point is by unified Grounding for its ac and dc systems primary structure.

Exchange the major parameter of main-transformer and converter power transformer as shown in Table 1 and Table 2,

Table 1 750kV autotransformer major parameter

Table 2 converter power transformer major parameter

Table 3 330kV bus harmonic current distortion (containing) rate (%)

Simulation result: when earth potential is 0, contain certain 3 times, 11 times and 13 subharmonic in 330kV side A phase current as can be seen from Table 3; Wherein 3 subharmonic increase along with earthy rising, and growth rate is relatively very fast; Due to alternating current filter effect, 11 times and 13 subharmonic are along with the neutral point earth potential of main-transformer and converter power transformer raises and generation significant change.Other each uncharacteristic harmonics is that 0 o'clock amplitude is all very little at earth potential, and all in rules allowed band, do not affect the normal stable operation of ac and dc systems.Along with earthy rising, its uncharacteristic harmonics amplitude increases, especially even-order harmonic (2 times, 4 times).When earth potential is 500V, total percent harmonic distortion has reached 1.629%, 2,3,4 subharmonic containing ratios and has been respectively 0.78%, 0.92%, 0.938% and has all exceeded the scope that electrical network rules allow, and friendship system has been produced to larger impact.

From Fig. 5, each harmonic power is known with position, place situation of change: along with earthy rising, DC transmission engineering one pole through-put power after Fourier analysis 3 times and the fluctuation of 6 component of degree n ns are the most obvious, and particularly 3 subharmonic power components, have reached 520kW.

Simulation result shows: the method that earth potential raises is the DC magnetic bias phenomena of analogue transformer and converter power transformer effectively, especially more suitable to containing the situation of many different models and parametric transformer DC magnetic bias phenomena in same transformer station/current conversion station.

According to above simulation result, can exploit and be used in transformer station/current conversion station each transformer neutral point and adopt the method for serial capacitors, neutral point crosstalk resistance and inverse injection electric current to suppress each transformer DC magnetic bias phenomenon in transformer station/current conversion station.

Be necessary to be pointed out that at this present embodiment is only used to further illustrate the present invention, can not be interpreted as limiting the scope of the invention, the person skilled in the art in this field can make some nonessential improvement and adjustment according to the content of foregoing invention.

Claims (5)

1. the transformer DC magnetic bias simulation and the inhibition method that based on earth potential, raise, is characterized in that comprising the following steps:

1), according to the earthy distribution of direct current grounding pole, try to achieve each transformer grounding point earth potential;

2) in simulation software, build ac and dc systems electro-magnetic transient model, comprise electro-magnetic transient model and the straight-flow system control model of single-phase high voltage autotransformer and transformer;

3) by each transformer grounding point earth potential that raises, carry out the impact of analog DC power transmission engineering earth current on static exciter branch road;

4), by detecting harmonic components and the DC transmission engineering through-put power in ac bus voltage and current, analyze and judge the influence degree to ac and dc systems;

5), according to the judged result of step 4), select transformer DC magnetic bias braking measure to suppress the DC magnetic bias phenomena that each transformer occurs.

2. the transformer DC magnetic bias raising based on earth potential according to claim 1 is simulated and inhibition method, it is characterized in that: while building ac and dc systems electro-magnetic transient model described step 2), first, set up electromagnetism saturation curve and the transformer correlation properties of range transformer, then, build based on this electro-magnetic transient model of range transformer.

3. the transformer DC magnetic bias raising based on earth potential according to claim 1 is simulated and inhibition method, it is characterized in that: in described step 3) according to the electro-magnetic transient model of each transformer, on each transformer grounding point, add a controlled voltage source and change each transformer neutral point earth point earth potential, the impact on static exciter branch road on electric current for analog DC earthing pole.

4. transformer DC magnetic bias simulation and the inhibition method raising based on earth potential according to claim 1, is characterized in that: in described step 4), by detecting ac bus each harmonic containing ratio and total percent harmonic distortion and the fluctuation of DC transmission engineering through-put power, judge the impact of transformer bias degree on ac and dc systems;

The computing formula of each harmonic containing ratio and total percent harmonic distortion is as the formula (1):

$\left\{\begin{array}{c}{\mathrm{THD}}_V=(\sqrt{\underset{n-2}{\overset{N}{\mathrm{\Σ}}}{V}_n^2}/V_1)\×100\%\\ {\mathrm{HR}}_{\mathrm{Vn}}=(V_n/V_1)\×100\%\end{array}\right.---\left(1\right)$

Vn in formula, V1 is respectively the effective value of nth harmonic voltage and fundamental voltage;

$P_d\left(t\right)=U_{\mathrm{dc}}{I}_{\mathrm{dc}}+\underset{k=1}{\overset{n}{\mathrm{\Σ}}}\left[\begin{array}{c}{P}_k+P_{1k}\sin (\mathrm{k\ωt}+{\mathrm{\β}}_k)\\ +P_{2k}\cos (2\mathrm{k\ωt}+{\mathrm{\α}}_k)\end{array}\right]---\left(2\right)$

DC transmission engineering transmit power calculation formula as the formula (2), P in formula _d(t) represent power relation, U over time _dc, I _dcrepresent DC voltage and the steady state value of electric current after Fourier transform; P _k, P _1k, P _2kthe power swing amplitude that represents respectively steady state value, power that the power that caused by k subharmonic changes the k time and 2k time; α _kthe phase differential that represents k direct current harmonic voltage and k direct current harmonic current, β _kthe initial phase that represents k power swing.

5. transformer DC magnetic bias simulation and the inhibition method raising based on earth potential according to claim 1, is characterized in that: in described step 5), selectable transformer DC magnetic bias braking measure has: at transformer neutral point serial capacitors, neutral point crosstalk resistance or inverse injection electric current, suppress transformer DC magnetic bias.

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