It kind of makes sense that you would get extended outages during a thunderstorm. Lightning might hit some power company equipment and blow it out, or a tree might fall on the lines and break the circuit. But today we had a bad storm and in the middle the power blipped and went out for only a half-second or so. Just long enough to reset all the clocks.
What is happening here?
Precisely what you wrote about. Somewhere within your part of the regional or national grid, something happened. It was detected and power was rerouted. In that split instance of rerouting your power, you lost it and had it restored. However, the instance was long enough to cause your clocks to reset.
IANAE, but that is what was explained to me by someone who is.
It’s almost certainly the switching of an ABT (automatic bus transfer). One source of power was lost, and an automatic bus transfer switch automatically switched so as to receive power from an alternate source. ABTs are generally “break-before-make” switches so that the two sources are not inadvertently paralleled. The split-second break in power is what you are seeing in your house.
Storm related momentary outages occur when the individual feeder the customer is on experiences a fault of some nature.
This could be a emporary short circuit or a temporary ground fault,or a lightning shot------it depends on the circuit configuration--------for instance a delta ------or a 4-wire y.
It could also be a momentay outage in the primary circuit to a substation----the possibilities are endless.
At any rate the protective relay system trips the breaker on the feeder, the recloser puts it it back on and if the fault has disappeared the feeder stays on ,
If the fault is still there it’ll probably try twice more at time intervals and after that you’re ion the dark.
Basically[very]that’s the story.
I wish he public had never heard the word GRID---------it has resulted in more mis-information than a politicians promises
EZ
The way it was explained to me is thus:
When a lightning bolt hits the earth, the bolt ionizes the air around it, making the air conductive to more electricity. Automatic sensing equipment can detect an unusual flow of electricity from the power lines to the surrounding environment and briefly interrupts the flow to prevent arcing. As soon as the ionization dissipates, the power is restored.
One morning a few weeks ago, well after a thunderstorm, my power blipped out five times. I called the power company and they said it was probably due to a tree branch brushing up against a line when the wind blew. I assume this happens during thunderstorms, too.
Protective devices can trip for all sorts of reasons. One of the most common reasons is in fact when a tree blows against the lines, or the lines blow against each other. Either condition creates a fault which trips the circuit protectors.
Wind is precisely the reason reclosers were invented. Wind is your textbook source of temporary faults. Give the wind a second or two to die down, and the fault goes away. Wind isn’t the only cause of temporary faults. For example, lightning can cause overcurrents and also trip protective relays. The reclosers don’t really care what caused the fault. They just try to fix it. You can think of a recloser as an automated breaker flipper on-er. If the breaker flips off, the recloser flips it back on.
Reclosers are typically designed to attempt to re-estabish the circuit once after about a second, and if that fails, it tries again a couple of seconds later, and if that fails, it waits about 30 seconds then tries again. If all three attempts fail, then it gives up and intervention by the guy in the truck is required to make your lights come on again. The number of retries and the time intervals between each may vary for your location.
Hoorah!—somebody else out there has worked with feeders.
If the momentary fault is intermittant at more than ,say,three minute intervals the ‘on and off’ cycle can go on all day------or more!
Furthermore the “grid” isn’t even in the picture.
It is interesting to note that some of the modern breakers have an instantaneous reclose that is so fast it has to be retarded to avoid seeing the same fault before it clears.’’ I’m talking fractional parts of a second for close-trip-close.
But enough-let’s get sosme more “salts” into the mix.
OL 'EZ
Yep. I can’t find a reference online (I’ve got my handy copy of the Electrical Engineers Reference Book), but typically, automatic reclosers will attempt to restore power almost immediately. If the fault then still exists, the reclosing system will wait, say, ten seconds and try again. If the fault persists, the system will try again after maybe a minute, and if there is still a fault, it gives up and notifies the utility of a problem.
One should not forget that if the current present in the fault is high enough[ as in a ‘bolted’ phase fault] there will be no reclosing action and the feeder is"off short".
At high current flow the recloser is disabled by the sensing relay--------and darkness prevails for the customeer on that feeder until the cavalry arrives.
Keep in mind that high-speed reclosing (as quick as 3 cycles) is generally used on transmission and that the normal distribution feeder is on delayed (typically 20-30 seconds) reclosing. The reason that most distribution feeders are on delayed reclosing is to allow isolating devices to function (i.e. fuses, isolators. etc.). This is commonly referred to as coordination and, especially in the case of fuses, high-speed reclosing may not allow enough time for a fuse to ‘clear’. Each fuse has a characteristic melting curve and high-speed reclosing may not allow enough time for the fuse to melt before the circuit is re-energized. You will generally not notice high-speed reclosing as anything other than a ‘blip’.
Another point is that the amount of times a circuit tries to reclose is entirely dependent on the individual utility and is predicated on a number of factors. Isolators ‘count’ the number of operations on a circuit and open on a preset number. Thus, if you have 2 isolators on a feeder the one furthest from the substation may operate on the second breaker operation whereas the one closest to the substation would operate on the third and the circuit would ‘lock-out’ on the forth. Advances in ‘intelligence’ have pretty much eliminated the need for newer isolators to ‘count’ operations as the newer models can sense fault current beyond and ‘talk’ to other isolators and even the circuit breaker. Circuits with these types of isolators generally only operate twice before lockout. Unfortunately, these devices are relatively new and there are enough of the older units out there that chances are (especially if you’re in a rural area) that you won’t see the benefits. The cost of upgrading is generally prohibitive unless there are other considerations driving it.
As to what is being reported to the Dispatch center, pretty much everything that happens is recorded or reported in one way or another. SCADA (Supervisory Control And Data Acquisition) logs pretty much everything that happens, both on the transmission and the distribution lines and substations. If a circuit experiences an R&R (Relay and Reclose) an alarm will sound notifying the dispatcher of the event. There are alarms for nearly everything; lock-outs; sudden pressure (normally associated with a through-fault in a station class transformer), high oil temp, loss of station power, operation of an ATS (automatic transfer switch), high/low voltage, etc.; even the loss of an air conditioning unit in a control house. In addition, most dispatch centers also have a logger stream that records and prints all operations and alarms in real time. I suppose that there are a few smaller utilities that do not have modern SCADA systems, but most utilities do.
There are also those instances where lightning will strike a circuit but will not cause the circuit to operate. A lightning arrester (there is one on the transformer located on the pole outside your house or on the riser on the pole with your underground dip) is designed to act like a pressure relief valve. On a 12KV wye circuit (7200 volts phase to ground) each conductor would have a 9KV arrester attached in parallel with the transformer. The circuit will not even see the arrester if the voltage is under 9000 volts, but should the voltage rise above 9000 volts (such as during a lightning strike), the arrester will shunt the voltage to ground. If the strike is far enough from the circuit breaker, the breaker might just see it as excess load and won’t operate. In these cases, you may see a dip or a short duration outage, but the circuit won’t operate.
Fiat Lux,
Generally I believe that most distribution feeders have an instantaneous try built in to the circuit. if the mechanism is one of those old time motor operators there is
Natural delay until the mechanism linkages reset.But if it is a solenoid operator,or compressed air, the reclose can come in about 3 seconds,or less in some cases.
And with that reminder ol’ EZ is leaving the building!
G’nite Y’all