Czy wolisz polską wersję strony elektroda?
Nie, dziękuję Przekieruj mnie tamProf. Roman Kurdziel „Podstawy elektrotechniki” wydanie II całkowicie zmienione. wrote:The magnetic field in a vacuum depends only on the electrical circuits that generate it. In material environments, there is also the influence of molecular currents in particles of matter. An electron moving around the nucleus at the angular velocity omega_zero in an orbit with radius r represents an elementary magnetic dipole. Magnetic dipoles are usually arranged chaotically in the matter, so that the body does not show a magnetic state unless it is subjected to an external magnetic field, i.e. generated by external causes, e.g. current in any electrical circuit.
The elementary magnetic dipole placed in the external magnetic field is subject to a mechanical moment, which sets the electron, regardless of the orbital motion, in a precessive motion, similar to the motion of a fob. The axis of the precession is the field strength vector H. As a result, an additional magnetic field is created which slightly weakens the external field. This phenomenon is called diamagnetism.
For the reason given above, all bodies should be diamagnetism. However, in many bodies placed in an external magnetic field, the opposite phenomenon is observed, i.e. a certain strengthening of the external magnetic field. The o phenomenon can be easily explained if it is assumed that the electron, apart from orbital motion, rotates around its axis, called the electron spin. The electron spin is accompanied, regardless of the magnetic moment resulting from the orbital motion, by the spin magnetic moment p_s.
In individual atoms, some electrons spin in one direction, others in the opposite direction, which corresponds to the opposite sense of the spin moment. If the numbers of electrons spinning back and forth are equal, the sum of the spin magnetic moments is zero and the body exhibits diamagnetic properties, resulting from the orbital motion of the electrons. On the other hand, if the number of electrons with a certain direction of spinning prevails, the sum of the spin magnetic moments is different from zero and the atom exhibits a certain resultant spin moment, which in the external magnetic field tends to assume a position consistent with the direction of the field intensity. The spin dipole field and the external magnetic field add up, i.e. the presence of this type of matter increases the magnetic field in relation to the field that a given electric circuit would generate in a vacuum. This phenomenon is called paramagnetism.
The influence of the environment on the magnetic field is thus marked: in diamagnetic environments a decrease, and in paramagnetic environments an increase in the magnetic inductance B in relation to the inductance B_o that a given external field of intensity H would cause in a vacuum. The ratio of the resultant induction B to the intensity of the external field H is called the magnetic permeability of the environment
$$u = \frac{B}{H}$$
(...) At certain values of the ratio of the distance D between atoms to the diameter of the atom d, namely when 1.5
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_lazor_ wrote 3795 posts with rating 1130 , helped 259 times. Live in city Wrocław. Been with us since 2016 year.
TL;DR: 45 turns per volt at 50 Hz is a classic rule, and “the gap increases the number of turns” [Elektroda, ArturAVS, #18116092; lazor, #18117941].
Why it matters: Correct turns, gaps and wire size mean cooler, quieter, safer transformers.
• Turns-per-volt for 50 Hz silicon-steel cores: 43–48 t/V depending on grade [Elektroda, ^ToM^, post #18117870] • Recommended copper current density: 2–3 A /mm² for hobby builds [Schmidt-Walter]. • Typical ferrite saturation flux density: 0.30–0.45 T at 25 °C 3C90 Spec. • Welded microwave oven transformer (MOT) no-load current: “very high” (>1 A) [Elektroda, ArturAVS, post #18115998] • Air gap cuts inductance roughly inversely with gap length TI SLUP126.
Comments
I wound up my first network hit (and the next few) in primary school. My father subscribed to a young technician in which all necessary calculations were described. These transformers are still working... [Read more]
In general, the topic is beyond me, so after reading I did not speak, but since the topic of network transformers was raised, then I will ask for one detail, maybe I can find the answer to such a question:... [Read more]
I'm not an expert on network transformers, but they probably weld to minimize costs. After all, everything must fit tightly so that it does not buzz too much and the use of screws and flat bars would... [Read more]
It can really be an optimization of production costs, but whether such welding does not increase the loss in the core and more specifically eddy current. [Read more]
It increases, it also causes a large no-load current. Note, however, that such luck works casual. [Read more]
Me too but once it was normal because buying a transformer was not so easy. There is a simple way not to count complicated designs. When the mains transformer is called, count the turns when unwinding... [Read more]
Yeah, and who will want to count those unwound rolls? Simple and proven pattern: As I remember, this pattern has two characters differing in number 45 vs 44, one for continuous work and the other... [Read more]
However, times are changing and network transformers are less and less used. Instead they are switched-mode power supplies, which are highly optimized and often you can forget about rewinding. However,... [Read more]
I also used this obvious method. My father rewound the engines, I had access to virtually any size of DNE, and the winder that counted the unwound turns helped me count the turns. :) Unfortunately, it... [Read more]
By all means I meant mains transformers, where we have sinusoidal voltage. [Read more]
I think he used to? You can scroll it on the stick .. Once on the net I found a spreadsheet in exel to calculate goes. If I find it I will post on the forum. [Read more]
The reality of the 1980s. There was nothing to do with the carcass. In the factory where I had apprenticeships, the bobbins were made of ... fiberboard. [Read more]
With microwave welding from a microwave it seems a simple matter. It is about magnetostriction and acoustic experience that would accompany this size of a fully loaded transformer. Welding the sheet metal... [Read more]
Hello, I used to use the article from the Young Technician for calculations, then the Excel spreadsheet. Now it is the low and medium power power supplies that are replaced by switching power supplies.... [Read more]
Modern low power industrial on classic EI shapes are also welded. I suppose that in this case the reduction of production costs is of particular importance. [Read more]
No, the higher value was for small transformers and the smaller for larger ones made of better transformer sheet. The counter ranged from 43 to even 48. It all depends on which core and transformer the... [Read more]
All in all, you don't need to include insulation between packet sheets in your formulas and add a column fill factor? [Read more]
It is a pity that the assumption in the calculations is the lack of a gap. In practice, the gap is very important, because although it reduces inductance, it protects against saturation of the core. Unfortunately,... [Read more]
Generally, the slit causes many unwanted effects like: - increasing the number of turns - the stream in the crevice likes to run sideways, which can cause problems with EMI - energy accumulation... [Read more]