Lightbulbs flicker occasionally - power frequency spikes to 70+ Hz

MeestaR

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Sep 17, 2016
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Hi guys,
This short, but noticeable flicker every now and then is driving me crazy.
Noticed there is a slight flicker/dim/bright flicker, like you would see if you switched on some heavy equipment like a grinder, that would momentarily 'blip' the lights.
I decided to plug in my smart multimeter, and measure the frequency and voltage on the line.

Nothing is running heavy that would cause 'blips' every 30 seconds. The voltage is 230V on the dot, then just goes .4V every now and then, not when the 'blips' occur.
My multimeter showed me that the frequency is 50Hz, then spikes to 70+ Hz, returns to 50Hz, occurring right on the 'blip'.
I can confirm that it happens, even with all my devices are disconnected and off. My inverter seems to have a clean 50Hz, constantly.

This is driving me nuts! Is there any knowledgeable armchair electrician(s) or electronic engineer that can explain this phenomena?
I live in a unit, so we (3 families) is submetering from the mains on the property.

I suspect that it may well be that there is some device on the mains (that I do not know of), or some thing on our power lines that's causing this?
We also have a Telkom exhange across the road from the property, so it may be something in there that is starting or doing something.
 

The_Librarian

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Not sure if it is just me, but I noticed that the fluorescent lights at work was also flickering.

Wonder if Eskom is doing something?
 

Gnome

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My multimeter showed me that the frequency is 50Hz, then spikes to 70+ Hz, returns to 50Hz, occurring right on the 'blip'.
Even expensive multimeters aren't great for measuring frequency. Is it a cheapy?

I can tell you one thing, if you have some weird frequency spike it would be highly localized to your transformer substation at most, unlikely it is beyond your house even. The grid is mighty. It consumes energy very rapidly. So for a high frequency spike to propagate through the grid would require a LOT of energy, even at a local level.

The actual grid frequency is very tightly locked. All the power stations on the grid generate power using turbines. The turbines spin at the frequency of the grid, that is why they call it synchronizing to the grid. Not only does it not change quickly, it can't, these are huge mechanical spinning masses. And it has a very, very narrow band in which it can operate. If the frequency is outside of specification the turbine will trip offline, to prevent it from ripping itself apart.

Voltage on the other hand does fluctuate quite a lot. In Sea Point we go anywhere from 220v -> 250v depending on the time of day. However again it does not change quickly.

Most voltage disturbances are local, so someone suddenly drawing a HUGE surge of energy on your local transformer (definitely not a house, maybe a factory).
 
Last edited:

MeestaR

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Even expensive multimeters aren't great for measuring frequency. Is it a cheapy?

I can tell you one thing, if you have some weird frequency spike it would be highly localized to your transformer substation at most, unlikely it is beyond your house even. The grid is mighty. It consumes energy very rapidly. So for a high frequency spike to propagate through the grid would require a LOT of energy, even at a local level.

The actual grid frequency is very tightly locked. All the power stations on the grid generate power using turbines. The turbines spin at the frequency of the grid, that is why they call it synchronizing to the grid. Not only does it not change quickly, it can't, these are huge mechanical spinning masses. And it has a very, very narrow band in which it can operate. If the frequency is outside of specification the turbine will trip offline, to prevent it from ripping itself apart.

Voltage on the other hand does fluctuate quite a lot. In Sea Point we go anywhere from 220v -> 250v depending on the time of day. However again it does not change quickly.

Most voltage disturbances are local, so someone suddenly drawing a HUGE surge of energy on your local transformer (definitely not a house, maybe a factory).
Define cheap multimeter. Its a AC/DC clamp meter from UNI-T. I think I paid like R3K for it, it can measure up to 400A of current, its not so cheap for me, though.

You have a valid explanation there, the 'blips' is gone now. I think it may have to do with the substation or it's loads. Will speak to landlord to see if they noticed the flickering. It's very subtle, but once you notice it, you cannot miss it.

On a side note, this morning, my lights almost went out for a moment, twice in 30 seconds. Not sure if related, though.
 

Pineapple Smurf

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:oops:
I have never ever seen anything but a constant 50Hz. Our generators at work will switch off if they reach 52Hz, so your 70Hz is just crazy. I am surprised nothing there has blown up yet
 

MeestaR

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:oops:
I have never ever seen anything but a constant 50Hz. Our generators at work will switch off if they reach 52Hz, so your 70Hz is just crazy. I am surprised nothing there has blown up yet
I'm just worried about the swicthing power supplies. Or, its my multimeter just glitching, causing a false reading. Best would be to use a oscilloscope...
 

Geoff.D

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I'm just worried about the swicthing power supplies. Or, its my multimeter just glitching, causing a false reading. Best would be to use a oscilloscope...
Yup. If you have one or can get one, preferably a storage scope, you might be able to localise it.
It would require the cooperation of everyone on the property though because at some point you might have to get everyone to disconnect switch off devices .
My guess would be that somewhere in your split feed there is a switch mode power supply or some thing similar that is actually faulty giving that frequency spike.
On the other hand the grid frequency is by no means as stable as some try to make it out to be either. But it would not change as suddenly as that.
ALL this LS switching that goes on can and will cause the frequency to vary, and localised as well.
If frequency was as stable as some would like us to believe there would be zero need for special power generation installations designed to help maintain that stability now would there?
 

SDM

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Hi guys,
This short, but noticeable flicker every now and then is driving me crazy.
Noticed there is a slight flicker/dim/bright flicker, like you would see if you switched on some heavy equipment like a grinder, that would momentarily 'blip' the lights.
I decided to plug in my smart multimeter, and measure the frequency and voltage on the line.

Nothing is running heavy that would cause 'blips' every 30 seconds. The voltage is 230V on the dot, then just goes .4V every now and then, not when the 'blips' occur.
My multimeter showed me that the frequency is 50Hz, then spikes to 70+ Hz, returns to 50Hz, occurring right on the 'blip'.
I can confirm that it happens, even with all my devices are disconnected and off. My inverter seems to have a clean 50Hz, constantly.

This is driving me nuts! Is there any knowledgeable armchair electrician(s) or electronic engineer that can explain this phenomena?
I live in a unit, so we (3 families) is submetering from the mains on the property.

I suspect that it may well be that there is some device on the mains (that I do not know of), or some thing on our power lines that's causing this?
We also have a Telkom exhange across the road from the property, so it may be something in there that is starting or doing something.
There's a loose connection upstream of you that's causing this. The brief interruptions caused by this are confusing your multimeter frequency measurement algorithm. You need to get an electrician to check it out.

The power system frequency of 50Hz is fixed throughout the Southern African region. Frequency is the main indicator of the relationship between demand and supply. If demand goes down, the frequency increases and Eskom automatically reduce generation to bring the frequency back to 50Hz and vice versa. This happens continuously with small variations around the 50Hz point. Big deviations cause wholesale disconnection of loads. The first stage of this kicks in at 49.2Hz as an example.
 

genetic

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70Hz is impossible. Don't think your multi-meter is accurate.
 

Gnome

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I'm just worried about the swicthing power supplies.
The way a switching power supply works is:
- AC voltage comes in and goes through rectifier diodes & high voltage capacitors. This converts it to DC.
- A switching circuit then switches at high frequency through a transformer to lower the high voltage DC voltage.
- Voltage coming out on the other side of the transformer is high frequency AC, goes through rectifier diodes and capacitors again.

That is pretty much it.

Because it immediately rectifies the voltage, it is very, very tolerant of frequency. Anything from DC to up to a 500 Hz is unlikely to make any difference (higher or slightly lower depending on rectifier diodes and input inductance)

Anyway, voltage is far more important for a switch mode regulator. The diodes and MOSFETs they use are typically very close to tolerances to save money and very sensitive to voltage. They don't tolerate voltage spikes at all. Typically more expensive supplies include the same circuitry as a surge plug to protect the electronics for the life of the warranty.
 

upup

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swicthing power supply is your problem, try to bypass it. If it does come from outside, it will be someone who pumps power into the system, with this 70 hz you get.
 

Pineapple Smurf

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70Hz is impossible. Don't think your multi-meter is accurate.
Ive seen lank movies where 70Hz is the norm in a house

This Week in Jobs DMV: Move-In-Ready Edition - Technical.ly Baltimore
 

lambch0p

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I've been meaning to test/check incoming AC frequency.. especially after what happened here with the voltage a couple of years ago: One day I noticed my power meter gadget was reading 260v on the incoming municipality AC. I reported it, and it went on for a couple days before an electrician was sent out.. they were kind of surprised themselves, and said that people in the area were lucky that I had noticed this problem. They simply went up the road, changed a tap on a transformer, and voltage has been perfect ~230v since. Can't take things for granted it seems..
 

Tacet

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My Victron occasionally disconnects Eskom in the late evenings as our Eskom AC is high. The first time that happened I was pretty shocked, but I've seen it go to about 254 V a couple of times. Frequency is pretty stable, though. I can't think of any kind of non-severe grid fault that could result in a 70 Hz frequency.
 

Thor

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This is my biggest fear, when Eskom becomes so incompetent it breaks the distribution and either voltage fluctuations or frequency fluctuations and then breaking very expensive electronics and industry

It will be a disaster.
 

Thor

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Even expensive multimeters aren't great for measuring frequency. Is it a cheapy?

I can tell you one thing, if you have some weird frequency spike it would be highly localized to your transformer substation at most, unlikely it is beyond your house even. The grid is mighty. It consumes energy very rapidly. So for a high frequency spike to propagate through the grid would require a LOT of energy, even at a local level.

The actual grid frequency is very tightly locked. All the power stations on the grid generate power using turbines. The turbines spin at the frequency of the grid, that is why they call it synchronizing to the grid. Not only does it not change quickly, it can't, these are huge mechanical spinning masses. And it has a very, very narrow band in which it can operate. If the frequency is outside of specification the turbine will trip offline, to prevent it from ripping itself apart.

Voltage on the other hand does fluctuate quite a lot. In Sea Point we go anywhere from 220v -> 250v depending on the time of day. However again it does not change quickly.

Most voltage disturbances are local, so someone suddenly drawing a HUGE surge of energy on your local transformer (definitely not a house, maybe a factory).

Thanks for this explanation, it does ease my fears a little bit.
 

Thor

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I've been meaning to test/check incoming AC frequency.. especially after what happened here with the voltage a couple of years ago: One day I noticed my power meter gadget was reading 260v on the incoming municipality AC. I reported it, and it went on for a couple days before an electrician was sent out.. they were kind of surprised themselves, and said that people in the area were lucky that I had noticed this problem. They simply went up the road, changed a tap on a transformer, and voltage has been perfect ~230v since. Can't take things for granted it seems..

Just checked mine, I'm on 239 IMG_0078.png
 

gboy

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I have also noticed some thing odd in Somerset West, my UPS randomly starts up for periods of time, correcting a voltage or something. Normally happens early morning between 2-6 am. Some days it does, some days it doesn't. People in our estate, have also commented on these wired changes. I think the best is the stabilizer plugs AC/DC sells, that will turn off if the electricity goes out of range. They are not cheap though so not on every plug
 

Geoff.D

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This is my biggest fear, when Eskom becomes so incompetent it breaks the distribution and either voltage fluctuations or frequency fluctuations and then breaking very expensive electronics and industry

It will be a disaster.
The voltage fluctuations yes, that has always happened and it is definitely worse during LS. The frequency variations are also worse, but can't reach extreme values. The stability was always +/- 0.5 Hz. Now I hear talk of + 1.0 Hz and -1.5 Hz being considered acceptable.
 

Gnome

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Now I hear talk of + 1.0 Hz and -1.5 Hz being considered acceptable.
I have serious doubts about that. A lot of the power stations are really expensive to repair, ie. Koeberg. They are already happy with rolling blackouts, why increase risk of turbine failure by allow it to dip that far.
 
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