Is it possible for the mains to stutter  down and up? (Eg in Aus/NZ/EU/USA) - Page 1
Forum section: electronics / projects

author: ocset
author_rank: Super Contributor
timestamp: January 17, 2018, 09:07:02 pm
content: Hello,We have an offline 40V LED driver with the attached input stage.It comprises a current clamp whose FET takes up voltage during transient spikes.However, if the mains stutters down and back up as shown, then the mains wiring inductance, in conjunction with the capacitor C20, causes a spike of 1000V across the current clamp FET. (this is due to the clamp FET momentarily switching off as it tries to clamp the current inrushing into C20)The attached LTspice simulation shows the 1000V spike across the clamp FET.Do you think this kind of mains stuttering can occur?What would cause it?

author: floobydust
author_rank: Super Contributor
timestamp: January 17, 2018, 09:24:24 pm
content: It is from electric utility breaker reclosing, and switching operations.An overcurrent on a distribution power line is detected and the protective relay will issue a breaker reclosing operation. The breaker opens for several msec to stop an (arc) somewhere, then switches back in. Generally, tried three times before the protective relay considers a hard fault (short) to exist on the power line and goes to lockout, lights out.Switching a power line in/out, or changing feeds also does this.edit: also switching the dist. grid

author: IanB
author_rank: Super Contributor
timestamp: January 17, 2018, 09:26:52 pm
content: Quote from: treez on January 17, 2018, 09:07:02 pmHave you never observed it yourself? It is called a momentary brown-out. All the lights go dim for a moment and then come back to full brightness. Most people have experienced it at some time or another.

author: rstofer
author_rank: Super Contributor
timestamp: January 18, 2018, 12:37:34 am
content: Quote from: IanB on January 17, 2018, 09:26:52 pmBrownouts happen very time my air conditioner starts. But it won't be for a tiny fraction of a cycle, it will be several cycles. The thing is, every computer in the house keeps running. It just doesn't matter. But this is a brownout. The trace jpg shows a subcycle transient, not a brownout.I think the time scale for distribution reclosers is more on the order of seconds, not milliseconds. First it trips, waits a few seconds, recloses and, if it trips again, the cycle is repeated twice more. After the 3rd attempt, the breaker stays open. The count can be higher than 3 but I doubt that it is. If the limb hasn't burned across in 3 attempts, it's probably a more significant problem.https://c03.apogee.net/contentplayer/?coursetype=foe&utilityid=wppi&id=4488The most likely source of a few millisecond transient is when the utility switches power factor correction capacitors. But, again, every rationally designed system on the planet survives these glitches.The problem with the LED driver is the driver design, not the world's utility systems. Even if it were the utility's fault, they wouldn't do anything about it. What you get is what you get.

author: Yansi
author_rank: Super Contributor
timestamp: January 18, 2018, 12:40:44 am
content: Quote from: IanB on January 17, 2018, 09:26:52 pmDoes not happen in EU, at least "here" where I live. The voltage here is very very stable. At least these events are very rare, so that I have never noticed anything like this.

author: coppice
author_rank: Super Contributor
timestamp: January 18, 2018, 12:45:24 am
content: Quote from: Yansi on January 18, 2018, 12:40:44 amIt is quite a rare event in most of Europe, but it happens everywhere. Faults happen, and then they happen you'd better hope the protection systems disconnect the faulty section with nothing more that a brief hiccup or two in the surrounding area. If they don't, the whole area will be plunged into darkness for a considerable period.

author: IanB
author_rank: Super Contributor
timestamp: January 18, 2018, 12:55:18 am
content: Quote from: Yansi on January 18, 2018, 12:40:44 amI think it may depend on which part of the world you are in. When I lived in the UK there were very few brownouts on the mains, but they did occur, for example during heavy snow falls. However, the mains supply in the UK does tend to be much "stiffer" than I have experienced here in the USA. Partly this may be because the low voltage distribution transformers tend to be enormous things weighing many tons and serving several streets, whereas here in the USA the distribution transformers tend to be much smaller and serve only a few houses. In the UK you do not tend to see dips in the mains voltage due to heavy loads starting up like you do here in the USA.

author: tggzzz
author_rank: Super Contributor
timestamp: January 18, 2018, 01:03:18 am
content: Quote from: treez on January 17, 2018, 09:07:02 pmYes, I've seen and suffered from that kind of thing in the UK.The cause was a chattering connection where the feed to my house was connected to the overhead cables in the street.Linesman climbed his fibreglass ladder, tightened the connection and all has been well.

author: ocset
author_rank: Super Contributor
timestamp: January 18, 2018, 06:15:40 am
content: Thanks, of course this is bad news for us as it causes the overvoltage spije to the current clamp fet....its because, as the sim shows, the current clamp actually momentarily turns off during the second on-coming, and this breaks the inductive current, causing the overvoltage.We notice in the sim that adding an RC damper of 10R//10n across the mains bridge solves it,but you wonder on tolerances in the BJT of the clamper, and that a higher damper cap may often be needed.The actual amount of mains wiring inductance has a significant impact on the size of the overvoltage.

author: Delta
author_rank: Super Contributor
timestamp: January 18, 2018, 07:08:36 am
content: Here in the UK our mains often reaches 290v for periods of a few minutes.

author: fourtytwo42
author_rank: Super Contributor
timestamp: January 18, 2018, 07:10:08 am
content: Quote from: Delta on January 18, 2018, 07:08:36 amRubbish!!!!!!!!!!!!!!!

author: fourtytwo42
author_rank: Super Contributor
timestamp: January 18, 2018, 07:13:31 am
content: I was going to say on the subject of reclosers we have very high winds this morning and living in a rural location branches touch lines. The re-closers have done there stuff twice this morning, once 3 times and a second ocasion twice. I remember the re-closing attempt rate is not fixed, I would guess the shortest (first) is only 100mS, then the gaps get progresevely longer, perhaps 250/500mS etc but I have never experienced more than a second, obviosly the branch or whatever on the 11/33Kv is blown/burnt away by then!

author: tggzzz
author_rank: Super Contributor
timestamp: January 18, 2018, 09:11:13 am
content: Quote from: Delta on January 18, 2018, 07:08:36 amDo you have extraordinary evidence for that extraordinary claim? Or even any evidence at all?

author: dmills
author_rank: Super Contributor
timestamp: January 18, 2018, 10:18:42 pm
content: Tap changers at the local sub station can also cause weird momentary dropouts, but again everyone elses stuff seems to survive somehow.Regards, Dan.

author: Someone
author_rank: Super Contributor
timestamp: January 18, 2018, 10:52:07 pm
content: Quote from: dmills on January 18, 2018, 10:18:42 pmThe honest manufacturers are testing their equipment to the well known standards that apply, those being the amalgamation of decades of experience from countries around the world. Then we have the pirates cutting corners and producing product barely able to function in normal conditions.To be fair many people won't have seen or experienced significant mains disturbances as being behind a LV distribution transformer sharing intermediate networks with widely distributed loads. Work at a site with significant demands and its own MV feed and you get well acquainted with all sorts of "interesting" conditions.

author: amyk
author_rank: Super Contributor
timestamp: January 19, 2018, 03:13:35 am
content: Quote from: tggzzz on January 18, 2018, 09:11:13 amI think he was just trying to be funny.

author: fourtytwo42
author_rank: Super Contributor
timestamp: January 19, 2018, 07:00:52 am
content: Quote from: amyk on January 19, 2018, 03:13:35 amUpon reflection I think your right so apologies for my hasty reply but don't you think the OP is suffering enough paranoia already

author: ocset
author_rank: Super Contributor
timestamp: January 20, 2018, 01:43:20 pm
content: Littelfuse told us not to buy MOVs for UK mains which have standoff voltage below 404V...because they said the UK mains may go up to 285VAC once in 20 years.