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Is this type of mains voltage waveform ever likely to occur?

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Flyback

Well-Known Member
Hello,
Is the attached mains waveform ever likely to occur? (i mean in the mains system and not due to any triac etc at the customer premises)
As you can see, it keeps going to zero for an interval, then suddenly coming back on at the mains peak.
As you can well imagine, this kind of waveform would be very bad for Single stage Power factor corrected LED lights, because they have little capacitance at their input, and this type of waveform could cause overvoltage ringing with the input LC filter of the LED light.
 

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alec_t

Well-Known Member
Most Helpful Member
Considering the mains is generated by multiple whacking-great alternators with huge inertia and at at different sites I would consider it most unlikely, if not impossible. Why would a utility want to do that and how would they achieve it? That said, there is of course lots of data and noise superimposed on the mains, but of relatively low amplitude.
 

JLNY

Active Member
I think your suspicion is correct that the waveform looks exactly like the output of a triac-based dimmer. Unsure of why it would only appear to be operating some of the time, though. As you suggest, this type of waveform could absolutely cause issues with many kinds of LED or CFL lights not designed for this kind of dimming.
 

Grossel

Well-Known Member
There is some very important key factors that is not mentioned here
- Is this an actual measurement on a real world wire?
- Does the measurement show voltage or current?
- Any description of the grid. Something is always better than nothing.

I too would suggest a dimmer. That said - there exists dimmers that never really turns completely off, I had one and ditched it and replaced by a regular manual switch. So there is a real possibility to being fooled to think that a dimmer shouldn't have any effect because you expect it to be turned off.
 

RODALCO

Well-Known Member
That is more a waveform from an inverter which is on load and possibly overloaded or an output from a triac.
Grid waveforms are always sinusoidal with the odd spikes or ripple on it but remain sinus shaped.
 
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Flyback

Well-Known Member
thanks, its a simulation waveform.....as discussed, we are worried about it ever happening as it would overvoltage our single stage pfc'd led lights which have little input capacitance and biggish filter inductors.....the repetitive, sudden on-coming at the mains peak woudl create overvoltage ringing which the tvs woudl repeatedly quench, but it would overheat and die if the "sudden oncoming at mains peak" was going on for a long time.

The grid here could be a micro-grid from solar or wind turbines etc or the national grid...whatever happens to get used for the street lighting.
 

AnalogKid

Well-Known Member
Most Helpful Member
The grid here could be a micro-grid from solar or wind turbines etc or the national grid.
I suppose a micro-grid inverter cold produce a weird waveform if it partially failed, but that would be one strange PWM output.

ak
 
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