CN105468874A - Field-circuit coupling modeling method for alternating current power grid - Google Patents

Abstract

The invention discloses a field-circuit coupling modeling method for an alternating current power grid. Data modeling is performed on the alternating current power grid, so as to analyze parameters in the alternating current power grid and achieve a purpose of accurately judging the risk of direct current magnetic bias.

Description

The field circuit method modeling method of AC network

Technical field

The present invention relates to power domain, particularly, relate to a kind of field circuit method modeling method of AC network.

Background technology

DC magnetic biasing is a kind of abnormal operating state of transformer, and because the former limit equiva lent impedance of transformer only presents resistance characteristic to DC component, and resistance is very little.Therefore, very little DC component will form very large DC magnetizing magnetic potential in the windings, and this direct current magnetic potential acts on transformer primary side together with interchange magnetic potential, causes the work magnetization curve of transformer core to offset, occur asymmetric about initial point, i.e. transformer bias phenomenon.Cause the reason of transformer DC magnetic bias different, mainly comprise direct current monopolar operation and earth induction.

The exciting current of large-scale power transformer is smaller, and a small amount of DC current flowing through transformer just may cause DC magnetic biasing, causes iron core cutter, causes current waveform to distort, and produces higher hamonic wave, the safe operation of harm transformer and electric system.The D.C. high voltage transmission monopolar ground return method of operation easily causes AC Substation transformer around to occur DC magnetic bias phenomena, and converter power transformer is multiple DC magnetic biasing harm also.The earth current of current China extra-high voltage direct-current transmission is larger than common DC transmission engineering: now generally ± and 500kV direct current transportation earth current is 3000A, the wide extra-high voltage of cloud is 3125A, Burner zone-Shanghai and Xi Luodu-West Zhejiang Province extra-high voltage are 4000A, and silk screen-southern Jiangsu is 4500A.A large amount of earth currents will cause more serious DC magnetic biasing harm, jeopardize AC network safe operation.

Summary of the invention

The object of the invention is to, for the problems referred to above, propose a kind of field circuit method modeling method of AC network, to realize the advantage accurately judging DC magnetic biasing risk.

For achieving the above object, the technical solution used in the present invention is:

A field circuit method modeling method for AC network, is characterized in that, comprise the following steps:

If AC network is total m transformer station always, b bus nodes, n independent neutral point, then had by the nodal method of analysis:

YV＝J(1)

In formula: V represents grid nodes column voltage vector, V=[V _s; V _n; V _b], V _s, V _n, V _brepresent transformer station's node voltage, independent neutral point voltage and busbar voltage column vector respectively;

Y represents grid nodes conductance matrix, Y=H ^tg+Q; H is transformer station's node and all internodal incidence matrix, H ^tfor the transposed matrix of H, H _{m × (m+n+b)}=[E _m0 _{m × n}0 _{m × b}], E _mfor m rank unit matrix; G is substation grounding conductance battle array, G=R ^-1, R=diag (R _g1, R _g2..., R _gm), R _gibe i-th transforming plant DC stake resistance; Q is AC network ground upper network node conductance matrix;

J represents grid nodes Injection Current column vector:

J＝[J _S；J _N；J _B]＝[GP；0；0]＝H ^TGP(2)

In formula: J _s, J _n, J _brepresent transformer station's node, independent neutral point and bus nodes Injection Current column vector respectively;

P represents the induced potential column vector of transformer station, is had by ground connection theory:

P＝MI _D+NI _A(3)

In formula: I _drepresent direct current pole earth current, I _arepresent the DC current injecting grounding net of transformer substation, M represents mutual resistance matrix between direct current pole and transformer station, and N represents the mutual resistance matrix not comprising self-acting between transformer station; P represents transformer station's induced potential, refers to the inlet potential between neutral point and zero point;

The DC current now injecting grounding net of transformer substation is:

I _A＝G(V _A-P)(4)

In formula: V _arepresent transformer station's node voltage, it is defined as:

V _A＝HV(5)

Simultaneous formula 1 to formula 5 draws:

(R-ZN)I _A＝ZMI _D(6)

In formula (6), Z=HY ^-1h ^tg – E, HY ^-1h ^ttransformer station's node-resistance matrix.

Preferably, if independent neutral point and transformer station's node short circuit, then leave out the independent neutral point at this station, only retain transformer station's node.

Technical scheme of the present invention has following beneficial effect:

Technical scheme of the present invention, by carrying out data modeling to AC network, thus analyzes the parameter in AC network, reaches the object accurately judging DC magnetic biasing risk.

Below by drawings and Examples, technical scheme of the present invention is described in further detail.

Accompanying drawing explanation

The 750kV transformer station theory diagram that Fig. 1 runs for the two self couplings change medium voltage side bus sections described in the embodiment of the present invention;

The Equivalent DC modular concept block diagram that Fig. 2 is the transformer station described in the embodiment of the present invention;

Fig. 3 a is autotransformer winding type schematic diagram;

Fig. 3 b is other Transformer Winding type schematic diagram except autotransformer.

By reference to the accompanying drawings, in the embodiment of the present invention, Reference numeral is as follows:

1-1 transformer 220kV bus; 2-2 transformer 220kV bus; 3-750kV bus; 4-1 transformer; 5-2 transformer; 6-neutral point series devices; 7-grounding net of transformer substation; 8-circuit; 9-750kV bus nodes; 10-750kV winding; 11-220kV bus nodes; 12-220kV winding; 13-neutral point; 14-transformer station node; 15-stake resistance; 16-induced potential.

Embodiment

Below in conjunction with accompanying drawing, the preferred embodiments of the present invention are described, should be appreciated that preferred embodiment described herein is only for instruction and explanation of the present invention, is not intended to limit the present invention.

For direct current transportation earth current, modern AC electrical network is a huge DC network, and the field circuit method model that the technical program proposes needs to set up corresponding realistic model to circuit, transformer station and other grid parts.

Circuit model: circuit model is exactly three resistance branch connecting transformer station's three-phase bus in fact, and its key parameter has two: direct current resistance and the mode of connection.The estimation equation of circuit direct current resistance is:

$R_L=\frac{\mathrm{\ρ}D}{S}---\left(1\right)$

In formula, R _lcircuit one phase resistance (Ω), the sectional area (m2) of ρ to be line material resistivity coefficient (Ω m), S be a phase circuit.Direct current resistance as the aluminum stranded conductor of the 2 × 400mm2 of long 1km is:

$R_L=\frac{2.94\×{10}^{-8}\×1000}{2\×400\×{10}^{-6}}=0.06375\mathrm{\Ω}$

Can find out, the direct current resistance of 1km circuit is very little, and the equivalent d.c. resistance of three-phase line is only 0.02125 Ω, therefore low-resistance circuit is the important factor in order of DC current distribution.

In power system component, the mode of connection of circuit often changes, and circuit can divide multiple electric pressure.The circuit of 110kV and above thereof is only considered when the calculating of DC current distribution.In addition, three-phase dc resistance and the mode of connection of circuit are consistent, can consider by parallel way.

Transformer station model: in DC network model, transformer station model is the most complicated, can be subdivided into aerial part and under ground portion.Transformer station's aerial part refers to more than the ground shown in Fig. 1 not containing the part of circuit, and under ground portion refers to the below ground part shown in Fig. 1.Fig. 2 is shown in by the Equivalent DC model of transformer station shown in Fig. 1.

(1) transformer station's aerial part model: transformer station's aerial part model belongs to pure circuit problem, model mainly comprises transformer station's node, transformer model, neutral point series devices model.Transformer station's nodal analysis method is see Fig. 3 a and Fig. 3 b.

Transformer model comprises Transformer Winding type, winding D.C. resistance, transformer bus.

During DC current distribution calculates, differentiating transformer is only needed whether to be autotransformer.Transformer Winding type schematic diagram is see Fig. 3 a and Fig. 3 b.

In Fig. 3 a, autotransformer series connection winding switching high voltage bus and middle pressure bus, middle pressure bus connects neutral point or neutral point series devices (as low reactance, neutral point suppress DC current equipment) through public winding again, in Fig. 3 b, other form transformers (as three-winding transformer) are then that high voltage bus and middle pressure bus connect neutral point or neutral point series devices through respective winding.

Transformer bus is the end points of circuit, as the voltage-dropping type autotransformer used a large amount of in current 500kV transformer station, mostly is neutral-point solid ground, and medium voltage side bus section often will be adopted in reality to run restriction single-phase short circuit current.As shown in Figure 2, two autotransformers show as a 500kV node and connect two 220kV bus nodes through series connection winding, and two 220kV bus nodes connect respective neutral point or neutral point series devices through respective public winding.

The core content of DC current distribution is the DC current distribution on winding, and transformer model has significant impact to it.

Neutral point series devices model is relatively simple, its equivalent resistance branch road connection transformer neutral point and transformer station's node.If neutral point series devices is electric capacity, then disconnect the connection of neutral point and transformer station's node.

(2) transformer station's under ground portion model: the under ground portion model of transformer station is field parameters, model carries out equivalence according to Dai Weinan principle: under whole neutral point disconnection, stake resistance is the equivalent resistance between transformer station's node and zero point, and induced potential is the entrance electromotive force between transformer station's node and zero point.

(3) the asymmetric disposal route of triphase parameter: if AC network three-phase dc parameter is symmetrical, the single-phase circuit that can be reduced to as Fig. 2 is analyzed; If asymmetrical three-phase, can when earth's surface be constant with drag, with the above model in the earth's surface of Fig. 2 to wherein one carrying out modeling mutually, then transformer station's node of short circuit three-phase.

The technical program is symmetrical by DC network parameter, and the model that three-phase is merged into a phase carries out.Meanwhile, the technical program derivation result has versatility, also comparatively flexible during practical application, if triphase parameter asymmetric (as inconsistent in Three-Phase Transformer winding D.C. resistance), as long as the correlation parameter of amendment model becomes triphase parameter.

If AC network is total m transformer station always, b bus nodes, n independent neutral point, then had by the nodal method of analysis:

YV＝J(2)

In formula (2):

V---grid nodes column voltage vector, V=[V _s; V _n; V _b], V _s, V _n, V _bfor transformer station's node voltage (V), independent neutral point voltage (V), busbar voltage column vector (V).If neutral point and transformer station's node short circuit, then leave out the neutral point at this station in this paper model, only retain transformer station's node.

Y---grid nodes conductance matrix, Y=H ^tg+Q.H is transformer station's node and all internodal incidence matrix, H ^tfor the transposition of H, H _{m × (m+n+b)}=[E _m0 _{m × n}0 _{m × b}], E _mfor m rank unit matrix; G is substation grounding conductance battle array, G=R ^-1, R=diag (R _g1, R _g2..., R _gm), R _gibe i-th transforming plant DC stake resistance (Ω).Q is AC network ground upper network node conductance matrix.

J---grid nodes Injection Current column vector:

J＝[J _S；J _N；J _B]＝[GP；0；0]＝H ^TGP(3)

In formula (3):

J _s, J _n, J _b---transformer station's node, independent neutral point, bus nodes Injection Current column vector (A);

The induced potential column vector (V) of P---transformer station, is had by ground connection theory:

P＝MI _D+NI _A(4)

In formula (4):

I _d---direct current pole earth current (A).

I _a---inject the DC current (A) of grounding net of transformer substation.

M---mutual resistance matrix (Ω) between direct current pole and transformer station.

N---the mutual resistance matrix (Ω) (not comprising self-acting) between transformer station.

P---transformer station's induced potential, refers to the inlet potential (V) between neutral point and zero point.

The definition of substation grounding resistance and induced potential can be called " the Dai Weinan equivalence " carried out at neutral point.The DC current now injecting grounding net of transformer substation is:

I _A＝G(V _A-P)(5)

In formula (5):

V _a---transformer station's node voltage (V), it is defined as:

V _A＝HV(6)

Simultaneous formula (2)-(6) have:

(R-ZN)I _A＝ZMI _D(7)

In formula (7), Z=HY ^-1h ^tg – E.HY ^-1h ^tbe equivalent to take out the part of node-resistance matrix about transformer station's node.As can be seen from formula (2.24), removing magnitude of current I _aand I _d, R, N and M are pure field amount, and Z matrix is the amount of a field circuit method.Make transformer station node-resistance matrix F=HY ^-1h ^t, therefore Z (i, i)=F (i, i)/R _gi-1, Z (i, j)=F (i, j)/R _gi, i ≠ j.In the model of direct current distribution, if transformer station's neutral point is in the state of cut-offfing, then there is Z (i, i)=0, I _a(i)=0; If substation grounding resistance F (i, i)/R _gi(this situation is limiting case to ≈ 1, and namely soil is good conductor, R _gimuch smaller than circuit and transformer resistance; Or circuit and transformer resistance much larger than stake resistance time), then have Z (i, i) ≈ 0, I _a(i) ≈ 0.In fact soil is not good conductor, circuit and transformer resistance less, these two kinds of factors cause AC network direct current distribution.From another perspective, if the line that this also illustrates a transformer station is more, the risk of this station DC magnetic biasing is also larger.

Last it is noted that the foregoing is only the preferred embodiments of the present invention, be not limited to the present invention, although with reference to previous embodiment to invention has been detailed description, for a person skilled in the art, it still can be modified to the technical scheme described in foregoing embodiments, or carries out equivalent replacement to wherein portion of techniques feature.Within the spirit and principles in the present invention all, any amendment done, equivalent replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (2)

1. a field circuit method modeling method for AC network, is characterized in that, comprise the following steps:

If AC network is total m transformer station always, b bus nodes, n independent neutral point, then had by the nodal method of analysis:

YV＝J(1)

In formula: V represents grid nodes column voltage vector, V=[V _s; V _n; V _b], V _s, V _n, V _brepresent transformer station's node voltage, independent neutral point voltage and busbar voltage column vector respectively;

Y represents grid nodes conductance matrix, Y=H ^tg+Q; H is transformer station's node and all internodal incidence matrix, H ^tfor the transposed matrix of H, H _{m × (m+n+b)}=[E _m0 _{m × n}0 _{m × b}], E _mfor m rank unit matrix; G is substation grounding conductance battle array, G=R ^-1, R=diag (R _g1, R _g2..., R _gm), R _gibe i-th transforming plant DC stake resistance; Q is AC network ground upper network node conductance matrix;

J represents grid nodes Injection Current column vector:

J＝[J _S；J _N；J _B]＝[GP；0；0]＝H ^TGP(2)

In formula: J _s, J _n, J _brepresent transformer station's node, independent neutral point and bus nodes Injection Current column vector respectively;

P represents the induced potential column vector of transformer station, is had by ground connection theory:

P＝MI _D+NI _A(3)

In formula: I _drepresent direct current pole earth current, I _arepresent the DC current injecting grounding net of transformer substation, M represents mutual resistance matrix between direct current pole and transformer station, and N represents the mutual resistance matrix not comprising self-acting between transformer station; P represents transformer station's induced potential, refers to the inlet potential between neutral point and zero point;

The DC current now injecting grounding net of transformer substation is:

I _A＝G(V _A-P)(4)

In formula: V _arepresent transformer station's node voltage, it is defined as:

V _A＝HV(5)

Simultaneous formula 1 to formula 5 draws:

(R-ZN)I _A＝ZMI _D(6)

In formula (6), Z=HY ^-1h ^tg – E, HY ^-1h ^ttransformer station's node-resistance matrix.

2. the field circuit method modeling method of AC network according to claim 1, is characterized in that, if independent neutral point and transformer station's node short circuit, then leaves out the independent neutral point at this station, only retains transformer station's node.