when there’s a lot of wind or rain, and the lights dim or flicker for a second, and then immediately kick back on, what is actually happening? I’m asking because it seems like if the power is going to disconnect, it would be from some wire breaking or something. So what is happening when it almost goes out, but it doesn’t?
In: Engineering
That’s a form of a brownout, which can be intentional or unintentional. Typically this happens when electrical demand is close to or above electrical production. A line didn’t break, but something happened somewhere on the grid that is causing increased demand (or reduced production) which results in some things (such as the lights in your house) to not get quite enough voltage to stay fully powered, so they may flicker or dim a bit.
It is sometimes used intentionally to avoid a full blackout. For example, they may shut down or reduce output of a generator that’s having a problem so it doesn’t overload and possibly knock out other generators, causing a larger problem.
Think of a power grid like the road network in a city. When a road gets blocked, traffic is prevented from reaching local destinations, but can re-route through traffic around the block so that it still reaches non-local destinations. Your power grid has similar capabilities. Your power goes out when your “local” power lines go out, or all of the “through” lines to you get blocked.
In addition, there’s some other issues that can lead to more widespread outages, which generally revolve around the system being damaged or taken off line at certain choke points near you (substations, transmission lines).
Could be a tree limb falls into or touched the lines or high winds blow the lines into each other. Causes a large arc and flash at that point, sometimes it’ll be enough to trip a circuit other times whatever cause the arc clears quick enough that you only see a flicker. Happens quite often if you live in a rural area farther away from a power station or substation.
A lot of power grids are designed with automatic fail over. If a part of the grid goes down, say from a blown transformer or a power pole being knocked out, the system is designed to detect that and reroute power through alternate paths. While that system can react extremely quickly, it can’t react as quickly as electricity flows, and the sudden change in load can briefly cause power levels to dip, so the flicker you see is the brief drop in current before the system can compensate.
The flip side of the coin is the people for whom power *does* go out, but only for a few seconds until the system switches over. Their power coming back on is what causes your power to “almost” go out.
The power grid is a constant changing balance where supply must meet demand. All the electrical equipment connected to it is tuned to expect it to be at a set frequency (50hz here in UK) +/- a very small difference.
When supply is interrupted and demand exceeds the load available on the local grid the frequency falls affecting all electrical equipment much of which is very sensitive to small changes in the frequency. Hence lights flicker etc.
Because the grid is very sophisticated and full of mechanisms to prevent blackouts etc then all this can happen and be resolved in less than a second. It is only very rarely things go wrong for more than a second or 2 but that it the point that more serious and blackouts happen because of the compounding problems caused by damage to electrical equipment.
Power grids have circuit breakers, just like your house does. Except the power grid breakers automatically turn back on. The first time they trip they turn back almost immediately. The next time it waits a little bit longer. If it trips too many times it stays off.
When you see the power “almost” go out, it’s the auto-breaker turning back on very quickly.
All electronics have a hold-up time. How long must electricity be lost before it shuts down? Some electronics, with a shortest time, were microwave ovens and VCRs. As indicated by a flashing clock while everything else worked uninterrupted.
If power goes off longer (ie many tens of milliseconds), all appliances simply power off. International design standards for electronics (long before the IBM PC existed) required all electronics to either work just fine or simply power off. Without any damage. One standard was so blunt about this as to put this expression, in all capital letters across the entire low and no voltage areas on charts: No Damage Region. Outages must never damage any electronics.
What protected electronics in a dishwasher, clock radios, central air, refrigerator, LED & CFL bulbs, TV, GFCIs, garage door opener, dimmer switches, microwave oven, recharging electronics, door bell, digital clocks, and smoke detectors? Invisible UPSes?
UPS has one purpose. To provide temporary and ‘dirty’ power so that unsaved data can be saved. To avert a reboot. Nothing more.
What does a surge protector do? Technically accurate answers are tempered by specification numbers. It has a let-through voltage – typically 330 volts. That means it does absolutely nothing (remains inert) until 120 volts well exceeds 330 volts. When does an outage (120 volts falling to zero) recreate a voltage that is approaching or exceeding 1000 volts? Never. Unfortunately many recommendations are only reiterating what advertising, hearsay, or urban myths promote. And ignore all numbers.
Read specification for that type protector. That $3 power strip with five cent protector parts, selling for $25 or $80, only protects profit margins. Superior protection is already inside electronics.
Sometimes a fault does occur. So power may be interrupted. And then restored by AC utility equipment. Generally, this happens three times. If that fault still exists, then power remains cut off.
Dimming can be due to some massive short on some other circuit. As soon as that other circuit disconnects, then lights return to full intensity. Meanwhile, incandescent bulbs can dim to 50% intensity. Even a voltage that low is perfectly good for all properly designed electronics. Because electronics are required to be that robust.
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