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You are watching: Why do lights flicker during a storm


A storm is rolling through and the lights just flickered. My 5YO asked why and I couldn"t wrap my head around a concise answer and I couldn"t find any help on Google. Can someone provide a technical explanation of this?
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Lightning strikes on the high-voltage lines hundreds of miles away can cause a slight surge in your voltage.High winds can cause intermittent opens which will cause the light to blink off.
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Like as not, a breaker pops somewhere in the network and an alternate circuit kicks in to keep the area supplied.
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There must be one of them cut offs in our neibourhood as sometimes you will see a flash a good way away then a stupidly loud massive bang then power goes off for a few mins. The lightening bang comes just after the bang from the power line breaker or what ever it is.
There can be several causes of flicker. At the distribution level (technically less than 69 KV but usually no more than 35 KV), flicker is primarily caused by substation breaker or recloser operation. Typical breaker or recloser operating sequences go something like this: Trip,close,trip,close,trip - wait 15 seconds, close, trip - wait 45 seconds, trip to lockout (no reclose at this point). The initial trip,close,trip,close timing is "no intentional time delay". That is to say that the speed of the reclose after the first two trips is governed by the mechanical limitations of the device. Oil breakers and reclosers tend to be slower than vacuum breakers as the movement of contacts under oil is slowed by the presense of the oil. The idea is to interrupt energy to a temporary fault (tree branch brushing the line, two phases slapping together due to wind or other mechanical influence, or, as previously mentioned, the operation of a lightning arrester) very briefly and reclose immediately (in hopes that the fault clears). However, if a fault is still present, the device immediately trips again and tries to reclose again. These will appear to be "flicker" at the service voltage level (120/240 volt) as these trip/close cycles are anywhere from 2-6 cycles (1/30th to 1/10 of a second). The really quick ones will have you wondering if if happened of if you merely blinked. If, at any point during the trip-close-trip-close-trip-close sequence the fault clears, the power simply stays on and the device resets itself back to the state to where it will trip-close-trip-close as previously described. If the fault reoccurs before the reclosing relay resets, it will resume operation in the state it was last in.Lightning strikes on distribution lines introduce a (higher) voltage on the line and this would manifest itself in a slight brightening of the lights and is generally not very noticeable. But this is very short-lived anyway as modern MOV arresters are very fast and there are usually a number of them that operate simultaneously to bleed off the voltage surge. However, when an arrester is driven into conduction, it looks like a fault to breakers and reclosers and the aforementioned proccesses kick in. This is called "follow current" and the ability of an arrester to return to its steady state very quickly is important. The reclosing relays will have different duration/current (more commonly referred to as "time/current") settings for the steps in the trip-close sequences. That is, the first two trip-closes are more sensitive than the third and fourth trips. Whereas, some may not even notice the first two events, the third trip is more noticeable as it allows more current to flow to the fault for a longer time before tripping. After that, it"s very noticeable because, well, you"re going to notice the lights being off for 15 seconds or more. Utlity operating people refer to this as something like "2 "A" curves and 2 "B" curves). Keep in mind that these faults can be behind fused cutouts. The reclosing relays are coordinated with downline fuses to also allow faults to clear downline beyond one of these fuses. You can also get flicker at the secondary level (120/240 volt) if you have open-wire secondary. Trees and wind can interfere with the bare conductors and cause the voltage to collapse without blowing the transformer primary fuse or tripping the secondary breaker of the transformer (if so equipped). Transmission lines (69 KV and up) generally are of shielded construction in areas where lightning is common. In these areas, it would be very rare for a lightning strike on a transmission line to be detectable at the distribution level, let alone is your home.I figure you"re sorry you asked by now. And to think, this is my super short explanation.

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