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Home > Archive > Electrical Engineering > July 2005 > UPS harmonics
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| Stilgar 2005-06-30, 4:25 am |
| Wondering if anyone has seen this before. Using a fluke 87 meter it
shows up with a varying frequency from 60.00 hz to 300 hz. Tried
three different flukes and one other brand still came up the same. I
have not put an o-scope on it yet. This is just turning up on one
unit. Several others are stable at 60 hz. The analog meter shows a
constant 60 hz. It does not appear to be affecting any downline
equipment, but it just bugs me. This has just recently turned up. It
had been reading good before. The readings are stronger the closer to
the ups, but it does show up downline at the load end. Obvious items
such as capacitors are good. As far as that goes it does not stay at
any normal multiple of 60 like a bad capacitor anyways. The frequency
board is operating well within range also.
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"Stilgar" <mstilgar@mailinator.com> wrote in message
news:6bv6c1pfql18rp64t9mqe0088m55c0qb02@4ax.com...
quote:
> Wondering if anyone has seen this before. Using a fluke 87 meter it
> shows up with a varying frequency from 60.00 hz to 300 hz. Tried
> three different flukes and one other brand still came up the same. I
> have not put an o-scope on it yet. This is just turning up on one
> unit. Several others are stable at 60 hz. The analog meter shows a
> constant 60 hz. It does not appear to be affecting any downline
> equipment, but it just bugs me. This has just recently turned up. It
> had been reading good before. The readings are stronger the closer to
> the ups, but it does show up downline at the load end. Obvious items
> such as capacitors are good. As far as that goes it does not stay at
> any normal multiple of 60 like a bad capacitor anyways. The frequency
> board is operating well within range also.
Perfectly normal for a lot of UPS's.
300 Hz would be the 5th harmonic and probably the 3rd as well.
Sure would like to know how your measuring " stronger closer to the ups".
The Fluke 87 does not have the capabilities to tell you how much/strong the
harmonic is. You will need a lot more expensive meter to do that. Fluke 43B
will work. Sorry O'scope will just show you the wave form. Which can be
quite interesting. I have done harmonic studies with instruments like the
RPM, BMI and Durantz.
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| w_tom 2005-06-30, 12:25 pm |
| Why could 300 Hz be a result of both the 3rd and 5th
harmonic?
SQLit wrote:
quote:
> ...
> 300 Hz would be the 5th harmonic and probably the 3rd as well.
> ...
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"w_tom" <w_tom1@hotmail.com> wrote in message
news:42C3F340.F60CBC17@hotmail.com...[vbcol=seagreen]
> Why could 300 Hz be a result of both the 3rd and 5th
> harmonic?
>
> SQLit wrote:
The Fluke 87 will only measure the highest value when it comes to harmonics.
If you have 5th then you usually will have the 3rd. Extremely rare
instances in my experience that when you have a higher order of harmonics
the lower ones do not follow.
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| phil-news-nospam@ipal.net 2005-06-30, 6:25 pm |
| On Thu, 30 Jun 2005 08:19:27 -0700 SQLit <sqlit@qwest.net> wrote:
|
| "w_tom" <w_tom1@hotmail.com> wrote in message
| news:42C3F340.F60CBC17@hotmail.com...
|> Why could 300 Hz be a result of both the 3rd and 5th
|> harmonic?
|>
|> SQLit wrote:
|> > ...
|> > 300 Hz would be the 5th harmonic and probably the 3rd as well.
|
|
| The Fluke 87 will only measure the highest value when it comes to harmonics.
| If you have 5th then you usually will have the 3rd. Extremely rare
| instances in my experience that when you have a higher order of harmonics
| the lower ones do not follow.
It depends on the waveform. A nice square wave will have lots of odd
harmonics. Sawtooth and trapezoidal waveforms have other combinations.
The 3rd is most likely in there with the 5th, but some cases can omit
the 3rd. Just subtract the 3rd out of various common waveforms and you
can see the oddball cases that would not have it.
--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------
| |
| operator jay 2005-06-30, 11:25 pm |
|
"SQLit" <sqlit@qwest.net> wrote in message
news:64Uwe.28$ss3.4406@news.uswest.net...
quote:
>
> "w_tom" <w_tom1@hotmail.com> wrote in message
> news:42C3F340.F60CBC17@hotmail.com...
>
>
> The Fluke 87 will only measure the highest value when it comes to
harmonics.
quote:
> If you have 5th then you usually will have the 3rd. Extremely rare
> instances in my experience that when you have a higher order of harmonics
> the lower ones do not follow.
>
>
Three phase three wire distorters usually have negligible zero sequence
current and typically 3rd is zero sequence. Big UPS is an example where I
would not have expected much 3rd harmonic current going in. A lot of three
phase rectifiers have the 'golden arches' waveform which has harmonics at
5,7,11,13,etc., leaving out the triplens.
j
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| Stilgar 2005-07-05, 6:25 pm |
| On Thu, 30 Jun 2005 08:19:27 -0700, "SQLit" <sqlit@qwest.net> wrote:
quote:
>
>"w_tom" <w_tom1@hotmail.com> wrote in message
>news:42C3F340.F60CBC17@hotmail.com...
>
>
>The Fluke 87 will only measure the highest value when it comes to harmonics.
>If you have 5th then you usually will have the 3rd. Extremely rare
>instances in my experience that when you have a higher order of harmonics
>the lower ones do not follow.
>
Harmonics I guess would not be the word. It picks up interference (AKA
showing a frequency reading) on the fluke as you get closer without
actually connecting the leads. And when connected the readings are
varying. They are not a stable or an even 300 hz. Actually connected
at the ups it may be 72, 110, 250, 310, etc. Also if I connect further
down the on the load side the frequency shows up lower but still at an
oddball number.
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| SQLit 2005-07-05, 11:25 pm |
|
"Stilgar" <mstilgar@mailinator.com> wrote in message
news:6qklc15sa9ugiq6pnf2p3kraa54rq4e0ml@4ax.com...
quote:
> On Thu, 30 Jun 2005 08:19:27 -0700, "SQLit" <sqlit@qwest.net> wrote:
>
harmonics.[vbcol=seagreen]
>
> Harmonics I guess would not be the word. It picks up interference (AKA
> showing a frequency reading) on the fluke as you get closer without
> actually connecting the leads. And when connected the readings are
> varying. They are not a stable or an even 300 hz. Actually connected
> at the ups it may be 72, 110, 250, 310, etc. Also if I connect further
> down the on the load side the frequency shows up lower but still at an
> oddball number.
Frequency movement/change is what the Fluke is measuring. Having the HZ
wander about leads me to think that either the inverter or converter is
having some IGBTO issues. (power transistors)
I could be way off. So consider what you paid for this advice.
Tracking the part down that is misbehaving may not be worth the trouble.
Depending on how big the parts are (physically) it might be time to just
replace the charging parts.
Some electrical manufactures produce VFD's that are completely
unserviceable. If they start being a problem you replace them.
The impedance of the wire will tend to soften/lessen the HZ the farther you
get from the source.
When K rated transformers first came out all they did was throw copper and
steel at the problem. Example. If you were applying a transformer to a
harmonic load you would choose one size bigger than what you really needed,
instead of a 500 kva you would install a 750 kva.
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