Distorted residential power, only at night?
Distorted residential power, only at night?
(OP)
For many weeks I have had this problem with my power. I hear a slight buzz from my audio equipment, only at night. Hooking up an oscilloscope shows this waveform.


At dusk the waveform becomes dirty. At dawn it becomes clean. Everyday like clockwork.
Some more clues:
1. The problem is only on one of the 120 volt legs. The other leg is always relatively clean.
2. I thought that street lights might be a problem because of the timing. However I observed them on a few occasions and they did not come on or off exactly with the start or end of the distortion.
3. This is a residential only neighborhood with 14 houses and 3 streetlights on one transformer as far as I can tell.
Any thoughts on what is causing this and a possible solution?


At dusk the waveform becomes dirty. At dawn it becomes clean. Everyday like clockwork.
Some more clues:
1. The problem is only on one of the 120 volt legs. The other leg is always relatively clean.
2. I thought that street lights might be a problem because of the timing. However I observed them on a few occasions and they did not come on or off exactly with the start or end of the distortion.
3. This is a residential only neighborhood with 14 houses and 3 streetlights on one transformer as far as I can tell.
Any thoughts on what is causing this and a possible solution?






RE: Distorted residential power, only at night?
RE: Distorted residential power, only at night?
That appears to be harmonic distortion. Have you tried using your osilloscope to check for which odd harmonic it being applied into your local line?
RE: Distorted residential power, only at night?
RE: Distorted residential power, only at night?
14 houses on one transformer is a lot of houses. Are you sure about this?
Also, where are you measuring this voltage?
One of your neighbors have an indoor plant growing operation?
David Castor
www.cvoes.com
RE: Distorted residential power, only at night?
RE: Distorted residential power, only at night?
This is not a combination of several SMPS-es, but looks more like one hefty rectifier taking a lot of current over a conduction angle that is close to 45 degrees, which is much more than one can see in a typical SMPS. The fact that current snaps off distintly and causes significant ringing at the end of the conduction angle also tells that this is one consumer and not the typical 'co-operation' of many small loads.
The ringing is probably the origin of the buzz you hear.
Charging an electric car could very well be such a load.
Interesting.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Distorted residential power, only at night?
I am pretty sure that there are 14 houses on the transformer.
I am not aware of any electric cars or indoor plant growing but I will ask around.
RE: Distorted residential power, only at night?
I would start by finding a friendly neighbor and ask to connect your scope to his system too and see if the problem exists outside of your home. If they don't have it, the problem is closer to home. If they do, and if you can get to enough other friendly neighbors, you may find a variation in the level of attenuation going on by distance and that may allow some gross triangulation toward the culprit.
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RE: Distorted residential power, only at night?
RE: Distorted residential power, only at night?
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Distorted residential power, only at night?
You'll be looking for a step in the load current that coincides with the notch in the voltage waveform.
Searching for radiated RF can fool you. At times, the signal can be conducted a ways along a service line and then radiated from a point some distance away from the culprit.
RE: Distorted residential power, only at night?
Don't forget that the US seem to use small pole-mount distribution transformers of a hundred kVA or so serving a small number of properties. That certainly contrasts with British practice where a suburban distribution transformer is more typically in the 0.5 - 1.5 MVA range and serving a much larger number of properties. The 'single big load' might not have to be all that big to cause a problem: maybe someone with a home workshop running a lathe or milling machine on an inverter? I have never looked at my domestic mains when my lathe is running, but it certainly upsets the ADSL broadband modem connection.
Another thought: how would a high primary voltage pushing the transformer core in to moderate saturation manifest itself in terms of secondary voltage waveform? Light loads on the system in the evening would tally with a high primary voltage.
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If we learn from our mistakes I'm getting a great education!
RE: Distorted residential power, only at night?
Is the time this starts in the evening and ends in the morning accurate and repeatable? I ask because if it is then it's probably not a consumer but rather a power company caused function like a switched capacitor voltage regulator. If it were, say, an electric car being charged it would end at different times and start with a multi minute variation.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Distorted residential power, only at night?
Yes, but even 100 kVA is big compared normal switch-mode power supplies. A conduction angle close to 45 degrees is not usual. I am very excited to learn what it actually turns out to be.
BTW, many PWM inverters take out communication. But they do it with HF from the PWM switchiing. Not with low-frequency distortion from the rectifier.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Distorted residential power, only at night?
"Is the time this starts in the evening and ends in the morning accurate and repeatable? I ask because if it is then it's probably not a consumer but rather a power company caused function like a switched capacitor voltage regulator. If it were, say, an electric car being charged it would end at different times and start with a multi minute variation."
RE: Distorted residential power, only at night?
RE: Distorted residential power, only at night?
The point is :harmonic/waveform distortion on the secondary/primary tx. of offending client can be transferred to the tx.secondary side of an unsuspecting client.
I would lodge a complaint with the utility and let them investigate.It could be a large load miles away that is turning on.
RE: Distorted residential power, only at night?
A switched capacitor is a shunt capacitor with an on/off switch.
A voltage regulator is an autotransformer with a tap changer.
I'm just curious what you mean by a switched capacitor voltage regulator.
RE: Distorted residential power, only at night?
How big a load? It looks like about 30 volts is chopped off the voltage waveform. Say the transformer is 25 kVA with a 2% impedance. This is about 0.012 ohms at 120 volts. Say the load is 200 ft from the transformer and the secondary is #1/0 aluminum. The two-way impedance would be 0.076 ohms. These are at 60 Hz. The impedance for the peak part of the current would be probably be 4 times this because of the increased frequency. So, we have 30 volts divided by 0.088 ohms, or 340 A peak, but only lasting . That's a very large load. If it was an electric car charging overnight, I would expect the load to be very small by morning when the batteries are fully charged.
RE: Distorted residential power, only at night?
Anyway, that's what I meant.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Distorted residential power, only at night?
Ok, I understand what you mean. It's a switched capacitor bank used to regulate voltage. I thought there might be some new gizmo out there.
Nonetheless, I wouldn't expect a cap bank to produce what was recorded.
RE: Distorted residential power, only at night?
RE: Distorted residential power, only at night?
I increased the gain of the scope to better see the distortion and there is similar distortion on the "good" leg but reduced in amplitude. I have taken pictures of the waveforms both at night and during the day. Any thoughts?
The "bad" leg at night.
The "good" leg at night.
The "good" leg during daytime.
The "bad" leg during daytime.
RE: Distorted residential power, only at night?
Backwards logic. If you are seeing this glitch on only one leg of the service, it is almost certainly problem somewhere on the secondary. There is no way I can thing of that a glitch on the primary side of your transformer will only appear on one half of the transformer's secondary winding.
*For non US folks, our distribution transformers are usually single phase to neutral on the primary side and center tapped (120V from the center) to each side of a 240V winding.
RE: Distorted residential power, only at night?
Have you taken your scope somewhere else to make sure it's not your scope, or probe, or something else?
If you're sure your view is correct you should take this to the power company. Print those pictures out with dates and times and carry them in. Tell them it's causing buzzing in your audio equipment if it is.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Distorted residential power, only at night?
That would be a big transformer in my area. There are 7 houses on the 25 kVA transformer that serves my house.
RE: Distorted residential power, only at night?
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If we learn from our mistakes I'm getting a great education!
RE: Distorted residential power, only at night?
Where I live in the midwest your house has to have 100A service 100A*240V=24Kva.
RE: Distorted residential power, only at night?
Many older homes have swamp coolers, or just fans for summer. The people moving here from somewhere else seem to want compressor AC.
It is possible this could be a lightning arrester failing, as the night time voltage goes up.
RE: Distorted residential power, only at night?
RE: Distorted residential power, only at night?
The utility doesn't follow the same rules as everyone else. For example, a building I worked in had #2 overhead feeding a 600A service. The #2 utility wire connected to something like dual 350mcm at the building.
RE: Distorted residential power, only at night?
RE: Distorted residential power, only at night?
RE: Distorted residential power, only at night?
Most utility guys think RMS and percent swell/sag. Some even think THD. But very few (none that I have met so far) will understand your waveforms.
You need to contact the power company's central office. There might be someone that understands.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Distorted residential power, only at night?
We typically size our services by the projected load of the residence. Utility pole mounted transformers are ANSI rated to handle 140% of the nameplate rating for short durations. We use this extra capacity to reduce system losses.
Happiness is a way of travel, not a destination.
RE: Distorted residential power, only at night?
RE: Distorted residential power, only at night?
RE: Distorted residential power, only at night?
RE: Distorted residential power, only at night?
RE: Distorted residential power, only at night?
RE: Distorted residential power, only at night?
RE: Distorted residential power, only at night?
You never told us if the buzz comes from the speakers or from your amplifier. Which one is it?
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Distorted residential power, only at night?
RE: Distorted residential power, only at night?
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Distorted residential power, only at night?
RE: Distorted residential power, only at night?