There are some references on the web you should examine:
http://en.wikipedia.org/wiki/Silicon_steel
Here you can download a material properties spreadsheet:
http://www.protolam.com/page5.html
Here is an online catalog with mostly powdered iron and ferrite specs, but there is some information about laminations:
http://www.tscinternational.com/tscwebcat2007.html
There is a page with pertinent formulas near the bottom.
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Good quality transformers are made with silicon steel laminations that come in different grades, with designations such as M6, M19, M27, and so forth. What they mean is this:
The number after the letter "M" is 10 times the
maximum power loss per pound, with sine wave excitation at 60 Hz, and a peak flux density of 15,000 gauss.
That is, M6 laminations will have a
maximum core loss of .6 watts/pound; M19 laminations will have a
maximum core loss of 1.9 watts/pound, etc. (all at 15,000 gauss and 60 Hz sine wave excitation).
There do exist grades M2, M3 and M4, but they are expensive, and generally not used except in special circumstances. Typically, a good quality transformer will use M6 lams, which is probably what your transformer uses.
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I have encountered the same problem you're having in the past. I suspect your problem is this:
M6 laminations are specified to have a
maximum loss of .6 watts/pound, but as typically shipped, they will have substantially less loss than that. I measured the loss in numerous shipments of M6 material, and typically the loss was 70% of the
maximum.
We had been using a certain transformer built with M6 laminations, and when the product was first designed, a person without intimate knowledge of magnetics had measured the no-load excitation current and added 10% to that value and set that number as the go/no-go limit for the transformer.
Then one day, we got a shipment that was right at the limit for core loss, and the excitation current was over that previously set limit. Everybody got all excited, believing that we had received a bad lot of laminations.
You can't determine a go/no-go limit that way.
What you have to do is get the dimensions of the core and calculate the weight of iron. Then, knowing the number of turns on the primary, the cross sectional area of the center leg, and the applied voltage (sine wave), you can calculate the peak flux density. If it's near 15,000 gauss, then you should expect a
maximum core loss of .6 watts/pound (if the core material is M6), and you just multiply the core weight (in pounds) by .6 to get the expected maximum core loss.
If the peak flux density is not 15,000 gauss, then you'll have to find a curve in the manufacturer's data showing core loss per pound for other flux densities.
The weight of standard core sizes, with a correction for stacking factor, is typically given in the manufacturer's data for a square stack. I see this data in:
http://www.tscinternational.com/tscwebcat2007.html
A square stack is a stack of laminations such that the height of the stack is the same as the width of the center leg. For other stack heights, use proportions.
Finally, in the spread sheet you posted, I see that you have used an LCR meter to make some measurements, and you have listed core loss as a resistance value. That is not core loss, nor is core loss the product of the primary exciting current and the exciting voltage. Core loss is measured in watts, and must be measured with rated voltage applied to the primary (the LCR meter is only applying about 1 volt or less). To get an accurate measurement of core loss you need a special wattmeter such as:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=230399762953&ssPageName=STRK:MEWAX:IT
or perhaps a more modern electronic wattmeter. Your transformer is rather small, and the core loss is probably under a watt.
I see that you have an Agilent scope, and I suspect it has a math function. You can get a value for the core loss to perhaps 10% accuracy using the scope.
Measure the primary current on channel 1 of the scope, and the applied primary voltage (set to 120 VAC) on channel 2. Use the math function, set to multiply channel 1 times channel 2, the use the measure function to display the mean (or average) of the math function. This will be the total no-load loss. You must subtract the copper loss to get the core loss. The copper loss is equal to the square of the excitation current times the DC resistance of the primary winding, where the DC resistance was measured at ambient temperature. Make the scope measurements with the transformer also at ambient temperature; don't allow the transformer to sit on the bench, powered up for hours, before making measurements.
To check the calibration of the method, temporarily replace the primary of the transformer with a 2 watt, 15,000 ohm resistor. The scope should indicate a power of 120*120/15000 = .96 watts.
It is very likely that in the past you have been receiving transformers whose core material was substantially better than the rated maximum loss, and now you have received some whose core loss is right at the maximum allowed. If this is the case, you have no complaint against the transformer manufacturer.
You shouldn't really care what the loss is at 132 VAC applied, but you certainly could determine what the loss should be at the flux density that occurs with 132 VAC applied.
You should also understand by now that the excitation current isn't really what you should care about; it's the actual loss, measured by a wattmeter method, that matters. And, especially, the excitation current at an elevated primary voltage may not be a significant indicator of core material quality. The elevated primary voltage pushes the core further into saturation, which increases the excitation current peaks. This increases the no-load copper loss proportionately more than it does the core loss.
You should get a suitable wattmeter to use for incoming inspection. The Kill-a-Watt meter mentioned in another post is not suitable. You could either use a scope to measure loss, or for best accuracy (at lowest cost; about US$650 for the electromechanical Yokogawa, several thousand for an electronic one), get a Yokogawa electromechanical meter such as the one I linked to on eBay. The one on eBay is not quite sensitive enough for your application, but Yokogawa does make one that would be. The lowest current range of the one on eBay is 1 amp, and you really should have one with a .2 amp range.
It's quite typical for small transformers to run into saturation somewhat, and that's ok. I have a high quality 12VA Stancor transformer, and the second image below shows the applied line voltage, and the excitation current. You can see that the core is driven into saturation.
The third image shows the result of using the scope to measure transformer loss. The red trace is the math function; it's the product of the applied current and voltage. The measured value is .419 watts. The measured DC resistance of the primary is 50 ohms, and the scope says the exciting current is .0282 amps, for a no-load copper loss of .04 watts. The no-load core loss is then .419 - .04 = .379 watts.
The first image shows formulas. It came from:
http://www.tscinternational.com/tscwebcat2007.html
So, before you get all worried, find out what core material the manufacturer of the transformer uses, and do the calculations. I would expect the transformer manufacturer to have an engineer on staff who knows all this, and they should be able to give you a
maximum core loss spec for that particular transformer.
