Within the last three days. One in evening and once in morning, The lights shut down for about 1/4 second. The event in the evening caused my computers operating system to re-boot, but the clocks were unaffected. The morning event cause the lights to blink and a ceramic heaters fan to stop and start, also in a fraction of a second, but with no op/sys re-boot. It seems like there was a momentary brownout condition.
Anybody come across this? What might be the cause?
Dave M.
Probably voltage sags (dips for the europeans). They are quite common. Cause? Usually a fault on a adjacent distribution circuit. This is a pretty simplistic answer but this topic has been the subject of many reports and even books so this discussion could be very long and tiring.
Charles Perry P.E.
Any number of things. A fault elsewhere in the system that is quickly cleared by a fuse or breaker can momentarily 'dip' the voltage like this.
Another *possibility* is the utility deliberately doing some 'dead-bus' switching to align substation or feeders differently for maintenance. Sometimes they can't parallel two feeders into a substation so they set it up for the secondary feeder to close as soon as the primary opens. Then they just open the primary, and bang, the secondary shuts. Lose power for about as fast as the breakers can operate (
That is the reason I bought a UPS. It is very common here (Fla) to see these little blinks.
What problems are caused for large industrial/commercial operations if one phase of a 3 phase feed fails? (motors etc.) I figure this must be fairly common and something must be done to protect against it (special circuit breakers that open if any phase fails?)
Well, I've seen it happen, but its not *that* common. Three-phase breakers and such will open all three phases if there is a fault on any two (or a trip signal from relaying such as ground-fault).
But yes, there are special 'phase-imbalance' and loss-of-phase relays that will detect a loss of one phase and shutdown a motor or other devices. But they don't seem to be the norm on a lot of the industrial equipment I've worked with.
A loss of one phase will show up as motors not starting, just sitting stalled, and running motors draw more current and trip on motor overloads a lot. Depending on the building, you may even lose 1/3 of the lighting and
120V outlets.daestrom
Dave M.
Some circuits may still be set up for "instantaneous reclosing". That is that when a fault is detected and the circuit breaker trips then it is immediately automatically reclosed. The time involved is the open-close time of the involved circuit breakers and is typically around 10 cycles for a high voltage oil circuit breaker (1/6 seconds) but longer for distribution breakers. The downside is that on a transmission line the arc products may not have dissipated and the reclose is into a short circuit. This is not an issue for distribution feeders since subsequent delayed automatic recloses (eg. 15, 30, and
45 seconds) will work when lightning or arc products have dissipated or when the short has been burned free. It is a problem on the bulk power system since it promotes instability and I assume that most instantaneous reclosing has been removed.Regards,
John Phillips
That one "rings a bell " .
Me too, after these episodes.
It is very common here (Fla) to see these
This seems a likely scenario too.
The downside is that on a
Generally, the single phase is opened on the upstream side of a DY transformer, which limits the effect upon a motor.
HR.
Is your utility Con Ed in NY? If so, it was the wind. Lots of recloser activity going on. My PC's kept going (on a UPS), but the lights blinked off/on several times the first day, once the second day.
I am in western NY. It's not Con Ed in my locality, but I think you are on the right track (if not on target), connecting the symptom and region. We might be buying from Con Ed, but I thought it was Niagara and a local Nuclear plant that provided our power.
I don't get power interruptions in general, so I hope the UPS wasn't just a panic buy.
Dave M.
Hi all, my apologies if people have already discussed this, as Ive just found this thread. It seems to me that everyone has looked at the high tech possibilities, and I suppose that they are possibilities, however, the most common reason for dips/sags/flicker on the power grid is motor starting. Sometimes capacitor switching at the Utility substation for voltage support will also do this but it is unlikely since this is something that is calculated so voltage steps are small during switching. Essentially, during a motor start, the standing rotor appears like a short to the distribution network. As the motor gathers speed, its current draw reduces and its electrical response changes. This is the reason for motor starting devices like star-delta starters or transformer starting which effectively reduce the current draw at start.
The most likely reason that a motor starting elsewhere on the distribution network is noticible to other users is that the motor (and its starter) is larger than what the electricity distribution system can withstand. In Australia we have a set of flicker limits and we check all large motor starting against the limits before permitting their connection to the distribution network. Perhaps this has not been properly done in Dave's area. If, as Dave suggests, the flicker occurs at the same time every morning it is highly likely that this is a motor start for say water pumping for irrigation at the local park, or perhaps sewage pumps. Largish air conditioners will also cause flicker.
Australian law permits the utility to disconnect a consumer who's power consumption is negatively affecting other consumers. I suppose that the laws are similar elsewhere and if the flicker is annoying, as someone suggested in regard having to continually adjust clocks, then complaining to the Utility might help. Of course, the flicker might be caused by your own equipment on your own property, so check this out first.
My 2c worth Paul
Quite true, even for the most part here in the US. The problem here is that there are large, intermittent demand loads in both industry and some research facilities that must, under US and state law, be serviced by the utility provider. For example, if you live in the vicinity of an aluminum plant or a foundry using electric arc furnaces, their starting demand by be far greater than that of the entire community. The same holds true for certain government research facilities, such as those containing large particle accelerators and/or fusion research facilities, Forrestal Research Center in New Jersey, as an example. Transit system are another large, intermittent demand user (the Washington, DC Metro system demand exceeds that of the balance of the entire Washington, DC area.)
That said, it is the legal responsibility of the utility to provide generation and distribution system that meet such demand, while maintaining voltage and frequency within the proscibed limits.
If the OP is failing to receive such service from his utility provider, it is entirely incumbent upon the utility company to resolve the problem.
Harry C.
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