Can I use a simple oscilliscope to see powerline harmonics?

[Frank White]

Wondering if I could measure the power quality on a 3ph 600V service
like this?


To send me e-mail remove the sevens
from my address.
[email protected]

 

[operator jay]

Wondering if I could measure the power quality on a 3ph 600V service
like this?


To send me e-mail remove the sevens
from my address.
[email protected]

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

 

[Charles Perry]

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.

 

[Roy Q.T.]

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.....

 

[Charles Perry]

Wondering if I could measure the power quality on a 3ph 600V service
like this?


To send me e-mail remove the sevens
from my address.
[email protected]

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.