CN103326331B - The method of healthy phases bus differential protection malfunction during prevention circuit re-switching - Google Patents

Abstract

The present invention relates to a kind of take precautions against circuit re-switching during the method for healthy phases bus differential protection malfunction, at least comprise in following measures: (1) is optimized electrical secondary system index and the TA of bus is replaced by 5P20, guarantees the edge of the load current value TA of 8 times away from 10% error curve; (2) differential protection arranges height definite value active region (3) increases the measure that harmonic inhibit criterion takes anti-saturation in logic, increases harmonic inhibit criterion, harmonic braking coefficient value & lt; 0.1; (4), when increasing power frequency variation comprehensive criterion bus generation external area error, power frequency differential logic is replaced with power frequency variation differential logic.

Description

The method of healthy phases bus differential protection malfunction during prevention circuit re-switching

Technical field

The present invention relates to a kind of prevent circuit re-switching during the method for healthy phases bus differential protection malfunction, belong to Relay Protection Technology in Power System field.

Background technology

Successively there is a few secondary line single phase ground fault in 110kV Dongcheng transformer station, Qingdao Power Plant etc. in recent years; bus differential or line differential protection action when line-breaker overlaps to permanent fault, circuit breaker trip cause the major accident of equipment large-area power-cuts; relevant devices has not only been excised in the generation of fault, also have impact on the stable operation of electrical network.

Such as; 110kV Dongcheng substation line single phase ground fault, when line-breaker overlaps to permanent fault, the secondary current waveform Severe distortion of circuit; cause bus differential protecting misoperation thus, cause the major accident that transformer station II bus has a power failure.

After line failure circuit breaker trip, take reclosing means to make up the switch trip because impermanency fault causes, the loss that line outage causes.But when circuit re-switching, the due effect of the problems affect of action reclosing is occurred for non-fault line, healthy phases bus differential protection and line differential protection, also disturb the analysis and treament of fault simultaneously.

Bus differential or line differential protection action when line-breaker overlaps to permanent fault, circuit breaker trip problem are very serious, though have relevant report in data before, the type of its fault, solve and differ greatly with the problem thinking of analysis.Be similar to the circuit single phase ground fault occurred in operation transformer station that above-mentioned example says, when line-breaker overlaps to permanent fault, the problem of bus differential protecting misoperation never finds reason and the processing method of fault for a long time.

Summary of the invention

Object of the present invention exactly for solving the problem, provide a kind of prevent circuit re-switching during the method for healthy phases bus differential protection malfunction, the problem of healthy phases bus differential protection misoperation during it efficiently solves circuit re-switching.

For achieving the above object, the present invention adopts following technical scheme:

A method for healthy phases bus differential protection malfunction during preventing circuit re-switching, at least comprises in following measures:

(1) electrical secondary system index is optimized

(2) differential protection arranges height definite value active region

(3) harmonic inhibit criterion is increased

In logic, take the measure of anti-saturation, increase harmonic inhibit criterion, harmonic braking coefficient value <0.1;

(4) power frequency variation comprehensive criterion is increased

During bus generation external area error, replace power frequency differential logic with power frequency variation differential logic.

In described (1) item, optimize electrical secondary system index, the TA of bus is replaced by 5P20, guarantees the edge of the load current value TA of 8 times away from 10% error curve.

In described (2) item, differential protection arranges low definite value and adjusts by Icdzd=0.4In, and In is secondary rated current, band 15ms deferred action outlet; High-set setting presses Icdzd=1.5In, is not with time delay 0s action to export.

The invention has the beneficial effects as follows: as long as above 4 measures can play a role jointly, the problem of healthy phases bus differential protection misoperation during just can solving circuit re-switching.Efficiently avoid that false protection, switch mis-jumping, signal are sent out by mistake, the series of problems of unit mistakenly stop thus; Thus avoid the shock effect that equipment large-area power-cuts causes electrical network.

Accompanying drawing explanation

Fig. 1, the position of transformer substation system structure and fault point

Fig. 2, TA electrical secondary system key wiring diagram

Fig. 3, line fault record ripple figure

Fig. 4, busbar fault record ripple figure

Fig. 5, remanent magnetism is to the current waveform figure of TA properties influence

Fig. 6, ratio differential element action characteristics curve

Fig. 7, TA equivalent circuit

10% error curve of Fig. 8, faulty line 4 bus protection TA actual measurement

The work block diagram of Fig. 9, II bus differential protection

Record ripple figure during the southern line fault of Figure 10,220kV green grass or young crops.

Embodiment

Embodiment: (for 110kV Dongcheng transformer station)

The present invention analyzes the example solving healthy phases bus differential protection malfunction during circuit re-switching, illustrate trouble-shooting detection method, determining the reason of healthy phases bus differential protection malfunction and setting up the work done in rational index system.

Substation line 8.4km place, 110kV Dongcheng single phase ground fault; when line-breaker overlaps to permanent fault; the secondary current waveform Severe distortion of circuit, causes II differential protection misoperation thus, causes the major accident that transformer station II bus has a power failure.The generation of fault has not only been excised equipment, has been interrupted a normal powered operation, causes very serious impact also to the safe and stable operation of partial electric grid simultaneously.

Fault has carried out a large amount of inspections and experiment work after occurring at the scene, tests, eliminate the factor of secondary circuit two points ground fault to the insulation resistance of TA secondary circuit; Test voltage-current characteristic, secondary impedance, result is shown to be that secondary impedance is high causes the saturated of short circuit current; The waveform of electric current is analyzed, and adopt cranking test to confirm with the method for simulation magnetic after effect, the reason of current waveform distortion is the impact of remanent magnetism, and remanent magnetism makes TA be in transient state saturation condition, the saturated distortion causing Transfer characteristic to degenerate and then cause secondary current of transient state.TA takes anti-saturation measure; Differential protection takes and arranges high and low definite value active region; Increase the measures such as harmonic braking link in logic after, problem is solved.

When overlapping to permanent fault to Dongcheng substation line below, the dynamic behavior of bus differential error protection action is analyzed.

One, phenomenon of the failure

On August 3rd, 2010, there is earth fault in transformer station #4 circuit 8.4km place, 18:57:25,110kV Dongcheng, and route protection action is tripped.Switch overlaps to permanent fault after the time delay of adjusting, route protection action tripping operation again, and meanwhile, the action of II bus protection B phase, all devices that this bus of tripping connects, Fig. 1 is seen in the position of system configuration and fault point.Phenomenon of the failure at that time has following doubtful point.

(1) unsymmetrical current of large poor protection is consistent with II bus protection, but why large poor protection does not have action;

(2) II bus protection B phase action during circuit generation earth fault is II false protection, or II bus exists fault and correct operation;

(3) II bus protection A differs stream much larger than B, C phase, but A phase is protected and do not had action, the action of B phase;

(4) when circuit first time, earth fault occurred, II bus protection do not have action, but action after coincidence;

(5), during circuit generation earth fault, is the saturated serious reason of fault current wherein?

Two, checking process

Around the doubtful point in phenomenon of the failure, comprehensive inspection is carried out to secondary circuits such as #4 circuit TA.TA second loop return wiring is for bus protection, and Fig. 2 is shown in by sketch.

1, megger test

Loop	Measured value (M Ω)	Loop	Measured value (M Ω)
				Route protection 421	80	Bus differential protection 310	30
Between 421AB	300	Between 310AB	400
				Between 421BC	500	Between 310BC	500
Between 421CA	400	Between 310CA	200
				Between 421AN	2000	Between 310AN	1500
Between 421BN	1500	Between 310BN	2000
				Between 421CN	1000	Between 310CN	2000

The insulation resistance detected is qualified, can determine that TA does not exist the phenomenon of two points ground fault for bis-times, and that is the misoperation of bus differential protecting and the problem of TA bis-ground connection have nothing to do.

2, TA no-load voltage ratio test

As shown in Figure 1, the no-load voltage ratio of faulty line TA is 600/5, and therefore no-load voltage ratio result is correct.

3, TA polarity test

Result of the test shows, the output of TA is positive polarity, and therefore polarity is correct.

4, D.C. resistance test

The D.C. resistance result tested is correct.

5, TA secondary load ac impedance measurement

Separate	A0	B0	C0
				421 impedances (Ω)	4.2	4.1	4.1
310 impedances (Ω)	4.1	4.1	4.1

6, volt-ampere characteristic test

(1) 421 current circuit (terminal box TA side)

(2) 310 current circuits (terminal box TA side)

Measured data result is correct.

7, transformer station 110kV bus protection electric current phasor test

Measured bus protection electric current phasor result is correct.

8, failure wave-recording inspection

Circuit and bus protection failure wave-recording are shown in Fig. 3, Fig. 4,

9, the test of TA characteristic is affected about remanent magnetism

In order to verify that remanent magnetism is to TA properties influence, to one in two TA, secondary coil 120 circle passes into the electric current of 5A, amounts to excitation 600 ampere-turn, and then two TA pass into electric current 20Ie simultaneously, then both poor stream reaches more than 6Ie, and this value is enough to the action causing protecting.Record ripple figure during test is shown in Fig. 5.

Three, bus protection Introduction on Principle

Bus differential protecting is made up of split-phase type percentage differential element, and TA polar requirement branch road TA Same Name of Ends is in bus bar side, and mother TA Same Name of Ends is in the female side of I section.The large difference of bus refers to the differential circuit that all branch currents are formed except bus connection switch and block switch, and the little difference of I (II) section bus refers to the differential circuit that all branch currents that this section of bus connects are formed.The large poor percentage differential of bus with differentiation bus district in and external area error, little poor percentage differential is for selecting fault bus.Percentage differential element movement criterion is:

$\begin{array}{ccc}{I}_{cd}=\left|\underset{j=1}{\overset{m}{\&Sigma;}}{I}_j\right|;& \left|\underset{j=1}{\overset{m}{\&Sigma;}}{I}_j\right|>I_{cdzd};& \left|\underset{j=1}{\overset{m}{\&Sigma;}}{I}_j\right|>K\underset{j=1}{\overset{m}{\&Sigma;}}\left|I_j\right|\end{array}$

Wherein: I _cd-differential starting current; M-connection circuitry number; K is ratio brake coefficient; I _jfor the electric current of a jth Connection Element; I _cdzdfor differential current starts definite value.Its operating characteristics curve as shown in Figure 6.

Four, TA10% error curve is determined

Adopt the exciting characteristic curve method of TA can obtain the error curve of 10%, way is as follows:

(1) the excitation impedance characteristic curve of TA

The equivalent circuit of TA is shown in Fig. 7.In Fig. 7, Z ₁for primary impedance, Z ₂' be secondary winding impedance, Z _lCfor excitation impedance, I _lCfor exciting current.The primary side of TA is opened a way, pass between secondary current, voltage is:

${\stackrel{\&CenterDot;}{U}}_2={\stackrel{\&CenterDot;}{I}}_{LC}(Z_{LC}+Z_2)$

Above formula can be write as

$Z_{LC}+{Z_2}^{\&prime;}={\stackrel{\&CenterDot;}{U}}_2/{\stackrel{\&CenterDot;}{U}}_{LC}$

Relative Z _lC, Z ₂' negligible, so the voltage-current characteristic of TA bis-times is approximately excitation impedance characteristic, i.e. Z _lC≈ U ₂/ I _lC, and voltage-current characteristic very easily obtains from test.

(2) 10% error curve is done

Be multiplied by 0.1 as the abscissa of 10% error curve with the ordinate of exciting characteristic curve, namely secondary allows impedance Z _r.

Z _r＝0.1Z _LC≈0.1U ₂/I _LC

2 are multiplied by as the ordinate of 10% error curve, i.e. primary current multiple m10 with the abscissa of exciting characteristic curve.

m ₁₀＝2I _LC

(3) 10% error curve (Fig. 8) of surveying

Survey the secondary voltage-current characteristic of TA, related data is in table 1.Three characteristics of the middle term data are basically identical, therefore only row one phase.

Bus protection B phase TA performance data table

I(A)	0.1	0.2	0.5	1.0	2.0	3.0	4.0	5.0	10.0	20.0
											U(V)	163	171	178	185	198	207	223	229	239	247
Zr(Ω)	163	85	36	18	10	6.9	5.6	4.5	2.3	1.2
											m10	0.2	0.4	1.0	2.0	4.0	6.0	8.0	10.0	20.0	40.0

Five, the analysis of causes

Be analyzed as follows for the doubtful point in phenomenon of the failure:

1, the large difference protection of II bus protection action does not have action to be the result that logic coordinates

Unsymmetrical current poor is greatly consistent with II bus protection; but large poor protection does not have action; the reason of II bus protection action is; after faulty line overlaps; the unsymmetrical current of large poor protection is consistent with II bus protection, but coordinates according to logic, and after reaching definite value, the action of II bus protection formerly; large poor protection act is rear, and after failure vanishes, large poor protection returns.

2, the action of II bus protection belongs to misoperation

During circuit generation earth fault, be the malfunction of II bus protection, or there is fault correct operation in II bus? from fault oscillograph, after faulty line first time excision, busbar voltage is normal, and this circuit overlaps to bus voltage drop after fault.Therefore circuit is only had to there is fault, bus normal operation.The action of II bus protection belongs to misoperation as can be seen here.

3, the misoperation of bus protection is relevant with the distortion of current waveform

Did not circuit first time, why II bus protection have action when there is earth fault, but action after coincidence? circuit first time, when there is earth fault, the secondary arc current of B, C Relative fault phase also existed, but spill current is comparatively light, and protection does not have action.After circuit coincides with permanent fault, the DC component of fault current improves, and unsymmetrical current obviously increases, and the duration that spill current reaches definite value is long, and after therefore overlapping, B phase II mother is differential trips.

4, the distortion of TA secondary current waveform is relevant with remanent magnetism

In operation, when dropping the operations such as transformer, emergency stop valve trip and capacitor switching, a lot of by the chance that there is DC component in the electric current of current transformer, the DC component of electric current is inevitable produces remanent magnetism at current transformer in iron core, and remanent magnetism is difficult to eliminate in operating conditions.Impact due to remanent magnetism can make the Transfer characteristic of current transformer degenerate; Due to Transfer characteristic degenerate cause current transformer to occur transient state is saturated; The saturated distortion causing TA secondary current waveform with the impact of DC component due to transient state.

For bus protection, if the initial condition of TA remanent magnetism is inconsistent, also there is difference in the transient state situation of electric current, thus cause the appearance of difference stream, and stream of being on duty reaches certain degree then can make protection misoperation.

5, test demonstrates the waveform influence of remanent magnetism to TA secondary current

In the sinusoidal quantity that the initial period 714 switch TA secondary current of line fault is standard substantially, and line-breaker is when overlapping to permanent fault, the waveform Severe distortion of TA secondary current, occurred that the TA of same model shows the problem of different qualities in the different periods, its difference is the impact of remanent magnetism.

Understand the impact of remanent magnetism on TA electric current in order to deep, complete " test affecting TA characteristic about remanent magnetism ", result shows, when TA exists remanent magnetism, secondary current departs from abscissa can reach more than 1/2.But; the current recording protected during line fault and test waveform Fig. 5 difference larger; reason is to test the fault current can not simulated completely at that time, and test can only illustrate that the impact of remanent magnetism can make current transformer occur transient state saturated phenomenon, causes the distortion of TA current waveform.

6, A phase and B phase are protected between the understanding of action behavior difference

Does II bus A differ stream much larger than B, C phase, but why A phase is protected does not have action, the but action of B phase? (1) B

The reason of phase protection act is caused by the transient state component of fault current

According to fault oscillograph, during A phase earth fault relatively then there is electric current in B, C, and A phase earth fault current 40A, B, C be electric current about 10A relatively.B, C phase current is the secondary arc current provided fault phase, is not that other factors such as secondary interference cause.

Although A phase spill current is comparatively large, each cycle has the break time of more than 1/3, and now protection returns, and therefore protection does not have action to export.The impact that A phase spill current is mainly saturated causes.

The reason of B phase protection act, be that the waveform transient state component of its fault current is obvious, the duration that spill current reaches definite value is long, in fact Icd>Icdzd=0.4In duration 10ms, thus start protection cause outlet to be tripped.

C phase relatively B is compared gently, and unsymmetrical current is less, protects motionless also reasonable.

(2) during circuit generation earth fault, A phase current is saturated has nothing to do with 10% error

During circuit generation earth fault, A phase TA secondary current reaches 40A, is equivalent to the load current value of 8 times, and now TA is seriously saturated is not right, may there is following problem.

1) lectotype selection improper or workmanship existing problems;

2) secondary circuit impedance exceeds standard, causes 10% error not meet the demands;

3) there is the impact of remanent magnetism, cause so-called transient state saturated.

Conclusion according to drawing test result analysis is, saturated and the remanent magnetism of short circuit current when fault starts has nothing to do, 10% error curve in conjunction with TA actual measurement is known, the load current value TA of 8 times is close to the edge of 10% error, but 10% error not yet exceeds standard, therefore A phase current is saturated has nothing to do with 10% error, is caused by TA characteristic issues; Reclosing period A phase current seriously saturated not only relevant with TA characteristic issues, also relevant with remanent magnetism, has nothing to do with 10% error.

It should be noted that B phase protection misoperation and A phase current saturated between difference very large, the front impact once addressing B phase protection misoperation and remanent magnetism is closely related.

Six, the precautionary measures

According to above-mentioned analysis, take following measure in conjunction with on-the-spot situation.

1, promote TA specification, optimize electrical secondary system index

The TA of bus is replaced by 5P20, guarantees the edge of the load current value TA of 8 times away from 10% error curve;

2, differential protection arranges height definite value active region

Differential protection arranges low definite value active region, adjusts by Icdzd=0.4In, and In is secondary rated current, band 15ms deferred action outlet; High-set setting active region is adjusted by Icdzd=1.5In, is not with time delay 0s action to export.

3, harmonic braking certificate is increased

In logic, take the measure of anti-saturation, increase harmonic braking link, harmonic braking coefficient value <0.1.The TA saturation detection element be made up of harmonic braking principle.Whether its principle make use of the TA saturated time difference and flows wave distortion and every cycle exists the features such as linear transform area, detect TA occur saturated according to the wave character of harmonic component in difference stream.The TA saturation detection element that this principle realizes has very strong anti-TA saturability.Fig. 9 is shown in by the work block diagram of bus differential protection.

In Fig. 9, I _cd-differential starting current; CD-large poor percentage differential element; CD _iI-II bus percentage differential element; SW-bus differential protection control word; YB-bus differential protection is thrown and is moved back pressing plate; U _iIthe locking of-II busbar voltage.

4, power frequency variation comprehensive criterion is increased

During bus generation external area error, due to fault, to start TA not yet saturated, power frequency variation difference element, the delayed power frequency variation voltage component of power frequency variation impedance, the sequential relationship of three is utilized to obtain self adaptation impedance weighted Criterion, when this criterion utilizes external area error, the saturated difference of injection time stream of TA is different from the feature of troubles inside the sample space, has very strong anti-saturation ability.

After taking above-mentioned measure, problem is solved.Annex: record ripple during the southern line fault of Figure 10,220kV green grass or young crops.

Claims (1)

1. a method for healthy phases bus differential protection malfunction during preventing circuit re-switching, is characterized in that, comprise following measures:

(1) electrical secondary system index is optimized

The TA of bus is replaced by 5P20, guarantees the edge of the load current value TA of 8 times away from 10% error curve;

(2) differential protection arranges height definite value active region

Differential protection arranges low definite value and adjusts by Icdzd=0.4In, and In is secondary rated current, band 15ms deferred action outlet; High-set setting presses Icdzd=1.5In, is not with time delay 0s action to export;

(3) harmonic inhibit criterion is increased

In logic, take the measure of anti-saturation, increase harmonic inhibit criterion, harmonic braking coefficient value <0.1;

(4) power frequency variation comprehensive criterion is increased

During bus generation external area error, replace power frequency differential logic with power frequency variation differential logic.