Tahaddarin Tushen Abin da ke Faruwa a Fagen Dukkana SF6 a Yanzu na Bisa

GIS (Gas Insulated Switchgear) ya amfani da gas SF₆ a matsayin hanyar da zai gane da kuma hanyar da zai kama tushen siffo. Ana da muhimmanci sosai saboda abubuwan da suka shafi ciki, kamar yawan kasa, tsari mai kyau, darasi mai kyau, da kuma ingantaccen inganta. Aikacewar karamin SF₆ wanda shi ne babban baka a cikin zaɓuɓɓukan GIS, ya fi girma a wurare da mutanen 110 kV zuwa runa.

Wannan makarantar yana bayyana nasarorin da aka faru a lokacin da an samun karkashin Unit 1 a wuri na ƙarfi kan da ba. Idan, lokacin da aikacewar karamin SF₆ 2201 a karshe na ƙarfi mai zurfi ta 220 kV ta ƙara, an kama jirgin C. Saboda haka, an sa protection da ya kama waɗanda suka biyo masu aikacewar da kuma protection da ya kama waɗanda suka biyo negative sequence current, wanda ya haifar da karkashin unit da kuma fuskantar ita a ƙarfin gwamnati.

1 Tarihin Abin da Yawancin Farkon Ta

A lokacin da an samun karkashin Unit 1 da kuma lokacin da an yi synchronization, systemin yan tabbatarwa ta ce protection da ya kama waɗanda suka biyo aikacewar, operation da ya kama waɗanda suka biyo inverse time negative sequence current, tripping da ya kama waɗanda suka biyo electrical protection, da kuma undervoltage messages na ƙarfin 220 kV Line Jia da Line Yi. Ba a nan da wani protection alarm na unit ba.

Unit 1 ta yi shiga procedure. Aikacewar 2211 na ƙarfin 220 kV Line Jia da Line Yi ta ƙara, kuma aikacewar auxilliary power transformer (2200 Jia) ta ƙara, sannan device da ya kama waɗanda suka biyo auxilliary power supply ta yi shiga. Bayan a tabbatar da grid dispatching and control personnel, ana ce wadanda ba a ƙarfin 220 kV Line Jia da Line Yi ba. Daga baya, ana ce aikacewar 2201 ya kasance da nasara.

Lokacin da aikacewar 2201 ta fito don in tuntubi, ana samun kungiyoyi da wasu abubuwa a cikin ƙaramin arc extinguishing chamber na Phase C na aikacewar 2201, wanda suka sanza a cikin gas chamber. Babu shiga-tsohon da a samu a faden aikacewar, kuma babu ground short-circuit phenomenon na aikacewar da aka samu. Daga baya, ana analisa da ce insulation da a bangaren break points na Phase C na aikacewar 2201 ta kama.

Don in taimaka da safe da stable operation na unit da kuma in yi analysis na abin, an yi replacement uniform da three phases na aikacewar 2201. An yi relevant electrical preventive tests da kuma manual startup, zero-voltage rise, da kuma grid connection tests na unit.

2 Analysis of Protection Action

By examining the fault oscillogram of Unit 1, it is found that when the protection acts, Unit 1 is still in the synchronization process and this process lasts for 25 seconds (the normal synchronization closing time is about 80 seconds), and no synchronization closing command is issued during this period. Subsequently, by checking the protection oscillogram of the generator-transformer unit, it is discovered that there is current in Phase B and Phase C on the low-voltage side of the main transformer, while there is no current in Phase A (the transformer wiring configuration is Yｎ／Ｄ１１).

The unbalanced value of the inverse time negative sequence overcurrent of Unit 1 during power generation exceeds the threshold and accumulates to trigger the tripping section, causing the protection to trip. The inverse time negative sequence overcurrent protection of Unit 1 during power generation trips the 2201 circuit breaker. Since the circuit breaker is still in the open state at this time, it is unable to cut off the breakdown current of Phase C. At this moment, the protection RCS - 921A of the 2201 circuit breaker receives the failure protection signal initiated by the three-phase trip of the generator-transformer unit. Meanwhile, there is current in Phase C, which exceeds the failure setting value, and the failure protection acts, causing Unit 1 to execute the shutdown procedure. The failure protection acts to remotely trip the 220 kV Line Jia and Line Yi 2211 circuit breaker through the line protection RCS - 931AM. Therefore, this protection action is caused by the breakdown of the break point of the 2201 circuit breaker when it fails to close, and all protection actions are correct.

3 Analysis of the Fault Cause

When the fault occurs, the voltage on the generator side of the unit has reached the rated value, but the conductive part of the switch has not been closed. At this time, the voltage across the switch reaches its maximum value. Before the insulation of the break point of Phase C of the 2201 circuit breaker breaks down, the monitoring system does not issue an alarm for the low pressure in the SF₆ gas chamber, and on-site inspection shows that the SF₆ density relays are all within the green zone.

The total number of operations of the 2201 circuit breaker is 535 times, which is far from the designed rated number of operations, which is 5000 times. Based on the on-site fault oscillogram data, the actual state of the faulty circuit breaker, and the relevant maintenance data of the circuit breaker of Unit 1, the possible causes of the insulation breakdown between the break points of Phase C of the 2201 circuit breaker are preliminarily analyzed as follows:
(1) There are structural problems inside the arc extinguishing chamber of the Phase C circuit breaker. The internal components may be loose, resulting in discharge and breakdown between the ports.
(2) There are impurity problems in the arc extinguishing chamber of the Phase C circuit breaker. During multiple operations of the circuit breaker, a discharge channel is gradually formed, causing insulation breakdown.
(3) There are material problems with the break point of the Phase C circuit breaker. Improper use of the break point material causes impurities to be generated during the operation of the circuit breaker and adhere to the outer surface of the port for a long time. Gradually, a discharge channel is formed, ultimately leading to insulation breakdown between the break points.

The faulty Phase C arc extinguishing chamber is transported back to the factory for disassembly and analysis. At the same time, either the non-faulty Phase A or Phase B (any one phase) is transported back to the factory for disassembly and comparative analysis. The conclusion of the analysis report is that discharge occurs between the contacts A and B of the arc extinguishing chamber.

4 Preventive Measures

Strengthen the procurement and usage management of SF₆ gas, and strictly carry out work in accordance with the requirements of the operation instruction manual and maintenance regulations during the maintenance operation process. During the replacement and installation of the arc extinguishing chamber, effective dust prevention measures should be taken. When holes, covers, etc. are opened, dust covers should be used for sealing. If the installation site environment is poor and there is a large amount of dust, the installation should be stopped.

5 Conclusion

Worldwide, there has been no occurrence of such a fault in this type of circuit breaker when it is in the open position. This fault can be attributed to an accidental coincidence or, more likely, influencing factors beyond normal statistical faults. This power plant is a pumped-storage power plant, and the unit frequently switches between the power generation and pumping conditions every day with a large number of operations, making it impossible to conduct a direct comparison. For a more in-depth investigation, transient recorders should be installed on both sides of the circuit breaker to search for possible causes based on the results of long-term observation.