Tambayar da ake kula da abin da ya jawo wa ɗaya na circuit breaker na SF6 a baka mai hukuma na 750 kV

Felix Spark

فیلڈ: Kashe da Kayan Aiki

China

Saboda hanyar da yake da kyau a tsarin kwalbar da na gaba shiga, gas sulfur hexafluoride (SF₆) ta fi amfani da ita a tarihin kwalbar da na gaba da kuma tarihin kwalbar mai yawa. Wannan ya haɗa da cikin manyan wurare da ke amfani da SF₆ circuit breakers suka zama mafi inganci da kuma suka zama da rike mai yawa. Amma, idan lokacin da ake amfani da ita da kuma takarda ya yi karfi, matattun SF₆ circuit breakers sun zo a faru, musamman matattun breakdown, wanda suka zama nasarar da ba a tabbatar da shiga ga gwamnatin kwalbar. Matattun breakdown ba tana iya jagoranci abubuwa baki daya, amma zai iya haifar da ci gaba-gaban kwalbar da kuma za su iya haifar da kisan hotuna masu yawa. Idan yanayin ya faru, da wasu arcs da fadin kasa, zai iya jagoranci abubuwan da suka dace da kuma mutanen kasa, kuma zai iya haifar da hotuna da kuma hotuna masu yawa. Saboda haka, yanayin a duba mekanismun matattun breakdown na SF₆ circuit breakers, samun sabbin abubuwan da ke sauya, da kuma bayar da ayyukan da za su iya sauya, yana da muhimmanci don in tabbatar da shiga ga gwamnatin kwalbar.

A halin yanzu, malamai a kan da na kai ne da kuma a kan da na biyu ne suka yi aiki a gaba-gaban mekanismun matattun SF₆ circuit breakers, musamman a kan abubuwan da ke nuna aiki, analisisi na rawa, da kuma tushen electric field distribution. Amma, saboda tsarin kwalbar na SF₆ circuit breakers da kuma babban abubuwan da ke da shi, aiki na gaba-gaba suka da batu. Musamman, idan an yi aiki a kan matattun breakdown a kan aiki, saboda batun lokacin da ke da shi da kuma rashin dolewa masu abubuwa, ba a da aiki na gaba-gaba da kula da shi.

Saboda haka, wannan rubutun ya yi aiki na gaba-gaba, a kan aiki na gaba-gaba, dolewa masu abubuwa, da kuma abubuwan da ke nuna aiki, don matattun breakdown na SF₆ circuit breaker a kan gwamnatin kwalbar. Ainihi shine in nuna mekanismun matattun da kuma in bayar da cikakken bayanai da kuma tushen teknologi don in dogara, aiki da kuma sauya da matattun da za su iya faru a kan abubuwan da ke dace.

(2) Tabbataccen Products of SF₆ Gas Decomposition, Micro - water Content, and Purity

An yi aiki a kan Products of SF₆ gas decomposition, micro - water content, da kuma purity na faulty circuit breaker. Bayanan aiki sun nuna a cikin Tabular 1. Daga bayanin aiki, Products of SF₆ gas decomposition da micro - water content a kan arc - extinguishing chamber na phase C na faulty circuit breaker sun zama da take da limits da aka nuna a "Code for Condition - based Maintenance Tests of Power Transmission and Transformation Equipment" (SO₂ ≤ 1 μL/L, H₂S ≤ 1 μL/L, micro - water ≤ 300 μL/L) [5]. Na farko, bayanan aiki na gas chambers na circuit breakers masu dace suka da shi, ba a sanya shi. Daga cikin bayanan, ana hasashen cewa ina iya kasance da fault na discharge a kan arc - extinguishing chamber na phase C na faulty circuit breaker.

Table 1 Test Data of SF₆ Gas Decomposition Products, Micro - water Content and Purity

(3) Inspection of the Main Insulation Resistance of the Circuit Breaker
A lokacin da ake yi aiki na insulation resistance test na phase C na faulty circuit breaker, ya kamata a yi da standard operating procedures, da kuma in tabbatar da cewa circuit breaker ya shiga open - circuit state. A lokacin da ake yi aiki, one - side bushing ya shiga ground while voltage is applied to the other side. Hakan ya haifar da in nuna aiki na insulation performance na kawo-kawon port na circuit breaker, da kuma aiki na conductive circuit da casing.
Daga bayanin aiki, ana hasashen cewa insulation performance na phase C na circuit breaker ya zama da take da shi, musamman insulation performance problem na disconnection port on the Ⅱ - bus side na circuit breaker ya zama da take da shi. Bayanan aiki sun nuna a cikin Table 2.

Table 2 Insulation Test Data at the Disconnection Port on the Ⅱ - bus Side of the Circuit Breaker

(4) Testing of Capacitance and Dielectric Loss of Parallel Capacitors between Circuit Breaker Interrupting Ports

A lokacin da ake yi aiki, saboda ba a iya yi aiki na capacitance na kowace interrupting port capacitor, an yi aiki na comparative testing method for the capacitance and dielectric loss of parallel capacitors between the interrupting ports of the ABC - phase circuit breakers. A lokacin da ake yi aiki, with the circuit breaker in the open - circuit state, an yi aiki na inter - bushing (positive connection) and bushing - to - ground (negative connection) methods to conduct capacitance and dielectric loss tests. Bayanan aiki sun nuna a cikin Table 3.

Table 3 Capacitance and Dielectric Loss Test Data of the Faulty Circuit Breaker

Daga bayanin Table 3, ana hasashen cewa capacitance value obtained by the positive - connection test between bushings ya zama da take da actual value. Amma, saboda stray capacitance inside the circuit breaker, ya zama da take da deviation between the measured value and the calculated value. Ba haka, from the test results of the parallel capacitances of the interrupting ports among the ABC phases, the differences in capacitance among the three phases were relatively small. Based on this, it was preliminarily judged that the state of the parallel capacitor of the C - phase interrupting port was normal.

(5) Inspection Inside the Circuit Breaker Tank

A lokacin da ake yi aiki, gas of phase C na faulty circuit breaker ya shiga recovery. Subsequently, an yi aiki na endoscope to conduct an in - depth inspection inside the tank. After a detailed inspection, it was found that the closing resistance near the Ⅱ - bus side had a breakdown. Black resistance chip fragments were scattered at the bottom of the tank. In addition, it was also found that the polytetrafluoroethylene sheath of one of the closing resistances had cracked and fallen to the bottom of the tank.

2.1.1 Inspection of the Disconnect Switch

After a detailed on - site inspection, obvious burning marks were found on the arcing finger parts of the moving contacts on both sides of phase C of the disconnect switches on both sides of the faulty circuit breaker. Subsequently, by manually operating the disconnect switch of phase C on - site, the entire operation process was smooth without any jamming. Moreover, during the inspection, it was observed that there was no welding phenomenon between the moving and static contacts. After the opening operation was completed, a detailed inspection of the static contact base and the contact fingers was further carried out, and no serious burning marks were found.

2.1.2 Inspection of Secondary Equipment

At 12:31:50.758 on June 18, 2022, phase C of the faulty circuit breaker in the 750kV substation was grounded. After the fault occurred, the line fiber - optic differential protection and the bus differential protection of 750kV Bus - Ⅱ both operated correctly. Through an in - depth analysis of the fault current and the operation of the bus differential protection and the line protection, when the disconnect switch was in the closed state (during which the system voltage remained stable without over - voltage), it was observed that 750kV Bus - Ⅱ supplied fault current to the fault point. It is worth noting that CT₇ and 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.

Ba da kyau kuma kara mai rubutu!