CN102904246A - Fast calculating method of transient stability transmission limit of point to grid power transmission system - Google Patents

Abstract

The invention belongs to the field of a power system and particularly relates to a fast calculating method of a transient stability transmission limit of a point to grid power transmission system. According to the fast calculating method, an equal-area method is used for analyzing, when the kinetic energy increasing area on a P-delta plane is equal to the available kinetic energy decreasing area, the current of a corresponding power transmission line is the transient stability output limit of the system, and an analytic expression of the transient stability limit is deduced. In specific solving, an initial transmission capability is firstly assumed, accordingly, the number of units n is determined, values of parameters in the analytic expression are calculated, the transient stability limit is solved according to the analytic expression, and then solving of the next round is performed according to the transient stability limit until values of two rounds of iteration solving approach to each other.

Description

A kind of quick calculation method to the net transmission system transient stability transmission of electricity limit

Technical field

The invention belongs to field of power, be specifically related to a kind of quick calculation method to the net transmission system transient stability transmission of electricity limit.

Background technology

Be accompanied by the construction of the strong intelligent grid of ultra high voltage and the exploitation in large power supply base, many transmission systems to the net access occurred, in planning and operating analysis, the ability to transmit electricity that often needs to calculate fast the transient stability limit of this kind system and be subjected to this restriction.At present, generally all be to adopt business-like trend and transient stability software for calculation (such as PSD-BPA and PSASP etc.), progressively adjust the transmission line trend with fixed step size, sound out by the method for time domain numerical simulation and obtain the transient stability limit.This method relies on simulation software and artificial adjustment experience very much, and owing to will carry out repeatedly the exploration of transient stability time-domain-simulation, so consuming time longer; Also it should be noted that, existing method is a kind of practical application algorithm, fails to excavate deeply from point of theory the physical essence of the transmission system transient stability limit.

To the net transmission system, among the figure, large power supply is transmitted electricity to receiving-end system by dual loop transmission line for as shown in Figure 1 point.The equation of rotor motion of this system is:

$\left\{\begin{array}{c}M\frac{\mathrm{d\ω}}{\mathrm{dt}}=P_m-P_e\\ \frac{\mathrm{d\δ}}{\mathrm{dt}}=\mathrm{\ω}\end{array}\right.$

According to law of equal areas, when power transmission system broke down, the transient stability of system can be described by Fig. 2.

Figure 2 shows that by the point of equation (1) the gained P-δ power-angle curve figure to valve systems such as nets, P _mBe the mechanical output of unit, wherein P _e ⁽¹⁾For front equivalent generator electromagnetic power curve, P occur in fault _e ⁽²⁾Be equivalent generator electromagnetic power curve between age at failure, P _e ⁽³⁾Be equivalent generator electromagnetic power curve after the fault disappearance, δ ₀Be generator's power and angle under the normal operating mode before the fault, after fault occured, system operation mode changed, and when fault disappeared, the merit angle was δ _cAfter fault disappeared, generator stable operation point merit angle was δ _S, irregular operation point merit angle is δ _uIf electromagnetic power curve P between age at failure _e ⁽²⁾With mechanical output P _mBetween the kinetic energy in zone (regional abcd) to increase area be A _Abcd, electromagnetic power curve P after fault disappears _e ⁽³⁾With mechanical output P _mBetween the maximum available kinetic energy of zone between (regional deu) to reduce area be A _Deu, according to law of equal areas, if A _Abcd＜A _Deu, if system stability then is A _Abcd＞A _DeuSystem's unstability then.And work as A _Abcd=A _DeuThen system's neutrality the present invention is based on this, has disclosed deeply the physical essence of the electric power system transient stability transmission of electricity limit from point of theory, and has proposed thus the quick calculation method of point to the net transmission system transient stability transmission of electricity limit.

Summary of the invention

For the deficiencies in the prior art, the invention provides a kind of quick calculation method to the net transmission system transient stability transmission of electricity limit, start with from physical essence, do not rely on business-like power system simulation software, can ask for fast a little to the net transmission system transient stability transmission of electricity limit, precision is higher, and simple and convenient.

A kind of quick calculation method to the net transmission system transient stability transmission of electricity limit provided by the invention, its improvements are, continue to increase active power and the number of units of sending end generator, carry trend constantly to increase, transmission power and merit angle to stable operating point before the fault of net transmission system on P-δ plane are constantly increased; The increase of transmission power will be increase trend so that kinetic energy increases area, the increase at merit angle then then is minimizing trend so that available kinetic energy reduces area, when kinetic energy increased area and equals available kinetic energy and reduce area, corresponding conveying trend was a little the transient stability of the net transmission system limit of transmitting electricity;

Computational methods comprise the steps:

(1) calculates receiving-end system equivalent reactance X _Sys

(2) determine transmission power and definite start number of units n; When carrying out this step for the first time, the initial power that transmission power is set for the user, during this step of recirculation, transmission power is last round of the definite transmission power of iterative value;

(3) constantly P-δ curve unstable equilibrium point, the equivalent inertia time constant of sending after P-δ curve excision angle, the fault of P-δ curve stable operating point, fault clearance before the maximum electromagnetic power of P-δ curve, the fault after the maximum electromagnetic power of P-δ curve, the fault in the interconnection reactance before the calculating generator group built-in potential, fault, the interconnection reactance in the fault, the interconnection reactance after the fault, the fault;

(4) find the solution the transient stability limit;

(5) with on take turns transient stability limit calculated value difference whether be not more than set point, be then to carry out step (6), otherwise the calculated value of the epicycle transient stability limit be assigned to transmission power and return step (2);

(6) the output transient stability limit.

Wherein, when the power of increase sending end generator and number of units, increase first the power of generator, after power is greater than rated power, increase again the number of units of generator.

Wherein, the front stable operating point of described fault comprises relative merit angle and the transmission power of sending end unit.

Wherein, the step of step (1) calculating receiving-end system equivalent reactance is:

1. calculate the short circuit current I of receiving-end system bus;

2. deduct the short circuit current component that the sending end power supply provides with described short circuit current I, obtain the short circuit current I ' of receiving-end system bus;

3. the perunit value of described short circuit current is asked reciprocal, obtained receiving-end system equivalent reactance X _Sys

Wherein, 2. step adopts the short circuit current I of direct calculating receiving-end system bus or the direct short circuit current I ' that calculates the receiving-end system bus after breaking point is to the net transmission line;

Described direct calculating refers to calculate with short-circuit current calculation program, or draws the data of short circuit current I ' from the boundary condition of planning material.

Wherein, the expression formula of step (3) computing system contact reactance is:

X _∑＝(X′ _d+X _T)/n+X _L+X _sys(1)

X _∑fault＝(X′ _d+X _T)/n+(X _L+X _sys)+(X′ _d+X _T)(X _L+X _sys)/(nX _Δ)(2)

X _∑post＝(X′ _d+X _T)/n+X _Lpost+X _sys (3)

In the formula, X _∑Be the reactance that contacts before the fault and between receiving-end system; X _{∑ fault}Be the reactance that contacts in the fault and between receiving-end system; X _{∑ post}Be the reactance that contacts after the fault and between receiving-end system; X ' _dTransient state reactance for generator; X _TBe the step-up transformer leakage reactance; X _LBe the transmission line reactance; N is the generating set number of units; X _ΔBe the fault additional impedance, the restriction fault is at the transmission line head end; X _LpostBe the transmission line reactance after the fault clearance; X _SysBe the receiving-end system equivalent reactance.

Wherein, the expression formula of step (3) calculating generator group built-in potential is:

$E^{\′}=\sqrt{{[U+\frac{Q_{\mathrm{sys}}(X_L+(X_d^{\′}+X_T)/n)}{U}]}^2+{\left[\frac{P(X_L+X_d^{\′}+X_T)/n}{U}\right]}^2}---\left(4\right)$

In the formula, Q _SysBe the terminal reactive power that flows out of transmission line reactance component; U is the receiving-end system busbar voltage; P is transmission line power.

Wherein, calculate in the step (3) in the fault and the maximum electromagnetic power of the P-δ curve after the fault, fault before P-δ curve stable operating point, fault clearance constantly after P-δ curve excision angle, the fault expression formula of P-δ curve unstable equilibrium point, the equivalent inertia time constant of sending be:

$P_{\mathrm{em}}^{\left(1\right)}=\frac{E^{\′}U}{X_{\mathrm{\Σ}}};$ $P_{\mathrm{em}}^{\left(2\right)}=\frac{E^{\′}U}{X_{\mathrm{\Σfault}}};$ $P_{\mathrm{em}}^{\left(3\right)}=\frac{E^{\′}U}{X_{\mathrm{\Σpost}}}---\left(5\right)$

${\mathrm{\δ}}_0=a\sin \left(\frac{P_m}{P_{\mathrm{em}}^{\left(1\right)}}\right);$ ${\mathrm{\δ}}_c={\mathrm{\δ}}_0+\frac{1}{2}\frac{P_m}{M}{t}_c^2{\mathrm{\ω}}_0;$ ${\mathrm{\δ}}_u=\mathrm{\π}-a\sin \left(\frac{P_m}{P_{\mathrm{em}}^{\left(3\right)}}\right)$

In the formula, P _Em ⁽¹⁾Be the electromagnetic power maximum on the P-δ curve before the fault, P _Em ⁽²⁾Be the electromagnetic power maximum on the P-δ curve in the fault, P _Em ⁽³⁾Be the electromagnetic power maximum on the P-δ curve after the fault; δ ₀Be angle stability operating point before the fault; δ _cBe fault clearance excision angle constantly; δ _uBe merit angle unstable equilibrium point after the fault; ω ₀=2 π f, M are the equivalent inertia time constant of n platform generating set, and namely the rotor inertia time constant of single unit multiply by n;

Wherein, finding the solution the transient stability algorithmic method of limit in the step (4) is:

When kinetic energy increase area equaled available kinetic energy minimizing area, its expression formula was:

${\∫}_{{\mathrm{\δ}}_0}^{{\mathrm{\δ}}_c}(P_m-P_e^{\left(2\right)})\mathrm{d\δ}={\∫}_{{\mathrm{\δ}}_c}^{{\mathrm{\δ}}_u}(p_e^{\left(3\right)}-P_m)\mathrm{d\δ}---\left(6\right)$

In the formula, P _mMechanical output for unit; P _e ⁽²⁾Electromagnetic power for unit between age at failure; P _e ⁽³⁾Electromagnetic power for unit after the fault fault clearance;

Solve the mechanical output of unit according to formula (6), namely the transient stability transmission pole is limited to:

$P_m=\frac{P_{\mathrm{em}}^{\left(3\right)}(\cos {\mathrm{\δ}}_c-\cos {\mathrm{\δ}}_u)-P_{\mathrm{em}}^{\left(2\right)}(\cos {\mathrm{\δ}}_c-\cos {\mathrm{\δ}}_0)}{{\mathrm{\δ}}_u-{\mathrm{\δ}}_0}---\left(7\right);$

When the restriction fault is power transmission line head end generation three-phase fault,

Following formula can turn to:

$P_m=\frac{P_{\mathrm{em}}^{\left(3\right)}(\cos {\mathrm{\δ}}_c-\cos {\mathrm{\δ}}_u)}{{\mathrm{\δ}}_u-{\mathrm{\δ}}_0}---\left(8\right)$

Formula (7) and formula (8) are transient stability transmission of electricity limit P _mAnalytical expression.

Compared with the prior art, beneficial effect of the present invention is:

This algorithm has disclosed the physical essence of the transmission system transient stability transmission of electricity limit at first deeply, and start with from physical essence, not relying on business-like power system simulation software, can ask for fast a little to the net transmission system transient stability transmission of electricity limit, precision is higher, and simple and convenient.

Description of drawings

Fig. 1 is that the extra-high-speed pressure point is to net transmission system schematic diagram;

Fig. 2 is transmission system electromagnetic power-merit angle (P-δ) curve chart;

Iteration schematic diagram when Fig. 3 is the long 200km of circuit provided by the invention;

Kinetic energy increased area and available kinetic energy minimizing area change tendency chart when Fig. 4 was the long 200km of circuit provided by the invention;

Transient stability limit P-δ curve synoptic diagram when Fig. 5 is the long 200km of circuit provided by the invention;

Fig. 6 is algorithm flow chart that the present invention provided by the invention carries.

Embodiment

Below in conjunction with accompanying drawing the specific embodiment of the present invention is described in further detail.

According to the power-angle curve figure that obtains of the prior art and the decision method of system stability, the present embodiment continues to extend its thought and obtains the transient stability transmission of electricity limit.

The present invention has at first disclosed the physical essence of the transient stability transmission of electricity limit: continue to increase the sending end generator exert oneself and number of units (preferential increase is exerted oneself, exert oneself and fill it up with stylish start group), the power transmission line trend constantly increases, generally will be so that constantly increase of stable operating point (being relative merit angle and the transmission power of sending end unit) before the fault of system on P-δ plane, the increase of transmission power will be increase trend so that kinetic energy increases area, the increase at merit angle then then is minimizing trend so that available kinetic energy reduces area relatively, when kinetic energy increase area equaled available kinetic energy minimizing area, corresponding power transmission line trend was the transient stability transmission of electricity limit of system.Suppose first an initial delivery ability when specifically finding the solution according to above-mentioned analysis, determine accordingly start number of units n, then calculate the value of each parameter in the analytic expression, and find the solution the transient stability limit according to analytic expression, again according to this temporarily steady limit carry out finding the solution of next one, until till the value of two-wheeled iterative approaches very much.

Concrete, the present embodiment is according to above-mentioned thought, and corresponding step is:

(1) breaking point calculates the short circuit current of receiving-end system bus after to the net transmission line, perhaps directly calculate the short circuit current of receiving-end system bus, obtain the short circuit current that receiving-end system provides after deducting again the short circuit current component that the sending end power supply provides, namely obtain receiving-end system equivalent reactance X after its perunit value is asked inverse _Sys, below each amount be perunit value.

(2) namely suppose first an initial delivery power, such as 1,000,000 kilowatts, determine accordingly start number of units n, or determine this round transmission power and start number of units n according to last round of iterative value.

(3) computing system contact reactance X _∑, X _{∑ fault}And X _{∑ post}, be respectively fault before, contact reactance (comprising system reactance) in the fault and after the fault between unit and system, computing formula is:

X _∑＝(X′ _d+X _T)/n+X _L+X _sys(1)

X _∑fault＝(X′ _d+X _T)/n+(X _L+X _sys)+(X′ _d+X _T)(X _L+X _sys)/(nX _Δ)(2)

X _∑post＝(X′ _d+X _T)/n+X _Lpost+X _sys(3)

In the formula, X _d' be the transient state reactance of generator, X _TBe the change leakage reactance of boosting, n is the generating set number of units, X _LBe transmission line reactance, X _ΔBe fault additional impedance (be 0 during the bus three-phase shortcircuit, the restriction fault is generally at the transmission line head end), X _LBe the transmission line reactance after the fault clearance.

The built-in potential E ' of calculating generator group, formula is:

$E^{\′}=\sqrt{{[U+\frac{Q_{\mathrm{sys}}(X_L+(X_d^{\′}+X_T)/n)}{U}]}^2+{\left[\frac{P(X_L+X_d^{\′}+X_T)/n}{U}\right]}^2}---\left(4\right)$

In the formula, Q _SysBe terminal idle (when circuit is not oversize, can be made as 0) of flowing out of transmission line reactance component.U is receiving-end system busbar voltage (can be made as 1), and P is transmission line power.

Calculate the maximum electromagnetic power of (afterwards) P-δ curve in the fault, front the P-δ of fault curve motion point, fault clearance moment P-δ curve and excise that the expression formula of equivalent inertia time constant is after P-δ curve unstable equilibrium point after angle, the fault, the fault:

$P_{\mathrm{em}}^{\left(1\right)}=\frac{E^{\′}U}{X_{\mathrm{\Σ}}};$ $P_{\mathrm{em}}^{\left(2\right)}=\frac{E^{\′}U}{X_{\mathrm{\Σfault}}};$ $P_{\mathrm{em}}^{\left(3\right)}=\frac{E^{\′}U}{X_{\mathrm{\Σpost}}}---\left(5\right)$

${\mathrm{\δ}}_0=a\sin \left(\frac{P_m}{P_{\mathrm{em}}^{\left(1\right)}}\right);$ ${\mathrm{\δ}}_c={\mathrm{\δ}}_0+\frac{1}{2}\frac{P_m}{M}{t}_c^2{\mathrm{\ω}}_0;$ ${\mathrm{\δ}}_u=\mathrm{\π}-a\sin \left(\frac{P_m}{P_{\mathrm{em}}^{\left(3\right)}}\right)$

In the formula, P _Em ⁽¹⁾Be the unit electromagnetic power maximum on the P-δ curve before the fault, P _Em ⁽²⁾Be the unit electromagnetic power maximum on (between age at failure) P-δ curve in the fault, P _Em ⁽³⁾Be the unit electromagnetic power maximum on (after the fault clearance) P-δ curve after the fault; δ ₀Stable operating point for merit angle before the fault; δ _cExcision angle for fault clearance moment unit; δ _uBe (behind the failure removal) merit angle unstable equilibrium point after the fault; ω ₀=2 π f, M are the equivalent inertia time constant of n platform generating set, and namely the rotor inertia time constant of single unit multiply by n.

(4) then calculate the value of each required in following formula (7), (8) parameter according to formula (5), and find the solution the transient stability limit according to formula (7), (8):

Reach the transient stability transmission pole in limited time corresponding kinetic energy increase the available following formula of relation that area and available kinetic energy reduce area and describe:

${\∫}_{{\mathrm{\δ}}_0}^{{\mathrm{\δ}}_c}(P_m-P_e^{\left(2\right)})\mathrm{d\δ}={\∫}_{{\mathrm{\δ}}_c}^{{\mathrm{\δ}}_u}(P_e^{\left(3\right)}-P_m)\mathrm{d\δ}---\left(6\right)$

${\∫}_{{\mathrm{\δ}}_0}^{{\mathrm{\δ}}_c}(P_m-P_{\mathrm{em}}^{\left(2\right)}\sin \mathrm{\δ})\mathrm{d\δ}={\∫}_{{\mathrm{\δ}}_c}^{{\mathrm{\δ}}_u}(P_{\mathrm{em}}^{\left(3\right)}\sin \mathrm{\δ}-P_m)\mathrm{d\δ}$

$P_m({\mathrm{\δ}}_c-{\mathrm{\δ}}_0)+P_{\mathrm{em}}^{\left(2\right)}(\cos {\mathrm{\δ}}_c-\cos {\mathrm{\δ}}_0)=P_{\mathrm{em}}^{\left(3\right)}(\cos {\mathrm{\δ}}_c-\cos {\mathrm{\δ}}_u)-P_m({\mathrm{\δ}}_u-{\mathrm{\δ}}_c)$

$-P_m{\mathrm{\δ}}_0+P_{\mathrm{em}}^{\left(2\right)}(\cos {\mathrm{\δ}}_c-\cos {\mathrm{\δ}}_0)=P_{\mathrm{em}}^{\left(3\right)}(\cos {\mathrm{\δ}}_c-\cos {\mathrm{\δ}}_u)-P_m{\mathrm{\δ}}_u$

$P_m({\mathrm{\δ}}_u-{\mathrm{\δ}}_0)=P_{\mathrm{em}}^{\left(3\right)}(\cos {\mathrm{\δ}}_c-\cos {\mathrm{\δ}}_u)-P_{\mathrm{em}}^{\left(2\right)}(\cos {\mathrm{\δ}}_c-{\cos \mathrm{\δ}}_0)$

$P_m=\frac{P_{\mathrm{em}}^{\left(3\right)}(\cos {\mathrm{\δ}}_c-\cos {\mathrm{\δ}}_u)-P_{\mathrm{em}}^{\left(2\right)}(\cos {\mathrm{\δ}}_c-\cos {\mathrm{\δ}}_0)}{{\mathrm{\δ}}_u-{\mathrm{\δ}}_0}---\left(7\right)$

In the formula: P _Em ⁽²⁾Be the unit electromagnetic power maximum on the P-δ curve between age at failure, P _Em ⁽³⁾Be the unit electromagnetic power maximum on the P-δ curve after the fault clearance.

When power transmission line head end generation three-phase fault (the restriction fault is generally at the transmission line head end),

Following formula can turn to:

$P_m=\frac{P_{\mathrm{em}}^{\left(3\right)}(\cos {\mathrm{\δ}}_c-\cos {\mathrm{\δ}}_u)}{{\mathrm{\δ}}_u-{\mathrm{\δ}}_0}---\left(8\right)$

(5) with on take turns transient stability limit calculated value difference whether be not more than set point, be then to carry out step (6), otherwise the calculated value of the epicycle transient stability limit be assigned to transmission power and return step (2).The set point of the present embodiment is 10MW.

(6) the output transient stability limit.

Concrete, the present embodiment further specifies as follows take Fig. 1 as example:

System's reference capacity is taken as 100MVA among Fig. 1, and generating set is chosen the 1000MVA unit, and generating set is gone straight up to ultra high voltage and transmitted electricity to Infinite bus system by the double loop; Step-up transformer short-circuit voltage percentage 18%, capacity are 1200MVA; The inertia of receiving-end system is infinitely great, and equivalent impedance is 0.0015.The time of supposing circuit two tip cut-off faults is: nearly fault end 0.09s (4.5 cycle), fault end 0.10s (5 cycle) far away.

When line length changed from 200km ~ 500km, the transient stability limit result of calculation that is subjected to three forever fault restrictions of utilizing institute of the present invention extracting method to calculate reached with the comparison of computational results of traditional numerical integrating gained as shown in the table.

Table 1 is subjected to the point of three forever fault restrictions to the transient stability LIMIT RESULTS comparative unit of net transmission system: MW

As can be seen from the above table, the transient stability limit that the stability limit that employing BPA software (numerical integrating) calculates and analytic method obtain is very approaching, thereby the correctness of analytic method has been described.

When line length is 200km, can try to achieve through 8 iteration (precision is 10MW) according to formula (7) that to be subjected to the ability to transmit electricity of temporarily steady restriction be 9850MW, the schematic diagram of iterative as shown in Figure 3, the P-δ curve when reaching the transient stability limit is as shown in Figure 4.If establishing passage trend incremental steps is 10MW, can obtain visually the variation tendency of kinetic energy increase area and available kinetic energy minimizing area as shown in Figure 5, notice that kinetic energy increases the curve of areas and two intersection points of available kinetic energy minimizing area existence among Fig. 5, corresponding 200km long transmission line then is described, carrying the trend parameter space to have two stable regions, i.e. [0,9850] and [10000,10120] MW.A rear stable region is very little, and the added benefit that the inertia that increases for new start group brings is disregarded therefore cast out, so stability limit is taken as 9850MW.

Variable acquiescence mentioned in the present embodiment all adopts perunit value.

Should be noted that at last: above embodiment is only in order to illustrate that technical scheme of the present invention is not intended to limit, although with reference to above-described embodiment the present invention is had been described in detail, those of ordinary skill in the field are to be understood that: still can make amendment or be equal to replacement the specific embodiment of the present invention, and do not break away from any modification of spirit and scope of the invention or be equal to replacement, it all should be encompassed in the middle of the claim scope of the present invention.

Claims (9)

1. a point is to the quick calculation method of the net transmission system transient stability transmission of electricity limit, it is characterized in that, continue to increase active power and the number of units of sending end generator, carry trend constantly to increase, transmission power and merit angle to stable operating point before the fault of net transmission system on P-δ plane are constantly increased; The increase of transmission power will be increase trend so that kinetic energy increases area, the increase at merit angle then then is minimizing trend so that available kinetic energy reduces area, when kinetic energy increased area and equals available kinetic energy and reduce area, corresponding conveying trend was a little the transient stability of the net transmission system limit of transmitting electricity;

Computational methods comprise the steps:

(1) calculates receiving-end system equivalent reactance X _Sys

(2) determine transmission power and definite start number of units n;

(3) constantly P-δ curve unstable equilibrium point, the equivalent inertia time constant of sending after P-δ curve excision angle, the fault of P-δ curve stable operating point, fault clearance before the maximum electromagnetic power of P-δ curve, the fault after the maximum electromagnetic power of P-δ curve, the fault in the interconnection reactance before the calculating generator group built-in potential, fault, the interconnection reactance in the fault, the interconnection reactance after the fault, the fault;

(4) find the solution the transient stability limit;

(5) with on take turns transient stability limit calculated value difference whether be not more than set point, be then to carry out step (6), otherwise the calculated value of the epicycle transient stability limit be assigned to transmission power and return step (2);

(6) the output transient stability limit.

2. quick calculation method as claimed in claim 1 is characterized in that, when the power of increase sending end generator and number of units, increases first the power of generator, after power is greater than rated power, increases the number of units of generator again.

3. quick calculation method as claimed in claim 1 is characterized in that, stable operating point comprises relative merit angle and the transmission power of sending end unit before the described fault.

4. quick calculation method as claimed in claim 1 is characterized in that, the step that step (1) is calculated the receiving-end system equivalent reactance is:

1. calculate the short circuit current I of receiving-end system bus;

2. deduct the short circuit current component that the sending end power supply provides with described short circuit current I, obtain the short circuit current I ' of receiving-end system bus;

3. the perunit value of described short circuit current is asked reciprocal, obtained receiving-end system equivalent reactance X _Sys

5. quick calculation method as claimed in claim 1 is characterized in that, 2. 1. step adopt the short circuit current I of direct calculating receiving-end system bus with step or directly calculate the short circuit current I ' of receiving-end system bus after breaking point is to the net transmission line;

Described direct calculating refers to calculate with short-circuit current calculation program, or draws the data of short circuit current I ' from the boundary condition of planning material.

6. quick calculation method as claimed in claim 1 is characterized in that, the expression formula of step (3) computing system contact reactance is:

X _∑＝(X′ _d+X _T)/n+X _L+X _sys(1)

X _∑fault＝(X′ _d+X _T)/n+(X _L+X _sys)+(X′ _d+X _T)(X _L+X _sys)/(nX _Δ)(2)

X _∑post＝(X′ _d+X _T)/n+X _Lpost+X _sys (3)

In the formula, X _∑Be the reactance that contacts before the fault and between receiving-end system; X _{∑ fault}Be the reactance that contacts in the fault and between receiving-end system; X _{∑ post}Be the reactance that contacts after the fault and between receiving-end system; X ' _dTransient state reactance for generator; X _TBe the step-up transformer leakage reactance; X _LBe the transmission line reactance; N is the generating set number of units; X _ΔBe the fault additional impedance, the restriction fault is at the transmission line head end; X _LpostBe the transmission line reactance after the fault clearance; X _SysBe the receiving-end system equivalent reactance.

7. quick calculation method as claimed in claim 1 is characterized in that, the expression formula of step (3) calculating generator group built-in potential is:

In the formula, Q _SysBe the terminal reactive power that flows out of transmission line reactance component; U is the receiving-end system busbar voltage; P is transmission line power.

8. quick calculation method as claimed in claim 1, it is characterized in that, calculate in the step (3) in the fault and after the fault before the maximum electromagnetic power of P-δ curve, the fault P-δ curve stable operating point, fault clearance constantly after P-δ curve excision angle, the fault expression formula of P-δ curve unstable equilibrium point, the equivalent inertia time constant of sending be:

In the formula, P _Em ⁽¹⁾Be the electromagnetic power maximum on the P-δ curve before the fault, P _Em ⁽²⁾Be the electromagnetic power maximum on the P-δ curve in the fault, P _Em ⁽³⁾Be the electromagnetic power maximum on the P-δ curve after the fault; δ ₀Be angle stability operating point before the fault; δ _cBe fault clearance excision angle constantly; δ _uBe merit angle unstable equilibrium point after the fault; ω ₀=2 π f, M are the equivalent inertia time constant of n platform generating set, and namely the rotor inertia time constant of single unit multiply by n.

9. quick calculation method as claimed in claim 1 is characterized in that, finds the solution the transient stability algorithmic method of limit in the step (4) to be:

When kinetic energy increase area equaled available kinetic energy minimizing area, its expression formula was:

In the formula, P _mMechanical output for unit; P _e ⁽²⁾Electromagnetic power for unit between age at failure; P _e ⁽³⁾Electromagnetic power for unit after the fault fault clearance;

Solve the mechanical output of unit according to formula (6), namely the transient stability transmission pole is limited to:

When the restriction fault is power transmission line head end generation three-phase fault,

Following formula can turn to:

Formula (7) and formula (8) are transient stability transmission of electricity limit P _mAnalytical expression.

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