CN100386935C - Generator stator single phase grounding protection method - Google Patents

Abstract

The present invention relates to stator single phase earthing protection methods for generators, and belongs to the technical field of power system main device relay protection. The present invention provides two stator single phase earthing protection methods for generators, and is based on zero sequence voltage fault components, and the two methods utilize the fault components of generator end zero sequence voltage and neutral point zero sequence voltage. The first method utilizes a third harmonic voltage fault component in the zero sequence voltage fault components, and utilizes the vector synthesis of the third harmonic voltage fault component to form a criterion. The second method directly uses the sum and the difference of the instantaneous value of the generator end zero sequence voltage fault components and the neutral point side zero sequence voltage fault components as protective action signals and brake signals, and the stator single phase earthing fault is detected by comparing the magnitude of the spectrum energy of corresponding signals in a data window. The present invention solves the insufficient problem of the sensitivity of the existing generator single phase earthing protection techniques, and has the advantages of strong robustness and simple setting.

Description

Generator unit stator one-phase ground protection method

Technical field

The invention belongs to the power system main equipment technical field of relay protection, relate in particular to a kind of generator stator single-phase earthing fault guard method based on the residual voltage fault component.

Background technology

Generator stator single-phase earthing fault has very big potential hazard, may cause even more serious short circuit in winding fault, so the stator winding one-phase ground protection is the pith in the generator protection system.The generator unit stator one-phase ground protection mainly contains two kinds of forms, and a kind of is the additional power source one-phase ground protection that adopts external signal, but it needs expensive attachment device, uses not extensive; Another kind is zero-sequence fundamental voltage and the protection of third harmonic voltage stator ground fault of adopting generator body signal, is used widely because criterion is simple.The protection of zero-sequence fundamental voltage type is simple and reliable, but has the dead band near generator neutral point, and along with the degree of asymmetry of stator winding three-phase ground capacitance increases, the ground protection dead band enlarges.Tradition is the protection easy malfunction that is in operation based on the third harmonic voltage of steady-state quantity, and along with the increase of stator winding direct-to-ground capacitance, sensitivity reduces, and is difficult to satisfy the requirement that sensitivity improves constantly.

At present the improved protection scheme of third harmonic voltage criterion is mainly contained the adaptive guard that the powerful memory function of utilizing microcomputer is followed the tracks of generator machine end and the variation of neutral point third harmonic voltage; but this scheme is different in underloading with the sensitivity of when heavy duty; setting value is adjusted by severe duty, thereby has sacrificed the sensitivity under the light duty.Another kind of improvement is to utilize the ratio of machine end and neutral point third harmonic voltage fault component and phase difference as criterion, but the constraints of adjusting of this criterion is too strong, will make its setting value bigger to the sensitivity and the reliability effect of protection in actual applications.

Summary of the invention

There is the under-sensitive problem in order to solve in the existing generator one-phase ground protection technology; the present invention according to generator generation single phase ground fault after machine end and the approximately uniform characteristics of zero sequence voltage on neutral point fault component, two kinds of generator unit stator one-phase ground protection methods based on the residual voltage fault component have been proposed.

First kind of generator unit stator one-phase ground protection method that the present invention proposes; contain the residual voltage stator ground fault protection step that adopts generator body signal; it is characterized in that: this method has utilized the fault component of machine end and zero sequence voltage on neutral point as protection institute consumption, may further comprise the steps:

(1) the machine end and the zero sequence voltage on neutral point of generator are sampled, and be to calculate corresponding machine end and zero sequence voltage on neutral point fault component instantaneous value Δ u the counting period respectively with a power frequency period according to sampled value _tAnd Δ u _n

(2) according to the instantaneous value Δ u of above-mentioned machine end and zero sequence voltage on neutral point fault component _tWith Δ u _n, utilize the Fourier filtering algorithm to distinguish the third harmonic voltage fault component of computer terminal and zero sequence voltage on neutral point

With

(3) calculate actuating signal ${\mathrm{\Δu}}_{\mathrm{op}}=|{\mathrm{\Δ}\stackrel{\·}{u}}_{3t}+\mathrm{\Δ}{\stackrel{\·}{u}}_{3n}|,$ Brake signal ${\mathrm{\Δu}}_{\mathrm{res}}=|\mathrm{\Δ}{\stackrel{\·}{u}}_{3t}-\mathrm{\Δ}{\stackrel{\·}{u}}_{3n}|;$ Calculate actuating quantity and braking amount in the power frequency period data window more respectively $\mathrm{E\Δ}{u}_{\mathrm{op}}\left(i\right)=\underset{k=i-L}{\overset{i}{\mathrm{\Σ}}}{\mathrm{\Δu}}_{\mathrm{op}}^2\left(k\right)\mathrm{\Δt},$ $\mathrm{E\Δ}{u}_{\mathrm{res}}\left(i\right)=\underset{k=i-L}{\overset{i}{\mathrm{\Σ}}}{\mathrm{\Δu}}_{\mathrm{res}}^2\left(k\right)\mathrm{\Δt},$ Wherein i is a sample sequence number, and L is the data length of data window, and k is the sampled point in the data window, and Δ t is the sampling interval, Δ t mark can be changed in the calculating;

(4) as follows based on the criterion expression-form of the synthetic amplitude description of the vector of third harmonic voltage fault component; E Δ u _Op＞β E Δ u _Res, wherein β is a coefficient of reliability, desirable 1～5.

If above-mentioned criterion satisfies M time continuously, then be judged as stator single-phase earthing fault; After judging stator generation single phase ground fault, obtain switching value output, carry out by relay and post a letter or trip.Desirable 1/2～2/3 the power frequency period sampling number of M.

The sampled point of a power frequency period described in first kind of above-mentioned generator unit stator one-phase ground protection method is no less than 12 points.

Second kind of generator unit stator one-phase ground protection method that the present invention proposes; contain the residual voltage stator ground fault protection step that adopts generator body signal; it is characterized in that: this method has utilized the fault component of machine end and zero sequence voltage on neutral point as protection institute consumption, may further comprise the steps:

(1) the machine end and the zero sequence voltage on neutral point of generator are sampled, and be to calculate corresponding machine end and zero sequence voltage on neutral point fault component instantaneous value Δ u the counting period respectively with a power frequency period according to sampled value _tWith Δ u _n

(2) calculate actuating signal u _Op=| Δ u _t+ Δ u _n|, brake signal u _Res=β | Δ u _t-Δ u _n|+u _ε, wherein β is a coefficient of reliability, desirable 1～5; u _εBe threshold voltage, 4～20% of desirable normal neutral point fundamental wave zero sequence offset voltage effective value, being provided with of threshold voltage mainly is for escaping the non-zero output of first-harmonic increment under the normal condition;

(3) calculate the interior actuating signal of data window of a power frequency period and the spectrum energy of brake signal respectively ${\mathrm{Eu}}_{\mathrm{op}}\left(i\right)=\underset{k=i-L}{\overset{i}{\mathrm{\Σ}}}{u}_{\mathrm{op}}^2\left(k\right)\mathrm{\Δt},$ ${\mathrm{Eu}}_{\mathrm{res}}\left(i\right)=\underset{k=i-L}{\overset{i}{\mathrm{\Σ}}}{u}_{\mathrm{res}}^2\left(k\right)\mathrm{\Δt},$ I is a sample sequence number, and L is the data length of data window, and k is the sampled point in the data window, and Δ t is the sampling interval, Δ t mark can be changed in the calculating;

(4) spectrum energy of getting actuating signal is for protecting actuating quantity, and the spectrum energy of brake signal is protection braking amount, obtains the criterion expression-form of being described by the signal spectra energy:

Eu _op＞Eu _res；

If above-mentioned criterion satisfies M time continuously, then be judged as stator single-phase earthing fault; After judging stator generation single phase ground fault, obtain switching value output, carry out by relay and post a letter or trip.Desirable 1/2～2/3 the power frequency period sampling number of M.

The sampled point of a power frequency period described in second kind of above-mentioned generator unit stator one-phase ground protection method is no less than 12 points.

First method is extracted corresponding third harmonic voltage fault component by machine end and zero sequence voltage on neutral point fault component, utilizes the synthetic formation of the vector criterion of third harmonic voltage fault component, makes the physical concept of criterion be more readily understood; Second method directly machine end and neutral point both sides residual voltage fault component instantaneous value and with difference as protection actuating signal and brake signal; spectrum energy size detection stator single-phase earthing fault by corresponding signal in the comparing data window; make that the expression-form of criterion is more succinct, calculate easier.The something in common of two kinds of criterions be all be utilize the fault component of machine end and zero sequence voltage on neutral point and machine end and zero sequence voltage on neutral point fault component and with actuating quantity and the braking amount of difference as protection.

Desirable stator ground fault protection should have following character: when earth fault took place, as long as the amplitude of characteristic signal or phase place have slight sudden change, criterion just should be moved; During normal operation, the amplitude of characteristic signal or phase place take place bigger gradual, and criterion should not moved yet.Protection criterion based on the third harmonic voltage fault component among the present invention has These characteristics, at first, the fault component of third harmonic voltage has reacted the sudden change degree of earth fault, the third harmonic voltage fault component that back machine end and neutral point take place earth fault is approximate identical, criterion left side actuating quantity is greater than right side braking amount, and criterion is sensitive moves; Secondly, normal opportunity end and neutral point the third harmonic voltage phase difference greater than 90 °, when changing or take place the third harmonic voltage that other reason causes machine end and neutral point, the generator operation mode changes, even have bigger gradual, criterion left side actuating quantity is always less than right side braking amount, and criterion can not moved.Further analyze, change in the opposite direction based on actuating quantity and braking amount before and after the protection criterion fault of third harmonic voltage fault component, variation that can the self adaptation generator operating condition, robustness is very strong, and it is simple to adjust.

The synthetic result of vector also can describe by the energy of signal in one-period, so just need not first-harmonic in the residual voltage and triple-frequency harmonics are separated, and obtains second kind of criterion expression-form based on spectrum energy thus.Because the winding-to-earth capacity of generator is asymmetric, neutral point has offset voltage in the time of may causing normally moving, and there is the dead band in feasible zero-sequence fundamental voltage protection based on steady-state quantity near neutral point.Owing to comprise the zero-sequence fundamental voltage fault component in second kind of criterion, even there is offset voltage to exist, when in the dead band single phase ground fault taking place, zero-sequence fundamental voltage also can produce fault component, so just can improve the sensitivity of protection.

Description of drawings

The simplification circuit diagram of residual voltage fault component when Fig. 1 is the generator unit stator single-phase earthing.

The simplification circuit diagram of third harmonic voltage when Fig. 2 normally moves for generator.

Fig. 3 is the master section wiring schematic diagram of the embodiment of the invention.

Fig. 4 is the operation principle block diagram of the embodiment of the invention.

Fig. 5 for criterion form among the present invention with the synthetic amplitude of vector describe the flow chart of determination methods.

Fig. 6 for criterion form among the present invention with the signal spectra energy describe the flow chart of determination methods.

Fig. 7 is the action situation map of first kind of vectorial type criterion in the single-phase earthing process in the embodiment of the invention.

Fig. 8 is embodiment of the invention middle-end and the variation diagram of neutral point third harmonic voltage before and after single phase ground fault.

Fig. 9 is the action situation map of second kind of energy type criterion in the single-phase earthing process in the embodiment of the invention.

Figure 10 is machine end and neutral point zero-sequence fundamental voltage and the variation diagram of third harmonic voltage before and after single phase ground fault in the embodiment of the invention.

Embodiment

Below in conjunction with accompanying drawing principle of the present invention and concrete execution mode are described once.

On principle, because the leakage reactance of generator unit stator winding and resistance are much smaller than the stator winding capacitance to earth, if ignore the influence of stator winding leakage reactance and resistance, behind generator generation stator ground fault, it can equivalence be circuit among Fig. 1 that the zero sequence of first-harmonic and triple-frequency harmonics fault component is simplified circuit, wherein Z _t, Z _nBe respectively machine end and neutral point equiva lent impedance, R _gBe the ground connection transition resistance,

Voltage for fault prior fault point.As can be seen from the figure, the fault component of machine end and zero sequence voltage on neutral point after the fault With

Approximate identical (comprising amplitude and phase place).During normal the operation, because there is zero-sequence fundamental voltage in asymmetric generator machine end and the neutral point of making of stator winding direct-to-ground capacitance, but both sizes much at one, and their variation is very little.

Just often the equivalent electric circuit of third harmonic voltage as shown in Figure 2, C wherein _tBe every camera end additional capacitor, C _gBe every phase winding direct-to-ground capacitance, R _n, L _nBe neutral resistance and inductance,

For generator triple-frequency harmonics electromotive force, for different neutral grounding modes, hold and the neutral point third harmonic voltage normal opportunity

With

Phase difference be 90 °～180 °.When the generator operation mode changes or causes that owing to other reason generator machine end and neutral point third harmonic voltage change, its ratio that shows as machine end and neutral point third harmonic voltage variable quantity is approximate constant, and the phase difference of variable quantity is similar to rule just often.

Device and existing microcomputer protective relay device that the present invention adopts are similar, are existing technology, as shown in Figure 3 and Figure 4.G represents generator among Fig. 3, and T represents main transformer, Z _nExpression generator neutral point impedance ground, TV ₁Expression generator neutral point side voltage transformer, TV ₂Expression generator terminal voltage instrument transformer.Present embodiment is measured generator machine end and zero sequence voltage on neutral point u by generator terminal voltage instrument transformer open delta winding and neutral point side voltage transformer secondary side _tAnd u _n, input among the CPU through interchange plug-in unit, A/D converter spare.With following two kinds of fault judgment methods making software respectively, CPU can carry out any in two softwares and judge earth fault, and the output switching value is to relay, is carried out by relay and posts a letter or trip.

May cause protecting the malfunction of criterion when preventing main transformer high-pressure side ground connection, must be with high-pressure side residual voltage latch-up protection criterion.

First embodiment of the present invention adopts first kind of criterion, its main flow chart as shown in Figure 5:

(1) gets the sampled value u of generator machine end and zero sequence voltage on neutral point _tAnd u _n, the instantaneous value Δ u of computer terminal and zero sequence voltage on neutral point fault component _t(t)=u _t(t)-u _t(t-t _c) and Δ u _n(t)=u _n(t)-u _n(t-t _c), t wherein _cBe the counting period, get a power frequency period;

(2) utilize fourier decomposition to calculate triple-frequency harmonics composition in the corresponding residual voltage fault component With

(3) calculate actuating signal $\mathrm{\Δ}{u}_{\mathrm{op}}=|\mathrm{\Δ}{\stackrel{\·}{u}}_{3t}+\mathrm{\Δ}{\stackrel{\·}{u}}_{3n}|,$ Brake signal $\mathrm{\Δ}{u}_{\mathrm{res}}=|\mathrm{\Δ}{\stackrel{\·}{u}}_{3t}-\mathrm{\Δ}{\stackrel{\·}{u}}_{3n}|;$ Calculate actuating quantity and braking amount in the power frequency period data window more respectively ${\mathrm{E\Δu}}_{\mathrm{op}}\left(i\right)=\underset{k=i-L}{\overset{i}{\mathrm{\Σ}}}{\mathrm{\Δu}}_{\mathrm{op}}^2\left(k\right)\mathrm{\Δt},$ ${\mathrm{E\Δu}}_{\mathrm{res}}\left(i\right)=\underset{k=i-L}{\overset{i}{\mathrm{\Σ}}}{\mathrm{\Δu}}_{\mathrm{res}}^2\left(k\right)\mathrm{\Δt},$ Wherein i is a sample sequence number, and L is the data length of data window, and k is the sampled point in the data window, and Δ t is the sampling interval;

(4) in the present embodiment, coefficient of reliability β gets 5, and sample frequency is 2kHz, and M gets 25; If criterion E Δ _Uop＞5E Δ u _ResSatisfy 25 times continuously, then be judged as stator winding generation single phase ground fault.

(5) judge single-phase earthing after, obtain switching value output, carry out by relay and post a letter or trip.

In first embodiment; generator A is in 0.07s through 3.554k Ω transition resistance generation earth fault near neutral point 14% mutually; provided the fault component of the machine end and the residual voltage of neutral point, corresponding residual voltage among Fig. 7 and, as can be seen from the figure protected criterion sensitive to move based on first kind of synthetic actuating quantity and braking amount of protecting criterion of third harmonic voltage fault component vector.Fig. 8 has provided the variation of fault front and back generator machine end and neutral point third harmonic voltage amplitude; as can be seen from the figure; before and after the fault machine end and neutral point third harmonic voltage change very little, so usually based on the criterion of third harmonic voltage steady-state value (ratio of machine end after the fault and neutral point third harmonic voltage amplitude greater than fault before ratio) akinesia.

Second embodiment of the present invention adopts second kind of criterion, its main flow chart as shown in Figure 6:

(1) gets the sampled value u of generator machine end and zero sequence voltage on neutral point _tAnd u _n, the instantaneous value Δ u of computer terminal and zero sequence voltage on neutral point fault component _t(t)=u _t(t)-u _t(t-t _c) and Δ u _n(t)=u _n(t)-u _n(t-t _c), t wherein _cBe the counting period, get a power frequency period;

(2) calculate actuating signal u _Op=| Δ u _t+ Δ u _n| with brake signal u _Res=β | Δ u _t-Δ u _n|+u _ε, threshold voltage u wherein _εGet 4% of normal neutral point fundamental wave zero sequence offset voltage effective value, coefficient of reliability β gets 1.

(3) in the present embodiment, sample frequency is 2kHz, so M gets 25; Calculate the interior corresponding spectrum energy of data window of a power frequency period ${\mathrm{Eu}}_{\mathrm{op}}\left(i\right)=\underset{k=i-L}{\overset{i}{\mathrm{\Σ}}}{u}_{\mathrm{op}}^2\left(k\right)\mathrm{\Δt}$ With ${\mathrm{Eu}}_{\mathrm{res}}\left(i\right)=\underset{k=i-L}{\overset{i}{\mathrm{\Σ}}}{u}_{\mathrm{res}}^2\left(k\right)\mathrm{\Δt},$ I is a sample sequence number, and L is the data length of data window, and k is the sampled point in the data window, and Δ t is the sampling interval.

If criterion Eu _Op＞Eu _ResSatisfy 25 times continuously, then be judged as stator winding generation single phase ground fault.

(4) judge single-phase earthing after, obtain switching value output, carry out and post a letter or trip.

In second embodiment, generator A is in 0.07s through 8.364k Ω transition resistance generation earth fault near neutral point 14% mutually, and generator neutral point just often has bigger offset voltage.Provided the fault component of the machine end and the residual voltage of neutral point, corresponding residual voltage among Fig. 9 and, as can be seen from the figure protected criterion sensitivity to move based on actuating quantity and the braking amount of second kind of form of energy protection criterion of residual voltage fault component.Figure 10 has provided the variation of fault front and back neutral point zero-sequence fundamental voltage amplitudes, machine end and neutral point third harmonic voltage amplitude, as we know from the figure, neutral point zero-sequence fundamental voltage amplitude is about 35.6V before the fault, be about 35.2V after the fault, so usually based on the criterion of residual voltage steady-state value (the zero-sequence fundamental voltage steady-state value after the fault greater than fault before value) akinesia; Because the fault transition resistance is very big; before and after the fault machine end and neutral point third harmonic voltage change very little, so can not move based on the criterion of third harmonic voltage steady-state value (ratio of machine end after the fault and neutral point third harmonic voltage amplitude greater than fault before ratio) usually.The stator ground fault protection criterion that contrasts among the present invention as can be known has higher sensitivity.

Claims (4)

1. generator unit stator one-phase ground protection method; contain the residual voltage stator ground fault protection step that adopts generator body signal; it is characterized in that: this method has utilized the fault component of machine end and zero sequence voltage on neutral point as protection institute consumption, may further comprise the steps:

(1) the machine end and the zero sequence voltage on neutral point of generator are sampled, and be to calculate corresponding machine end and zero sequence voltage on neutral point fault component instantaneous value Δ u the counting period respectively with a power frequency period according to sampled value _tWith Δ u _n

(2) according to the instantaneous value Δ u of above-mentioned machine end and zero sequence voltage on neutral point fault component _tWith Δ u _n, utilize the Fourier filtering algorithm to distinguish the third harmonic voltage fault component of computer terminal and zero sequence voltage on neutral point

With

(3) calculate actuating signal $\mathrm{\Δ}{u}_{\mathrm{op}}=|\mathrm{\Δ}{\stackrel{.}{u}}_{3t}+\mathrm{\Δ}{\stackrel{.}{u}}_{3n}|,$ Brake signal $\mathrm{\Δ}{u}_{\mathrm{res}}=|\mathrm{\Δ}{\stackrel{.}{u}}_{3t}-\mathrm{\Δ}{\stackrel{.}{u}}_{3n}|;$ Calculate actuating quantity and braking amount in the power frequency period data window more respectively $\mathrm{E\Δ}{u}_{\mathrm{op}}\left(i\right)=\underset{k=i-L}{\overset{i}{\mathrm{\Σ}}}\mathrm{\Δ}{u}_{\mathrm{op}}^2\left(k\right)\mathrm{\Δt},$ $\mathrm{E\Δ}{u}_{\mathrm{res}}\left(i\right)=\underset{k=i-L}{\overset{i}{\mathrm{\Σ}}}\mathrm{\Δ}{u}_{\mathrm{res}}^2\left(k\right)\mathrm{\Δt},$ Wherein i is a sample sequence number, and L is the data length of data window, and k is the sampled point in the data window, and Δ t is the sampling interval, Δ t mark can be changed in the calculating;

(4) as follows based on the criterion expression-form of the synthetic amplitude description of the vector of third harmonic voltage fault component: E Δ u _Op＞β E Δ u _Rea, wherein β is a coefficient of reliability;

If above-mentioned criterion satisfies M time continuously, then be judged as stator single-phase earthing fault; After judging stator generation single phase ground fault, obtain switching value output, carry out by relay and post a letter or trip.

2. generator unit stator one-phase ground protection method according to claim 1 is characterized in that: the sampled point of a described power frequency period is no less than 12 points.

3. generator unit stator one-phase ground protection method; contain the residual voltage stator ground fault protection step that adopts generator body signal; it is characterized in that: this method has utilized the fault component of machine end and zero sequence voltage on neutral point as protection institute consumption, may further comprise the steps:

(1) the machine end and the zero sequence voltage on neutral point of generator are sampled, and be to calculate corresponding machine end and zero sequence voltage on neutral point fault component instantaneous value Δ u the counting period respectively with a power frequency period according to sampled value _tWith Δ u _n

(2) calculate actuating signal u _Op=| Δ u _t+ Δ u _n|, brake signal u _Res=β | Δ u _t-Δ u _n|+u _ε, wherein β is a coefficient of reliability, u _sBe threshold voltage, get 4～20% of normal neutral point fundamental wave zero sequence offset voltage effective value;

(3) calculate the interior actuating signal of data window of a power frequency period and the spectrum energy of brake signal respectively $E{u}_{\mathrm{op}}\left(i\right)=\underset{k=i-L}{\overset{i}{\mathrm{\Σ}}}{u}_{\mathrm{op}}^2\left(k\right)\mathrm{\Δt},$ $E{u}_{\mathrm{res}}\left(i\right)=\underset{k=i-L}{\overset{i}{\mathrm{\Σ}}}{u}_{\mathrm{res}}^2\left(k\right)\mathrm{\Δt},$ I is a sample sequence number, and L is the data length of data window, and k is the sampled point in the data window, and Δ t is the sampling interval, Δ t mark can be changed in the calculating;

(4) spectrum energy of getting actuating signal is for protecting actuating quantity, and the spectrum energy of brake signal is protection braking amount, obtains the criterion expression-form of being described by the signal spectra energy:

Eu _op＞Eu _res；

If above-mentioned criterion satisfies M time continuously, then be judged as stator single-phase earthing fault; After judging stator generation single phase ground fault, obtain switching value output, carry out by relay and post a letter or trip.

4. generator unit stator one-phase ground protection method according to claim 3 is characterized in that: the sampled point of a described power frequency period is no less than 12 points.

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