High-voltage power outage
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What are the common causes of power returning immediately after a high-voltage outage? Is it the protection of the high-voltage cabinet, or does the power go out momentarily due to a fault outside and then come back on? If it’s protected by the high-voltage cabinet, it should trip, right? The high-voltage cabinet hasn’t tripped at the moment; the fault reported by the high-voltage PT cabinet is metal grounding in phase A. The high-voltage cables in the plant are all placed inside cable trays, and they’re not overhead. Could the experts please explain this? Thank you!
I also want to know why, so I can learn about it.
When power is restored immediately after a blackout, there are several possible scenarios; this list is not exhaustive. 1. After a fault causes the circuit breaker in the substation to trip, the system’s reclosing mechanism takes effect, resulting in power being restored again after the outage； 2. Single-phase grounding of the overhead line causes a sudden drop in voltage, which is immediately restored ； 3. Three-phase or two-phase short circuits in overhead lines cause the voltage to drop sharply before returning to normal ； The metal grounding in phase A you mentioned doesn’t necessarily mean there’s a fault in your factory; it could be a fault somewhere along your incoming line, which has been detected by you. This type of fault is most likely the second type I mentioned.
You need to check whether your high-voltage circuit breaker has under-voltage protection; if not, it won’t trip in the event of a power outage
If under-voltage protection is active, it will trigger a trip; there will be no instant power interruption followed by automatic restoration. The phenomenon he described is that the switch does not move
Yes, I understand; so a sudden power outage doesn’t result in the power coming back on automatically
The phrase \"instant power restoration after a high-voltage outage\" is incorrect; what actually happens is that the voltage drops suddenly before returning to normal, which is known as voltage fluctuation. This usually occurs when the higher-level power grid resets its circuit breakers. But if the PT cabinet can detect metal grounding in phase A, what kind of protection is that?
It is recommended to implement low-voltage protection, as fluctuations in the power grid can be caused by external grounding or short circuits.
Reclosing devices cannot be installed on the switches for internal power usage in factories; reclosing devices are used on power transmission lines. If your cabinet is in the closed position, it means it hasn’t tripped; power outages are caused 100% by fluctuations and arcing in the external power supply lines. High-voltage distribution systems are usually ungrounded. An extremely low voltage on phase A may lead to false alarms indicating a metal ground connection on phase A, but the criterion should also be an increase in the voltage of phases A and B with respect to ground. Check it specifically; the possibility of internal grounding is basically non-existent. Metallic grounding represents a real connection to ground, and it’s impossible for such a connection to not exist.