Compact Fluorescent THD >= 120, problem?

[Jun]

I'm finally getting around to buying some CFL bulbs and for the lamps
in my den/computer room I'd like roughly 25-28 watt 41K mini-spirals
(length needs to be approx 5.5" or less to fit). I found two bulbs so far,
but both of them have a fairly large THD...

GE FLE26HT3/2: 120% THD, 0.6 PF, 26W, 82 CRI
SpringLamp 28927M: <150% THD, > 0.5 PF, 27W, 84 CRI

Somewhere I read something that suggested there are different ways
to measure THD but regardless of which you use, the result should be
well under 100. I'm wondering if I need to be concerned about those
THD/PF figures? There is computer and AV equipment in the den,
and one or possibly two bulbs may end up sharing a circuit with some
of that equipment (not sure). I don't currently have any X10 gear or
what not in the house, but I am actually kicking around the idea.
Thanks for any advice.

 

[TKM]

I'm finally getting around to buying some CFL bulbs and for the lamps
in my den/computer room I'd like roughly 25-28 watt 41K mini-spirals
(length needs to be approx 5.5" or less to fit). I found two bulbs so
far,
but both of them have a fairly large THD...

GE FLE26HT3/2: 120% THD, 0.6 PF, 26W, 82 CRI
SpringLamp 28927M: <150% THD, > 0.5 PF, 27W, 84 CRI

Somewhere I read something that suggested there are different ways
to measure THD but regardless of which you use, the result should be
well under 100. I'm wondering if I need to be concerned about those
THD/PF figures? There is computer and AV equipment in the den,
and one or possibly two bulbs may end up sharing a circuit with some
of that equipment (not sure). I don't currently have any X10 gear or
what not in the house, but I am actually kicking around the idea.
Thanks for any advice.

A few CFLs with high THD are not likely to cause any problems especially if
the total house load (watts) is reduced overall by substituting CFLs for
conventional incandescent bulbs. I've not had any interference problems
with CFLs and computers; but I do notice TV interference (picture only) from
a few fluorescent under-cabinet lights powered by electronic ballasts.
Other commercial electronic ballasts (more than a dozen) powering F32T8
lamps do not cause any problems.

Terry McGowan

 

[Victor Roberts]

A few CFLs with high THD are not likely to cause any problems especially if
the total house load (watts) is reduced overall by substituting CFLs for
conventional incandescent bulbs. I've not had any interference problems
with CFLs and computers; but I do notice TV interference (picture only) from
a few fluorescent under-cabinet lights powered by electronic ballasts.

Probably due to radiated or conducted high frequency
interference, not high THD.

--
Vic Roberts
http://www.RobertsResearchInc.com
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[Jeff Waymouth]

You beat me to it, Vic!

Terry, are those undercabinet fixtures FCC rated for Consumer or
non-Consumer or not rated at all?

Jeff Waymouth

 

[SQLit]

I'm finally getting around to buying some CFL bulbs and for the lamps
in my den/computer room I'd like roughly 25-28 watt 41K mini-spirals
(length needs to be approx 5.5" or less to fit). I found two bulbs so far,
but both of them have a fairly large THD...

GE FLE26HT3/2: 120% THD, 0.6 PF, 26W, 82 CRI
SpringLamp 28927M: <150% THD, > 0.5 PF, 27W, 84 CRI

Somewhere I read something that suggested there are different ways
to measure THD but regardless of which you use, the result should be
well under 100. I'm wondering if I need to be concerned about those
THD/PF figures? There is computer and AV equipment in the den,
and one or possibly two bulbs may end up sharing a circuit with some
of that equipment (not sure). I don't currently have any X10 gear or
what not in the house, but I am actually kicking around the idea.
Thanks for any advice.

I know of only one way to measure THD, total harmonic distortion. That is at
the closest point to the utility, usually just before or at the main
over-current device.

Measuring THD out put from a single lamp or a single circuit is worthless.
Example if you have 40% THD and your electrical equipment is not effected.
Then there is no problem. If you have 10% THD and your systems are
effected, you have a problem.

THD is measured in voltage and in current. A reading of less than an amp
and lower than 10 volts is ignored, by most of us that do the measurements.

@ 27 watts of usage, I would not be all that worried about the harmonics
in your home.
Every bulb in my home except the refrigerator and the oven is a CFL. I do
not have any problems.

If your really worried verify the grounding on your electrical service. 25
ohms is safety code, my service measures, < 5 ohms. Had to add another
ground rod 10 feet away but that was easy.
Give the stuff a place to go and it will.

 

[Jun]

I know of only one way to measure THD, total harmonic distortion...

First of all, thanks for the replies folks.

WRT THD, what I read might have been this:

"Two different definitions of THD are commonly used. One is expressed in
terms of percent RMS current or voltage. The other is based on percent
fundamental current or voltage...

Values below 20% (of either RMS or fundamental) are generally considered
tolerable; values exceeding 50% of RMS or 40% of fundamental are often
considered high"

from this article on compact fluorescents:
http://irc.nrc-cnrc.gc.ca/pubs/cp/lig3_e.html

I see that article also suggests that a couple of "bad" CFLs likely won't be
a problem. Having heard that several times now I am feeling better about
the idea, so to speak.

 

[Victor Roberts]

First of all, thanks for the replies folks.

WRT THD, what I read might have been this:

"Two different definitions of THD are commonly used. One is expressed in
terms of percent RMS current or voltage. The other is based on percent
fundamental current or voltage...

Values below 20% (of either RMS or fundamental) are generally considered
tolerable; values exceeding 50% of RMS or 40% of fundamental are often
considered high"

from this article on compact fluorescents:
http://irc.nrc-cnrc.gc.ca/pubs/cp/lig3_e.html

There are two definitions of THD, but both use RMS values of
the various harmonics, so it is very confusing when the
author of the above article means when he states "One is
expressed in terms of percent RMS current or voltage. The
other is based on percent fundamental current or voltage. "

The first definition of THD, and the one used by the
lighting industry in the US (and perhaps other places), is
the ratio of the square root of the sum of the squares of
all the harmonics greater than 1, divided by the fundamental
frequency - the first harmonic. The dominator is often
expressed as the square root of the square of the
fundamental, which is just the fundamental. This definition
can be found in Section 3.7 of ANSI C82.77-2002, Harmonic
Emission Limits - Related Power Quality Requirements for
Lighting Equipment. A PDF copy of this document can be
obtained for no charge at www.nema.org. Using this
definition the THD can range from 0 to infinity.

The second definition of THD is similar to the first except
that the dominator is the square root of the sum of the
squares of all the harmonics including the first. Obviously
using this definition the THD can vary from 0 to 100%

I see that article also suggests that a couple of "bad" CFLs likely won't be
a problem. Having heard that several times now I am feeling better about
the idea, so to speak.

Even relatively high CFL THD makes a only minor contribution
to the THD of a residential building. You can find a good
discussion of the relative contribution of CFL THD to total
residential building THD in NEMA LSD 8-1999, Power Quality
Implications of Compact Fluorescent Lamps in Residences. A
PDF copy of this document is also available for no charge at
www.nema.org.

--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
replace xxx with vdr in the Reply to: address
or use e-mail address listed at the Web site.

This information is provided for educational purposes only.
It may not be used in any publication or posted on any Web
site without written permission.