Voltage and Current Distortion Measurements

[ccw]

I have a Fluke 345 clamp meter on hand and have questions about the results shown below.

Mainly, I'm wondering if the distortion shown on the Current waveform and it's THD readings should be considered significant and worth trying to address, or not?

Some context: I live one utility transformer away from our neighborhood water pump station (which has it's own double utility transformer). I'm curious if its electric motor is throwing an inductive load on the grid that would result in this distortion.

The measurements were taken with the audio system completly powered up.

Thanks

 

[RayDunzl]

Looks normal enough to me eyeball.

Last picture, I see you measured the Neutral wire.

The spike is when the rectifiers in your gear are passing current, and causing a voltage drop on that branch circuit.

I don't have a meter but here's my waveform from a few years ago, hot and neutral refenced to Earth.

The very local transformer is on the ground on the other side of the house next door, with underground wires. The transformer probably feeds six or eight houses. A small pump station is a half mile away on the local mains.

Originally, the volts at the house would drop down to 110 or so, when all the air conditioners were running. That would cause an alarm on a power strip, and it would sometime shut itself off. Called the Power Company, they hung a meter on my meter for a month, agteed, and installed a (I guess) higher capacity transformer there one day.

Told the engineer they weren't meeting specs, and he agreed in the end,

 

[DVDdoug]

The current you're measuring is only on your local circuit, not your neighborhood... Whatever circuit the amp-clamp is on. It could be a switching power supply or a light dimmer. A pure inductive load creates a phase shift (a phase difference between voltage & current) but it would still be a sine wave. The kind of motor with a commutator and brushes might have abrupt changes in current.

Switching power supplies might do "strange things" but they operate at high frequencies so the noise-variation wouldn't be in-sync with the power line frequency.

Mainly, I'm wondering if the distortion shown on the Current waveform and it's THD readings should be considered significant and worth trying to address, or not?

Unless you are getting noise in your audio I wouldn't worry about it. Every audio device has a power supply that converts AC into filtered DC and it usually does a very good job of filtering.

Sometimes, you can have a DC offset (an asymmetrical waveform) and sometimes that creates mechanical buzz in the transformer but it usually doesn't get into the audio.

P.S.
Fluorescent lights MIGHT be nonlinear and cause a current waveform like that.

You can also unplug or turn-off one thing at a time to see what's causing it.

 

[AnalogSteph]

Going by the amount of odd-order distortion due to rounded peaks, it looks like the utility transformer (or one before it) may be a tad unhappy with its life, but there is nothing much you can do about that.

The current waveform looks more or less normal to me; looks like you may have some equipment with bigger power supplies and no PFC running (the big spikes are typical reservoir capacitor replenishment).