CN103577633B - A kind of transformer DC magnetic bias raised based on earth potential is simulated and suppressing method - Google Patents

Abstract

The invention discloses a kind of transformer DC magnetic bias raised based on earth potential to simulate and suppressing method, according to the earthy distribution of direct current grounding pole, try to achieve each transformer grounding point earth potential, ac and dc systems electrical-magnetic model is built in simulation software, by raising each transformer grounding point earth potential, carry out analog DC power transmission engineering earth current to the impact of static exciter branch road, by the harmonic components in detection ac bus voltage and current and DC transmission engineering through-put power, analyze and judge the influence degree to ac and dc systems, according to the DC magnetic bias phenomena that simulation judged result selects suitable transformer DC magnetic bias braking measure to suppress each transformer to occur, can effectively simulate in same transformer station/current conversion station, the transformer of multiple stage different model and parameter is in identical earthy situation, actual influence to ac and dc systems during generation DC magnetic biasing, the braking measure of selecting properly DC magnetic biasing, transformer station and safe operation of electric network are provided.

Description

A kind of transformer DC magnetic bias raised based on earth potential is simulated and suppressing method

Technical field

The invention belongs to transformer DC magnetic bias field, relate to a kind of transformer DC magnetic bias raised based on earth potential and simulate and suppressing method.

Background technology

When DC transmission engineering one pole ground return circuit is run, cause AC transformer and converter power transformer generation DC magnetic bias phenomena than being easier to.With reference to figure 1, transformer station and current conversion station site and DC transmission system earthing pole nearer time, 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 transformer core saturated, it is made to 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 harmonic (especially even-order harmonic), transformer is made to become a harmonic source of ac and dc systems.

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

At present, the main method of research transformer DC magnetic bias injects certain DC current to simulate at the neutral point of transformer the DC component flowing through transformer, and the method is used for studying the situation that single transformer or the identical transformers connected in parallel of multiple stage model parameter run.When transformer station and current conversion station merge build time, different transformer is under same earth point condition, although transformer grounding point earth potential is consistent, flows through the electric current of each transformer neutral point and 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, correct braking measure can not be taked 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 the defect overcoming prior art, a kind of transformer DC magnetic bias raised based on earth potential is provided to simulate and suppressing method, especially different model parameter uses transformer DC magnetic bias phenomena simulation and the suppressing method of same earth point, has fully demonstrated earth point earth potential change to the impact of power transformer to suppress.

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

The transformer DC magnetic bias simulation raised based on earth potential and a suppressing method, comprise the following steps:

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

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

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

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

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

Described step 2) in when building ac and dc systems electrical-magnetic model, first, set up electromagnetism saturation curve and the transformer correlation properties of various transformer, then, build the electrical-magnetic model of various transformer based on this.

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

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

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

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

V in formula _n, V ₁be respectively the effective value of nth harmonic voltage and fundamental voltage;

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

DC transmission engineering transmit power calculation formula such as formula shown in (2), P in formula _dt () represents 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 _2krepresent the power swing amplitude of the steady state value of the changed power caused by k subharmonic, power kth time and 2k time respectively; α _krepresent the phase differential of k direct current harmonic voltage and k direct current harmonic current, β _krepresent the initial phase of k power swing.

Described step 5) in selectable transformer DC magnetic bias braking measure have: at transformer neutral point serial capacitors, neutral point crosstalk resistance or inverse injection electric current to suppress transformer DC magnetic bias.

The present invention by building ac and dc systems electrical-magnetic model in simulation software, by raising each transformer grounding point earth potential analog DC power transmission engineering earth current to the impact of static exciter branch road, fully demonstrate the impact of earth point earth potential change on power transformer, compared with research method in the past, this research method can embody and reflect the DC magnetic biasing degree that each transformer is different separately when earth potential changes and the impact on ac and dc systems.Can effectively simulate in same transformer station/current conversion station, the transformer of multiple stage different model and parameter is in identical earthy situation, actual influence to ac and dc systems during generation DC magnetic biasing, according to the DC magnetic bias phenomena that simulation judged result selects suitable transformer DC magnetic bias braking measure to suppress each transformer to occur, in solution prior art in same transformer station/current conversion station, the transformer of multiple stage different model and parameter cannot selecting properly DC magnetic biasing braking measure problem, provides transformer station and safe operation of electric network.

Accompanying drawing explanation

Fig. 1 is that in ground, direct current flows through AC network schematic diagram;

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 schematic diagram of building a station;

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

Fig. 6 is that transformer station/current conversion station to merge when building a station current potential schematic diagram equivalently.

Embodiment

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

The transformer DC magnetic bias simulation raised based on earth potential and a suppressing method, comprise the following steps:

1. for the Ac/dc Power Systems of DC transmission engineering Relatively centralized; According to the earthy distribution of direct current grounding pole, try to achieve each transformer station/current conversion station primary ground net (i.e. each transformer grounding point) earth potential.

2. may use the transformer of different model different parameters in transformer station and current conversion station, 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 various transformer, and build the electrical-magnetic model of various transformer based on this.

3. the electrical-magnetic model of the various transformers built according to the one or two step, in conjunction with the needs of actual DC power transmission engineering, be applied in (spy) high voltage direct current transmission project electrical-magnetic model, transformer station and current conversion station to merge when building the main transformer of transformer station/current conversion station and configure as shown in Figure 4.As Fig. 6 be transformer station/current conversion station merge build a station time current potential schematic diagram equivalently, exchanging main-transformer and the earth point of DC converter transformer adding a controlled voltage source to change the earth potential of its transformer (comprise and exchange main-transformer and converter power transformer) neutral ground point, for the impact of analog DC earthing pole on this transformer station/current conversion station.

4. the fluctuation by detecting ac bus each harmonic containing ratio and total percent harmonic distortion and DC transmission engineering through-put power judges 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 such as formula shown in (1):

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

V in formula _n, V ₁be respectively the effective value of nth harmonic voltage and fundamental voltage.

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

In addition, can analyze transformer DC magnetic biasing in various degree to the impact of DC transmission system by the fluctuation observing DC transmission engineering unipolar transmission power, its main formulas for calculating is such as formula shown in (2), and in formula, Pd (t) represents that relation, Udc, Idc represent DC voltage and the electric current steady state value after Fourier transform to power over time; Pk, P1k, P2k represent the power swing amplitude of the steady state value of the changed power caused by k subharmonic, power kth time and 2k time respectively; 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 (trying to achieve by harmonic voltage and harmonic current) of k power swing.

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

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

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

DC transmission engineering adopts bipolar 12 pulse conversion valve groups, and rectification side adopts Given current controller mode, and inverter side employing is determined voltage, determined hold-off angle 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 forms continuous print flex point curve by knee voltage, hollow reactance and exciting current three parameters.Knee voltage, hollow reactance and exciting current (perunit value) are respectively 1.25,0.32 and 1.0%; Exchanging main-transformer adopts UMEC (UnifiedMagneticEquivalentCircuit) to adopt V-I curve to carry out the saturation characteristic of indication transformer as shown in Figure 3, the saturation characteristics exchanging main-transformer and converter power transformer is BH curve, is V-I family curve by its equivalency transform in the present embodiment.

Except transformer station's current conversion station major part, all adopt equivalent method that it is equivalent in AC system, in Fig. 5, the equivalent systematic parameter (perunit value) of 750kV top-cross stream is: E=1.0118; R+jX=0.0077+j0.0026; The equivalent systematic parameter (perunit value) of the interchange of 330kV side except straight-flow system 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 1750kV autotransformer major parameter

Table 2 converter power transformer major parameter

Table 3330kV bus Harmonic Current Distortion (containing) rate (%)

Simulation result: as can be seen from Table 3 when earth potential is 0, containing certain 3 times, 11 times and 13 subharmonic in the A phase current of 330kV side; Wherein 3 subharmonic increase along with earthy rising, and growth rate is relatively very fast; Due to alternating current filter effect, not there is significant change along with the neutral point earth potential of main-transformer and converter power transformer raises in 11 times and 13 subharmonic.Other each uncharacteristic harmonics amplitude when earth potential is 0 is all very little, and all in code allowed band, the normal table not affecting ac and dc systems runs.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 reaches 1.629%, and 2,3,4 subharmonic containing ratios are respectively 0.78%, 0.92%, 0.938% all beyond the scope that electrical network code allows, and create larger impact to friendship system.

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

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

Can exploit according to above simulation result and be used in that each transformer neutral point in transformer station/current conversion station adopts serial capacitors, the method for neutral point crosstalk resistance and inverse injection electric current suppresses each transformer DC magnetic bias phenomenon in transformer station/current conversion station.

What be necessary to herein means out is that the present embodiment is only used to further illustrate the present invention, and 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 raised based on earth potential is simulated and a suppressing method, it is characterized in that comprising the following steps:

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

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

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

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

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

2. the transformer DC magnetic bias raised based on earth potential according to claim 1 is simulated and suppressing method, it is characterized in that: described step 2) in when building ac and dc systems electrical-magnetic model, first, set up electromagnetism saturation curve and the transformer correlation properties of various transformer, then, the electrical-magnetic model of various transformer is built based on this.

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

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

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

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

V in formula _n, V ₁be respectively the effective value of nth harmonic voltage and fundamental voltage;

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

DC transmission engineering transmit power calculation formula such as formula shown in (2), P in formula _dt () represents 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 _2krepresent the power swing amplitude of the steady state value of the changed power caused by k subharmonic, power kth time and 2k time respectively; α _krepresent the phase differential of k direct current harmonic voltage and k direct current harmonic current, β _krepresent the initial phase of k power swing.

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