Tahalilin Kudarwa na 750 kV Tank Type SF₆ Compressed Gas Circuit Breaker

Halayyar da Dukkana
Bayanai na Halayya da Turanci na Iyyarar Aiki Da Dukkana

A lokacin da daga-riga 17:53:50 ta ranar 16 ga watan Mayu, 2016, an yi aiki na hanyoyin da biyu a Jingchuan II Line. An zaɓe B don haɗa, kuma fagen B na ci gaban 7522 da 7520 an yi haɗa. Hanyoyin ci gaban 7522 ya samun abin da ke tsawon da yake da ita, bayan lokaci 0.6s. Kafin haka, fagen ABC na ci gaban 7522 suka haɗa.

A cikin wannan lokaci, hanyoyin dukkana fagen B na ci gaban 7522 ya yi aiki na hanyoyin Bus II, kuma fagen 7512 an yi haɗa, wanda ya shafi jirgin 750kV Bus II. Turanci na iyyarar aiki da yanayin aiki suna nuna a Figura 1. Zama aiki na Unit #1 tana 645MW, kuma zama aiki na Unit #2 tana 602MW. Jingchuan I da II Lines sun yi aiki na musamman. Tsarin step-up substation tana 3/2 wiring, kuma step-up substation tana yi aiki a cikin halin closing loop.

Bayanai na Idashen Halayya
Idashen Yawan Samun Fagen

Idashen yawan samun fagen 7522 tana nuna cewa amfani na mekaniki na fagen A/B/C tana nuna idan fagen tana buɗe, wanda tana "0" position. Tsarin aiki na hydraulic operating structure tana cikin hali na spring compression. Don WB - 2C fagen, fagen A/B/

Don fagen C, idashen yawan samun panel na operation box tana nuna cewa maza TWJ indicator tana sa. Tsari na SF₆ gas pressure na fagen A/B/C tana 0.62MPa (relative pressure), kuma babu nasara mai sauƙi a fagen 7522.

Bayanai na Aiki na Hanyoyi

• Hanyoyin Jingchuan II Line Protection IRCS - 931BM Protection Device: A lokacin da daga-riga 17:53:50:404 ta ranar 16 ga watan Mayu, 2016, aiki na B-phase current differential protection tana yi aiki. Aiki na current differential protection tana haɗa fagen A, B, da C bayan lokaci 767ms, kuma maɗaɗin haɗawa na fagen A, B, da C tana bage a lokacin 825ms.

• Hanyoyin Jingchuan II Line Protection IICS - 103C Protection Device: A lokacin da daga-riga 17:53:50:454 ta ranar 16 ga watan Mayu, 2016, aiki na B-phase current differential protection tana yi aiki, kuma phase-differential tana haɗa fagen ABC bayan lokaci 790ms.

• 7522 Circuit Breaker Protection Screen PRS - 721S Protection Device: Fagen 7522 tana haɗa fagen B. Aiki na follow-up tripping tana yi aiki. Bayan lokaci 0.6s, aiki na reclosing tana yi aiki, kuma aiki na three-trip tana yi aiki. Bayan lokaci 0.15s, aiki na failure-tripping na fagen tana yi aiki, kuma bayan lokaci 0.25s, aiki na failure-tripping na fagen masu sashe tana yi aiki.

• 7520 Circuit Breaker Protection Screen PRS - 721S Protection Device: Fagen 7520 tana haɗa fagen B. Aiki na follow-up tripping tana yi aiki, kuma aiki na three-phase follow-up tripping tana yi aiki. Saboda aiki na reclosing na fagen 7520 tana da takalma 0.9s (don reclose ita da fagen da ke gaba kuma yin hanyoyi na unit), aiki na reclosing ba ta yi aiki ba.

• 7512 Circuit Breaker Protection Screen PRS - 721S Protection Device: Fagen 7512 tana haɗa fagen uku, kuma lokaci na bage na maɗaɗin haɗawa na fagen uku tana 1143ms.

• II-Bus Mother Protection I Screen RCS - 915E Protection Device: A lokacin da daga-riga 17:53:51:258 ta ranar 16 ga watan Mayu, 2016, aiki na failure-tripping na bus-line tana yi aiki.
  

Bincike na Test na Ci Gaban

An yi magana da Ningxia Electric Power Research Institute don binciken components na SF₆ gas na fagen uku na 7522. Components na sulfur compounds na SF₆ gas na fagen B tana da take da standard. Tsari na decomposition product content a gas chamber tana da take, wanda tana nuna cewa ana iya samun high-energy partial discharge, wanda tana ba da cikakken solid insulation materials, kamar yadda ake nuna a Tabula 1.

Ba a bincika breaking-circuit loop na fagen B, an tabbatar da cewa loop tana buɗe, wanda tana nuna cewa fagen tana buɗe. Ningxia Electric Power Research Institute ta yi test na opening time da circuit resistance na fagen A da C na fagen 7522, kuma resultattun test tana daidai da standards.

Bincike Ba Da Sakamakon Da Halayya

Don fagen 7522, an fito SF₆ gas na fagen B, an yi nitrogen purging, kuma an bude door na breaker body. An samun dust (arc-ablation decomposition products) a cikin. Bayan marubucin technicians na ABB factory, an yi disassembly na insulator, kuma an samun 2 broken electrodes. Broken electrodes suna haɗa da outer wall. Connecting rod da moving contact suna nuna cewa akwai ablation marks, kuma mechanism na moving contact tana nuna cewa akwai melting decomposition products. Mechanism na hydraulic spring-type operating structure na fagen tana bincika, kuma tana nuna cewa tana yi aiki na musamman.

Tambayar na Halayya
Prinsipi na Extinguishing na Arc

Ranar da aka fiye da AC arc tana da kyau a lokacin da arc current tana cikin zero every half-cycle. A lokacin da current zero-crossing period, arc tana yi 2 recovery processes:

• Dielectric Strength Recovery Process: Saboda enhancement na de-ionization process, dielectric strength between arc electrodes tana yi recovery gradually.

• Arc Voltage Recovery Process: Power supply voltage tana yi reapplied to contacts. Arc voltage tana yi rise from arc-extinguishing voltage to power supply voltage. Idan dielectric strength recovery process tana da take da arc voltage recovery process, kuma amplitude na arc voltage recovery process tana da take, arc voltage recovery process tana da take da dielectric strength recovery process, wanda tana ba da breakdown of dielectric between electrodes, kuma arc tana yi reignite. Idan arc voltage recovery process tana baya saboda dielectric strength recovery process, arc tana yi reignite.

Kalmomi

Daga bincikan fault recording waveform na CSL103 protection device, bayan fagen B na 7522 tana yi reclose, protection tana ba da three-phase tripping command a lokacin 767 ms, kuma fagen uku na 7522 tana buɗe a lokacin 825 ms, wanda tana da action time 58 ms. A lokacin da arc-extinguishing process na fagen B tana yi aiki, current waveform ba tana cross zero, kuma arc tana yi continue to provide short-circuit current inside the circuit breaker.

Daga bincikan arc-extinguishing performance analysis na SF₆ gas: under the action of the arc, SF₆ gas tana absorb electrical energy and generate low-fluorine compounds. Amma, when the arc current crosses zero, low-fluorine compounds tana recombine into SF₆ gas quickly. Dielectric strength of the arc gap tana recover relatively quickly. Since the arc current ba tana cross zero, arc-extinguishing performance of SF₆ gas tana decrease. At this time, only by activating the circuit breaker failure protection can the adjacent 7512 circuit breaker cut off the fault current. The time from the three-phase tripping position contact of the 7522 circuit breaker returning to the three-phase tripping position contact of the 7512 circuit breaker returning was 317 ms in total, indicating that the high-energy arc of the B-phase circuit breaker burned for 317 ms. After the 7512 circuit breaker opened, the arc was extinguished.

In conclusion, the line protection and circuit breaker failure protection in this event both operated normally, and the circuit breaker tripped normally. The actions of primary and secondary equipment were all correct. For the B-phase of the 7522 circuit breaker, from the gas composition analysis, there was high-intensity energy in the arc-extinguishing chamber, which was sufficient to increase the gas pressure. However, the current of the 7522B phase did not cross zero, and the arc was not extinguished. But the valve of the lower compression chamber had been opened, and the excess gas was discharged from the lower part, which might carry the arc out and burn out the insulating tie-rod of the moving contact and the shunt capacitor.

Tambayar na Sababin Burn-out na Closing Resistance na Circuit Breaker da Breakdown na Uniform Shielding Cover on the Outer Side of the Resistance

Operation of the circuit breaker is the cause of most switching over-voltages. Installing a closing resistance can effectively limit the over-voltages during line closing and single-phase reclosing. The 550/800PMSF₆ gas-blast circuit breaker manufactured by ABB Company used in our company has a closing resistance composed of stacked silicon carbide resistance plates. According to the manufacturer's instruction manual, the heat capacity of the closing resistance is as follows: when closing 4 times at 1.3 times the rated phase voltage, the time interval between the first two times is 3 minutes, and the time interval between the last two times is 3 minutes; the time interval between the two groups of tests (front and back) does not exceed 30 minutes.

The breaker has a series-type break structure, which consists of 3 main breaks, 1 auxiliary break, and a combined closing resistance, as shown in Figure 2. The main feature of the series-type break is that during the closing operation of the circuit breaker, the auxiliary break closes after the main break in the arc-extinguishing chamber, and during the opening operation, the auxiliary break also separates after the main break in the arc-extinguishing chamber.

That is, the action sequence of the auxiliary break is closing later and opening later. Its working principle is as follows: during closing, the main break closes first, forming a current-conducting loop in series with the resistance, and the closing resistance is connected. After about 8-11 ms (according to the manufacturer's instruction manual), a current-conducting loop is formed through the closing contact of the auxiliary break, short-circuiting the closing resistance; during opening, the main break disengages first, opening the main current loop, and then the auxiliary break separates.

Therefore, the auxiliary break carries the rated current and the short-circuit current during opening. After the B-phase mechanical opening, the closing resistance is connected to the circuit. Since the arc between the B-phase breaks lasted for 317 ms through the closing resistance, and the arc current was approximately 1620 A, according to the calculation, the heat capacity borne by the closing resistance was greater than its rated capacity. This led to the over-limit heat capacity of the connection ring between the closing resistance and the auxiliary break, eventually causing fusing, discharging to the outer-wall grading ring, resulting in the breakdown of the grading ring and the blackening of the resistance.

Tambayar na Sababin Operation of Circuit Breaker Failure Protection

In circuit breaker failure protection, when the current element is activated and meets the failure protection criteria, the failure protection will be initiated as long as the protection trip input is received and the corresponding phase current is greater than 0.05 In.

As can be seen from the reports of 7522, from 775 ms when the PRS-721S protection device of the 7522 circuit breaker protection panel received the three-phase trip signal input from the IRC-931BM protection device of the Jingchuan II line protection, to 925 ms when it tripped the local circuit breaker due to failure, and to 1025 ms when it tripped the adjacent circuit breaker due to failure, with a delay of 0.15 s for tripping the local circuit breaker and 0.25 s for tripping the adjacent circuit breaker respectively, which is in line with the operation logic of failure protection, and the protection operated correctly, as shown in Figure 3. In the oscillogram, it can be seen that although the B-phase tripping position contact of 7522 had returned at 825 ms, there was still current (arc) flowing between the moving and stationary contacts.

Kalmomi

• Due to the severe distortion of the fault current, the waveform shifted to the lower side of the time-axis. The fact that the waveform did not cross zero within the effective arc-extinguishing time of the circuit breaker was the main reason for the non-extinction of the arc. The failure of the gap insulation to recover after the circuit breaker opened and the decline in the arc-extinguishing performance of SF₆ gas were secondary reasons for the non-extinction of the arc.

• The non-extinction of the arc and the expulsion of the remaining gas from the arc-extinguishing chamber, which carried out the arc, were the main reasons for the blackening of the insulating tie-rod and the outer wall of the capacitor.

• After the mechanical opening of phase B, the closing resistance was connected to the circuit. Since the arc between the breaks of phase B flowed through the closing resistance for 317 ms, the heat capacity caused the heat capacity of the connection between the closing resistance and the auxiliary break to break down, eventually leading to fusing, discharging to the outer-wall grading ring, resulting in the breakdown of the grading ring and the blackening of the resistance.

• The presence of arc current in phase B and its compliance with the operation logic of the circuit breaker failure protection were the main reasons for the tripping of the busbar.