Hi Jim
On (12 Jun 96) Jim Mcandrew wrote to All...
 JM> Wishing to observe first hand the effect of partially
 JM> interconnecting two out-of-phase AC power sources, I determined
 JM> to observe the effect via the 'Dark Lamp Method' often used to
 JM> determine when the full inter-connection of , say, two
 JM> generators, can be properly made.
Nice. The old ways are the good ways.
In this technique, a lightbulb
 JM> is placed between the phase conductors to be mated- two
 JM> lightbulbs if it's a three phase situation.  The remaining leg is
 JM> interconnected (this is often done through transformers to limit
 JM> current).  In a single phase situation, the single light bulb
 JM> should pulse at the difference frequency (if there is a frequency
 JM> difference) or remain steady at some constant level if the
 JM> frequency is the same.  If the two sources are in syncronization,
 JM> that is, in phase, that steady level is zero, and the bulb will
 JM> be 'dark'.
Yup. And it's a bad day when we don't learn something!
 JM> I expected to observe a slowly pulsing light bulb and thereby
 JM> know how closely the 60hz from each source matched, as well as
 JM> confirming my expectations in general.
 JM>  
 JM> Instead, the bulb grew quite bright over a period of about 1/2
 JM> second, culminating in a blown lightbulb and a $70 smoke signal
 JM> from the inverter.
Expensive lesson. I have spent many happy minutes watching synch lamps in
generating stations.
 JM> I should have used two bulbs in series.  Hmmmm..., or maybe I
 JM> should have just watched a movie or read to the kids.
Seems to me, you didn't spend enough time with your grandpa. He might have
known, in those glorious days before inverters and diodes.
My first rectifiers were a Tungar bulb with a 6amp plate and a 2volt 25amp
filament; and a jar of electrolyte with two aluminum plates immersed. These
were the first two battery chargers I made up, in 1940s
Oh yes, synch lamps here had carbon filaments not tungsten filaments.
You might be interested in the technique called "rough synchronising": the
incoming machine is run at about the right speed, unexcited. Then the AC
breaker is closed. Then the field of the incoming machine is switched on. The
machine is thus pulled into synch as the field [slowly] builds but without
the harmful transient and magnetic forces, that would occur if the field was
"on" prior to paralleling.
Cheers..ALEC
PS to All who may be reading, the HOMPOWER echo traffic here has dropped to
less than half normal, messages are probably failing to reach NSW so any
unanswered callers, please accept my condolences.
... In two words: Im- possible [Sam Goldwyn]
--- PPoint 1.92
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