Analyse malfuctionis interruptoris SF6 in substatione 750 kV

Felix Spark

Campus: Defectus et Manutentio

China

Propter suas excellentes proprietates insulantis electrici et extinguendi arcus, sulfur hexafluoride (SF₆) gas est late usitatum in systemibus electricis altae et extra altae tensionis. Comparatis cum interruptoribus circuituum traditionibus, interruptores circuituum SF₆ sunt magis fideles et habent longiorem vitam utilem. Tamen, cum tempore usu et onere crescente, defectus interruptorum circuituum SF₆ paulatim emergunt, praecipue defectus rupturae, qui facti sunt periculum latens operativae securitati rete electricum. Defectus rupturae non solum laedunt instrumenta, sed possunt etiam ad magnas intermissiones electricitatis et ad instabilitatem rete electricum ducere. Cum defectu accidit, cum arcubus et altis temperaturis, potest interna materia insulantia et componentia metallica laedi, etiam ignes et explosiones provocare. Itaque, studium mechanicae defectus rupturae interruptorum circuituum SF₆, identificatio causarum radicum, et propositio praemonitionum praeventionis sunt magna momenta ad securitatem operativam systematis electrici assecurandam.

Nunc, doctores domi et foris fecerunt extensa studia de mechanicis defectus interruptorum circuituum SF₆, praecipue in aspectibus sicut testando performance electrica, analysando senescens materialis, et simulando distributionem electrici campi. Tamen, propter structuram internam complexam interruptorum circuituum SF₆ et involvement multarum factorum, studia existentia adhuc limitationes habent. Praecipue pro defectibus rupturae in operatione actuali, propter limitationes conditionum in loco et difficultatem disassembly instrumentorum, deficit studia systematica et comprehensiva.

Itaque, haec scriptio facit analysis comprehensive, includens investigationem defectus in loco, analysis disassembly instrumentorum, et testationem performance electrica, pro defectu rupturae interruptoris circuituum SF₆ in quadam substatione. Scopus est revelare comprehensiviter mechanicam defectus et praebere fundamentum scientificum et support technicum ad meliorationem design, operationem et maintenance, et praeventionem defectus similibus instrumentis in futurum.

(2) Detectio Productorum Decompositionis Gas SF₆, Contentus Micro-aquae, et Purity

Testes in loco fuerunt effecti super productis decompositionis gas SF₆, contentu micro-aquae, et puritate interruptoris circuituum defectivi. Data testium ostenduntur in Tabula 1. Ex analysi resultatorum testium, producta decompositionis gas SF₆ et contentus micro-aquae in camera extinguendi arcus phase C interruptoris circuituum defectivi significanter excesserunt limites normales definitos in "Codice pro Testibus Maintenance Condition-based Instrumentorum Transmissorum et Transformationis Electricae" (SO₂ ≤ 1 μL/L, H₂S ≤ 1 μL/L, micro-aqua ≤ 300 μL/L) [5]. Contrario, resultata testium camerarum gassarum reliquorum interruptorum circuituum erant omnia normalia, nulla abnormia detecta. Ex datis supradictis, initio coniecturatur posse esse defectus emissive intra camera extinguendi arcus phase C interruptoris circuituum defectivi.

Tabula 1 Data Testium Productorum Decompositionis Gas SF₆, Contentus Micro-aquae et Purity

(3) Inspectio Resistentiae Insulationis Principali Interruptoris Circuituum
Durante testibus resistentiae insulationis phase C interruptoris circuituum defectivi, oportet sequi proceduras operativas standard, et certum esse interruptorem circuituum esse in statu aperto. Durante testibus, unum bushing ponitur ad terram dum voltas applicatur ad alterum. Sic, perficitur evaluatio completa performance insulationis unicuique porto interruptoris circuituum, sicut etiam inter viam conductivam et casum.
Ex analysi datorum testium, inventum est performance insulationis phase C interruptoris circuituum generaliter deficiens, praecipue problema performance insulationis ad portu disconnectionis lateris bus Ⅱ interruptoris circuituum valde prominens. Data testium ostenduntur in Tabula 2.

Tabula 2 Data Testium Insulationis ad Portu Disconnectionis Lateris Bus Ⅱ Interruptoris Circuituum

(4) Testatio Capacitatis et Perditationis Dielectricae Condensatorum Parallelorum Inter Portus Interrumpentes Interruptoris Circuituum

Sub conditionibus testium in loco, quia non fuit possibile testare capacitatem unicuique condensatori portus interrumpentis individualiter, methodus comparativa testandi capacitatis et perditationis dielectricae condensatorum parallelorum inter portus interrumpentes interruptorum circuituum phase ABC adoptata est. Durante operatione specifica, cum interruptore circuituum in statu aperto, methodi testandi inter-bushing (positiva conexio) et bushing-ad-terra (negativa conexio) usi sunt ad capacitatis et perditationis dielectricae testes. Data testium ostenduntur in Tabula 3.

Tabula 3 Data Testium Capacitatis et Perditationis Dielectricae Interruptoris Circuituum Defectivi

Per analysin comparativam Tabulae 3, inventum est valor capacitatis obtentus ex teste positivo connexionis inter bushings fuit relativus proximus ad valorem actualem. Tamen, affectus per capacitatem stragalem intra interruptorem circuituum, adhuc fuit quaedam deviatio inter valorem mensuratam et calculatum. Tamen, ex resultatis testium capacitatum parallelarum portus interrumpentis inter phases ABC, differentiae capacitatis inter tres phases erant relativae parvae. Ex hoc, initio iudicatum est status condensatoris parallelus portus interrumpentis phase C esse normalis.

(5) Inspectio Interna Vasculi Interruptoris Circuituum

In loco curae defectus, gas phase C interruptoris circuituum defectivi fuit professionaliter recuperatus. Deinde, endoscopium usum est ad inspectionem profundam internam vasculi. Post inspectionem detegentem, inventum est resistens claudens prope latus bus Ⅱ habuit rupturn. Fragmenta nigrorum chip resistance dispersa erant in fundo vasculi. Praeterea, inventum est etiam sheath polytetrafluoroethylene unius resistens claudens fuit fissus et cecidit in fundum vasculi.

2.1.1 Inspectio Disconnectoris

Post inspectionem detegentem in loco, signa incendi manifesta inventa sunt in partibus digitis arcanis contactuum mobilium utriusque lateris phase C disconnectorum utriusque lateris interruptoris circuituum defectivi. Deinde, per operationem manualem disconnectoris phase C in loco, totus processus operationis fuit lenis sine ulla obstruxione. Praeterea, durante inspectione, observatum est non fuisse phenomenum coesionis inter contactus mobiles et staticos. Post completionem operationis aperturae, inspectio detegens contactuum basis staticorum et digitorum contactuum facta est, et nulla signa incendi gravis inventa sunt.

2.1.2 Inspectio Instrumentorum Secundariorum

Ad 12:31:50.758 die 18 Iunii 2022, phase C interruptoris circuituum defectivi in 750kV substatione fuit ad terram. Post defectum, protectio differentialis fibra-optica lineae et protectio differentialis bus 750kV Bus-Ⅱ ambae recte operatae sunt. Per analysin profunda currentis defectus et operationis protectionis differentialis bus et protectionis lineae, quando disconnector erat in statu clauso (durante quo tensio systematis remansit stabilis sine over-voltage), observatum est 750kV Bus-Ⅱ suppeditavit currentem defectus ad punctum defectus. Notabile est CT₇ et CT₈ involved in the bus differential protection of the faulty circuit breaker did not detect the existence of fault current. Based on this observation, it was determined that the fault point should be in the area between circuit breaker CT₇ and the bus. Meanwhile, CT₁ and CT₂ for line protection detected the existence of fault current, and the value of the fault current reached a primary current of 4.5kA. Therefore, it was further inferred that the fault point was in the area between CT₂ of the faulty circuit breaker and the interrupting port on the Ⅱ-bus side of the circuit breaker. This inference was consistent with the location of the fault point found in the on-site internal inspection.

2.2 Dismantling Inspection

As shown in Figure 2, during the inspection of the inside of the tank during the circuit breaker dismantling process, fragments of the closing resistance and its protective sheath were observed scattered around. Some resistance chips of the fourth-column closing resistance, which was connected in parallel with the main interrupting port on the mechanism side of the circuit breaker, had exploded, and the corresponding two resistance protective sheaths had also ruptured. End shield A of the resistance showed traces of discharge ablation on the inner wall of the tank, and shield B also had traces of discharge ablation on A. In addition, the surface of the insulating support rod showed blackened traces. By checking the assembly, factory test, and on-site installation data of the circuit breaker, and inspecting the main insulating parts, no abnormalities were found.

3 Fault Cause Analysis

Through dismantling analysis, the following conclusions were drawn: During the closing process of the disconnect switch, the end shield A of the resistance first discharged to the inner wall of the tank. This led to abnormal currents in the fourth, third, and second-column closing resistances. Subsequently, shield B discharged to A, causing the second and third-column resistances to short-circuit, and the current was mainly concentrated in the fourth column. This phenomenon caused the temperature of the resistance chips in the fourth column to rise sharply, eventually leading to explosion, and the resistance protective sheath broke and fell off. During the discharge process, the generation of high-temperature arcs caused the surface of the insulating support rod to become blackened.

The tank-type circuit breaker can withstand a lightning impulse voltage of up to 2100kV. During the normal closing process of the disconnect switch, although over-voltage may occur, under normal operating conditions, this level of over-voltage is not sufficient to trigger the discharge mechanism of the circuit breaker. However, through in-depth analysis and inference, it is preliminarily suspected that there may be foreign objects inside the tank. These foreign objects may have an adverse impact on the electric field distribution, causing the electric field to distort and exceeding the insulation strength that the SF₆ gas gap can withstand. In this case, end shield A of the resistance may first discharge to the inner wall of the tank. Considering that the foreign objects inside the tank may be hidden in imperceptible crevices, when the disconnect switch is closed with power on, the over-voltage generated may, under the action of the electric field force, move the foreign objects to areas with a stronger electric field, thereby causing electric field distortion and leading to the occurrence of discharge phenomena.

4 Conclusion

Given the extensive application of advanced switchgear in the power system, accidents such as tripping of tank-type circuit breakers and GIS equipment due to foreign objects occur frequently. To prevent such faults, it is necessary to strengthen live-line detection work, especially increasing the detection frequency for circuit breakers that operate frequently. At the same time, during on-site acceptance, it should be strictly checked whether the equipment has completed 200 mechanical operations to ensure the running-in of the mechanism and avoid the adverse effects of metal debris on the operation of the equipment after commissioning.

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