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KB2VXA > INFO 05.07.02 21:06l 80 Lines 3717 Bytes #999 (0) @ WW
BID : 50838_WT3V
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Subj: Re: VK2AAB
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Sent: 020704/0501Z @:WT3V.#JS.NJ.USA.NOAM #:50838 [Lakehurst] $:50838_WT3V
From: KB2VXA@WT3V.#JS.NJ.USA.NOAM
To : INFO@WW
Hello Barry and all,
Well, all I can say about power factor and capacitors is what was
explained to me. I was told that when induction motors are heavily used,
such as in industry, the load becomes largely inductive and power factor
falls. Tha capacitors are to make the load more resistive, keeping the
power factor high. Making the meters read correctly is "a by product",
an advantage to the supplier so the customer is properly billed. It was
explained that a typical motor having a 90% Pf would cause the meter to
read 90% of the overall power consumed. Nobody said anything about
current, I must assume that is because the KWh meter takes voltage into
account
In large installations where a standard HWh meter is impractical because
of high currents encountered, a current transformer is employed, which is
simply a torroidial pickup coil fitted around a single conductor. When
such is employed, special "burdening resistors" are used to keep the coil
voltage output to reasonable levels. BTW, I did QC/QA production testing
on 400~ units and believe me, they are a booger to get right! Slight
variations in the core material greatly affect the output, so quite a bit
of time is spent trimming turns and it has to be correct + - 1 turn. I
also spent quite a bit of time working with engineers both from my
company and Bendix Aeronautical getting that darn test "machine" to
produce coils that would pass thier incoming inspection.
Nobody said electrical engineers ever get it right the first time!
I can't say I know anything about using an alternator as a motor, I
suppose it can be done easily enough by supplying the rotor with DC
excitation current. Anybody got a better idea?
Motors are used as alternators all the time, ask any railroader. The
traction motors are used in dynamic braking and feed current to resistor
banks where it's dissapated as heat. This saves the pneumatic brakes from
going into meltdown on downgrades and when reducing speed.
Flourescent lamps I don't believe have anything to do with what this is
all about, but to answer the question (sort of), the inductive ballast is
simply a current limiting series reactor and arc stabilizer. The lamp
uses a mercury arc which like any plasma would present a short circiut to
the line and a resistor would have to be extremly large and generate
considerable heat. Inductibe reactance is a much more efficient current
limiter. Starting is accomplished one of two ways. A bimetal strip
contained in an atmosphere of rarified neon or argon gas acts as a
thermal switch. When cold it is open, but when voltage is applied, it
glows like any other glow lamp and the strip heats, bends and the switch
closes. This applies current through doiled filaments in the ends of the
lamp which are similar to ordinary lamp filaments except the don'need
get any hotter than to vaporize the mercury. Since the glow no longer
appears in the starter, the bimetal cools and opens. A high voltage spike
is produced by the suddenly collapsing field in the ballast reactor and
arcs the tube, starting current flow.
The more modern type of ballast employs a high voltage winding to
accomplish the same purpose. The internal construction by design shuts
off the high voltage once the arc is struck. This type of ballast can be
found in everything from home lighting to high power HID and HPS lamps
for street and industrial lighting.
*********************************
I'm a technician, not a magician!
*********************************
73 de Warren, KB2VXA
e-mail: kb2vxa@juno.com
Message timed: 05:02 on 04 Jul 02 UTC
[ Received via HF CLOVER at KB6LE ]
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