Discuss LED Lights flickering, Harmonics Issue? in the Electrical Forum area at ElectriciansForums.net

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First post on here, but i'm honesty at my wits end! I installed four Lutron in-line dimmers about 9 months ago, all on the same new lighting circuit. Last week the client rang to say that there had been a power cut locally, and when the power was restored, all his Lutron dimmed circuits were flickering, badly.

I attended today, and they are flickering, and this is worse when dimmed. I broke the circuit down and it's good. I checked the supply characteristics and they're good. I changed the main switch and RCBO and they're good. With all other circuits in the house, all the connected dimmed loads flicker.

Finally, I made a test rig with one of the affected dimmers and placed this on a plug top. It still flickers on any socket circuit. The next door neighbour even kindly allowed us to try his sockets, and it still flickers.

I took it home to mine and it's perfect. I tried it in an property on the next street along, and it's perfect smooth dimming.

I spoke to the manufacturer an the NICEIC and they both said speak to the DNO, possible harmonics issue.

The DNO have just been out, done and EFL test and said nothing more they can do or check! The client mentioned possible harmonics issue, but the DNO lad said the supply was good.

The loads are 2 circuits of 10 x 10w 350ma LED lamps (Trailing edge dimmable), 1 x 30w 12v LED driver, and 1 x 10W LED Pendant lamp, all have been working flawlessly up until this power cut. I immediately thought they must have been damaged by a surge, but I can prove they're good at my property and others!?!

Any advice on where to go from here would be massively appreciated.

Thanks in advance.
 

marconi

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You have your own and the clients testimony that all was well before the power cut but not subsequently nor with the neighbours supply. The dimmers work fine in your remote home And in a nearby street. You could buy one new Lurton and try at the client’s and then your own home to show the problem is indeed supply related. Then you can take the dno behind the bike sheds and discuss their initial response, it would have been more believable to blame covid. Tell them to earn their supply service charge.
 

Lucien Nunes

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Welcome aboard @anthonini and thanks for your clearly explained and detailed first post.

Yes, harmonic content i.e. distortion on the mains could easily be a factor. But the question is how much distortion is too much As I was only saying the other day, some combinations of dimmer and LED are only stable under ideal conditions. As soon as the supply varies a little, some nuisance behaviour shows up like flickering or interaction between dimmers. Perhaps after the outage that supply was transferred to a different transformer, or the same transformer on a different tap, and the voltage has changed. Or there is a bit more 3f on this supply, or whatever.

The headache now is that the supply might still technically be within spec, but not quite good enough for a marginal setup of dimmer and driver. Although the dimmers had worked fine after installation, they had probably never been subjected to a wide range of legitimate supply variations.

Please keep us updated with your findings.
 

marconi

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You might want to:

1. Compare how many electric vehicle charging points there are in the client's street with the neighbouring street and your own street. Does the client have an EV CP?

2. Does the flickering occur at all times or when it is likely that electric vehicles are being charged in the evening and overnight, so the problem does not exist during the day.

3. Is it an old overhead line with a reduced thickness neutral as compare with the line conductors.

4. Is the sub-station 'far away'?

5. Is there electric heating in the home and in this road?

Background: Non-linear loads such as big battery chargers which rectify and then smooth the incoming ac produce harmonics, the most troublesome generally being the third because instead of the out of balance third harmonic phase currents adding to tend to cancel out, they add up. This large third harmonic neutral current can be 3 times the phase current - see diagram. This current will cause a third harmonic voltage drop along the neutral which will/might/could interfer with devices which like a dimmer which rely on switching on and off depending on the point in the voltage/current waveform. Dimmers are designed/assume the waveform is sinusiodal at 50Hz. The supply transformer itself can start to produce harmonics when it becomes heavily loaded because it enters non-linear regions of the B-H curve eg: if starts to saturate - remembering this happens for 50Hz current and its harmonics. You get the gist......Such knowledge may help you 'push back' on the DNO.
 

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