Field Situation and Analysis of Capacitor Cabinet Explosion Accident in Substation

2023-08-29 16:45:52 曙熔

1. On-site phenomenon:

1. There is a car wash outside the wall of the power station, and there is a lot of water vapor. There are fan holes on the wall of the power station that communicate with the car wash (but the wind is blown out from the substation).

2. The temperature and humidity in the substation are very high, especially the humidity is high (temperature 31 degrees, humidity 60% --- 2014.08.06. morning, rainy, it is said that the temperature is above 40 degrees at ordinary times), in the capacitor cabinet that has been powered off The wire on the left is covered with dew, but the wire on the right is dew-free.

3. When the damaged fuse box was disassembled, it was found that a fuse had burst into multiple petals, and there was a hole in the upper magnet.

4. The insulating partition (lower partition) between the burst fuse and the adjacent fuse was burnt out a gap, and there were signs of short circuit between the two fuses.

5. After the blown fuse base and the upper part of the adjacent fuse base are measured with a megger, the insulation resistance is Zab=2 MQ, Zbc=2 MQ, Zac=5 MQ; the insulation resistance of the lower part is average It is 500MQ.

6. The insulation resistance between the burst fuse box grooves was measured with a megger afterwards, and the upper and lower parts were both 500 MI. Even the black carbonized part is insulated (the shaker is in an open circuit state) and not short-circuited.

7. The left and middle phases of the first group of fuses from the left in the upper row are normally on and not blown, and the right phase is blown; the left and right phases of the second group of fuses from the left are blown, and the middle phase is not blown.

8. After testing, the contactor under the fuse is normal, and the compensation capacitor under the contactor is normal. That is, there is no phase-to-phase short circuit under the load of the fuse.

9. The insulation resistance between the wiring terminal below the fuse and the grounding terminal row PE of the box body is 500M. The insulation resistance between the upper terminal and PE is 2 megaohms (measured with a shaker)

10. About 6 cm away from the base of the fuse is a three-phase bare busbar, and a short circuit between three phases has occurred at the left end of the busbar. There are obvious melting defects in the lower left corners of the left ends of the three bare copper bars.

11. The color of the upper and lower ends of the blown fuse is severely discolored, and the color discoloration of the lower part is more severe than that of the upper part, which is caused by overheating (it is caused by poor contact without being clamped after the fuse is inserted).

12. The blown fuse The connection screw of the lower incoming line has poor contact. It can be twisted when tightened, but it can only be twisted half a turn (tightened with a screwdriver).

13. The adjacent fuse group on the left side of the exploded fuse was also affected, the fuse holder was damaged, and the appearance of the fuse was also slightly damaged.

14. After the three insulators at the short-circuit blasting part of the three-phase bare busbar are removed, they have not been broken down by the megger, and the insulation is good.

15. There are serious color traces after arc discharge on the side of the distribution cabinet close to the end of the three-phase bare busbar.

16. The left two of the three wires that supply power to the first group of fuse seats near the bare female discharge power have been blown out, leaving only the right one. 

17. It is impossible to measure whether there are harmonics and how large the harmonic current is.

18. Other fuse holders that have not failed also have the phenomenon of yellowing and discoloration of the base due to poor contact at the fuse insertion point.

Second, the reason analysis:

1. There are two parts of the blown fuse that have been in poor contact before the fault occurs, one is the lower wiring bolt, and the other is the lower end of the fuse where the knife is inserted (here the spring snap ring has been overheated and burnt short), There are serious overheating and discoloration phenomena (of course, what you see now should be the superimposed effect before and after the burst), and the contact resistance caused by poor contact and loosening will lead to severe overheating until arc discharge, and the arc will make the insulation barrier next to it The plate burns out a gap, and then the arc passes through the gap to the adjacent fuse inserting knife, and then a phase-to-phase short circuit occurs.

After the phase-to-phase short circuit, the fuse should have been blown quickly, but the fuse failed to blow instantly due to quality problems. The internal arc extinguishing failure caused the excessive pressure of the combustion gas inside the narrow fuse to cause the fuse to burst and spray arcs, and the solitary light was sprayed to a distance of about 6 Centimeters of exposed copper bars lead to phase-to-phase short-circuit discharges of copper bars.

2. The indoor temperature of the substation was too high. It rained on the morning of the 5th, and the indoor temperature was 31 degrees, and the normal indoor temperature reached above 40 degrees. Exceeds substation specification requirements. Has a long-term effect on the insulation properties of electrical components and shortens the service life of the equipment. needs improvement.

3. The humidity in the substation is relatively high, which has exceeded the limit humidity of the national standard. The water molecules and gas molecules in the air can easily form an adsorption film on the surface of the electrical contact, resulting in poor contact. needs improvement.

4. After repeated measurements on the base of the exploded fuse and its surrounding connecting parts, there is no phase-to-phase short circuit or short circuit to ground under the fuse and under the load, and the lock-load short circuit is caused | There is no short circuit phenomenon in the upper and lower port bases.

5. Regarding whether there is a large harmonic current in the compensation capacitor circuit, it cannot be measured and judged without relevant instruments. Its impact on the accident could not be assessed. But if it exists, the cause of harmonics is not ruled out.

6. All of its contact numbers on the Internet are empty numbers.

in conclusion:

1. Poor contact at the inserting part of the fuse is the cause, and the quality problem of the fuse itself is the main cause. The fuse is produced by XXXXXXXX Co., Ltd. It is necessary to conduct further investigations on the quality of this product.

2. The high temperature and high humidity of the power station has exceeded the requirements of the National Electrical Code GB7251.1-2005. needs improvement. However, high temperature and high humidity are not believed to be the main cause of the accident.

3. As for the existence of harmonic current, it is necessary to use professional instruments to measure, but the conditions are not yet available, so it is impossible to make an assessment of the impact on the accident.

4. Problems such as poor contact of existing wiring screws need to be rectified and tightened. However, it is not believed that loose screws were the cause of the accident.

5. After the fuse is inserted, it does not clamp itself tightly. The overheating of the fuse caused by it is a great hidden danger and needs to be rectified.

6. The meter used in this measurement is the project’s own meter, and the meter was borrowed from an external unit to conduct a recheck measurement afterwards. The measurement results of the two meters are consistent.

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