Re: [TCML] MOT Measurements

[johnbrooks@xxxxxxxxxxx]

Hi Bart,
   15/30 eh?
Would these measurements (X2) work for the 15/60?
Joe

On Mon, 12 Jan 2009 19:58:53 -0800, "bartb" <bartb@xxxxxxxxxxxxxxxx>
said:
> 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
> 
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