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Transformer steel ageing?
Transformer steel ageing?
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Old 19th April 2018, 03:12 PM   #11
popilin is offline popilin  Argentina
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Quote:
Originally Posted by Kay Pirinha View Post
This situation happens every time when a power transformer accidently is powered up at, or near the input voltage's zero crossing. In the next half wave a big current surge occurs, limited mainly by the primary's DC resistance. This may magnetize and saturate the core instantaneously. But within the next few full waves this magnetization vanishes.
That's the reason why we provide soft start circuitries to big power trannies.
Best regards!
Thanks for a very clear explanation. Fortunately it is a reversible process.

The same reversal mechanism is (was) used in CRT TVs at switch on, a "degaussing coil" (From Gauss I guess) uses the inrush current surge to remove the possible permanent magnetization of the CRT (its internal mask really)

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Old 19th April 2018, 05:22 PM   #12
VictorDQ is offline VictorDQ  Russian Federation
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Yes, over time, steel loses its magnetic permeability. Although insignificant. There are several reasons. One of them is the aging of steel due to the heating of the magnetic circuit due to losses during magnetization reversal of the cores and the release of heat by magnetizing windings. Electrotechnical steel is a magnetically soft material and features a small area of ​​the hysteresis loop.
The main parameter determining the area of ​​the hysteresis loop is the coercive force Hc.
Hc is mainly affected by internal stresses and non-metallic inclusions. The main reason for the growth in losses due to magnetic hysteresis is related to the distortion of the domain structure, while the carbon and nitrogen impurities have the greatest negative impact here. Those. heating impurities leads to a change in the internal structure of the metal. (the process is very, very long). If your transformer is not heated very much, then you can, do not worry about its magnetic properties.
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Old 19th April 2018, 06:22 PM   #13
Kay Pirinha is offline Kay Pirinha  Germany
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Quote:
Originally Posted by popilin View Post
The same reversal mechanism is (was) used in CRT TVs at switch on, a "degaussing coil" (From Gauss I guess) uses the inrush current surge to remove the possible permanent magnetization of the CRT (its internal mask really)
Not exactly the same. No CRT loves magnetizing the internal mask during the power up sequence. Due to a PTC in series and a NTC in parallel, the AC current through the degaussing coil starts at a high value and decreases within a few seconds to almost zero.

Best regards!
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Old 19th April 2018, 11:14 PM   #14
popilin is offline popilin  Argentina
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Yes, over time, steel loses its magnetic permeability. Although insignificant. There are several reasons. One of them is the aging of steel due to the heating of the magnetic circuit due to losses during magnetization reversal of the cores and the release of heat by magnetizing windings. Electrotechnical steel is a magnetically soft material and features a small area of ​​the hysteresis loop.
The main parameter determining the area of ​​the hysteresis loop is the coercive force Hc.
Hc is mainly affected by internal stresses and non-metallic inclusions. The main reason for the growth in losses due to magnetic hysteresis is related to the distortion of the domain structure, while the carbon and nitrogen impurities have the greatest negative impact here. Those. heating impurities leads to a change in the internal structure of the metal. (the process is very, very long). If your transformer is not heated very much, then you can, do not worry about its magnetic properties.
i) Steel does not lose its magnetic permeability over time, always is ferromagnetic.
ii) The increase on loses and decrease on magnetic permeability over time is called magnetic ageing.
iii) The magnetic circuit does not heat up, the magnetic material does.
iv) The solubility of C in Fe-3% Si is about 0.005% at 700C (!)
v) There is experimental evidence that the magnetic ageing is not only dependent on precipitate fraction (impurities) but also on other factors such as grain size and texture.
vi) On reasonable quality magnetic materials, the total losses (hysteresis and eddy current loss) decrease after heat treatment (80 hours at 225C). Furthermore, grain size and precipitate fraction increase whereas the texture slightly improves.

Experimental results mentioned by lcsaszar on post#8 are consistent with results from other researchers.


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Originally Posted by Kay Pirinha View Post
Not exactly the same. No CRT loves magnetizing the internal mask during the power up sequence. Due to a PTC in series and a NTC in parallel, the AC current through the degaussing coil starts at a high value and decreases within a few seconds to almost zero.

Best regards!
The mechanism is the same, but degaussing coil is designed to… how to say… degaussing.

In all my years as a TV repairman, never saw an NTC in parallel, just the PTC in series.

The NTC is to prevent the inrush current surge due to the uncharged big electrolytic capacitor on the input of PSU, and it has nothing to do with the degaussing circuit.
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Last edited by popilin; 19th April 2018 at 11:38 PM.
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Old 20th April 2018, 01:33 AM   #15
PRR is offline PRR  United States
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Totally off-topic: iron losses and aging was a big deal over a century ago. The old plain iron had high idle losses. For utility companies powered-up 24 hours with significant load only a few hours a day, this hurts. Transformer makers experimented, but didn't always know what they were doing. There is one case of guaranteed low-loss transformers that had to be taken-back after 4 months because they aged into high-loss transformers that quickly.

By 1910-1912 the makers knew about impurities. Some Silicon is good. Too much Carbon is bad. Raw iron has *many* other impurities, some of which do alter the iron over time, and the metallurgists learned to measure and control these.

The time period is interesting. Recall that the 1912 sinking of the Titanic partly involved unsuspected influence of Phosphorous and Sulfur in steel, making it brittle when cold. It was maybe the best they had at the time; we can wish they knew more.
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Old 20th April 2018, 03:08 AM   #16
popilin is offline popilin  Argentina
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Metallurgists now know how to deal with Carbon content, Nitrogen content is even easier to deal with.

I must wind my own transformers, for high quality the most available here is Brazilian M4 GOSS from Aperam South America, this company also published some papers, and the Carbon content for a cheap lamination (non-oriented grain, 2% Silicium content) is about 40ppm.

I want to think that the highest quality material is even better.
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Old 21st April 2018, 02:08 AM   #17
PRR is offline PRR  United States
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Quote:
Originally Posted by popilin View Post
Metallurgists now know how to deal with ...
1912 was a long time ago.

Quote:
Originally Posted by popilin View Post
...Brazilian M4 GOSS from Aperam...
I want to think that the highest quality material is even better.
I strongly suspect your M4 GOSS is about the same as M4 GOSS from anywhere else. Aperam is a global operation and everything they learn in europe or asia goes back to the Brazillian steel-makers. I do note that the Brazil plant cooks with eucalyptus charcoal instead of coal-coke; but as you say "none" of that carries over to the steel. The blast furnace turns iron-oxide ore plus carbon into carbon-dioxide and iron; ideally all the carbon burns out. Some lingers but a later step (perhaps the electric hearth) can adjust carbon up/down as needed for hard knives or mild laminations.
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Old 21st April 2018, 02:49 AM   #18
popilin is offline popilin  Argentina
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Originally Posted by PRR View Post
I strongly suspect your M4 GOSS is about the same as M4 GOSS from anywhere else. Aperam is a global operation and everything they learn in europe or asia goes back to the Brazillian steel-makers.
I do not know others, but Aperam M4 GOSS has high mechanical deviations in the same batch, from 0.23mm to 0.28mm, maybe is my provider, lamination quality is quite good.


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I do note that the Brazil plant cooks with eucalyptus charcoal instead of coal-coke...
Are you sure? Energy difference is high, mineral has about double than vegetal.

It can be seen in Aperam catalogs an eucalyptus forest, and the bio-friendly chatter, but do not trust so much in people from this side of the world.

Ah, by the way, carbon content of Aperam GOSS seems to be (11.7 0.9)ppm, but who knows...
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Last edited by popilin; 21st April 2018 at 03:14 AM.
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Old 21st April 2018, 08:09 PM   #19
Kay Pirinha is offline Kay Pirinha  Germany
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Originally Posted by popilin View Post
In all my years as a TV repairman, never saw an NTC in parallel, just the PTC in series.

The NTC is to prevent the inrush current surge due to the uncharged big electrolytic capacitor on the input of PSU, and it has nothing to do with the degaussing circuit.
German color TV's usually used a three pin component that combines both the PTC and the NTC which work as I've described. If present at all, the PSU's NTC was quite another story,

Best regards!
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Old 21st April 2018, 09:37 PM   #20
popilin is offline popilin  Argentina
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Originally Posted by Kay Pirinha View Post
German color TV's usually used a three pin component that combines both the PTC and the NTC which work as I've described. If present at all, the PSU's NTC was quite another story,

Best regards!
German color TVs used a three pin component which has two PTCs inside, one series connected to degaussing coil and the other paralleled with mains, replace one of them by an NTC is a recipe for disaster.

Dismantle an old Siemens or Telefunken 3 pin PTC and measure by yourself.
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Last edited by popilin; 21st April 2018 at 09:40 PM.
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