CN100373729C - Stator grounding protection with combined third harmonic dynamic alignment criterion and voltage ratio criterion - Google Patents

Abstract

The present invention relates to a relay protection method in the technical field of an electric power system, and discloses a generator stator winding earth fault identifying method by distinguishing generator neutral point voltage third harmonic components and generator end opening triangle voltage third harmonic components. The method comprises the following steps: a generator protection device samples the voltage waveform of a voltage mutual inductor to obtain a voltage instantaneous value; a complex form of third harmonic voltage is determined by a Fourier algorithm and a digital filter algorithm; a variable quantity is worked out by memory third harmonic voltage, and a third harmonic electric potential is worked out; an improved dynamic regulation third harmonic voltage difference is automatically determined under a heavier burden operating condition; the third harmonic voltage ratio is automatically determined under a light load operating condition and before merging a network; when an auxiliary criterion is simultaneously met, the present invention carries out the protection through a certain delay time. The method can be automatically suitable for different operating conditions, accurately identify the earth fault, enhance the sensibility and simultaneously ensure safe and reliable operation of the protection.

Description

The stator ground fault protection of combined third harmonic dynamic alignment criterion and voltage ratio criterion

Technical field

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

Background technology

The large synchronous generator group is the basic equipment of electrical energy production, occupies important status in electric power system.The generator single-machine capacity continues to increase in recent years, and their costs are very expensive, and structure is more complicated, damaged in case hinder for some reason, the maintenance difficulty is big, the time is long, can have influence on system stability simultaneously, and the direct and consequential damage that national economy is caused is very huge.So just selectivity, rapidity, reliability, the sensitivity of generator protection device are had higher requirement.

The stator winding single phase ground fault is one of modal fault of generator; and the tendency of even more serious often winding internal short circuit fault generation; reliable and the sensitive action of stator winding one-phase ground protection can reduce the occurrence probability of internal short circuit fault, reduces the loss that fault causes.The increase of generator single-machine capacity generally makes the stator winding direct-to-ground capacitance increase, and corresponding single-phase-to-ground current also increases, and as not taking measures, single phase ground fault will jeopardize stator core, damages with simple stator winding and compares, and overhauls more difficult.For big-and-middle-sized unit, stator ground fault protection that must installing 100% protection zone, and require at the stator winding any point during through certain transition resistance ground connection, protection can sensitive action.When single-phase-to-ground current during less than certain safety ground electric current, stator ground fault protection can move in signal, but should in time handle, and burns generator in order to avoid another earth fault takes place again; Otherwise stator ground fault protection should move in tripping operation, to guarantee unit and iron core safety thereof.

General first-harmonic zero-pressure and the common formation of third harmonic voltage criterion 100% stator ground fault protection of adopting.Wherein first-harmonic zero-pressure stator ground fault protection can react the stator grounding fault of machine end to neutral point 95%～85%, and the triple-frequency harmonics zero voltage protection is mainly used to protect the stator grounding fault of neutral point to machine end 25% left and right sides scope.In the reality; first-harmonic zero-pressure stator ground fault protection ruuning situation is better; but the on-the-spot ruuning situation of triple-frequency harmonics stator ground fault protection is relatively poor; main cause is that triple-frequency harmonics content is smaller when normally moving; bring a series of problem for the design of sampling circuit and the design of high accuracy filtering algorithm; add on-the-spot zero sequential potential transformer and (be called for short TV; as follows) loop is unusual and the protection implementation is perfect inadequately; make the triple-frequency harmonics stator ground fault protection become a kind of protection of very easy malfunction, have a strong impact on the safe and stable operation of generator.

At the present situation of triple-frequency harmonics stator ground fault protection, the present invention proposes third harmonic voltage ratio and the dynamic differential composite stator earthing protecting method that combines of adjustment type third harmonic voltage, can improve the ruuning situation of generator greatly.

Summary of the invention

For realizing large-scale unit 100% stator ground fault protection, improve the reliability of triple-frequency harmonics stator ground fault protection, guarantee the sensitivity of this protection simultaneously.The invention provides a kind of with third harmonic voltage than and dynamically the adjustment type third harmonic voltage is differential combines, realize the method for composite stator ground protection.The method comprising the steps of: protection equipment for generator is sampled to the voltage waveform of voltage transformer and is obtained instantaneous voltage; Add the plural form that digital filtering algorithm is obtained third harmonic voltage by fourier algorithm; Third harmonic voltage by memory is calculated its variable quantity, and calculates the triple-frequency harmonics electromotive force; Under than the heavy load operating mode, enter improved dynamic adjustment third harmonic voltage differential criterion automatically; Before being incorporated into the power networks and under the light load operating mode, enter third harmonic voltage automatically and compare criterion; Change simultaneously when machine end and neutral point side triple-frequency harmonics in addition, at least one side of machine end or neutral point side has triple-frequency harmonics, and E3 changes assistant criteria such as little when satisfying simultaneously, and protection is moved through certain time-delay.This method can adapt to different operating conditions automatically, and is more accurate to the identification of earth fault, can guarantee the safe and reliable operation of protecting when improving sensitivity.

According to the present invention, provide a kind of by differentiating generator neutral point voltage third-harmonic component and machine end opening three angle voltage third-harmonic components, differentiate the method for generator unit stator winding earth fault, by dynamic adjustment third harmonic voltage differential criterion, third harmonic voltage is formed than criterion and assistant criteria, and the method comprising the steps of:

Protective device is sampled to the voltage waveform of voltage transformer and is obtained instantaneous voltage;

Add the plural form that the digital filter algorithm is obtained third harmonic voltage by fourier algorithm;

Third harmonic voltage by memory is calculated its variable quantity, and calculates triple-frequency harmonics electromotive force E3;

Automatically enter dynamic adjustment third harmonic voltage differential criterion at load current under more than or equal to the operating mode of 20% rated current;

Before being incorporated into the power networks, compare criterion less than entering third harmonic voltage under the operating mode of 20% rated current automatically with load current;

After above criterion satisfied, when machine end and neutral point side third harmonic voltage change simultaneously, protection was moved through delaying time after when assistant criteria satisfied simultaneously;

When device detects among a certain side TV triple-frequency harmonics when approaching zero for a long time, send alarm signal.

When generator load electric current during, enter dynamic adjustment type third harmonic voltage differential protection criterion automatically more than or equal to 20% rated current:

$\left.\begin{array}{c}\mathrm{\Δ}{U}_3=|{\stackrel{\·}{U}}_{3n}^{\′}-{\stackrel{\·}{K}}_P\·{\stackrel{\·}{U}}_{3t}|>K_{32}\left|{\stackrel{\·}{U}}_{3n}^{\′}\right|\\ I_{\max }\≥20\%I_{\mathrm{Ge}}\end{array}\right\}$

In the formula:

Third harmonic voltage phasor for the neutral point side residual voltage after the no-load voltage ratio compensation;

Third harmonic voltage phasor for the distolateral residual voltage of machine; I _GeBe the rated current of generator; K ₃₂Be triple-frequency harmonics restraint coefficient definite value; I _MaxBe the distolateral maximum phase current of generator machine;

Be the dynamic adjustment coefficient of real-time tracking operating condition,

Make the normal amount of moving greater-than sign the right in the up-to-date style approach zero, wherein:

$U_{3n}^{\′}=U_{3n}\·\frac{3N_{\mathrm{TVn}}}{n_{\mathrm{TVt}}}$

In the formula: U _3nThird-harmonic component for the neutral point side residual voltage of reality; n _TVnBe neutral point TV no-load voltage ratio; n _TVtFor

Machine end TV no-load voltage ratio,

Dynamic adjustment type third harmonic voltage differential protection should satisfy following assistant criteria simultaneously and could export:

A) triple-frequency harmonics electromotive force E3 changes greatly, and judged result is false;

B) machine end and neutral point triple-frequency harmonics all are false less than the judged result of definite value;

C) Kp calculates invalid judged result is false;

D) one of machine end or neutral point third harmonic voltage change, and another judged result that does not have to change is false;

When e) machine end and neutral point third harmonic voltage changed simultaneously, starting was dynamically adjusted criterion and is differentiated.In addition, dynamically adjust coefficient

Be plural number, its computational methods are as follows:

A) triple-frequency harmonics electromotive force E3 changes greatly,

It is invalid to calculate:

When b) machine end and neutral point triple-frequency harmonics are all less than definite value this It is invalid to calculate;

C) machine end and neutral point one side have third harmonic voltage and opposite side does not have third harmonic voltage to keep last computation

When d) machine end or neutral point third harmonic voltage change, keep last time

When e) dynamically adjustment type third harmonic voltage differential protection starts, the maintenance last computation

F) machine end and neutral point triple-frequency harmonics be all greater than certain value, and its variable quantity calculates this during all less than another default definite value

According to the present invention,, enter third harmonic voltage automatically than the protection criterion when generator load electric current during less than 20% rated current:

$\left.\begin{array}{c}\left|\frac{{U^{.}}_{3t}}{{U^{.}\&prime;}_{3n}}\right|>K_{31}\\ I_{\max }<20\%I_{\mathrm{Ge}}\end{array}\right\}$

In the formula: K ₃₁For third harmonic voltage than definite value, must determine by field measurement through according to industry standard DL/T684-1999 " high-rating generator transformer relay protecting adjust calculate guide rule ",

Third harmonic voltage should satisfy assistant criteria simultaneously than protection:

A) triple-frequency harmonics electromotive force E3 changes greatly, and judged result is false;

B) machine end and neutral point triple-frequency harmonics all are false less than the judged result of definite value;

C) one of machine end or neutral point third harmonic voltage change, and another judged result that does not have to change is false;

When machine end and neutral point third harmonic voltage changed simultaneously, the starting triple-frequency harmonics was differentiated than criterion.

Description of drawings

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

Fig. 2 has shown the protection logic diagram that the present invention simplifies.

Embodiment

The installation site of TV and TA 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 machine end general T V, and TV2 is middle machine point TV (or arc suppression coil or distribution transformer), and TA1 is machine end TA, and TA2 is neutral point TA.For the generator of neutral point indirect earthing, because electric machine structure, all can there be certain triple-frequency harmonics in its machine end and neutral point side when normal operation, can induce certain third harmonic voltage at the TV secondary side

With

And generator can equivalence be a triple-frequency harmonics potential source, and its electromotive force is:

${\stackrel{\&CenterDot;}{E}}_3=\stackrel{\&CenterDot;}{U_{3t}}-\stackrel{\&CenterDot;}{U_{3n}}---\left(1\right)$

With

Size all relevant with the operating condition of generator.When stator one point earth fault takes place near the generator neutral point after, the neutral point third harmonic voltage To reduce machine end third harmonic voltage

To increase, but

Can great changes have taken place.Feature in the time of can summing up the stator grounding fault: neutral point third harmonic voltage

With machine end third harmonic voltage

Variation has all taken place, the neutral point third harmonic voltage With machine end third harmonic voltage

Have at least one non-vanishing.At above stator grounding fault signature following criterion is proposed:

(1) dynamic adjustment type third harmonic voltage differential protection

The protection logic diagram that shows according to Fig. 2 drops into dynamic adjustment type third harmonic voltage differential protection when the operating mode of generator operation more than 20% rated current, the operating criterion of protection is:

$\left.\begin{array}{c}\mathrm{\&Delta;}{U}_3=|\stackrel{\&CenterDot;}{U_{3n}}-\stackrel{\&CenterDot;}{K_P}\&CenterDot;{\stackrel{\&CenterDot;}{U}}_{3t}|>K_{32}\left|{\stackrel{\&CenterDot;}{U}}_{3n}\right|\\ I_{\max }\&GreaterEqual;20\%I_{\mathrm{Ge}}\end{array}\right\}---\left(2\right)$

In the formula,

Third harmonic voltage phasor for the neutral point side residual voltage after the no-load voltage ratio compensation; Third harmonic voltage phasor for the distolateral residual voltage of machine; I _GeBe the rated current of generator;

Be plural number, when generator normally moves, obtain that make that revising later machine end equates with the neutral point third harmonic voltage, equation actuating quantity i.e. left side amount approaches zero, thereby obtains maximum relative variation when earth fault takes place according to computed in software; K ₃₂Be triple-frequency harmonics restraint coefficient definite value, value then only depends on the error of calculation, and is desirable very little, helps discerning fault; I _MaxBe the distolateral maximum phase current of generator machine.

Wherein:

$U_{3n}^{\&prime;}=U_{3n}\&CenterDot;\frac{3n_{\mathrm{TVn}}}{n_{\mathrm{TVt}}}---\left(3\right)$

In the formula: U _3nThird-harmonic component for the neutral point side residual voltage of reality; n _TVnBe neutral point TV no-load voltage ratio; n _TVtFor

Machine end TV no-load voltage ratio.

Dynamically in the adjustment type third harmonic voltage differential criterion

Design conditions be:

A) E3 changes greatly,

It is invalid to calculate;

When b) machine end and neutral point triple-frequency harmonics are all less than a certain threshold,

It is invalid to calculate;

C) machine end and neutral point one side have third harmonic voltage and opposite side does not have third harmonic voltage, keep last time

When d) machine end or neutral point third harmonic voltage change, keep last time

E) dynamically adjust the criterion starting, keep last time

F) machine end and neutral point triple-frequency harmonics be all greater than a certain threshold, and variable quantity calculates this during all less than a certain threshold

For improving the reliability of protection, adopt following assistant criteria:

A) E3 changes greatly, dynamically adjusts criterion and returns;

When b) machine end and neutral point triple-frequency harmonics are all less than a certain threshold, dynamically adjust criterion and return;

C)

It is invalid to calculate, and dynamically adjusts criterion and returns;

D) one of machine end or neutral point third harmonic voltage change, and when another does not change, dynamically adjust criterion and return;

When e) machine end and neutral point third harmonic voltage changed simultaneously, starting dynamically adjustment criterion was differentiated, and criterion is satisfied then to keep certain hour if dynamically adjust, and dynamically adjusts criterion and do not satisfy in this retention time, dynamically adjusts criterion and returns.

When dynamic adjustment type third harmonic voltage differential criterion and above-mentioned assistant criteria all satisfied, the action of triple-frequency harmonics stator ground fault protection can or be posted a letter according to definite value tripping operation that the user adjusted.

(2) third harmonic voltage is than protection

The protection logic diagram that shows according to Fig. 2 drops into third harmonic voltage than protection when the operating mode of generator operation below 20% rated load, the operating criterion of protection is:

$\left.\begin{array}{c}\left|\frac{{U^{\&CenterDot;}}_{3t}}{{U^{\&CenterDot;}}_{3n}^{\&prime;}}\right|>K_{31}\\ I_{\max }<20\%I_{\mathrm{Ge}}\end{array}\right\}---\left(4\right)$

In the formula: K ₃₁For third harmonic voltage than definite value, must be through field measurement.

For improving the reliability of protection, increase following assistant criteria:

A) E3 changes greatly, and third harmonic voltage returns than criterion;

When b) machine end and neutral point triple-frequency harmonics were all less than a certain threshold, third harmonic voltage returned than criterion;

C) one of machine end or neutral point third harmonic voltage change, and when another did not change, third harmonic voltage returned than criterion;

When d) machine end and neutral point third harmonic voltage change simultaneously, the starting third harmonic voltage is differentiated than criterion, then do not keep certain hour if third harmonic voltage does not satisfy than criterion, third harmonic voltage does not satisfy than criterion in this retention time, and third harmonic voltage returns than criterion.

When third harmonic voltage all satisfied than criterion and above-mentioned assistant criteria, the action of triple-frequency harmonics stator ground fault protection can or be posted a letter according to definite value tripping operation that the user adjusted.

Third harmonic voltage adopts filtering at zero point to add fourier algorithm and calculates, and makes the first-harmonic filtration ratio up to more than 100 times, even under the situation of system frequency excursion, still can guarantee very high first-harmonic filtration ratio.

Under the generator normal operation, all can there be certain triple-frequency harmonics at machine end and neutral point side residual voltage loop, when device detects among a certain side TV triple-frequency harmonics when approaching zero for a long time, will send alarm signal, so that the operations staff in time handles.

Claims (4)

1. one kind is passed through to differentiate generator neutral point voltage third-harmonic component and machine end opening three angle voltage third-harmonic components, differentiate the method for generator unit stator winding earth fault, by dynamic adjustment third harmonic voltage differential criterion, third harmonic voltage is formed than criterion and assistant criteria, and the method comprising the steps of:

Protective device is sampled to the voltage waveform of voltage transformer and is obtained instantaneous voltage;

Add the plural form that the digital filter algorithm is obtained third harmonic voltage by fourier algorithm;

Third harmonic voltage by memory is calculated its variable quantity, and calculates triple-frequency harmonics electromotive force E3;

Automatically enter dynamic adjustment third harmonic voltage differential criterion at load current under more than or equal to the operating mode of 20% rated current;

Before being incorporated into the power networks, compare criterion less than entering third harmonic voltage under the operating mode of 20% rated current automatically with load current;

After above criterion satisfied, when machine end and neutral point side third harmonic voltage change simultaneously, protection was moved through delaying time after when assistant criteria satisfied simultaneously;

When device detects among a certain side TV triple-frequency harmonics when approaching zero for a long time, send alarm signal.

2. method as claimed in claim 1 when generator load electric current during more than or equal to 20% rated current, enters dynamic adjustment type third harmonic voltage differential protection criterion automatically:

$\left.\begin{array}{c}{\mathrm{\&Delta;U}}_3=|{\stackrel{\&CenterDot;}{U}}_{3n}^{\&prime;}-{\stackrel{\&CenterDot;}{K}}_P{\&CenterDot;\stackrel{\&CenterDot;}{U}}_{3t}|{>K}_{32}\left|{\stackrel{\&CenterDot;}{U}}_{3n}^{\&prime;}\right|\\ I_{\max }\&GreaterEqual;20\%I_{\mathrm{Ge}}\end{array}\right\}$

In the formula:

Third harmonic voltage phasor for the neutral point side residual voltage after the no-load voltage ratio compensation; Third harmonic voltage phasor for the distolateral residual voltage of machine; I _GeBe the rated current of generator; K ₃₂Be triple-frequency harmonics restraint coefficient definite value; I _MaxBe the distolateral maximum phase current of generator machine;

Be the dynamic adjustment coefficient of real-time tracking operating condition, make the normal amount of moving greater-than sign the right in the up-to-date style approach zero,

Wherein:

$U_{3n}^{\&prime;}=U_{3n}\&CenterDot;\frac{{3n}_{\mathrm{TVn}}}{n_{\mathrm{TVt}}}$

In the formula: U _3nThird-harmonic component for the neutral point side residual voltage of reality; n _TVnBe neutral point TV no-load voltage ratio; n _TVtBe machine end TV no-load voltage ratio,

Dynamic adjustment type third harmonic voltage differential protection should satisfy following assistant criteria simultaneously and could export:

A) triple-frequency harmonics electromotive force E3 changes greatly, and judged result is false;

B) machine end and neutral point triple-frequency harmonics all are false less than the judged result of definite value;

C) Kp calculates invalid judged result is false;

D) one of machine end or neutral point third harmonic voltage change, and another judged result that does not have to change is false;

When e) machine end and neutral point third harmonic voltage changed simultaneously, starting was dynamically adjusted criterion and is differentiated.

3. method as claimed in claim 2 is dynamically adjusted coefficient Be plural number, its computational methods are as follows:

A) triple-frequency harmonics electromotive force E3 changes greatly,

It is invalid to calculate;

When b) machine end and neutral point triple-frequency harmonics are all less than definite value this

It is invalid to calculate;

C) machine end and neutral point one side have third harmonic voltage and opposite side does not have third harmonic voltage to keep last computation

When d) machine end or neutral point third harmonic voltage change, keep last time

When e) dynamically adjustment type third harmonic voltage differential protection starts, the maintenance last computation

F) machine end and neutral point triple-frequency harmonics be all greater than certain value, and its variable quantity calculates this during all less than another default definite value

4. method as claimed in claim 1 when generator load electric current during less than 20% rated current, enters third harmonic voltage automatically than the protection criterion:

$\left.\begin{array}{c}\left|\frac{{\stackrel{\&CenterDot;}{U}}_{3t}}{{\stackrel{\&CenterDot;}{U}}_{3n}^{\&prime;}}\right|>K_{31}\\ I_{\max }<20\%I_{\mathrm{Ge}}\end{array}\right\}$

In the formula: K ₃₁For third harmonic voltage than definite value, must determine by field measurement through according to industry standard DL/T 684-1999 " high-rating generator transformer relay protecting adjust calculate guide rule ",

Third harmonic voltage should satisfy assistant criteria simultaneously than protection:

A) triple-frequency harmonics electromotive force E3 changes greatly, and judged result is false;

B) machine end and neutral point triple-frequency harmonics all are false less than the judged result of definite value;

C) one of machine end or neutral point third harmonic voltage change, and another judged result that does not have to change is false;

When d) machine end and neutral point third harmonic voltage changed simultaneously, the starting triple-frequency harmonics was differentiated than criterion.

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