CN104750994A - Method for judging transient instability dominance based on outer region power ratio - Google Patents

Abstract

The invention discloses a method for judging a transient instability dominance based on an outer region power ratio. The method comprises the following steps: step 1, selecting a target profile form an electric power system; step 2, constructing a Thevenin equivalent model, including (a) dividing the electric power system into a local portion, the target profile and other electric power system portions based on the segmentation of the target profile; allowing the local portion to be equivalent to a local power generation portion and a local load portion; and (b) allowing the other electric power system portions to be equivalent to a first power generator, and allowing the local power generation portion to be equivalent to a second power generator; step 3, defining an outer region power ratio as M:M=P1/PD; calculating an outer region power ratio MV under a voltage instability critical state and an outer region power ratio Mg under a power angle instability critical state; and step 4, calculating the outer region power ration M on the basis of the actually measured parameters, and judging a dominant instability mode based on the distances among the M, the MV and the Mg. The dominant instability mode can be intuitively obtained with the disclosed method, accordingly providing references for safe and stable operation, real-time data analysis as well as fault reflection strategy of the electric power system.

Description

Based on the Transient Instability dominance method of discrimination of outskirt electric power ratio

Technical field

The present invention relates to a kind of Transient Instability dominance method of discrimination based on outskirt electric power ratio.

Background technology

In today that electric network composition becomes increasingly complex, by the Primary element pointed out in electrical network Transient Instability that traditional reductive approach can not be clear and definite, and this is for power system computation analysis, after failure prevention and fault dispatcher to debug behavior most important, in Power System Stability Analysis, there are two kinds of egregious cases in it, Voltage Instability and merit angle unstability respectively, these two kinds of unstabilitys usually occur simultaneously in some cases, cannot specifically judge to be occupied an leading position by any unstability, and then cause another unstability and follow generation, such as during Voltage Instability, because electrical network supplies the needs that can not meet load to the power of load, if be mistaken for merit angle unstability, carry out cutting machine operation, then can worsen Voltage Instability further, thus the differentiation of unstability dominance is required to accomplish accurately in electrical network analysis, in real time, because safe and stable operation is more and more related to national economy and national security, and along with the growth of electrical network scale, coupled relation between its each operational factor becomes increasingly complex, the impact of single factors cannot illustrate its unstability dominance completely.

Objective, the voltage stability of electric system and power-angle stability are two kinds of very extreme situations in Power System Analysis, for electric system Infinite bus power system network model, namely a PV node is connected with a balance node, there is not Voltage-stabilizing Problems in it, and for infinite busbar on-load system, it is made up of a PQ node and a balance node, therefore there is not angle stability problem.Over nearly 20 years, there is contacting between literature research power system voltage stabilization and angle stability successively, by the phenomenon of Voltage Instability and merit angle unstability, the feature that analytical voltage unstability and merit angle unstability have with contact, it derives generator and matrix of loadings mainly through permanent Potential Equivalent Model, and under the method for operation, tend to unusual degree differentiation Voltage Instability and merit angle unstability by its matrix, also the leading Failure Model that approach application Thevenin's equivalence following principle is come in judgement system unstability is had, system equivalent is all that a load bus receives two node systems of a voltage source power transmission by an impedance by any time, by following the tracks of Thevenin's equivalence electromotive force and equivalent impedance mould differentiation its mutually corresponding leading Failure Model in unstability situation, and researcher more finds recently, angle stability problem and Voltage-stabilizing Problems are based upon under two different prerequisites respectively, attempt to unify, but at present, its effect is also pessimistic.

In electric system method of discrimination in the past, mostly devise a kind of real-time Transient Instability criterion, this criterion combines the mission nonlinear properties influence in transient state process mostly, by the trend that analysis section characteristic information changes, obtain INSTABILITY CRITERION, and then judge its leading unstability situation, and in analysis in the past, major part research work all mainly lays particular emphasis on voltage stabilization or one of them aspect of angle stability, the criterion proposed has certain limitation, up to the present a kind of comprehensive evaluation voltage stability of practicality and the criterion of power-angle stability is not also had, do not formed and unified research and analyse judges law yet, due to above reason, about the leading factor between voltage stability and power-angle stability, transformation rule, conversion condition progress is extremely slow, pertinent literature is few.

Electric system break down so that Transient Instability process in, because different change can occur more POWER SYSTEM STATE parameter, therefore judge in the information of electric parameters, the Failure Model of estimating system, extract the index being easy to judge system unstability pattern can realize, simultaneously this index also needs to have in real time, is easy to the features such as calculating.

Summary of the invention

The technical problem to be solved in the present invention is, for the deficiency that existing criterion method exists, a kind of Transient Instability dominance method of discrimination based on outskirt electric power ratio is provided, leading Failure Model can be obtained intuitively, for power system safety and stability operation, real-time data analysis, fault reflection strategy provide reference.

Technical solution of the present invention is as follows:

Based on a Transient Instability dominance method of discrimination for outskirt electric power ratio, comprise the following steps:

Step 1: selected target section in electric system;

Step 2: build electric system Dai Weinan equivalent model:

A electric system is divided into local part, target section and electric system other parts according to the segmentation of target section by (); Local part is equivalent to two parts: local power generation part and local loaded portion;

B electric system other parts, according to Thevenin's equivalence following principle, are equivalent to the first generator by (), the Dai Weinan equivalent potential of the first generator is first generated output power is wherein P ₁be the active power that the first generator exports, Q ₁it is the reactive power that the first generator exports; Between first generator and target section, the Dai Weinan equiva lent impedance of circuit is z ₁₂;

Local power generation part is equivalent to the second generator, and the Dai Weinan equivalent potential of the second generator is , the second generated output power is wherein P ₂be the active power that the second generator exports, Q ₂it is the reactive power that the second generator exports; Between second generator and target section, the Dai Weinan equiva lent impedance of circuit is z ₂₁;

The power that target section is transferred to local loaded portion is wherein P _dfor target section is transferred to the active power of local loaded portion, Q _dfor target section is transferred to the reactive power of local loaded portion;

Step 3: definition outskirt electric power ratio is M:M=P ₁/ P _d; According to Dai Weinan equivalent model parameters relationship, the outskirt electric power ratio M of calculating voltage unstability critical conditions _vwith the outskirt electric power ratio M of merit angle unstability critical conditions _g;

1) the outskirt electric power ratio M of Voltage Instability critical conditions _vcomputing method be:

$M_V=\frac{{\stackrel{\·}{Z}}_K{\stackrel{\·}{Z}}_{22}\sin {\mathrm{\δ}}_{12}}{X_{12}^2\sin {\mathrm{\α}}_{22}}$

Wherein,

for looking over from electric system other parts, local part is equivalent to equiva lent impedance during single constant-impedance, for Z _sphase angle; X ₁₂be that the input reactance of the first generator [ignores the resistance of transmission line, namely z ₁₂in active component, then have ], be the input impedance of the second generator, α ₂₂for the complementary angle of angle of impedance, δ ₁₂it is the merit angular difference of the first generator and the second generator;

[as the M>M calculated according to actual measurement parameter _vtime, there is Voltage Instability, M<M _vtime, voltage stabilization; ]

2) the outskirt electric power ratio M of merit angle unstability critical conditions _gcomputing method be:

$M_g=\frac{{\stackrel{\&CenterDot;}{E}}_1\sin {\mathrm{\&delta;}}_{12}}{X_{12}}\sqrt{\frac{{\stackrel{\&CenterDot;}{Z}}_{22}}{\sin {\mathrm{\&alpha;}}_{22}{P}_D}}$

[work as M<M _gtime, there is merit angle unstability, M>M _gtime angle stability; ]

Step 4: calculate outskirt electric power ratio M according to actual measurement parameter, and judge dominance Failure Model by following situation:

Work as M _g≤ M≤M _vtime, be stable or critical stable state; If now (M _v-M) > (M-M _g), then more easily there is merit angle unstability; If (M _v-M) < (M-M _g), then more easily there is Voltage Instability;

Work as M>M _vor M<M _gtime, there is unstability; If now M>M _vand M>M _g, then only there is Voltage Instability; If M<M _gand M<M _v, then only there is merit angle unstability; If M _v<M<M _g, two kinds of unstabilitys occur simultaneously, and if | M _v-M|>|M-M _g|, then Voltage Instability takes Failure Model as the leading factor; If | M _v-M|<|M-M _g|, then merit angle unstability takes Failure Model as the leading factor.

Further, described Z _sthrough-put power between the target section obtained according to actual measurement and local part and section voltage calculate.

Further, described X ₁₂with according to practical power systems network topology structure, obtained by nodal impedance matrix.

Principle of work of the present invention is: from single Voltage-stabilizing Problems and single angle stability problem, according to the difference of aims of systems section two ends equivalence method, local part is equivalent to single constant-impedance Z respectively _s, or local loaded portion is equivalent to constant-impedance load Z _d, and then analyze the change of different electric parameter for the impact of unstability dominance, calculate Thevenin's equivalence parameter according to Thevenin's equivalence tracking, and then the leading Failure Model in Transient Instability process can be identified.

The invention has the beneficial effects as follows:

1, this method is used to quantize the distinguishing indexes of different dominant pattern, by the situation of change of each state parameter under collection electric system instability status, situation is dominated by outskirt electric power ratio identification unstability fast and accurately, dominant pattern can be obtained intuitively, and the transformation situation of different Failure Model can be obtained, and then provide data supporting for power system safety and stability runs, and provide reference for the dispatcher after fault operates.

2, the impact using method of the present invention can calculate each Parameters variation to change for stable operation situation, has reference for the fast quick-recovery after electric system generation unstability.

3, in conjunction with the method adopting real-time follow-up Dai Weinan parameter equivalence, the steady operational status of any time electric system can be obtained further, the stability margin (distance of nargin and current state and critical stable state) changing up till now according to parameters of electric power system, if nargin reduces, just need by parameter change and carry out emulation to observe whether nargin to be increased, if can nargin be increased, then can take same operation in practical power systems is run, realize leaving enough nargin spaces when stable operation to system, and then prevent the generation of extensive unstability situation.

Accompanying drawing explanation

Fig. 1 is the schematic diagram of system before local part Thevenin's equivalence;

Fig. 2 is the schematic diagram of system after local power generation part Thevenin's equivalence

Fig. 3 is the schematic diagram of system after the overall Thevenin's equivalence of local part

Fig. 4 is local power generation part and the loaded portion schematic diagram of system after Thevenin's equivalence respectively

Embodiment

Below in conjunction with the drawings and specific embodiments, the present invention is described in more detail.The Transient Instability dominance method of discrimination that the present invention is based on outskirt electric power ratio comprises the following steps:

(1) selected target section: in the interconnection that electric system is a large amount of, [transmission section refers in electric system and connects between the two regions to extract a target section, the set of one group of transmission line of electricity selected under certain operational mode] (repeating the situation that can obtain whole system Internet Transmission section), assuming that this target section voltage is now U ₂, and according to power system dynamic equivalence principle, obtain the electric system other parts equivalent model that separated by target section and local part equivalent model, its concrete extracting method is as follows:

1., electric system other parts are extracted: the side that the network composition being comparatively speaking not easy to be subject to fault effects after being split by target section is larger is extracted as electric system other parts, and its equivalent voltage and transmission line impedance can be obtained by Thevenin's equivalence following principle; The larger side of network composition is exactly the more side of the more side of node and circuit or power supply number, mainly relies on the operating experience choosing people; Electric system other parts are equivalent to the first generator, and its Dai Weinan equivalent potential is E ₁, output power is S ₁=P ₁+ jQ ₁, between the first generator and target section, the Dai Weinan equiva lent impedance of circuit is z ₁₂.

2., local part is extracted: the rest network composition beyond electric system other parts and target section is equivalent to two parts, is respectively local power generation part and local loaded portion, the summation of local power generation part and local all generators.And local loaded portion is the summation of local all loads; Line impedance, according to the voltage after equivalence and through-put power, utilizes Load flow calculation to obtain; Local power generation part is equivalent to the second generator, and its equivalent potential is E ₂, output power is S ₂=P ₂+ jQ ₂, between the second generator and target section, the equiva lent impedance of circuit is z ₂₁; The power that target section is transferred to local loaded portion is S _d=P _d+ jQ _d, now consider that local loaded portion is constant power load model, as shown in Figure 2, this model can obtain the relation between each parameter.

For any time k that electrical network complication system runs, be that 2 voltage sources are powered to load simultaneously by system equivalent, consideration first generator is without loss of generality powered to load through an impedance, and the second generator is the local generator of load, as depicted in figs. 1 and 2.Wherein, and z ₁₂be respectively Thevenin's equivalence electromotive force and the Thevenin's equivalence impedance of circuit between the first generator and target section of k moment first generator (electric system other parts), and z ₂₁be respectively Thevenin's equivalence electromotive force and the Thevenin's equivalence impedance of circuit between the second generator and target section of k moment second generator (local power generation part), U ₂for load busbar voltage [i.e. target section voltage]; P ₁, Q ₁, P ₁₀, Q ₁₀, P ₂, Q ₂, P ₂₀and Q ₂₀be respectively active reactive that electric system other parts export before and after line impedance and the active power that local power generation part is carried before and after line impedance and reactive power, P _dand Q _dbe respectively active power and the reactive power of load, δ ₁, δ ₂and δ ₁₂be respectively with phase angle [δ ₁₂also the merit angular difference of the first generator and the second generator is represented, δ ₁₂=δ ₁-δ ₂], and to define M be outskirt electric power ratio, then have M=P ₁/ P _d, Dai Weinan parameter identification can be implemented under WAMS, obtain equivalent impedance.

3., as shown in Figure 3, under above-mentioned equivalent situation, conveniently analyze, further by power off line on target section, the through-put power sum namely between target section and local part and section voltage, be equivalent to single constant-impedance Z by local part _s, Z _sphase angle be this model is used for analytical voltage stability.

4., in order to what consider local transmission of electricity affect situation, on basis 2., do not consider that local loaded portion is constant power load model, be assumed to be constant-impedance load Z _d, Z _dphase angle be β, as shown in Figure 4, this model can be used for analyze power-angle stability.

(2), build electric system two end model: by said extracted method, the equivalent network and the equivalent power that obtain section both sides transmit situation, form 4 kinds of equivalent models as accompanying drawing:

(3), Dai Weinan equivalent model parameters relationship: by above-mentioned network equivalent model, after selected target section, all power system networks can be equivalent to 4 kinds of equivalent networks, then have in fig. 2:

$P_1=\frac{E_1^2}{\left|Z_{11}\right|}\sin {\mathrm{\&alpha;}}_{11}+\frac{E_1{E}_2}{\left|Z_{12}\right|}\sin ({\mathrm{\&delta;}}_{12}-{\mathrm{\&alpha;}}_{12})---\left(1\right)$

$P_2=\frac{E_2^2}{\left|Z_{22}\right|}\sin {\mathrm{\&alpha;}}_{22}-\frac{E_1{E}_2}{\left|Z_{12}\right|}\sin ({\mathrm{\&delta;}}_{12}+{\mathrm{\&alpha;}}_{12})---\left(2\right)$

Wherein, E ₁for the Thevenin's equivalence electromotive force of k moment first generator, E ₂for the Thevenin's equivalence electromotive force of k moment second generator; Z ₁₁, Z ₂₂be the input impedance of the first generator and the second generator, Z ₁₂=Z ₂₁=z ₁₂+ z ₂₁for transfer impedance, α ₁₁, α ₁₂, α ₂₁, α ₂₂be respectively Z ₁₁, Z ₁₂, Z ₂₁, Z ₂₂the complementary angle at respective impedance angle; δ ₁₂represent the merit angular difference of the first generator and the second generator, Z ₁₂and Z ₂₁for transimpedance, Z ₁₁and Z ₂₂for self-impedance, can be obtained by nodal impedance matrix according to actual track.Assuming that now ignore the resistance of transmission line, namely z ₁₂in active component, and consider that the equivalent electrical distance between local second generator and load bus is negligible relative to the equivalent electrical distance between the first generator (electric system remainder) and load bus, then have:

Z ₁₁＝Z ₁₂＝Z ₂₁＝jX ₁₂，Z ₂₂＝Z _D‖X ₁₂， (3)

α ₁₁＝α ₁₂＝α ₂₁＝0 (4)

(3) (4) are substituted in (1) (2) and obtain:

$P_1=\frac{E_1{E}_2}{X_{12}}\sin {\mathrm{\&delta;}}_{12}---\left(5\right)$

$P_2=\frac{E_2^2}{Z_{22}}\sin {\mathrm{\&alpha;}}_{22}-\frac{E_1{E}_2}{X_{12}}\sin {\mathrm{\&delta;}}_{12}=P_D-P_1---\left(6\right)$

(4), calculating voltage dominance index: [what is called is depending on entering impedance depending on entering impedance with Fig. 3, exactly local part is regarded as a black box, only know its voltage and power, and with impedance=voltage square divided by power come equivalent, as depending on entering impedance] system schematic after equivalence is example, relation between actual measurement parameter and Voltage Instability is described, according to traditional Voltage Instability condition, as the Thevenin's equivalence modulus of impedance Z of local part _s, namely depending on entering modulus of impedance Z _sequal the Dai Weinan equiva lent impedance z of circuit between the first generator and target section ₁₂film time, load busbar voltage [i.e. target section voltage] is limiting voltage, now has:

Wherein, I ₂it is the equivalent current that the second generator flows to section;

(8) are substituted into (7) and in conjunction with Kirchhoff law, obtains

Wherein have

The outskirt electric power ratio that (8) (9) (10) (11) are substituted into (5) (6) now corresponding has when time, be Voltage Instability critical conditions; Work as M>M _vtime, there is Voltage Instability, M<M _vvoltage stabilization.

(5), calculate merit angle dominance index: for the system schematic after the equivalence of Fig. 4 load impedance, the relation between actual measurement parameter and merit angle unstability is described, the equation of rotor motion of two generators is:

$M_1\mathrm{\&Delta;}{\stackrel{\&CenterDot;\&CenterDot;}{\mathrm{\&delta;}}}_1=-\frac{{\mathrm{dP}}_1}{{\mathrm{d\&delta;}}_{12}}\mathrm{\&Delta;}{\mathrm{\&delta;}}_{12}---\left(12\right)$

$M_2\mathrm{\&Delta;}{\stackrel{\&CenterDot;\&CenterDot;}{\mathrm{\&delta;}}}_2=-\frac{{\mathrm{dP}}_2}{{\mathrm{d\&delta;}}_{12}}\mathrm{\&Delta;}{\mathrm{\&delta;}}_{12}---\left(13\right)$

Wherein, M ₁represent the equivalent moment of inertia of the first generator, represent the first generator's power and angle [namely phase angle] second-order differential, M ₂represent the equivalent moment of inertia of the second generator, represent the second-order differential of the second generator's power and angle, △ δ ₁₂represent the variable quantity of the merit angular difference of the first generator and the second generator.

M ₁be (existing) EEAC method with the computing method of M2.

According to second-order system stable condition, and if only if meets:

$\frac{1}{M_1}\frac{{\mathrm{dP}}_1}{{\mathrm{d\&delta;}}_{12}}<\frac{1}{M_2}\frac{{\mathrm{dP}}_2}{{\mathrm{d\&delta;}}_{12}}---\left(14\right)$

Shi Fasheng merit angle unstability, assuming that now load consumes active power is P _d, when considering that the changed power of electric system other parts input this locality is less relative to power supplied locally changed power, have under limiting case:

$\frac{{\mathrm{dE}}_2}{{\mathrm{d\&delta;}}_{12}}\sin {\mathrm{\&delta;}}_{12}+E_2\cos {\mathrm{\&delta;}}_{12}\&ap;0---\left(15\right)$

$\frac{2}{E_2}\frac{{\mathrm{dE}}_2}{{\mathrm{d\&delta;}}_{12}}+\cot {\mathrm{\&alpha;}}_{22}\frac{{\mathrm{d\&alpha;}}_{22}}{d{\mathrm{\&delta;}}_{12}}=\frac{1}{Z_{22}}\frac{{\mathrm{dZ}}_{22}}{{\mathrm{d\&delta;}}_{12}}---\left(16\right)$

Then have and now have

$E_2=\sqrt{\frac{P_D{Z}_{22}}{\sin {\mathrm{\&alpha;}}_{22}}}---\left(17\right)$

(17) are substituted into (5) (6) then have:

work as M=M _gtime, be merit angle unstability critical conditions; Work as M<M _gshi Fasheng merit angle unstability, M>M _gtime angle stability.

(6), stable deflection and unstability dominance mainly depend on actual measurement outskirt electric power ratio and voltage critical outskirt electric power ratio M _v, merit angle critical outskirt electric power ratio M _gdistance determine, specific as follows:

Work as M _g≤ M≤M _vtime, be stable or critical stable state; If now (M _v-M) > (M-M _g), then more easily there is merit angle unstability; If (M _v-M) < (M-M _g), then more easily there is Voltage Instability;

Work as M>M _vor M<M _gtime, there is unstability; If now M>M _vand M>M _g, then only there is Voltage Instability; If M<M _gand M<M _v, then only there is merit angle unstability; If M _v<M<M _g, two kinds of unstabilitys occur simultaneously, and if | M _v-M|>|M-M _g|, then Voltage Instability takes Failure Model as the leading factor; If | M _v-M|<|M-M _g|, then merit angle unstability takes Failure Model as the leading factor.

Claims (3)

1., based on a Transient Instability dominance method of discrimination for outskirt electric power ratio, it is characterized in that, comprise the following steps:

Step 1: selected target section in electric system;

Step 2: build electric system Dai Weinan equivalent model:

A electric system is divided into local part, target section and electric system other parts according to the segmentation of target section by (); Local part is equivalent to two parts: local power generation part and local loaded portion;

B electric system other parts, according to Thevenin's equivalence following principle, are equivalent to the first generator by (), the Dai Weinan equivalent potential of the first generator is first generated output power is wherein P ₁be the active power that the first generator exports, Q ₁it is the reactive power that the first generator exports; Between first generator and target section, the Dai Weinan equiva lent impedance of circuit is z ₁₂;

Local power generation part is equivalent to the second generator, and the Dai Weinan equivalent potential of the second generator is second generated output power is wherein P ₂be the active power that the second generator exports, Q ₂it is the reactive power that the second generator exports; Between second generator and target section, the Dai Weinan equiva lent impedance of circuit is z ₂₁;

The power that target section is transferred to local loaded portion is wherein P _dfor target section is transferred to the active power of local loaded portion, Q _dfor target section is transferred to the reactive power of local loaded portion;

Step 3: definition outskirt electric power ratio is M:M=P ₁/ P _d; According to Dai Weinan equivalent model parameters relationship, the outskirt electric power ratio M of calculating voltage unstability critical conditions _vwith the outskirt electric power ratio M of merit angle unstability critical conditions _g;

1) the outskirt electric power ratio M of Voltage Instability critical conditions _vcomputing method be:

$M_V=\frac{{\stackrel{\&CenterDot;}{Z}}_K{\stackrel{\&CenterDot;}{Z}}_{22}\sin {\mathrm{\&delta;}}_{12}}{X_{12}^2\sin {\mathrm{\&alpha;}}_{22}}$

Wherein,

for looking over from electric system other parts, local part is equivalent to equiva lent impedance during single constant-impedance, for Z _sphase angle; X when ignoring line resistance ₁₂=z ₁₂+ z ₂₁be the input reactance of the first generator, be the input impedance of the second generator, α ₂₂for the complementary angle of angle of impedance, δ ₁₂it is the merit angular difference of the first generator and the second generator;

2) the outskirt electric power ratio M of merit angle unstability critical conditions _gcomputing method be:

$M_g=\frac{{\stackrel{\&CenterDot;}{E}}_1\sin {\mathrm{\&delta;}}_{12}}{X_{12}}\sqrt{\frac{{\stackrel{\&CenterDot;}{Z}}_{22}}{\sin {\mathrm{\&alpha;}}_{22}{P}_D}}$

Step 4: carry out Thevenin's equivalence tracking according to current operating parameter, and obtain the outskirt electric power ratio M under the current method of operation, and judge dominance Failure Model by following situation:

Work as M _g≤ M≤M _vtime, be stable or critical stable state; If now (M _v-M) > (M-M _g), then more easily there is merit angle unstability; If (M _v-M) < (M-M _g), then more easily there is Voltage Instability;

Work as M>M _vor M<M _gtime, there is unstability; If now M>M _vand M>M _g, then only there is Voltage Instability; If M<M _gand M<M _v, then only there is merit angle unstability; If M _v<M<M _g, two kinds of unstabilitys occur simultaneously, and if | M _v-M|>|M-M _g|, then Voltage Instability takes Failure Model as the leading factor; If | M _v-M|<|M-M _g|, then merit angle unstability takes Failure Model as the leading factor.

2. the Transient Instability dominance method of discrimination based on outskirt electric power ratio according to claim 1, is characterized in that, described Z _sthrough-put power between the target section obtained according to actual measurement and local part and section voltage calculate.

3. the Transient Instability dominance method of discrimination based on outskirt electric power ratio according to claim 1, is characterized in that, described X ₁₂with according to practical power systems network topology structure, obtained by nodal impedance matrix.