Re: [TCML] PFC Question (again)

[FutureT@xxxxxxx]

In a message dated 5/27/2008 9:28:58 P.M. US Eastern Standard Time,  
FutureT@xxxxxxx writes:

>Hi  John,

>Yes, I would agree that one would almost have  to run  LTR to run
>EFFICIENTLY at ONLY 120 BPS and we do know that   Kevin
>is runing his rotary at just 120 BPS. However, just from  the  sheer
>power levels that Kevin runs (up to 55 kVA & 21.6  kV  according 
>to the Youtube vids - that's over 2.5 amps!!),  the  transformer's 
>natural (Z) impedance would dictate closer to  .7 uFd, at  60 hz mains, 
>as Bart stated, for it to be LTR. Of  course with 400 amp  service and 
>running  >50 kVA, who  needs to worry about running  efficiently ;^)

>David  Rieben



Hi David,
 
I just want to clarify further regarding my prior postings.   Using a large 
pig
at 120 bps sync, one can vary both the cap value and the ballast  setting
to simulate a large coil or a small one.  But they should be  efficient
pretty much in all cases, unless the coil is real small maybe or too  large.  
For any particular choice of
cap value, one can adjust the ballast to obtain an STR, LTR, or  resonant
mode of operation.  There are limits to how large the cap can be of  course.
At some point the transformer won't be able to supply enough current  to
charge the cap.  But within some range, more or less equal  "efficiency"
will be seen regardless of the cap value.  A proper setting of the  ballast
will give slightly LTR operation (ballast-wise), and will give an  excellent
power factor.  I cannot stress enough that the term "STR, LTR, or  resonant"
is determined mostly by the setting of the ballast for pig or PT  systems.
In this sense they are very different than NST systems regarding the 
definition of those terms.  This has been discussed previously on  this
list years ago.
 
I don't happen to know if Kevin's present ballast is lossy or not.  I  know
that his original ballast was lossy, and he estimated that it may  have
been wasting half the power of the system if I remember correctly.  
He was probably only really using about 28kVA, and the rest of the
power was heating the ballast to terribly high temperatures very 
quickly.  It's possible too that Kevin has increased the  power and
perhaps the spark length, since the early days of 24 foot sparks.
In any case any lack of efficiency in Kevin's coil may be due to
ballast losses mostly.  It's possible too that he often simply
cranks up the power beyond what is really needed to obtain
a particular spark length.  It's often very windy in Oklahoma so he  may
need extra power to combat the wind, etc.  When the power is 
cranked really high from let's say a 140 volt variac, some saturation
will occur in the transformer and ballast, and contribute to  additional
"wasted" power draw.  If the system is running in resonant mode,
the extra high primary transformer voltage and ballast voltage 
due to resonance) will also increase saturation and losses to a great  
degree.  
 
Cheers,
John



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