CN101363885A - Method for discriminating voltage instability and load angle instability based on thevenin equivalent - Google Patents

Abstract

The invention provides a method for judging power angle instability and voltage instability based on the dynamic Thevenin equivalence. When a power system fails and instable, and the voltage is greatly reduced, the system operation and analysts is difficult to judge whether the instable property of the system belongs to the power angle instability or the voltage instability. Based on the dynamic Thevenin equivalence method, the real-time variation of the Thevenin equivalent potential of a load node to be monitored after the failure occurs can be obtained; and compared with the Thevenin equivalent potential, the instable property of the system can be judged. The method can be applied to the on-line analysis control and the off-line emulation analysis of the power system, facilitate the system operation and the analysts to adopt the effective measure in time and improve the safe and stable operation level of the power system.

Description

A kind of based on the equivalent method of differentiating voltage unstability and merit angle unstability of dynamic Dai Weinan

Technical field

The present invention relates to the method for Power System Analysis, particularly how to differentiate the method for merit angle unstability and voltage unstability, belong to field of power.

Background technology

Stability of power system is meant that electric system is subjected to keeping after the accident disturbance ability of stable operation.Angle stability and voltage are stable to be two importances of stable problem.Ripe relatively to the research of angle stability at present, formed more complete analysis, the hierarchy of control.Yet to the stable research of voltage, still be in developing stage from the notion to the analytical approach, corresponding research work also has suitable distance from maturation.Criterion to the voltage unstability does not have unified standard at present, China's accepted standard on engineering is to differentiate according to voltage backbone point busbar voltage fall and duration, be that system voltage backbone point busbar voltage descend to continue (being generally 1 second) and is lower than limit value (being generally 0.75p.u.) in the dynamic process, just think the system voltage unstability.Yet, if system's generation merit angle unstability equally also can cause the instability of system voltage.Therefore in actual engineering, no matter be in on-line analysis or the off-line analysis, all be faced with when system voltage descends that how the unstability character of discrimination system is the problem of merit angle unstability or voltage unstability.

In the engineering off-line simulation is analyzed, what comparatively approve at present is to judge it is merit angle unstability or voltage unstability by the validity of control measure, but this method does not have clear and definite explanation as yet on mechanism, its correctness also needs further demonstration, and is not suitable for being applied in the on-line analysis control of electric system.And in the online fortune analysis and Control of electric system, from existing document and actual engineering system, when system voltage declines to a great extent after the fault, the index that real-time judge system unstability character is not also arranged as yet, thereby the further deterioration of adopting which kind of effective control measure to suppress system's unstability for the system call personnel has brought puzzlement, lost the best opportunity of the system that saves, cause system's unstability further to worsen, even the generation systems collapse, social influence that it brings and economic loss are immeasurable.

When electric system is broken down, when system voltage declined to a great extent, the unstability character that system's operation and analyst often are difficult to discrimination system was merit angle unstability or voltage unstability, has proposed the present invention based on this.

Summary of the invention

Content of the present invention is to overcome the deficiencies in the prior art, and a kind of method of differentiating merit angle unstability and voltage unstability is provided.This method is a starting point with the essential distinction on the mechanism of merit angle unstability and voltage unstability, by the equivalent electromotive force of the dynamic Dai Weinan of dynamic Dai Weinan equivalence method real-time acquisition system, carry out the judgement of electric power system fault character, be beneficial to the dispatching system personnel and in time take effective measures, improve the maintenance level of system.

The present invention proposes a kind of method based on dynamic Dai Weinan equivalent differentiation voltage unstability and merit angle unstability, this method may further comprise the steps:

Steps A: when electric system is broken down, when voltage declines to a great extent, select voltage is minimum in the system after the fault load bus as monitoring target;

Step B: utilize synchronous measuring apparatus that voltage phasor, the electric current phasor of node are carried out synchronized sampling (if be applied to the off-line simulation analysis, voltage, the electric current phasor value of node in going on foot in the time of can directly obtaining emulation), by dynamic Dai Weinan equivalence method, the corresponding equivalent electromotive force E of Dai Weinan of step when obtaining sampled point t _t, compare E simultaneously _tWith the equivalent electromotive force E of critical Dai Weinan _H

Step C: comparative result, if E _t＜E _H, then judging system's generation merit angle unstability, system's operation, analyst can take to comprise control measure such as cutter, and system is retracted the synchronous operation state; If E _tE _H, then judging system's generation voltage unstability, system's operation, analyst can take to comprise control measure such as cutting load, increase reactive-load compensation.

E in described step B wherein _tBe the equivalent electromotive force of Dai Weinan, its Equivalent Model is:

${\stackrel{.}{E}}_t={\stackrel{.}{V}}_t+Z_t*{\stackrel{.}{I}}_t$

In the formula

Z _tBe respectively that this equation has two amounts to be determined, is respectively by synchronous measuring apparatus (or off-line simulation analysis) obtain loading busbar voltage phasor, current vector and Dai Weinan equivalent impedance

And Z _t, need the related data of at least two group voltage and currents just can find the solution.Only need utilize the data that pacing gets when previous

Thereby the dynamic Dai Weinan that goes on foot when obtaining obtaining t is equivalent electromotive force E _t

E in described step B wherein _HBe the equivalent electromotive force of critical Dai Weinan.If the two ends power source voltage is used respectively

Expression, the voltage at load point place is V _L∠ θ ₁, line impedance is used Z respectively ₁, Z ₂Expression, the active power of load, reactive power are represented with P, Q respectively;

The Dai Weinan equivalent parameters of seeing into from load point toward system orientation can calculate by following formula, wherein

Z _ThevBe respectively equivalent electromotive force of Dai Weinan and Dai Weinan equivalent impedance:

${\stackrel{.}{E}}_{\mathrm{Thev}}={\stackrel{.}{E}}_1-\frac{{\stackrel{.}{E}}_1-{\stackrel{.}{E}}_2}{Z_1+Z_2}{Z}_1=\frac{Z_2{\stackrel{.}{E}}_1+Z_1{\stackrel{.}{E}}_2}{Z_1+{\mathrm{<figure-callout\; id="2"\; label="Z"\; filenames="A200810119923E00111.png,A200810119923E00112.png"\; state="\{\{state\}\}">Z</figure-callout>}}_2}$

$Z_{\mathrm{Thev}}=\frac{Z_1\&CenterDot;Z_2}{Z_1+{\mathrm{<figure-callout\; id="2"\; label="Z"\; filenames="A200810119923E00111.png,A200810119923E00112.png"\; state="\{\{state\}\}">Z</figure-callout>}}_2}$

Get E ₁=E ₂=E, Z ₁=Z ₂=Z, δ ₁-δ ₂=δ, then

${\stackrel{.}{E}}_{\mathrm{Thev}}=\frac{{\stackrel{.}{E}}_1+{\stackrel{.}{E}}_2}{2}=\frac{E\&angle;{\mathrm{\&delta;}}_1+E\&angle;{\mathrm{\&delta;}}_2}{2}$

Suppose motor q axle transient internal voltage

Keep constant, then the critical merit angular difference δ of angle stability is 90 °, therefore when δ=90 °, and when E=1p.u., the equivalent electromotive force E of critical Dai Weinan _HCan represent with following formula:

$E_H=\frac{\sqrt{2}}{2}E=0.707p.u.$

Based on dynamic Dai Weinan equivalence method, whether the equivalent electromotive force parameter of the Dai Weinan of the load bus that declines to a great extent by real-time judge voltage drops to critical value belongs to merit angle unstability or voltage unstability with the discrimination system unstability character of getting off, have real-time, intuitive and operability, can not only satisfy the off-line analysis of system, also can satisfy simultaneously the analysis and judgement of online in real time, being beneficial to the system call personnel in time takes effective measures, the further deterioration of inhibition system unstability improves the safe and stable operation level of electric system.

Description of drawings

Fig. 1 is valve systems such as Dai Weinan;

Fig. 2 is valve systems such as dual power supply list load;

Fig. 3 is the process flow diagram of online differentiation voltage unstability and merit angle unstability;

Fig. 4 IEEE9 node system electric hookup;

Fig. 5 is the merit angle and the voltage curve of system, and wherein Fig. 5-a is the power-angle curve figure of generator 3 relative generators 1; Fig. 5-b is the voltage curve of bus 1,2,3; Fig. 5-c is the voltage curve of bus A, B, C.

Embodiment

Embodiment 1: with the analysis of IEEE9 node system off-line simulation is example, and three phase short circuit fault takes place node 2 in the time of 0 second, and 0.16 second owing to protect the circuit that moves between disconnected node 2 and node A, system's generation unstability.

The first step: after fault takes place, the minimum load bus of voltage behind the faults of monitoring system, in this example, the monitoring point is a node 2.The voltage that each node goes on foot when each emulation of back takes place fault is as shown in the table:

Second step: based on dynamic Dai Weinan equivalence method, the equivalent potential results of the voltage of node 2 and dynamic Dai Weinan is as shown in the table, and this example step-length is 0.02 second.

Time (s)	The equivalent electromotive force (p.u.) of the dynamic Dai Weinan of node 2	Node 2 voltages (p.u.)
			0.16	0.735	0.7253
0.18	0.7795	0.7692
			0.2	0.7977	0.7871
0.22	0.8022	0.7916
			0.24	0.7995	0.7889
0.26	0.7929	0.7824
			0.28	0.7841	0.7737
0.3	0.7741	0.7639
			0.32	0.7635	0.7534
0.34	0.7527	0.7427
			0.36	0.7419	0.7321
0.38	0.7313	0.7216
			0.4	0.721	0.7114
0.42	0.7110	0.7016
			0.44	0.7015	0.6923
0.46	0.6926	0.6834
			0.48	0.6841	0.6750

0.5	0.6761	0.6672
			0.52	0.6687	0.6598
0.54	0.6618	0.6530
			0.56	0.6553	0.6467
0.58	0.6493	0.6407
			0.6	0.6438	0.6353

The 3rd step: from the equivalent potential results of the dynamic Dai Weinan of node 2 as can be seen, the equivalent electromotive force of Dai Weinan continues to descend, after 0.44 second less than the equivalent electromotive force E of the critical Dai Weinan of merit angle unstability _H(0.707), therefore, it is because the merit angle unstability of system causes that voltage that can decision node 2 descends.

The 4th step: take the safety and stability control measure of merit angle unstability, at 0.45 second excision generator 2, system recovery was to steady operational status.The merit angle of system and voltage are as shown in Figure 5

Invention has been described according to specific exemplary embodiment herein.It will be conspicuous carrying out suitable replacement to one skilled in the art or revise under not departing from the scope of the present invention.Exemplary embodiment only is illustrative, rather than to the restriction of scope of the present invention, scope of the present invention is by appended claim definition.

Claims (2)

1, a kind of based on the equivalent method of differentiating merit angle unstability and voltage unstability of dynamic Dai Weinan, this method may further comprise the steps:

Steps A: when electric system is broken down, when voltage declines to a great extent, select voltage is minimum in the system after the fault load bus as monitoring target;

Step B: utilize synchronous measuring apparatus that voltage phasor, the electric current phasor of node are carried out synchronized sampling (if be applied to the off-line simulation analysis, voltage, the electric current phasor value of node in going on foot in the time of can directly obtaining emulation), by dynamic Dai Weinan equivalence method, the corresponding equivalent electromotive force E of Dai Weinan of step when obtaining sampled point t _t, compare E simultaneously _tWith the equivalent electromotive force E of critical Dai Weinan _H

Step C: comparative result, if E _t＜E _H, then judging system's generation merit angle unstability, system's operation, analyst can take to comprise control measure such as cutter, and system is retracted the synchronous operation state; If E _tE _H, then judging system's generation voltage unstability, system's operation, analyst can take to comprise control measure such as cutting load, increase reactive-load compensation.

2, according to the method for claim 1, it is characterized in that:

E in described step B wherein _tBe the equivalent electromotive force of Dai Weinan, its Equivalent Model is:

${\stackrel{\&CenterDot;}{E}}_t={\stackrel{\&CenterDot;}{V}}_t+Z_t*{\stackrel{\&CenterDot;}{I}}_t$

In the formula

Z _tBe respectively that this equation has two amounts to be determined, is respectively by synchronous measuring apparatus (or off-line simulation analysis) obtain loading busbar voltage phasor, current vector and Dai Weinan equivalent impedance

And Z _t, need the related data of at least two group voltage and currents just can find the solution.Only need utilize the data that pacing gets when previous

Thereby the dynamic Dai Weinan that goes on foot when obtaining obtaining t is equivalent electromotive force E _t

E in described step B wherein _HBe the equivalent electromotive force of critical Dai Weinan.If the two ends power source voltage is used respectively

Expression, the voltage at load point place is V _L∠ θ ₁, line impedance is used Z respectively ₁, Z ₂Expression, the active power of load, reactive power are represented with P, Q respectively;

The Dai Weinan equivalent parameters of seeing into from load point toward system orientation can calculate by following formula, wherein

Z _ThevBe respectively equivalent electromotive force of Dai Weinan and Dai Weinan equivalent impedance:

${\stackrel{\&CenterDot;}{E}}_{\mathrm{Thev}}={\stackrel{\&CenterDot;}{E}}_1-\frac{{\stackrel{\&CenterDot;}{E}}_1-{\stackrel{\&CenterDot;}{E}}_2}{Z_1+Z_2}{Z}_1=\frac{Z_2{\stackrel{\&CenterDot;}{E}}_1+Z_1{\stackrel{\&CenterDot;}{E}}_2}{Z_1+Z_2}$

$Z_{\mathrm{Thev}}=\frac{Z_1\&CenterDot;Z_2}{Z_1+Z_2}$

Get E ₁=E ₂=E, Z ₁=Z ₂=Z, δ ₁-δ ₂=δ, then

${\stackrel{\&CenterDot;}{E}}_{\mathrm{Thev}}=\frac{{\stackrel{\&CenterDot;}{E}}_1+{\stackrel{\&CenterDot;}{E}}_2}{2}=\frac{E\&angle;{\mathrm{\&delta;}}_1+E\&angle;{\mathrm{\&delta;}}_2}{2}$

Suppose motor q axle transient internal voltage

Keep constant, the critical merit angular difference δ of angle stability is 90 °, therefore when δ=90 °, and during E=1p.u., the equivalent electromotive force E of critical Dai Weinan _HCan calculate with following formula:

$E_H=\frac{\sqrt{2}}{2}E=0.707p.u.$ 。

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