Can I use a simple oscilliscope to see powerline harmonics?

That's a broad question. I would expect that you would use CTs / transducers and PTs and measure those with your oscilloscope. You would probably want some software that did data logging, triggering on certain events (high / low amperages ... significant amperage changes ... harmonic level thresholds ... imbalance ... transients ... etc.) and processing (Fourier spectra, sequence values, imbalance, RMS values, data trending) depending which aspects of 'power quality' you want to 'measure'. There are PQ loggers available that have stuff like this built in, and have software available for analysis. Those I'm aware of are expensive and typically sample at a relatively low rate (say, 128 samples per cycle or stuff like that, as opposed to oscilloscopes which might be sampling as high as millions of samples per cycle).

I hope that helps. If you have something specific in mind, though, post it.

j

in article snipped-for-privacy@4ax.com, Frank White at snipped-for-privacy@telus.net wrote on 1/15/05 10:50 AM:

No! You must remember that electrical systems are grounded and so are oscilloscopes meeting safety codes. Thus, to look at line waveforms while keeping a protective ground on the scope it is necessary to use dual input oscilloscopes in the difference mode. Some scopes have plug-in amplifiers that will simplify that kind of measurement. Dual trace scopes also help.

There may be special techniques or equipment that would allow you to look at the waveform for your specific application.

Bill

Duh, I think you would use step-down transformers before hooking to a scope, huh?

Something to keep in mind, some transformers have horrible frequency responses at frequencies other than 60hz. Also, in the real world a transformer does not simply act like a lowpass filter. So, unless you know the frequency response of the transformer, you really can't be sure of what you are measuring. Most magnetic transformers will perform good enough to see 13th harmonic or so. Above that it depends on a lot of factors. If you do see something at a high frequency, it may or may not really be there and if it is really there, you cannot be sure of its actual amplitude.

Charles Perry P.E.

In a word, no. Oscilloscopes work in the time domain displaying signals vs. time. To see harmonics, you have to observe in the frequency domain. That is, signals vs frequency, a spectrum if you will. Of course if the waveforms are highly distorted, the fact that they are not clean sine waves may be seen on a scope but you couldn't tell which or how much the harmonics were present in the distortion. You can separate harmonics from a waveform using selective filters sharply tuned to the expected frequencies and display this on a scope (time domain) but it is an expensive and awkward way to do it. Filters can be used to measure the total harmonic distortion present but are less appropriate for individual harmonics or to view a broad spectrum. The usual way this is done is by the FFT (Fast Fourier Transform) which uses mathematics in real time to display a signal in the frequency domain. FFT software is available for the PC but also requires an Analog to Digital converter board in the computer. Needless to say, the measuring device must be isolated from the line through a transformer with sufficient bandwidth to handle the expected harmonics. Bob

1) Most probes are rated for 600V peak 600Vrms == 850V peak. 2) A delta measurement will have ground problems (already mentioned).

in article snipped-for-privacy@4ax.com, dave y. at snipped-for-privacy@ameritech.net wrote on 1/15/05 1:06 PM:

Duh?

If I were looking at line voltage waveforms, I would be using 10X probes. Most scope differential amplifiers are capable those voltages. 100X and

1000X probes are also available.

Bill

There are some spectrum analyzer plug-ins for Tektronix 7000 series mainframes

--but at that point, calling it an oscilloscope is a stretch.

in article snipped-for-privacy@c13g2000cwb.googlegroups.com, JeffM at jeffm snipped-for-privacy@email.com wrote on 1/15/05 9:08 PM:

Digital osscilloscopes can be found with built in FFY capability. I would not call that simpe, however. Another approach may be the battery operated oscilloscopes that look like digital multimeters. Because they would not be connected to a power ground, single ended input is OK.

Bill

you know it's good you posted this,

I have trouble with this,

Conventionally you should be able to get measurements from it but according to the manufacturer and the way they teach this in school you have to bridge a circuit of a known value to reference from.,

I Hate That .," for the sake of pete"

if we're going to design a scope and tell people it can measure upto thousands of volts & mega hertz in different scales, then why not design one you can just Plug and Play to obtain the measurements of available equipment with common or known waveforms.

I am just a bit of a procrastinator i guess, or i wouldv'e had a better response for you };-) lost interest right after i got the eliptical egg shape waveform, lot of good learning that did.....

I thought of spectrum analyzers then thought naw, this guy isn't going to go pay $30,000 for a spectrum analyzer. His best bet is FFTsoftware for his PC with an ADC board. Bob

Yup. I was trying to be inclusive and informative, while you were actually helpful. More likely he'll get software than rent a spectrum analyzer.

The instrument should be (IEC1010-1/EN61010-1/UL61010B-1) rated at least 600V category-III for application to 60Hz power equipemnt.

?s falke

If you are taking spot measurements, I would recommend buying/renting a Fluke 43. I think they can be had for less than $2k. They are meant to measure harmonics, and other power quality phenoma, at 600V. It is a single phase device, but this is not a problem for spot measurements. Fluke now makes a three phase version, but I am not familiar with the pricing.

Charles Perry P.E.