Werid Mains power effect today  - Page 1
Forum section: electronics / beginners

author: MathWizard
author_rank: Super Contributor
timestamp: January 06, 2021, 02:03:59 am
content: Today I was in my room just surfing on PC, with 3 low wattage 15W CFL, and my Siglent 3065X running. And then the CFL coil type light started getting dimmer, then normal, then dimmer...about maybe every 3-5-8? secondsAnd the Siglent SDM3065X, it's FAN, is also changing pitch, sounded like maybe 1/2 -1 step in pitch, but it sounded like a lot.So I changed the DMM to ACV and plugged into a free cord, connected to the plug all or most this is on, and the voltage was going from the normal 118V, to 111V, about every few seconds. This whole thing, lasted 1-2 minutes, and I've never seen this happen in any house, with new or old wiring.I went to another room to check a plug but by that time it seemed to stop, the light was normal, and the fan was normal. I find it odd the fan speed changes so noticably from 111V to 118V.I asked my roommates if they saw it, like just 3-5 minutes after this happened, and she said she had her hair dyer going right at about the same time. But never saw the quite obvivious light level changes I was seeing. I didn't ask how long she had it on for.But how much of this, is me with my PC SMPS, 3x CFL's w/ SMPS's, and the Siglent DMM w/ SMPS........and the lady running the hairdryerThis never happened when the clothes dryer is on...or other motors, or anything else.So what the hell happened today? Was it my street transformer and something from outside ?? Can old wiring do this ? Was it some wacky thing between my PC's SMPS and her hairdryer ? It's not on the same circuit breaker. I was just reading on the internet, so not much load at all on my part. And no electric heat, or other motors were on.Then I went to set a portable DMM to record the min AC voltage for the next while, but rather than record the min Vrms, it just told me the lowest voltage below zero...DOH

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 06, 2021, 05:04:03 am
content: Shrug, maybe someone was having a bad day. Could've been a neighbor's heater going crazy, could've been a more distant but much larger (industrial?) customer. Probably not a line fault, reclosers are only supposed to cycle a few times.Maybe it was even some crusty wires in your house. Which, if you can manage to repeat the observation but also log voltages elsewhere in the house proving it's local, that would be a chilling discovery, heh.Tim

author: amyk
author_rank: Super Contributor
timestamp: January 06, 2021, 06:24:03 am
content: That's only around 6% change in voltage, well within the tolerances for which devices are built.It could be someone nearby doing some brief arc welding.

author: innkeeper
author_rank: Unknown
timestamp: January 08, 2021, 09:31:40 am
content: i have a solar farm up the road from me and I will see this happening during the day, though, i always assumed its both phases. I never checked both.

author: Whales
author_rank: Super Contributor
timestamp: January 08, 2021, 09:49:10 am
content: Rooftop solar voltage rise is certainly an interesting theory. Scale of minutes and a gentle rate of voltage change makes sense (clouds).

author: Syntax Error
author_rank: Frequent Contributor
timestamp: January 08, 2021, 12:03:40 pm
content: Did you measure the AC frequency? Some defect somewhere may have sent your grid frequency out of phase?

author: Zero999
author_rank: Super Contributor
timestamp: January 08, 2021, 01:28:15 pm
content: Quote from: innkeeper on January 08, 2021, 09:31:40 amQuote from: Whales on January 08, 2021, 09:49:10 amI wouldn't have thought it would be due to solar, since the orignial poster is in Canada, where's there's very little solar energy, at this time of year. A large load, such as a heater, turning on and off, is more likely.

author: innkeeper
author_rank: Unknown
timestamp: January 08, 2021, 02:46:23 pm
content: I am near the canadian border, and we have a lot of solar farms here. I guess solar doesn't work across the border

author: SeanB
author_rank: Super Contributor
timestamp: January 08, 2021, 03:42:29 pm
content: Automatic voltage stabiliser somewhere upstream of you was operating to make the voltage downstream comply with specifications, so was sitting right at the point input and output wise that it was oscillating between 2 tap points in the tank of the transformer. Either there was a load change downstream that shifted the point to outside this narrow band of oscillation, or likely a PLC controller noted that there were too many tap changes over a period and disabled the automatic control, or switched it to a less sensitive range instead. Very common thing, but often not noticed much as the voltage change is not enough to see, unless you are at a low voltage point and the system flips in and out of the minimum supply voltage range. 111VAC is very close to the low level for 125VAC systems, and in most countries the way that they harmonised various voltage systems was to pencil whip the loowed voltage range, as changing out thousands of transformers is expensive.Thus I have a nominal 230VAC mains, which runs pretty much always at 238VAC, and upcountry the old 250VAC systems run at around 256VAC at low load, which was about the lowest the taps could be set to. New transformers get set to the old system ratio, because they often can be interconnected on the primary and secondary side, so have to match exactly. Nobody wants to be near a 1MVA transformer when it's companion 200kVA unit wants to circulate 6kA in the cabling, because there is a 3V difference in terminal voltage, and resistance is in the milliohm range, along with impedance.

author: tszaboo
author_rank: Super Contributor
timestamp: January 08, 2021, 03:59:56 pm
content: Quote from: innkeeper on January 08, 2021, 09:31:40 amSolar inverters have to switch off their output, if the voltage on the line becomes too large. This is a technical and legal requirement and all inverters are sold with this. Now depending on the inverter's control algorithm, if may reduce the generated power gradually, or just switch off completely. It makes it worse, if you have more than 1 inverters on the same line, they might play ping-pong who generates power and other issues like this. It's a distributed system and it was designed, so power flows in reverse (from your nearest coal power plant to your house) and not the other way around. So transformers are also sized that way. Inverters switch off all the time, few years ago I saw a study that 5-10% of Belgian installations had this issue.The DSO needs to install thicker cables, so there is less voltage rise/drop on those lines. But guess what, that costs money.

author: MathWizard
author_rank: Super Contributor
timestamp: January 30, 2021, 06:19:20 pm
content: It's the winter time here, and it's happened 2 more times that I know of, once before the girl with the hair dryer went to work, and another time in the night.Same effect, my low power CFL bulbs get abruptly dimmer, than a few moments later, abruptly returns to normal. I noticed it almost right away (I'm a long time veteran of BattleField games, so my senses are on the edge).I measured it again but only in my room, at 116V normal to 109/110V. Out in the kitchen was a steady 116V but maybe it was over by then, but the lights in the other rooms looked normal, but IDK if they are they same kind. She's on another floor, IDK what the wiring in this house is or if it should even matter.If it happens in the morning again I'll ask her. I have no idea why the voltage changes from 1 level to the other, much more like a squarewave, relative to the few seconds it's rms is stable. The rise/transistion time must be tenths of a second or so.I have a HV differential probe, next time it happens, I'll try to record it.

author: TimFox
author_rank: Super Contributor
timestamp: January 30, 2021, 06:28:01 pm
content: Your roommate was running a hair dryer at the time of the problem. Was it set to a lower power heat level? Some dryers do that with a series diode, which puts a dc load on the mains supply.

author: Zero999
author_rank: Super Contributor
timestamp: January 30, 2021, 06:49:22 pm
content: Quote from: innkeeper on January 08, 2021, 02:46:23 pmBut in the middle of winter? Yes, the solar farms will still generate some power at this time of year, but is it really that much it could have such a big impact? I doubt it.

author: Jwillis
author_rank: Super Contributor
timestamp: January 31, 2021, 11:45:19 pm
content: Welcome to Canada . Depending on were you live it's really not unusual to have intermittent brown outs. Weather can have a real impact on your service in this country with sudden changes in temperature , humidity , high winds , precipitation , over hanging trees ,ect . Here on the prairies , brown outs are common . There can be atmospheric electrical discharges with out a storm and weather conditions can change suddenly without any forecast. And any of these changes or events don't need to be local. Service lines can be hundreds of kilometres long from supplier to customer .But you can check a few things yourself aside from the weather.Check that individual circuits are not being overloaded .Faulty circuit design, like a corroded circuit breaker, bad main terminals, or faulty neutral wires, etc.Large electrical power draws. These can occur anywhere on your service including neighbours .