CN104852355A - Injection-type stator earth-fault protection method without being affected by generator winding - Google Patents

Abstract

Provided is an injection-type stator earth-fault protection method without being affected by a generator winding. The method comprises: acquiring voltage Uz of the secondary side of a grounding transformer from a voltage divider on the secondary side winding of the grounding transformer, acquiring current Iz of the secondary side of a grounding transformer from a current transformer connected in series with the secondary side winding of the grounding transformer, with Iz being ahead of the Uz for 45 DEG as a boundary, when the impedance angle of the Uz and the Iz is -45 DEG to -225 DEG, determining protection as normal operation; when the impedance angle of the Uz and the Iz is -45 DEG to -135 DEG, and determining protection as earth fault, at the time, according to voltage Uz and current Iz of a measured injection signal, calculating earth fault resistance R ' g, and resistance value converted to a primary side being Rg, and according to relations of the earth resistance and a setting value, giving out an earth fault alarm or taking action on trip.

Description

A kind of not by the injected type stator ground protection method that generator windings affects

Technical field

The invention belongs to power system main equipment technical field of relay protection, refer more particularly to a kind of injection type power generator earthing protection method for stator.

Background technology

Easily there is the destruction of insulating between winding bar and stator core in generator, the ratio that therefore single phase ground fault occurs is very high, accounts for 70% ~ 80% of stator failure.The phase fault that generator stator ground fault is even more serious often or the tendency that shorted-turn fault occurs, the reliable and sensitive action of stator ground fault protection significantly can reduce the occurrence probability of these catastrophe failures.Allow in current range if earth fault current is limited in safety, electricity generator stator core can from damage, and the direct and indirect economic loss caused by fault also will greatly reduce.For 100MW and above generating set, not only require the stator ground fault protection of installing 100% protection zone, also require stator winding any point through fault resstance ground connection time, protection can sensitive action, to prevent the further expansion of earth fault.Therefore, stator ground fault protection is the important component part in generator relaying protection system.

At present, the principle forming generator stator ground protection mainly contains first-harmonic zero voltage protection, third harmonic voltage protection, zero stream protection and injected type stator ground protection.Dead band is had because first-harmonic zero voltage protection zero flows protection; the poor reliability of third harmonic voltage protection; by contrast; injected type stator ground protection signal used is additional; there is reliability high, highly sensitive and irrelevant with position of failure point; and the advantages such as insulating monitoring effect can be played, newly-built and generally will adopt in the Large-scale machine set built, wherein with additional 12.5Hz type and 20Hz type stator ground fault protection most widely used.

Injected type stator ground protection is as Protection criteria with the earth resistance recorded.The grounding resistance of existing injected type stator ground protection calculates according to node-pair method, and have ignored inductance and the Resistance Influence of generator unit stator winding, can increase measure error, protection may occur incorrect operation.

Summary of the invention

The object of the invention is to eliminate generator unit stator winding to the impact of grounding resistance measurement, improve the reliability of protection act, ensure generator stable operation, propose a kind of not by the injected type stator ground protection method that generator unit stator winding affects.

The present invention is concrete by the following technical solutions:

Not by the injected type stator ground protection method that generator unit stator winding affects, it is characterized in that, said method comprising the steps of:

Step 1: using the output signal of low frequency signal source after low pass filter as Injection Signal, be injected into the neutral point of generator by the secondary side of the grounding transformer of generator neutral point;

Step 2: from the grounding transformer secondary side winding of generator neutral point and the voltage signal of this grounding transformer secondary side of Real-time Collection and the component of voltage of Injection Signal the voltage divider connect the current signal of this grounding transformer secondary side of Real-time Collection and the current component of Injection Signal from the current transformer be serially connected in grounding transformer secondary side winding

Step 3: according to following formula, the Injection Signal voltage that calculation element records and the impedance angle θ of Injection Signal electric current:

$\mathrm{\θ}=\arg ({\stackrel{\·}{U}}_Z/{\stackrel{\·}{I}}_Z)$

Step 4: according to step: the 3 impedance angle θ calculating gained judge whether generator unit stator earth fault occurs;

When-225 °≤θ≤-45 °, judge generator unit stator fault-free;

When-45 °≤θ≤135 °, judge generator unit stator generation earth fault;

Step 5: if judge that generator unit stator there occurs earth fault by step 4, the component of voltage of the Injection Signal now recorded according to step 2 current component and the impedance angle θ that step 3 obtains calculates the ground fault resistance R' of conversion to grounding transformer secondary side _g:

$R_g^{\′}=\frac{U_Z\cos \mathrm{\θ}}{I_Z};$

Step 6: calculate the stator over the ground fault resstance R of conversion to grounding transformer primary side as follows _g;

R _g＝k ²R' _g

Wherein, k represents resistance conversion factor, and namely protective device calculates the ratio that the sub-value of earth resistance of gained and protective device calculate two sub-values of gained;

Step 7: by the earth resistance R of protection calculation gained _gcompare with the setting value of protective earthing fault resstance,

Work as R _gbe greater than the high setting value R of protective earthing fault resstance _set.Htime, generator unit stator fault-free;

Work as R _gbe less than the high setting value R of protective earthing fault resstance _set.H, but be greater than the low setting value R of protective earthing fault resstance _set.Ltime, generator continues to run, but alarm signal sent out by protective device;

Work as R _gbe less than the low setting value R of protective earthing fault resstance _set.Ltime, protective device action is in tripping operation, and generator is out of service.

The invention has the beneficial effects as follows: solve the impact because of generator unit stator winding inductance and resistance, the grounding resistance error being calculated gained by node-pair method causes comparatively greatly the problem protecting incorrect operation; When utilizing criterion of the present invention, first to sentence stator winding before protection act and whether earth fault occur, calculate earth resistance R _gnot by the impact of generator unit stator winding, improve the reliability of protection correct operation.

Accompanying drawing explanation

Fig. 1 is additional low frequency signal stator ground fault protection master section winding diagram;

Fig. 2 is when disregarding ground connection variable element, the equivalent circuit diagram of additional low frequency signal stator ground fault protection;

Fig. 3 is the Γ shape equivalent circuit diagram of the additional low frequency signal stator ground fault protection considering grounding transformer parameter;

Fig. 4 is the schematic flow sheet of the injected type stator ground protection method do not affected by generator unit stator winding disclosed by the invention.

Embodiment

Below in conjunction with accompanying drawing, principle of the present invention and specific implementation method are described.

Fig. 1 is system wiring figure of the present invention.In figure, G represents generator, and TV represents main transformer, and Tn represents the grounding transformer of generator neutral point, and Rn represents the secondary side earth resistance of generator neutral point when grounding transformer high resistance grounding, and VD is the voltage divider of secondary side, and CT is current transformer.Injection of the present invention sends low frequency signal by low frequency generator, produces through corresponding low pass filter, is injected into the neutral point of generator from the secondary winding side of the grounding transformer of generator neutral point.

When Fig. 2 is the parameter influence not considering grounding transformer, principle schematic during generator unit stator winding generation single phase ground fault, X' in figure _grepresent the reactance between the fault point of stator winding to neutral point.The Injection Signal voltage u being injected into grounding transformer secondary winding side is gathered from the voltage divider VD of Fig. 1; the Injection Signal current i of grounding transformer secondary winding side is injected into from the Current Transmit collection of Fig. 1; u and i, after the filtering of pouring-in protective device inside, obtains the voltage of Injection Signal frequency according to the voltage ratio of voltage divider VD the electric current of Injection Signal is obtained according to the current ratio of current transformer according to company fault loop R' can be calculated _g+ jX' _gimpedance angle θ.Judge whether stator winding there occurs earth fault according to θ:

1) if-225 °≤θ≤-45 °, judge that generator normally runs, protection is failure to actuate.

2) if-45 °≤θ≤135 °, judge that generator unit stator there occurs earth fault;

If generation earth fault, according to the component of voltage of the Injection Signal frequency recorded and current component calculate conversion to connecing

Ground becomes the earth resistance R' of secondary side _g, its formula is as follows:

$R_g^{\′}=\frac{U_Z\cos \mathrm{\θ}}{I_Z}$

Ground fault resistance two sub-value calculating gained is converted the primary side of grounding transformer, formula is as follows:

R _g＝kR' _g

Wherein, k represents the conversion factor of earth resistance.

With the ground fault resistance one sub-value R calculating gained _gcompare with the setting value of protective earthing fault resstance, work as R _gwhen being greater than the high setting value of ground fault resistance, represent the no ground fault of generator unit stator; Work as R _gbe less than the high setting value of ground fault resistance, and when being greater than the low setting value of ground fault resistance, alarm signal is sent out in protection; Work as R _gwhen being less than the low setting value of ground fault resistance, protection act is in tripping operation.

Fig. 3 is when taking into account grounding transformer parameter influence, equivalent schematic during generator unit stator winding generation single phase ground fault.When taking into account the affecting of grounding transformer parameter, to compensate protection, to reduce the measure error of ground fault resistance.

Note: Fig. 2 and Fig. 3 is the zero sequence equivalent electric circuit only having Injection Signal frequency, does not consider the impact that 50Hz measures in figure.

In fact, the exciting impedance of grounding transformer is not infinitely great, and leakage impedance also can produce pressure drop.When considering grounding transformer parameter influence, primary side ground fault resistance R can be calculated based on the Γ shape equivalent electric circuit of transformer _g.Fig. 3 is the Γ shape equivalent electric circuit taking into account grounding transformer leakage impedance and exciting impedance parameter, wherein, and R _σrepresent two sub-values of grounding transformer equivalence ohmic leakage, X _σrepresent two sub-values of grounding transformer equivalence leakage reactance, R' _mrepresent two sub-values of the excitatory resistance of grounding transformer, X' _mrepresent two sub-values of the excitatory reactance of grounding transformer.The parameter of grounding transformer can be recorded by no-load test and short circuit test.Note, reactance involved in figure, capacitor value are all the reactance under Injection Signal frequency, capacitor value.

According to above analysis, Fig. 4 shows the schematic flow sheet of the injected type stator ground protection method do not affected by generator unit stator winding of the present invention, said method comprising the steps of:

Step 1: using the output signal of low frequency signal source after low pass filter as Injection Signal, be injected into the neutral point of generator by the secondary side of the grounding transformer of generator neutral point;

Step 2: from the grounding transformer secondary side winding of generator neutral point and the voltage signal of this grounding transformer secondary side of Real-time Collection and the component of voltage of Injection Signal the voltage divider connect the current signal of this grounding transformer secondary side of Real-time Collection and the current component of Injection Signal from the current transformer be serially connected in grounding transformer secondary side winding

Step 3: according to following formula, the Injection Signal voltage that calculation element records and the impedance angle θ of Injection Signal electric current:

$\mathrm{\θ}=\arg ({\stackrel{\·}{U}}_Z/{\stackrel{\·}{I}}_Z)$

Step 4: the impedance angle θ calculating gained according to step 3 judges whether generator unit stator earth fault occurs;

When-225 °≤θ≤-45 °, judge generator unit stator fault-free;

When-45 °≤θ≤135 °, judge generator unit stator generation earth fault;

Step 5: if judge that generator unit stator there occurs earth fault by step 4, the component of voltage of the Injection Signal now recorded according to step 2 current component and the impedance angle θ that step 3 obtains calculates the ground fault resistance R' of conversion to grounding transformer secondary side _g:

$R_g^{\′}=\frac{U_Z\cos \mathrm{\θ}}{I_Z};$

Step 6: calculate the stator over the ground fault resstance R of conversion to grounding transformer primary side as follows _g;

R _g＝kR' _g

Wherein, k represents resistance conversion factor;

Step 7: by the earth resistance one sub-value R of protection calculation gained _gcompare with the setting value of protective earthing fault resstance,

Work as R _gbe greater than the high setting value R of protective earthing fault resstance _set.Htime, generator unit stator fault-free;

Work as R _gbe less than the high setting value R of protective earthing fault resstance _set.H, but be greater than the low setting value R of protective earthing fault resstance _set.Ltime, generator continues to run, but alarm signal sent out by protective device;

Work as R _gbe less than the low setting value R of protective earthing fault resstance _set.Ltime, protective device action is in tripping operation, and generator is out of service.

The above; be only the present invention's preferably embodiment, but protection scope of the present invention is not limited thereto, any people being familiar with this technology is in the technical scope disclosed by the present invention; the change that can expect easily or replacement, all should be encompassed within protection scope of the present invention.Therefore, protection scope of the present invention should be as the criterion with the protection range of claim.

Claims (1)

1., not by the injected type stator ground protection method that generator unit stator winding affects, it is characterized in that, said method comprising the steps of:

Step 1: using the output signal of low frequency signal source after low pass filter as Injection Signal, be injected into the neutral point of generator by the secondary side of the grounding transformer of generator neutral point;

Step 2: from the grounding transformer secondary side winding of generator neutral point and the voltage signal of this grounding transformer secondary side of Real-time Collection and the component of voltage of Injection Signal the voltage divider connect the current signal of this grounding transformer secondary side of Real-time Collection and the current component of Injection Signal from the current transformer be serially connected in grounding transformer secondary side winding

Step 3: according to following formula, the Injection Signal voltage that calculation element records and the impedance angle θ of Injection Signal electric current:

$\mathrm{\θ=arg}({\stackrel{.}{U}}_Z/{\stackrel{.}{I}}_Z).$

Step 4: the impedance angle θ calculating gained according to step 3 judges whether generator unit stator earth fault occurs;

When-225 °≤θ≤-45 °, judge generator unit stator fault-free;

When-45 °≤θ≤135 °, judge generator unit stator generation earth fault;

Step 5: if judge that generator unit stator there occurs earth fault by step 4, the component of voltage of the Injection Signal now recorded according to step 2 effective value Uz, current component effective value Iz and the impedance angle θ that obtains of step 3 calculate the ground fault resistance R ' of conversion to grounding transformer secondary side _g:

$R_g^{\′}=\frac{U_Z\cos \mathrm{\θ}}{I_Z};$

Step 6: calculate the stator over the ground fault resstance R of conversion to grounding transformer primary side as follows _g;

R _g＝kR′ _g

Wherein, k represents resistance conversion factor, and namely protective device calculates the ratio that the sub-value of earth resistance of gained and protective device calculate two sub-values of gained;

Step 7: by the earth resistance one sub-value R of protection calculation gained _gcompare with the setting value of protective earthing fault resstance,

Work as R _gbe greater than the high setting value R of protective earthing fault resstance _set.Htime, generator unit stator fault-free;

Work as R _gbe less than the high setting value R of protective earthing fault resstance _set.H, but be greater than the low setting value R of protective earthing fault resstance _set.Ltime, generator continues to run, but alarm signal sent out by protective device;

Work as R _gbe less than the low setting value R of protective earthing fault resstance _set.Ltime, protective device action is in tripping operation, and generator is out of service.