My attempt is to put in more quantitative explanation of the phenomenon. The damage to the 60hz transformer on 50hz operation arises because of initial the operating point on the B/H curve of the transformer core. Assume, for example, the initial operating point is B=1.2T, H=1000 At/m (from post#48) instead of B=1.5T, H=3000 At/m. For 20% increase in flux density i.e for B=1.44T, H=2600 At/m (approximately). So the increase is 2.6 times and so the corresponding no-load current is only 13%. So no problem with no load operation of 60hz transformer on 50hz.
Relative size and Arc Flash Hazards of 50 Hz versus 60 Hz transformers at same KVA
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mivey
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You could design a transformer to work at both 50 and 60 Hz. The part of the puzzle that you are missing is that a 60 Hz transformer will be designed with efficiency in mind. It will operate near the knee point and actually slightly beyond for higher voltages. They design them to operate at near maximum flux density that keeps the transformer within specs (and allow for 10% overvoltage).
For a 60 Hz transformer, there is just not enough goody left to operate it on a 50 Hz system. The opposite is true for the reverse: You could operate a 50 Hz transformer on a 60 Hz system but it will not be as efficient as a 60 Hz transformer so it makes more sense to use a 60 Hz transformer on a 60 Hz system.
mivey:
You should note that after knee point i.e after saturation, the relative permeability of the transformer core is unity and the transformer behaves as if it is air-cored. But even at this stage there is increase in flux density (albeit very slight) with increase in field intensity ( Examine the magnetization curve for steel in post#48) So it is interesting to find answer to the question in
You should note that after knee point i.e after saturation, the relative permeability of the transformer core is unity and the transformer behaves as if it is air-cored. But even at this stage there is increase in flux density (albeit very slight) with increase in field intensity ( Examine the magnetization curve for steel in post#48) So it is interesting to find answer to the question in
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One result is that if the applied voltage drives the core past saturation, the "magnetization" current in the primary will become larger by the ratio of the original permeability to one. Would five times the design current affect the performance of the transformer?
Assuming that your assumed B is a valid assumption.
It isn't - if we're sticking with real transformers in the real world, that is.
I suspect that you picked 1.2T to get an answer you wanted.
But Mivey is right. Transformers are designed to operate at or about the knee and typically around 1.5 - 1.6T.
To operate at a lower flux density would make the transformer larger and heavier and thus more costly to manufacture which would disadvantage the manufacturer against competitors.
To find a close estimate of the ratio, examine the curve for steel in post#48 at point B=1.5T and H=3000At/m. Since the curve may be assumed to be a straight line ( saturation!) from this point onward, an estimate of the angle it makes at this point with the line parallel to the X-axis is required. Shall we take the tan of this angle to be 0.000002?
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So, what do you calculate from that?
And what value of H did you get?
mbrooke
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Just jumping in and reading this for the first time, I never thought about it before considering all my work is with 60hz rather than 50.
2 questions came up for me. Doesn't a higher impedance mean poorer voltage regulation? Does this mean a 50hz transformer has poorer voltage regulation?
2 questions came up for me. Doesn't a higher impedance mean poorer voltage regulation? Does this mean a 50hz transformer has poorer voltage regulation?
All other things being equal, which of course they are not, inductive impedance is lower at lower frequencies.
Inductive impedance is XL
XL = wL
w = 2*Pi * f
Lower frequency f, lower w, lower 2*Pi * f, lower XL
w is omega but I can't post the correct symbol here.
Others might know how to.
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mbrooke
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180000 At/m.
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So, what would you conclude from that?
What an entirely unreasonable and, actually, quite erroneous conclusion!
I printed out the curves, made some physical measurements to get scale and came up with a slightly lower figure of 150,000 At/m.
Within the resolution possible on A4 and the thickness of the line, the values are certainly comparable.
So, what do you conclude from that? From either figure?
mivey
Senior Member
That you will need to procure some fuses from the plumbing department.
Or a CO2 fire extinguisher?
mivey
Senior Member
Running shoes.
A good alibi.
Marshmallows.
Any number of things other than a precise At/m value.
Do you think the penny has dropped?
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