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Bill[_37_]

wrote:
On Thu, 2 Dec 2010 14:36:55 -0800 (PST), Robatoy
wrote:

On Dec 2, 3:47 pm, Larry wrote:
On Thu, 02 Dec 2010 14:10:40 -0500,
wrote:

On 12/2/2010 8:23 AM, Larry Jaques wrote:
On Thu, 02 Dec 2010 02:02:06 -0500, wrote:
I had to move a few bit to accommodate obstacles (like garage door
opener). The luminaires with electronic ballasts featuring "instant
start" and less than 10% THD are about $40 each--lamps extra.

Total harmonic distortion in fluors? New one on me.

Wikipedia says 1% THD is supposed to be inaudible to the human ear.
"Standard" (Lithonia) electronic ballasts are 20% THD
"Instant on and Rapid start" electronic ballast by Lithonia are 10% THD.

So they're saying that these babies HUM LIKE HELL, or what?
WTF is an audio distortion figure doing on a light fixture?!?

Don't get me started. THD is a useless spec. It 's like a single
number indicating impurities in ice cream. Some impurities are straw,
some are bat ****.

'Even order' harmonics are much easier to put up with than 'odd
order' (not related to the fundamental note) harmonics. (Please, all
you musicians and psycho-acousticians keep your shirts on, I know it
is an over simplification.)
Even order harmonics is how we tell instruments apart, odd order
is ..is.. like..Celine Dijon (without AutoTune.)

THD is not so much about accoustics as it is about "dirty power".
Low TDH ballasts are becoming much more common in
industrial/commercial lighting applications (specifically those with 3
phase power)

according to ITS Intertek Testing Services (Boxborough, MA)

Power line harmonics is just one of the many power quality issues that
arise with public utilities. Effectively, current harmonics represent
a distortion of the normal sine wave provided by the utility. When a
product such as an SCR switched load or a switching power supply
distorts the current, harmonics at multiples of the power line
frequency are generated. Two significant consequences arise as a
result of harmonic generation. First, because of finite impedances of
power lines, voltage variations are generated that other equipment on
the line must tolerate. Second, when generated in a three-phase
system, harmonics may cause overheating of neutral lines.

Power line harmonics are generated when a load draws a non-linear
current from a sinusoidal voltage. The harmonic component is an
element of a Fourier series which can be used to define any periodic
waveshape. The harmonic order or number is the integral number defined
by the ratio of the frequency of the harmonic to the fundamental
frequency (e.g., 150 Hz is the third harmonic of 50 Hz; n = 150/50). A
second harmonic is therefore two times the fundamental frequency of
the supply line volt current. If the supply voltage had been generated
by an ideal source (zero impedance), the current distortion would have
little effect on the supply voltage sine wave. However, because a
power system has a finite impedance, the current distortion caused by
a nonlinear load creates a corresponding voltage distortion in the
supply lines. This voltage distortion can subsequently disrupt
operation of other sensitive equipment connected to the same line.
Voltage distortion can also cause motors operating on the line to
overheat

The only thing I can add to that is that really high THD can cause a
fire (really)!

Bill