[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [TCML] MOT Measurements
Hi Bart,
the thread seems by no means boring! Apart from the sparkgap, the
transformer seems the most misunderstood element of a classic TC, even
though very old, and well known...
For my HV-transormers, since 2001, I'm routinely performing the kind of
measurements you nowadays do for the MOT (including wattmeter power
measurement). The interpretation of the measurements I do by means of an
"old 4-pole T-equivalent" Excel spreadsheet. The example for a 15kV/60mA NST
(230V/50Hz prim.)can be downloaded here:
http://twfpowerelectronics.com/~kurt/Downloads/FART_15_60_C.xls
The Excel can give a good feeling about the behaviour of a transformer, even
allowing to generate the vector graph in the complex plane, for different
loads: R, RL, L, RC, C. The parameter representation for use in Microsim's
linear transformer model is generated as well (Tab XFRM-Lin). Jim Lux's and
Terry's evaluations are recorded in separate tabs. The experiments are in
tab "FART 15-60". Unfortunately the sheet is not very presentable and self
explaining, and I've not yet added a description. The T seems a bit
overloaded with numbers, 'cause both views of the transformer - the one seen
from primary side, and the one from secondary side - are squeezed in the
same T (Primed ' values mean: as seen from the opposite side). I also have
to say sorry for part of the texts beeing yet in german language.
The additional wattmeter power measurements, allow the separation of the
resistive components of the transformer in iron and copper losses (as real
AC, instead of DC resistances).
I'm on the way to enter "Bart's MOT measurements" to the T-Excel.
What I begin to see:
MOT's are much more magnetically nonlinear than my NST's! - Soo..
the T for a MOT will be valid for essentially only a choosen point of
operation, while for an NST it can be considered valid for about the whole
nominal-power range. - Since I began investigating my transformers as T's,
I'm no longer wondering, why one can draw more than nominal power with an
NST. If the magnetic shunts begin saturating, ferroresonace may come to
play. But that's stuff for another posting.
The old Kapp-representation of the transformer reduces the T to just one of
the sides (LV or HV). This can be done, without loosing too much of
applicabability to real situations ('cause, anyway, it's difficult to
separate primary from secondary leak-inductance, copper resistance etc.).
This is well suited to investigate resonance effects. An Excel for the same
15/60 NST as above can be downloaded here:
http://twfpowerelectronics.com/~kurt/Downloads/NST_15_60_reso.xls
It also contains the generation of a complex-plane vector plot.
Best regards
Kurt
bartb wrote:
Hi All,
I hope I'm not boring you with this (I'm sure some are). But I think
the next step is to look at a 15/30 NST which has not been modified.
I have a couple on hand (Franceformers). I have a "gut feeling" that
we really don't know where shunted transformers (NST's, MOT's, etc.)
are truly at. Some resonant charging may or may not be occurring with
our tank cap values. All the programs (including my own Javatc) are
looking at Cres of non-shunted transformers. The shunted transformer
is a different beast and without measurements, only guesses.
These transformers force leakage inductance via the shunts to apply
regulation. This changes the transformer as we assume it to be as far
as currents, voltages, Cres, etc. The load also changes the output.
NST's will begin to suffer a voltage drop even with a small load.
MOT's are current beasts, and they will require larger loads before
significant change in output voltage is seen. Load impedance of
shunted transformers is yet another set of tests that should be
performed at some point.
I'll run through my normal 10V increment routine with one of my
15/30's. I'll set a variac to as near 10V as I can get, then measure
the open and short circuit primary currents as well as open secondary
voltage. Then head up to 20V and do all again. This is my routine as
it keeps the source voltage unchanging, and thus, the numbers for
Ioc, Isc, Vin, and Vout are all in very good agreement. My plan is to
first do this unloaded (basic transformer testing). But loading is
yet another issue.
If anyone has any additional thoughts, please let me know. For the
NST, considering it's low power, I can will also measure true power
as well as VA.
Best regards,
Bart
bartb wrote:
For an unmodified NST (shunts in tact), I expect Cres to be somewhat
near what we would expect (maybe), but Cres will change depending on
magnetizing current and current through the magnetic shunts. The
shunts have inductance with the AC cycle, and as current is
increased, the leakage inductance is increased. The result is a
rather significant changing reactance dependent ultimately on the
input voltage, and thus Cres will not be a constant throughout a
voltage range (such as driving an NST with a variac). The impedance
of a shunted transformer is not constant with varying input voltages
(which is counterintuitive to non-shunted power transformers).
Best regards,
Bart
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla