CN100424955C - Variable slope differential ratio protection method - Google Patents

Abstract

The present invention relates to a method of differential protection for variable-slope ratios; a ratio differential action characteristic adopts a braking curve of the variable-slope ratio and adopts a harmonic to open criterions; the starting and the braking are synchronous; the method carries out action under an action equation; the setting value range of starting ratio differential slope is from 0 to 0.10, and 0.05 is preferable; the setting value range of maximum ratio differential slope is from 0.30 to 0.70, and 0.5 is preferable. In order to prevent the malfunction of differential protection in TA saturation, the measure of 'asynchronous TA saturation criterion' is added. Since the starting and the braking of the present invention are synchronous, differential protection action characteristic is well matched with differential flow imbalance electric current; thus, the differential starting setting value can be lowered safely. The present invention enhances the sensibility when slight faults appear in generators and transformers, especially the sensibility of differential protection for interior slight faults in the processes of the starting and stopping of a machine set (45 to 55Hz), and can prevent malfunction caused by different TAs during external faults.

Description

The differential ratio protection method of variable slope

One, technical field

The present invention relates to a kind of method of relaying protection, especially the method for the biased differential protection of variable slope.

Two, background technology

Protective relaying device is the vitals that electrical network comprises large-scale plant safe operations such as generator, transformer, and the biased differential protection of generator, transformer fixed slope is a kind of method of protection generator, power transformer interior fault.

There is following problem in the biased differential protection of at present existing generator, transformer fixed slope:

1) generator, transformer differential protection generally adopt P level TA, external area error TA unsymmetrical current big (especially when non-Switching Synchronization), and the biased differential protection of fixed slope can not well cooperate with the TA change of unbalance current.

2) for preventing the malfunction under the situations such as external area error TA is inconsistent, the method that the biased differential protection of existing fixed slope is taked to improve differential initial definite value usually and improved the braking slope has reduced the sensitivity of generator slight internal fault.

Three, summary of the invention

The objective of the invention is: the principle that a kind of percentage differential of new variable slope is provided; the differential braking characteristic curve is cooperated with difference stream unsymmetrical current preferably; the differential initial definite value of reliable reduction; when troubles inside the sample space, guarantee maximum sensitivity; when external area error, can escape transient unbalanced current; improve the sensitivity of unit internal fault, take effective measures the malfunction that prevents differential protection when TA is saturated simultaneously, improve the reliability of variable slope percentage differential.

The object of the present invention is achieved like this: the operating characteristics of percentage differential adopts variable slope ratio brake curve (as Fig. 2 .1).The definite value of rationally adjusting Kbl1 and Kbl2 adopts the open criterion of harmonic wave, and is initial with regard to band brake, reliably reduces differential initial definite value, increases the sensitive volume of troubles inside the sample space, reduces the malfunction district of external area error.

For preventing the malfunction of differential protection when TA is saturated, increase the measure of " the saturated differentiation of asynchronous method TA ".

Operation equation of the present invention is as follows:

In the following equation:

Id: differential current

Ir: stalling current

Icdqd: be differential current starting definite value

Ie: the rated current of generator.

I ₁, I ₂, I ₃, I ₄: be respectively each side electric current;

$\left\{\begin{array}{cc}{I}_d>K_{\mathrm{bl}}\&times;I_r+I_{\mathrm{cdqd}}& (I_r<{\mathrm{nI}}_c)\\ K_{\mathrm{bl}}=K_{\mathrm{bl}1}+K_{\mathrm{blr}}\&times;(I_r/I_e)& \\ I_d>K_{b/2}\&times;(I_r-{\mathrm{nI}}_e)+b+I_{\mathrm{cdqd}}& (I_r\&GreaterEqual;{\mathrm{nI}}_e)\\ K_{\mathrm{blr}}=(K_{\mathrm{bl}2}-K_{\mathrm{bl}1})/(2\&times;n)& \\ b=(K_{\mathrm{bl}1}+K_{\mathrm{blr}}\&times;n)\&times;{\mathrm{nI}}_e& \end{array}\right.$

$\left\{\begin{array}{c}{I}_r=\frac{\left|{\stackrel{\&CenterDot;}{I}}_1\right|+\left|{\stackrel{\&CenterDot;}{I}}_2\right|+\left|{\stackrel{\&CenterDot;}{I}}_3\right|+\left|{\stackrel{\&CenterDot;}{I}}_4\right|}{2}\\ I_d=|{\stackrel{\&CenterDot;}{I}}_1+{\stackrel{\&CenterDot;}{I}}_2+{\stackrel{\&CenterDot;}{I}}_3+{\stackrel{\&CenterDot;}{I}}_4|\end{array}\right.$

The ratio brake coefficient definition:

Kbl: the percentage differential restraint coefficient,

Kblr: be percentage differential restraint coefficient increment

Kbl1: initial percentage differential slope, definite value scope are 0～0.10,

Kbl2: the differential slope of maximum rate, definite value scope are 0.30～0.70,

N: the stalling current multiple during the maximum rate restraint coefficient.

Characteristics of the present invention:

-because band brake at the very start, the differential protection operating characteristics cooperates with difference stream unsymmetrical current preferably, so differential initial definite value can reduce safely;

(the sensitivity of 45～55Hz) slight internal fault differential protections in-sensitivity, especially the startup and shutdown of units process protected when having improved generator, transformer slight internal fault;

-can prevent the inconsistent malfunction that causes of external area error TA.

Four, description of drawings

Fig. 1 is the operating characteristics of variable slope percentage differential of the present invention

Fig. 2 is that variable slope of the present invention and conventional percentage differential operating characteristics compare

Fig. 3 is a variable slope percentage differential logic diagram of the present invention

Five, embodiment

Operating characteristics of the present invention has been described among Fig. 1.The present invention and conventional percentage differential operating characteristics be more as shown in Figure 2: will provide ordinary curve among Fig. 2, easily mistaken ideas are overcome by the present invention.

By finding among the figure, to compare with conventional percentage differential, the braking curve of variable slope percentage differential can be good at and the curve fitting of TA unsymmetrical current, and differential initial definite value has reduced, and many two sensitive active regions have lacked an easy malfunction district on the operating space.Logic diagram of the present invention:

Kbl1: initial percentage differential slope, definite value scope are 0～0.10, generally get 0.05;

Kbl2: the differential slope of maximum rate, definite value scope are 0.30～0.70, generally get 0.5;

N: the stalling current multiple during the maximum rate restraint coefficient, get 5-10.

For preventing the malfunction of differential protection when TA is saturated, the measure that increases " the saturated differentiation of asynchronous method TA " is as follows:

At troubles inside the sample space, when troubles inside the sample space TA is saturated, make the differential protection quick acting, reliably braking under the saturated situation of external area error and external area error TA can malfunction.It is inconsistent or saturated reliably to differentiate each side TA transient state.

In troubles inside the sample space, the spill current of generator, transformer differential and the power frequency variation of stalling current almost occur simultaneously.In external area error, saturated if generator, each side TA of transformer differential do not have, at this time have only the power frequency variation of stalling current to occur at instant of failure, spill current can not change.If distinguish outer catastrophe failure and cause TA saturated, in fault moment t0 takes place constantly, the power frequency variation of stalling current is also existing together with walking out of, but this moment because TA does not also have saturatedly, then the power frequency variation of spill current can not occur; And when t1 moment TA was saturated, the power frequency variation of stalling current just occurred.

By above analysis, whether external area error or troubles inside the sample space appear differentiating synchronously according to the power frequency variation of spill current and stalling current, if occur synchronously, be judged to troubles inside the sample space, do not throw the anti-saturation algorithm, make the differential protection quick acting; If the power frequency variation of stalling current occurs earlier, external area error appears being judged to behind the spill current variable quantity of generator, drop into the saturated algorithm of anti-TA, two formulas satisfy simultaneously in the following formula, drop into the saturated criterion of TA, can get the TA saturation time by right area: about 5ms.Make generator, not malfunction of transformer differential protection.

External area error is differentiated criterion:

ΔI _r＞I _th1

dI＜I _th2

Δ I _r: the stalling current power frequency variation

DI: spill current power frequency variation

I _Th1, I _Th2: the judgement threshold that is respectively the power frequency variation of stalling current and spill current.

Saturated criterion of anti-TA or algorithm are: this is conventional method, promptly utilizes in transformer, the generator spill current harmonic content and wave character to discern the saturated of current transformer.

The present invention reaches again

-troubles inside the sample space, troubles inside the sample space TA are saturated, and the differential protection quick acting is not subjected to saturated the influence

-external area error drops into TA anti-saturation criterion, and differential protection can malfunction

-permission TA the fastest saturated time: 5ms

-criterion is simple and practical, the reliability height

Conclusion: the present invention is incorporated into no-load voltage ratio rate differential principle in generator, the transformer differential protection first; the sensitivity of protecting when utilizing the microcomputer generator transformer protection of this principle and logic realization to improve generator, power transformer interior fault; can prevent external area error, TA broken string, the malfunction that causes under the unusual service condition such as TA transient state is inconsistent.

Claims (2)

1. the differential ratio protection method of variable slope is characterized in that the operating characteristics of percentage differential adopts variable slope ratio brake curve, adopts the open criterion of harmonic wave, and initial with regard to band brake, operation equation is as follows:

$\left\{\begin{array}{cc}{I}_d>K_{\mathrm{bl}}\&times;I_r+I_{\mathrm{cdqd}}& (I_r<{\mathrm{nI}}_e)\\ K_{\mathrm{bl}}=K_{\mathrm{bl}1}+K_{\mathrm{blr}}\&times;(I_r/I_e)& \\ I_d>K_{\mathrm{bl}2}\&times;(I_r-{\mathrm{nI}}_e)+b+I_{\mathrm{cdqd}}& (I_r\&GreaterEqual;{\mathrm{nI}}_e)\\ K_{\mathrm{blr}}=(K_{\mathrm{bl}2}-K_{\mathrm{bl}1})/(2\&times;n)& \\ b=(K_{\mathrm{bl}1}+K_{\mathrm{blr}}\&times;n)\&times;{\mathrm{nI}}_e& \end{array}\right.$

$\left\{\begin{array}{c}{I}_r=\frac{\left|{\stackrel{\&CenterDot;}{I}}_1\right|+\left|{\stackrel{\&CenterDot;}{I}}_2\right|+\left|{\stackrel{\&CenterDot;}{I}}_3\right|+\left|{\stackrel{\&CenterDot;}{I}}_4\right|}{2}\\ I_d=|{\stackrel{\&CenterDot;}{I}}_1+{\stackrel{\&CenterDot;}{I}}_2+{\stackrel{\&CenterDot;}{I}}_3+{\stackrel{\&CenterDot;}{I}}_4|\end{array}\right.$

Wherein:

Id: differential current

Ir: stalling current

Icdqd: be differential current starting definite value

Ie: the rated current of generator

I ₁, I ₂, I ₃, I ₄: be respectively each side electric current;

The ratio brake coefficient definition:

Kb1: the percentage differential restraint coefficient,

Kb1r: be percentage differential restraint coefficient increment

Kb11: initial percentage differential slope, definite value scope are 0～0.10

Kb12: the differential slope of maximum rate, definite value scope are 0.30～0.70;

N: the stalling current multiple during the maximum rate restraint coefficient.

2. by the differential ratio protection method of the described variable slope of claim 1, it is characterized in that Kb11: initial percentage differential slope, definite value gets 0.050～0.10; Kb12: the differential slope of maximum rate, definite value gets 0.5.

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