CN103780176A - Low-excitation limit and field loss protection coordination method - Google Patents

Abstract

The invention discloses a low-excitation limit and field loss protection coordination method. The method comprises the following steps: a generator impedance per unit value and a system impedance per unit value in which the generator basic impedance is taken as the reference are calculated, and the characteristic circle of field loss protection impedance criterions is mapped onto a P-Q plane to derivate a static stability impedance circle based on the P-Q coordinate system; in consideration of the engineering field actual situation, a certain reserve factor should be reserved for the obtained static stability impedance circle, and in general, the reserve factor is 10%, that is the circle center and the radius of the static stability impedance circle are multiplied by a coefficient 0.9; and the obtained static stability impedance circle, the generator leading phase test value and the straight line P=PN (or P= grid specified generator maximum operating load) are drawn on the P-Q plane together according to an unified proportion, and finally, the above three curves and the Q-axis negative half axis are synthesized, and in a P-Q region determined by the four curves, corresponding points are selected according to the low-excitation limit equation and low-excitation limit (5) and static stability impedance circle (6) coordination requirements to determine the low-excitation limit equation.

Description

A kind of low fiting tuning method of encouraging restriction and field loss protection

Technical field

The present invention relates to a kind of low fiting tuning method of encouraging restriction and field loss protection, belong to the low restriction technologies field of encouraging of generator excited system.

Background technology

After loss of exicitation, will be transitioned into asynchronous operation, there is slip in rotor, and stator current increases, and stator voltage declines, and active power declines, and reactive power oppositely and increase; In rotor loop, there is difference frequency electric current; The voltage drop of electric power system and some current branch overcurrent.The variation of all these electric parameters, will destroy the stable operation of electric power system, the safety that threatens generator itself under certain condition.Thereby adjusting of generator loss-of-excitation protection directly has influence on the safe and stable operation of system.Generator loss-of-excitation protection is generator protection, is again system protection.

The domestic field loss protection application being made up of low impedance element and rotor low-voltage element is more.It is main criterion that this principle adopts impedance circle, is aided with the situations such as other criterion energy distinguish short-circuits, system oscillation, PT broken string and monitors the impact of loss of excitation fault on unit and system.

The low effect of encouraging restriction of generator excited system is in the time that exciting current drops to limits value, and restriction exciting current declines or increases exciting current, makes unit in the time of operation, not cross steady state stability limit.Lowly encourage restriction and adjust and generally have two kinds of methods, to be that straightway is low encourage restriction to one, and to be that step-out circle characteristic is low encourage restriction to another kind.

Lowly excitation system service aisle is switched to alternate channel or will automatically be switched to manual operation while encouraging limit movement.Field loss protection when action off-the-line, can obtain from both principle and action behavior the principle that cooperatively interacts, and excitation system is low encourages restriction and should move prior to generator loss-of-excitation protection.

Low encourage restriction be the protection of excitation system, the low restrictive curve of encouraging of excitation system adopts P-Q plane coordinates to describe, generator loss-of-excitation protection impedance operation equation adopts R-X plane coordinates to describe, because both belong to different coordinate systems, cannot compare intuitively both matching relationships, coordinate the unreasonable situation that causes field loss protection malfunction to happen occasionally, therefore, for promoting net factory coordinated operation level, be necessary to low encourage restriction and field loss protection fiting tuning between the two further investigate, find the fiting tuning numerical procedure that is applicable to engineering application, calculate with the fiting tuning that instructs both.

Summary of the invention

The object of the invention is, in order to solve, generation current machine excitation system is low encourages fiting tuning between restriction and field loss protection and calculates irrational problem, and the present invention disclose a kind of low restriction and fiting tuning method of field loss protection of encouraging.

Realizing technical scheme of the present invention is, the step of a kind of low fiting tuning method of encouraging restriction and field loss protection of the present invention is:

(1) calculate with generator base impedance

for generator impedance perunit value and the system impedance perunit value of benchmark, the characteristic circle of field loss protection impedance criterion is mapped in P-Q plane, release the quiet steady impedance circle based on P-Q coordinate system; For salient pole generator, due to non-uniform air-gap, its quiet steady impedance circle is apple shape, corresponding make to its analysis than non-salient pole machine complexity many, but can take under P-Q coordinate system the reliable circle that surrounds apple shape to carry out matching.

(2) consider engineering site actual conditions, the quiet steady impedance circle of step (1) gained should leave certain reserve factor, is generally taken as 10%, and the center of circle of quiet steady impedance circle and radius are multiplied by coefficient 0.9.

(3) quiet steady impedance circle, the generator of step (2) gained are entered to phase study value and straight line P=P _n(or the maximum operating load of P=electrical network regulation generator), according to unified ratio, be plotted in the lump P-Q plane, last comprehensive above 3 curves and the negative semiaxis of Q axle, in these 4 the determined P-Q of curve regions, encourage constrain equation and lowly encourage restriction and will ask for corresponding point and determine the low constrain equation of encouraging with quiet steady impedance circle fiting tuning according to low.

The invention has the beneficial effects as follows, the present invention encourages restriction and field loss protection fiting tuning is between the two furtherd investigate to low, finds the fiting tuning numerical procedure that is applicable to engineering application, to instruct both fiting tuning calculating; The present invention provides good method for promoting net factory coordinated operation level.

The present invention is applicable to generator to low restriction and the field loss protection fiting tuning between the two of encouraging.

Accompanying drawing explanation

Fig. 1 is low matching relationship of encouraging restriction and field loss protection on P-Q coordinate plane;

Fig. 2 is low matching relationship of encouraging restriction and quiet steady impedance circle;

Picture in picture number: the low restraining line of encouraging of 1 finger; 2 finger field loss protection borders; 3 finger static stability boundaries; 4 finger loss of excitation asynchronous impedance circles; 5 fingers are low encourages restriction; The quiet steady impedance circle of 6 finger.

Embodiment

Field loss protection impedance circle is mapped to P-Q coordinate system

If the center of circle of field loss protection impedance circle is (0, X ₀) radius is R ₀, its equation is:

$R^2+{(X-X_0)}^2<R_0^2---\left(1\right)$

The characteristic circle of field loss protection impedance criterion is mapped in P-Q plane

$\hat{S}=P+\mathrm{jQ}=U\hat{I}=\frac{U^2}{\hat{Z}}---\left(2\right)$

$Z=\frac{U^2}{\hat{Z}}=\frac{U^2}{P-\mathrm{jQ}}=\frac{U^2}{P^2+Q^2}P+j\frac{U^2}{P^2+Q^2}Q---\left(3\right)$

?

$\left\{\begin{array}{c}R=\frac{U^2}{P^2+Q^2}P\\ X=\frac{U^2}{P^2+Q^2}Q\end{array}\right.---\left(4\right)$

By the expression formula substitution formula (1) of R and X,

$\left(\frac{U^2}{P^2+Q^2}\right)P^2+{(\frac{U^2}{P^2+Q^2}Q-X_0)}^2<R_0^2---\left(5\right)$

For quiet steady impedance circle, abbreviation obtains:

$P^2+{(Q-\frac{X_0{U}^2}{X_0^2-R_0^2})}^2>{\left(\frac{R_0{U}^2}{X_0^2-R_0^2}\right)}^2---\left(6\right)$

In formula: the apparent power that S is generator, the active power that P is generator, the reactive power that Q is generator, the stator line voltage that U is generator.

From above formula, the mapping of quiet steady impedance circle in P-Q plane is a circle, and circle is outer is active region.

For asynchronous impedance circle,

abbreviation obtains:

$P^2+{(Q-\frac{X_0{U}^2}{X_0^2-R_0^2})}^2<{\left(\frac{R_0{U}^2}{X_0^2-R_0^2}\right)}^2$

From above formula, the mapping of asynchronous impedance circle in P-Q plane is a circle, in circle, is active region.

Contrast accompanying drawing 1, illustrates and in P-Q plane, judges intuitively low restriction and the whether correct method of field loss protection matching relationship of encouraging:

If encourage below restrictive curve low on field loss protection border, as shown in Figure 1, show lowly to encourage restriction and field loss protection matching relationship is correct.When generator is underexcitation or when low magnetic, generator power is introduced into the low restricted area of encouraging, when low encourage restriction not startup effect just can enter in field loss protection circle (quiet steady impedance circle or asynchronous impedance circle), can prevent field loss protection malfunction.As shown in Figure 1; there is low encourage or when loss of excitation at generator; first operation state of generator crosses quiet steady impedance circle; just arrive asynchronous impedance circle; that is to say that quiet steady impedance circle is higher than asynchronous impedance circle sensitivity; so in low fiting tuning problem of encouraging restriction and field loss protection; what no matter generator loss-of-excitation protection adopted is quiet steady impedance circle or asynchronous impedance circle; low encourage adjusting of restriction all there is no need consider coordinate with asynchronous impedance circle; need only consider and the coordinating of quiet steady impedance circle, and it is highly sensitive in quiet steady impedance circle.

Contrast accompanying drawing 2, illustrates the low fiting tuning method of encouraging restriction and field loss protection of generator based on P-Q plane: concrete steps are:

(1) calculate with generator base impedance

for generator impedance perunit value and the system impedance perunit value of benchmark, then release the quiet steady impedance circle based on P-Q coordinate system according to formula 6; For salient pole generator, due to non-uniform air-gap, its quiet steady impedance circle is apple shape, corresponding make to its analysis than non-salient pole machine complexity many, but can take under P-Q coordinate system the reliable circle that surrounds apple shape to carry out matching.

(2) consider engineering site actual conditions, the quiet steady impedance circle of step (1) gained should leave certain reserve factor, is generally taken as 10%, and the quiet steady impedance circle center of circle and radius are multiplied by coefficient 0.9.

(3) quiet steady impedance circle, the generator of step (2) gained are entered to phase study value and straight line P=P _n(or the maximum operating load of P=electrical network regulation generator), according to unified ratio, be plotted in the lump P-Q plane, last comprehensive above 3 curves and the negative semiaxis of Q axle, in these 4 the determined P-Q of curve regions, encourage constrain equation and lowly encourage restriction and will ask for corresponding point and determine the low constrain equation of encouraging with quiet steady impedance circle fiting tuning according to low.

Claims (3)

1. a low fiting tuning method of encouraging restriction and field loss protection, is characterized in that, the step of described method is:

(1) calculate generator impedance perunit value and the system impedance perunit value take generator base impedance as benchmark, the characteristic circle of field loss protection impedance criterion is mapped in P-Q plane, release the quiet steady impedance circle based on P-Q coordinate system; For salient pole generator, due to non-uniform air-gap, its quiet steady impedance circle is apple shape, corresponding make to its analysis than non-salient pole machine complexity many, but can take under P-Q coordinate system the reliable circle that surrounds apple shape to carry out matching;

(2) consider engineering site actual conditions, the quiet steady impedance circle of step (1) gained should leave certain reserve factor, is generally taken as 10%, and the center of circle of quiet steady impedance circle and radius are multiplied by coefficient 0.9;

(3) quiet steady impedance circle, the generator of step (2) gained are entered to phase study value and straight line P=P _n(or the maximum operating load of P=electrical network regulation generator), according to unified ratio, be plotted in the lump P-Q plane, last comprehensive above 3 curves and the negative semiaxis of Q axle, in these 4 the determined P-Q of curve regions, encourage constrain equation and lowly encourage restriction and will ask for corresponding point and determine the low constrain equation of encouraging with quiet steady impedance circle fiting tuning according to low.

2. a kind of low fiting tuning method of encouraging restriction and field loss protection according to claim 1, is characterized in that, the equation of described quiet steady impedance circle is wherein, P is generator active power; Q is generator reactive power; U is generator unit stator phase voltage; X ₀for the center of circle of impedance circle in X-axis; R ₀for quiet steady impedance radius of a circle.

3. a kind of low fiting tuning method of encouraging restriction and field loss protection according to claim 1, is characterized in that, the equation of described asynchronous impedance circle is

wherein, P is generator active power; Q is generator reactive power; U is generator unit stator phase voltage.

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