CN100420114C - Anti-TA transient imbalance differential protection for generator - Google Patents

Abstract

The present invention relates to a method for relay protection in the field of a power system, particularly to a method for differential protection of a generator differential protection method for preventing the unbalanced transient states of current transformators on both sides of a generator. The method is composed of a brake characteristic of a phasor ratio and a multiple-constant value brake open criterion of a sampling value ratio, and ensures correct protection action behaviors in a transient state of the system by a variable data window algorithm and a circulation locking principle. The method also has a parallel network detection criterion of the generator, an external fault detection criterion, an intermittent wire break criterion of a secondary loop of the current transformators on both of the two sides of the generator, and a TA saturation criterion.

Description

The anti-TA transient imbalance differential protection for generator method

Technical field

The present invention relates to field of power, relate more specifically to the method for relaying protection.

Background technology

Differential protection is the quick main protection of internal fault of electric generator, has natural selectivity in principle, and highly sensitive, quick action, uses very extensive.On-the-spot ruuning situation shows, differential protection for generator has malfunction still the time.Particularly, when external area error excision or the non-simultaneous interconnecting of generator, differential protection for generator generation malfunction.The operate time of generation current machine differential protection is substantially all about 20ms; and the time constant of big unit is bigger; when big disturbance is arranged; both sides P level current transformer (being called for short TA down together) is under long transient current effect; be difficult to keep the unanimity of progress of disease characteristic, can occur bigger transient state material unaccounted for stream unavoidably.This material unaccounted for stream constitutes serious threat to the reliability service of differential protection for generator, if differential protection for generator is not taked the unbalanced measure of anti-TA transient, and then may malfunction.

Operation shows that the mould entry loop is one of the weakest link of differential protection.Because components and parts damage, A/D makes mistakes in the loop, the instantaneous reason such as fall of power supply voltage under disturbing, and the sampling circuit of differential protection may go wrong, even 1 bad data also might make QA differential protection malfunction.Fail safe, the reliability of differential protection for generator are in urgent need to be improved.

Improve the differential protection reliability, remove and select the higher TA of conversion precision for use, coupling TA secondary load, protective device is selected reliable hardware for use and with outside the methods such as double A/D " two get two " outlet, can also be taken measures on protection scheme.

Sampling value difference is the differential protection that directly utilizes current sampling data to constitute, and general adopt relatively has S point to satisfy condition in the R point then to protect the criterion of moving.Characteristics such as it is compared with the phasor differential protection of routine, and it is few to have amount of calculation, and speed is fast often are used in the responsiveness requirement than higher occasion, in bus protection.Yet there is a shortcoming in this method; because the randomness of sampling initial time; make sampling value differential protection have certain confusion region, thereby the measurement of sampling value difference operating characteristics threshold and slope has been brought inconvenience with the work of adjusting for the relaying protection staff.Because generator self is a power-supply system, when the internal fault excision takes place, still have quite long transient process, so differential protection for generator there is no need the ultrafast responsiveness that covets, the reliability of what is more important assurance protection.The present invention is directed to the problem that generation current machine differential protection exists, the comprehensively sampling value difference moves and the differential advantage of phasor, has proposed the method for the open differential protection for generator of a kind of many definite values sampled value ratio brake.

Summary of the invention

For improving fail safe, the reliability of differential protection for generator, the invention discloses a kind of method of anti-TA transient imbalance differential protection for generator.This method as main criterion, relies on the open criterion of many definite values sampled value ratio brake to reach the purpose of bad data in the saturated and anti-protective device A/D sampling of inconsistent, the anti-TA transient state of anti-generator both sides TA transient characterisitics by the phasor ratio-restrained characteristic.This method also has generator connecting in parallel with system detection criteria, external area error detection criteria, generator both sides TA secondary circuit intermittence broken string criterion and the saturated criterion of TA.

The present invention includes step:

The differential protection for generator device is sampled to the voltage waveform of the voltage transformer of the current waveform of the current transformer of generator machine end and neutral point and generator end and is obtained electric current and instantaneous voltage;

Obtain the plural form of each electric current and voltage by becoming data window recurrence fourier algorithm;

Calculate differential current and stalling current according to following formula:

In the formula: I _Dz, I _ZdBe respectively differential current and stalling current; I _T ^﹠amp;, I _N ^﹠amp;Be respectively the electric current phasor of generator machine end and neutral point side;

According to the described phasor ratio-restrained characteristic of following formula criterial equation, add generator connecting in parallel with system detection criteria, external area error detection criteria, generator both sides TA secondary circuit intermittence broken string criterion and the saturated criterion of TA and enter phasor ratio-restrained characteristic criterial equation and differentiate:

$\left.\begin{array}{c}{I}_{\mathrm{dz}}>I_{\mathrm{CD}}\\ I_{\mathrm{dz}}>K_{\mathrm{res}}{I}_{\mathrm{zd}}\end{array}\right\}$

In the formula: I _CDBe differential current initial value, K _ResBe restraint coefficient;

After the action of above phasor ratio-restrained characteristic, enter sampled value percentage differential braking characteristic and differentiate, according to following formula calculating sampling value difference streaming current and sampled value stalling current:

$\left.\begin{array}{c}{i}_{\mathrm{dz}}=|i_T-i_N|\\ i_{\mathrm{zd}}=|i_T+i_N|/2\end{array}\right\}$

In the formula: i _Dz, i _ZdBe respectively sampling value difference electric current and stalling current; i _T, i _NBe respectively the current sampling data of generator machine end and neutral point;

Enter the open criterion of many definite values sampled value ratio brake according to following formula, when phasor ratio-restrained characteristic criterion, the open criterion of many definite values sampled value ratio brake is positioned at differential protection for generator instantaneous operation behind the active region simultaneously:

$\left.\begin{array}{c}{i}_{\mathrm{dz}}>k_{\mathrm{CD}}{I}_{\mathrm{CD}}\\ i_{\mathrm{dz}}>K_{\mathrm{res}}{i}_{\mathrm{zd}}\end{array}\right\}$

In the formula: $k_{\mathrm{CD}}\∈(0,\sqrt{2})$ Be constant, be called differential constant coefficient.

The present invention has improved the ability of malfunction when both sides TA transient state was uneven when differential protection for generator prevented the non-simultaneous interconnecting of generator, external area error and external area error excision greatly; and prevent that A/D sampling bad data from making the ability of protection malfunction, improved the reliability of protection under the prerequisite that does not reduce differential protection for generator sensitivity and responsiveness.

Description of drawings

Fig. 1 has shown the installation site of current transformer and voltage transformer and the definition of polarity;

Fig. 2 has shown the differential protection for generator operating characteristics;

Fig. 3 has shown differential protection for generator logic diagram of the present invention.

Specific embodiments

The present invention realizes anti-TA transient imbalance differential protection for generator according to following formula.The installation site of current transformer and voltage transformer and the definition of polarity please refer to Fig. 1, and GS is a generator among the figure, and MT is a main transformer, and TV1 is a machine end common voltage instrument transformer, and TA1 is machine end TA, and TA2 is neutral point TA.

The computational methods of differential current and stalling current are seen formula (1):

In the formula: I _Dz, I _ZdBe respectively differential current and stalling current; I _T ^﹠amp;, I _N ^﹠amp;Be respectively the electric current phasor of generator machine end and neutral point, all with pointing system for just.

Guarantee that not malfunction of external area error, the calculating of differential current and stalling current adopt parameter according to window algorithm when improving serious internal fault responsiveness.Adopt half cycle data window fourier algorithm to calculate differential current and stalling current earlier, at this moment, the definite value of minimum working current improves 18% automatically.The operate time that protection is the fastest after adopting parameter according to window algorithm is within 12ms.If the akinesia as a result that the half cycle algorithm obtains, protection automatically switches into full-wave fourier algorithm, can improve the reliability of protection.

The operation equation of ratio brake differential protection is seen formula (2), and the ratio brake operating characteristics of realization please refer to Fig. 2:

$\left.\begin{array}{c}{I}_{\mathrm{dz}}>I_{\mathrm{CD}}\\ I_{\mathrm{dz}}>K_{\mathrm{res}}{I}_{\mathrm{zd}}\end{array}\right\}---\left(2\right)$

In the formula: I _CDBe differential current initial value, K _ResBe restraint coefficient.

After above phasor ratio-restrained characteristic action, enter sampled value ratio brake criterion, wherein the calculating of sampling value difference electric current and stalling current is as the formula (3):

$\left.\begin{array}{c}{i}_{\mathrm{dz}}=|i_T-i_N|\\ i_{\mathrm{zd}}=|i_T+i_N|/2\end{array}\right\}---\left(3\right)$

In the formula: i _Dz, i _ZdBe respectively sampling value difference electric current and stalling current; i _T, i _NBe respectively the current sampling data of generator machine end and neutral point.

Sampled value ratio brake criterion is as the formula (4):

$\left.\begin{array}{c}{i}_{\mathrm{dz}}>k_{\mathrm{CD}}{I}_{\mathrm{CD}}\\ i_{\mathrm{dz}}>K_{\mathrm{res}}{i}_{\mathrm{zd}}\end{array}\right\}---\left(4\right)$

In the formula: $k_{\mathrm{CD}}\∈(0,\sqrt{2})$ Be constant, be called differential constant coefficient.

If have the S point to satisfy formula (4) in the R point, then sampled value ratio brake criterion action.For differential protection for generator, R is chosen as the sampling number of a cycle, and promptly the protective device R for all 24 point samplings equals 24.According to pre-determined k _CDBe worth, can determine the value of S by the method for offset of sinusoidal function sampling.Because the randomness of sampling initial time makes the protection of sampled value ratio brake have certain confusion region.And this method is with the open criterion of sampled value ratio brake as raising protection reliability; suitably reduce the value of S; in the time of can making the phasor ratio-restrained characteristic be positioned at critical operating point; the sampled value ratio brake reliably drops on active region, thereby has avoided the intrinsic shortcoming that has the confusion region of sampled value ratio brake.

For further improving the reliability of differential protection for generator, can adopt many definite values sampled value ratio-restrained characteristic.Promptly determine m k earlier _CDValue: k _CD1, k _CD2, Λ Λ k _CDm, then corresponding m S value S ₁, S ₁, Λ Λ S _mIf for each k _CDValue satisfies counting all greater than corresponding S value of formula (4) in R point sampling Value Data, then many definite values sampled value ratio-restrained characteristic is satisfied.

For example: get m=2, k _CD1=0.8, k _CD2=1.2

$\left.\begin{array}{c}{i}_{\mathrm{dz}}>0.8I_{\mathrm{CD}}\\ i_{\mathrm{dz}}>K_{\mathrm{res}}{i}_{\mathrm{zd}}\end{array}\right\}---\left(5\right)$

$\left.\begin{array}{c}{i}_{\mathrm{dz}}>1.2I_{\mathrm{CD}}\\ i_{\mathrm{dz}}>K_{\mathrm{res}}{i}_{\mathrm{zd}}\end{array}\right\}---\left(6\right)$

If satisfy counting of formula (5) in R sampled point greater than S1, and satisfy formula (6) count that (S2＜S1), then many definite values sampled value ratio-restrained characteristic is satisfied greater than S2.Its Chinese style (5) is low definite value criterion, and formula (6) is the high-set setting criterion.Adopt the reason of many definite values sampled value ratio-restrained characteristic to be, when there is bad data in sampling, the positive maximum that this point sampling value may can be represented for A/D or negative maximum, its absolute value is very big but bad data is counted possible fewer, this moment is because normal data is a load current, its difference is very little, so just can rely on action to count many and the lower sampled value ratio-restrained characteristic of action definite value guarantees to protect not malfunction; And when external area error excision, when generator both sides TA transient characterisitics were inconsistent, the difference stream that is produced was may the time long but amplitude is less, can rely on the action definite value high and sampled value ratio-restrained characteristic that action is counted few guarantees to protect not malfunction.In addition, owing to when TA is saturated, a TA linear transform area is arranged after current zero-crossing point, make some points of sampled value ratio brake be positioned at the braking district, so the sampled value ratio-restrained characteristic also have certain anti-TA saturability.

This differential protection has the generator connecting in parallel with system detection criteria.Be not judged to generator and be not incorporated into the power networks when generator machine end and neutral point TA have stream for a long time, illustrate that generator is incorporated into the power networks at this moment if a certain size electric current appears suddenly in machine end and neutral point TA simultaneously.Declare generator connecting in parallel with system after, can suitably increase the slope of ratio brake, protection malfunction when preventing non-Switching Synchronization.

This differential protection has the external area error detection criteria, and a period of time after the jump-value of current startup, if protection is in non-active region, then explanation is that external area error starts, and can increase the differentiation number of times this moment and cause the protection malfunction to prevent external area error.

Below in conjunction with Fig. 3, the action logic of protection once is described.Because differential protection for generator is only protected phase-to phase fault, the circulation locking principle is adopted in protection, can improve reliability.The circulation locking principle has only that protection just can export when two-phase and above differential action shown in first's logic diagram among Fig. 3.

Shown in second portion logic diagram among Fig. 3, for protect a bit in the district, 2 earth faults outside a bit distinguishing, also be provided with machine end negative sequence voltage element.When differential protection only has one to satisfy operation condition mutually, judge unusually the number of times that except that increasing calculation times and TA when holding opportunity negative sequence voltage big, trip signal is just sent out in protection.

Shown in third part logic diagram among Fig. 3, this method has generator both sides secondary loop of mutual inductor intermittences broken string criterion, and protection can malfunction during owing to the loose contact of wiring reason when the TA secondary.But maximum phase current will be opened differential protection during greater than 1.2 times of rated current.This method also has the saturated criterion of TA in addition, and protection can malfunction when catastrophe failure makes generator one side TA saturated outside the district.

Shown in the 4th partial logic block diagram among Fig. 3, when differential protection is not moved, but one when reaching above difference stream mutually and surpassing the out-of-limit definite value of difference stream, and the out-of-limit signal of difference stream is sent in protection, and the prompting operations staff checks the secondary circuit wiring.

Because Microcomputer Protection can be realized resource-sharing, the protection that increases a kind of principle can't increase hardware complexity and reduce reliability.Can draw the high-rating generator of two groups of TA for neutral point; this method has been considered by the mode to high-performance CPU time-sharing multiplex; in same protective device, finish a cover generator longitudinal difference protection; one cover splits the phase transverse differential protection; two cover incomplete differential protections, thus realize the comprehensive differential protection of generator.Wherein split phase transverse differential protection and incomplete differential protection, can protect the stator winding turn-to-turn fault, except that needn't adopting the circulation closedown mode, other implementation method is identical with the generator longitudinal difference protection.

The present invention has improved the ability of malfunction when both sides TA transient state was uneven when differential protection for generator prevented the non-simultaneous interconnecting of generator, external area error and external area error excision greatly; and prevent that A/D sampling bad data from making the ability of protection malfunction, improved the reliability of protection under the prerequisite that does not reduce differential protection for generator sensitivity and responsiveness.

Claims (4)

1. the method for an anti-TA transient imbalance differential protection for generator, the method comprising the steps of:

The differential protection for generator device is sampled to the voltage waveform of the voltage transformer of the current waveform of the current transformer of generator machine end and neutral point and generator end and is obtained electric current and instantaneous voltage;

Obtain the plural form of each electric current and voltage by becoming data window recurrence fourier algorithm;

Calculate differential current and stalling current according to following formula:

$\left.\begin{array}{c}{I}_{\mathrm{dz}}=|I_T-I_N|\\ I_{\mathrm{zd}}=|I_T+I_N|/2\end{array}\right\}$

In the formula: I _Dz, I _ZdBe respectively differential current and stalling current; I _T, I _NBe respectively the electric current phasor of generator machine end and neutral point side;

According to the described phasor ratio-restrained characteristic of following formula criterial equation, add generator connecting in parallel with system detection criteria, external area error detection criteria, generator both sides TA secondary circuit intermittence broken string criterion and the saturated criterion of TA and enter phasor ratio-restrained characteristic criterial equation and differentiate:

$\left.\begin{array}{c}{I}_{\mathrm{dz}}>I_{\mathrm{CD}}\\ I_{\mathrm{dz}}>K_{\mathrm{res}}{I}_{\mathrm{zd}}\end{array}\right\}$

In the formula: I _CDBe differential current initial value, K _ResBe restraint coefficient;

After the action of above phasor ratio-restrained characteristic, enter sampled value percentage differential braking characteristic and differentiate, according to following formula calculating sampling value difference streaming current and sampled value stalling current:

$\left.\begin{array}{c}{i}_{\mathrm{dz}}=|i_T-i_N|\\ i_{\mathrm{zd}}=|i_T+i_N|/2\end{array}\right\}$

In the formula: i _Dz, i _ZdBe respectively sampling value difference electric current and stalling current; i _T, i _NBe respectively the current sampling data of generator machine end and neutral point;

Enter the open criterion of many definite values sampled value ratio brake according to following formula, when phasor ratio-restrained characteristic criterion, the open criterion of many definite values sampled value ratio brake is positioned at differential protection for generator instantaneous operation behind the active region simultaneously:

$\left.\begin{array}{c}{i}_{\mathrm{dz}}>k_{\mathrm{CD}}{I}_{\mathrm{CD}}\\ i_{\mathrm{dz}}>K_{\mathrm{res}}{i}_{\mathrm{zd}}\end{array}\right\}$

In the formula: $k_{\mathrm{CD}}\∈(0,\sqrt{2})$ Be constant, be called differential constant coefficient.

2. method as claimed in claim 1 is wherein according to a pre-determined m k _CDValue: k _CD1, k _CD2, Λ Λ k _CDm, can determine m corresponding S value S by the method for offset of sinusoidal function sampling ₁, S ₁, Λ Λ S _mIf, for each k _CDValue satisfies counting all greater than corresponding S value of above-mentioned many definite values sampled value ratio brake equation in R point sampling Value Data, then many definite values sampled value ratio-restrained characteristic is satisfied.

3. method as claimed in claim 1, the generator connecting in parallel with system detection criteria is: be not incorporated into the power networks when generator machine end and the long-time no current of neutral point TA are judged to generator, illustrate that generator is incorporated into the power networks at this moment if a certain size electric current appears suddenly in machine end and neutral point TA simultaneously.

4. method as claimed in claim 1, the external area error detection criteria is: a period of time after jump-value of current starts, if protection is in non-active region, then explanation is that external area error starts.

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