Totul despre... TRANSFORMATOARE de retea. Intrebati aici!

[Marian]

Tessla este o procarie sa crezi ca un traf toroidal este ceva mai mult decat un banal traf, si ca functioneaza diferit fata de cele EI, zau asa, este inadmisibil sa sustii o asemenea elucubratie. Defineste tu tehnic cum anume functioneaza un traf toroidal altfel decat cel EI? Da, geometria este altfel, asa si? ce il face pe el mai cu mot?

 

Emil, morala motivului pentru care am sters link-ul ala este ca nu e bine sa pui botul la toate prostiile de pe iutub, ci trebuie sa incerci tu sa iti explici teoretic cum functioneaza fiecare lucru, sa cauti raspunsuri in lucrari tehnice consacrate, si nu in mituri fanteziste de pe iutub...

[flomar60]

Conteaza foarte mult si cuplajul electromagnetic intre primar/secundar...la toroidal cuplajul este f. strans, modul de bobinaj si forma miezului permit asta si merge calculul cu o constanta mai mica...la traful meu de 1000W am 70% din suprafata miezului acoperit de bobinaj, de asemenea cuplaj strans, rezultate bune....am terminat de curand un alt proiect/experiment cu un traf extraplat adica bobinajul este scurt si inalt fata de celalalt la care era lung si subtire...si acest traf a fost calculat cu 1,1T inductie tot pe 8cmp dar rezultatele sunt mai slabe...voi prezenta tot proiectul in curand si vom putea face comparatii...

[Emil 1986]

ok marian!acum nu sunt rautacios dar  explica-mi tu cum merge traful ala cu tole L+L  toata ziua bobinat cu 38/s daca nu geometria il face mai cu mot cum zici tu,sau cele toroidale care sunt bobinate si cu 35/S?

[danpin]

Toroidal Transformer Basics  

General

A toroid is a doughnut-shaped object whose surface is a torus. Its annular shape is generated by revolving a circle around an axis external to the circle.

A coil of insulated wire in a doughnut shape (usually with a core of iron or similar metal) is an example of a toroidal object. These are used as inductors in circuits such as low frequency transmitters and receivers because they possess higher inductance and carry greater current than similarly constructed solenoids. They are also used as transformers in main power supplies. Toroidal coils reduce resistance, due to the larger diameter and smaller number of windings. The magnetic flux in a toroid is confined to the core, preventing its energy from being absorbed by nearby objects.

In the geometry of torus-shaped magnetic fields, the poloidal flux direction threads the "donut hole" in the center of the torus, while the toroidal flux direction is parallel the core of the torus.

Advantages of Toroidal Power Transformers

Toroidal transformers offer many advantages over standard laminated power transformers. Toroidals provide quiet, efficient operation with very low stray magnetic fields. Their small size and weight support a package that is easy to design into any application.

The Toroidal Core

At the heart of the toroidal is a highly efficient donut shaped core. To construct the core, grain-oriented silicon-iron is slit to form a ribbon of steel which is then wound, like a very tight clock spring. The result is a core in which all of the molecules are aligned with the direction of flux. Molecules not aligned with the flux direction increase a core's reluctance (the capacity for opposing magnetic induction), degrading performance to the level of common steel when the molecules are 90 degrees out of phase. EI laminated cores, which are stamped from grain-oriented Si-Fe, may have as much as 40% of the total core area perpendicular to the ideal grain direction, with another 40% acting only as a return flux path. This more efficient use of the core material in a toroidal can result in a size and weight reduction of up to 50% (depending on power rating), allowing the design engineer to innovate by exploiting the toroidal's small size, low weight, ease of mounting, and flexible dimensions.

Efficiency

Since toroidal cores are constructed of a continuously wound ribbon, there is virtually no air gap. The windings are evenly wrapped over the entire core allowing the transformer to operate at a higher flux density than in standard transformers. Toroidal transformers can operate at 1.6 to 1.8 Tesla (16,000 to 18,000 Gauss) while EI cores are limited to 1.2 to 1.4 Tesla (12,000 to 14,000 Gauss). The magnetic flux of the windings is oriented in the same direction as the grain-oriented core, thus achieving very high electrical efficiencies. Efficiency is a measure of a transformer's ability to deliver the input power to the load. Efficiency is expressed as a percent by:

% = ( P_O / P_I ) x 100

where; P_O = Output power, P_I = Input power, % = Efficiency

Also, standby losses are greatly reduced under no-load operation due to the lower magnetizing currents required by the toroidal core.

Stray Magnetic Fields

The primary cause of leakage flux from any transformer is the air gap. Ideally, a magnetic circuit should have no air gap. In traditional transformers with EI laminations stacked to form the core, the air gap at the junction of the I and the E is the source of most of the leakage flux. This flux strays into the surroundings due to the high reluctance of the air and the concentration of flux in the laminations. For the same reasons, mounting holes and grooves in the laminations also cause a small amount of leakage flux. The tape wound cut-C core is an improvement; but there is still an large air gap causing unwanted stray flux. Since toroidal cores are wound from a continuous ribbon of steel, stray fields from air gaps are eliminated.

In addition, the windings of the toroidal transformer uniformly encase the core in copper. This results in a natural magnetic screening effect which, in combination with the elimination of the air gap, results in an 8:1 reduction of radiated magnetic field over an equivalent rated EI transformer. The windings covering the solid ring core also help reduce magnetostriction -- the main source of acoustic "hum" in standard transformers. Audible noise can be reduced even further by varnish impregnating the toroidal core and/or the copper windings.

Duty Cycle

Significant reductions in transformer size and weight may be realized in many cases where the transformer is loaded intermittently. In such cases, the load is on (t_ON) for only a small portion of the total period (t_CYCLE). The period is much shorter than the thermal time constant of the transformer. To calculate the nominal power rating (VA) of the transformer use the following equation:

P_NOM = P_LOAD t_ON / t_CYCLE

where; t_CYCLE = t_ON + t_OFF

Regulation

The regulation (percentage of voltage drop) may be expressed with the following equation:

% Regulation = [( V_NL - V_FL ) / V_FL ] x 100

V_NL = Open circuit, no load voltage

V_FL = Full load voltage

Common values for regulation are around 5%. However, regulation can be adjusted to conform to most requirements. Regulation is inversely proportional to efficiency, physical size, and cost, and is directly proportional to temperature rise. All these factors should be taken into consideration when the regulation spec is determined.

Size Considerations

While the cross-sectional area of the toroidal core must be held constant, the height and diameter may be varied to meet package constraints. The functional optimum ratio of diameter to height is 2:1. A 3:1 ratio may be used in applications where a very low profile is required. And if a minimum footprint is required an aspect ratio of 1.5:1 could be considered. The only physical restrictions on the size of a toroidal transformer are the limitations of the winding machinery. A minimum center hole must be maintained in order to permit the insertion of the winding magazine, for application of the wire and insulation.

Temperature Considerations

Operating temperature is an important safety factor which must be considered. It is common to see a 60C to 70C rise above ambient at rated power. Heat generated by the power transformer is due to the sum of the copper and, to a lesser extent, the core losses. Since copper has a positive temperature coefficient, its resistance increases with temperature. As the temperature of the coil rises, the DC resistance of the windings also increases, resulting in a self heating cycle. Temperature rise can be reduced by increasing both the diameter of the winding wire and the size of the transformer. However this is at the expense of increased costs. Tabtronics transformers utilize UL recognized insulation systems for Class B (130C) operation. Temperature rise will also depend on where and how the transformer is mounted and how well it is cooled. When higher temperature ratings are needed, we offer UL recognized systems to Class F (155C) and Class H(180C).

 

 

"Transformer Basics

 

Part II: Toroidal vs Laminated Construction

 

Tradeoffs associated with the selection of EI laminated or tape-wound toroidal cores include cost, circuit application, weight efficiency, shape and volume.

Power transformers are available in a variety of configurations, primarily determined by the type of core selected. For the most part, they boil down to one of two types: EI laminations and tape- wound toroidal cores. The tradeoffs involved in selecting one over the other usually include cost, circuit application, weight efficiency, shape and volume. Regardless of which type is chosen, the electrical function is the same: one or more electrically conducting coils coupled together through magnetic induction.

 

Core selection has the greatest effect on transformer size and volume. EI laminations and tape- wound toroidal cores, though available in the same materials exemplify these differences. Toroidal construction is the winner in most of these areas, for the following reasons:

 

Because of its construction, the winding occupies the full periphery of the core, resulting in reduced leakage inductance and stray magnetic fields, as well as reduced hum.

The tape used in building toroidal cores is usually thinner than the commonly-used laminates (tapes are usually 9 or 11 mils thick, as opposed to 14 mils in 29M6 or 18 mils in 26M50). This permits the transformer to be operated at higher influx densities without undue increase in core loss and exciting current.

The air gap in toroidal cores is significantly lower than that of interleaved EI cores. This results in a higher stacking factor (0.95 vs 0.90) and improved volumetric efficiency.

Toroidal cores do not require a bobbin, making more window room available for magnet wire.

There are two disadvantages associated with toroidal cores. The first is price. The nature of a toroidal core necessitates slower, more complex winding techniques, particularly for high-voltage or multi-output transformers where many wire changes or many turns are required. In addition, high levels of isolation to meet safety agency requirements are easier to achieve with EI laminations because of ability of split bobbin and dual bobbin assemblies. The price differential is most significant for sizes up to 300 VA.

 

In addition, for high-power units 1500 VA and up, the improved stacking factor due to low air gap also causes high inrush current. EI laminations offer inherently lower inrush current, and the problem can be further reduced by introduction of an air gap into the construction. This is far more difficult and expensive to do with a toroid. It sometimes becomes necessary to add a resistor in series with a primary of a toroidal transformer to prevent destruction of overload protectors on turn-on.

 

At the same time, there are ways of minimizing the disadvantages of laminated construction. The detrimental effects of stray magnetic fields and induced hum can be reduced by locating the transformer as far away from sensitive areas as possible, rotating the transformer so that magnetic fields are perpendicular to one another, or via magnetic shielding. Mechanical hum within the transformer can be reduced with a quality impregnation/potting system (i.e., vacuum impregnation and/or overpressure).

 

Stray field emissions can be reduced by using UI laminations. This structure, often called hum-bucking or semi toroidal, uses opposing fields in opposite legs of the core to cancel one another. Signal's LP and IF series are built this way.

 

Today, most power transformers are built with EI laminations. Most engineers, recognizing the quality and price advantages of a wide array of standard, off-the-shelf products, reserve toroidal construction for those applications where the size and weight benefits outweigh availability and price."

 

Why toroidal transformers and inductors are better: magnetic field structure

     

 Efficiency with toroidal transformer is higher than with E cores transformers. Efficiency of up to 98% can be reached without significant increase in cost or size.

 

Sursa:

http://www.raftabtronics.com/TECHNOLOGY/ElectromagneticBasics/ToroidalTransformerBasics/tabid/112/Default.aspx

http://www.avsforum.com/forum/90-receivers-amps-processors/552532-transformer-questions-toroidal-vs-standard.html

http://www.traftor.com/why-toroidal-transformers-and-inductors-are-better-magnetic-field-structure-12/

[Emil 1986]

http://www.emil.matei.ro/tor.php

[flomar60]

Daca observi,Emil, in calculul prezentat de d-l Matei , pe masura ce creste puterea trafului scade sectiunea cu un coeficient 1,1...1,3 dar creste numarul de spire pt. ca acel coeficient se imparte la sectiune care e mai mica...apoi scade si densitatea de curent admisa pt. conductoarele bobinajului...

[Emil 1986]

da dm flomar,era pt marian care spune ca toroidalele nu-s mai cu mot

[TESSLA]

. Toroidal transformers can operate at 1.6 to 1.8 Tesla (16,000 to 18,000 Gauss) while EI cores are limited to 1.2 to 1.4 Tesla (12,000 to 14,000 Gauss). The magnetic flux of the windings is oriented in the same direction as the grain-oriented core, thus achieving very high electrical efficiencies[

Q. E. D.Cred ca acum e clar ca valoarea inductiei din formula nu depinde doar de calitatea materialului din care e facut miezul ci depinde si de geometria miezului iar asta nu din cauza ca miezurile toroidalelor s-ar raci mai bine.

[Mishu_17]

Buna ziua, doresc sa achizitionez un transformator toroidal Indel (150VA, 30V) pentru o sursa de alimentare. Are cineva in dotare un transformator Indel? Daca da, va rog sa imi spuneti cat de mult se incalzeste in gol si in sarcina ? Merita sa achizitionez unul sau mai bine ma orientez spre alt producator ? 

Editat Iunie 11, 2015 de Mishu_17

[vera]

Fiecare vrea sa aiba dreptate. Adevarul, este undeva la mijloc. La rece, pt. tole EI, FeSi, grosime 0,35mm, B variaza functie de putere (pt. acelasi material), intre 0,9T (cativa VA) si 1,35T (pt. puteri peste 400VA). La cald, B poate fi luat mai mare.

Intr-adevar, tolele EI, particula orientata, au un dezavantaj, fata de toroid, deoarece pe 2 laturi, fluxul nu este in aceeasi directie cu orientarea particulelor.

Editat Iunie 11, 2015 de vera

[UDAR]

 Nu insist cu chestia că toroidalul se răcește mai bine , poate greșesc.

Totuși : http://www.traftor.com/toroidal-inductors-transformers-advantage-thermal-issue/

[gica70]

Se stie ca la E+I fluxul central este suma celor 2 de pe laturi dar, din ratiuni practice, sectiunea centrala este egala cu fiecare sectiune de pe laturi; si de aici apare "risipa" de miez.

[TESSLA]

Da, pai se vede clar, in stanga un miez mai rece si in dreapt un miez mai cald!Bravo domnul Vera, ca ati avut puterea sa recunoasteti ca tolele e plus i au un dezavantaj fata de toroidale. Nu ca domnu Marian care a stiut doar sa mă ironizeze si sa-mi spuna ca e o PORCĂRIE sa sustin ca trafurile toroidale is mai cu mot, ca sa il citez tot pe el. Fără sa argumenteze in nici un fel. Atitudinea sa lasa de dorit! Moderator fiind ar fi trebuit sa fie mai retinut, mai ales daca nu avea alte argumente sa mă contrazica!

[Marian]

Daca este ceva ce detest cel mai mult, aia este asazisa "manipulare" a discutiei, lucru pe care si tu l-ai facut aici Tessla, sa rezumam:

 

http://www.elforum.info/topic/11-totul-despre-transformatoare-de-retea-intrebati-aici/?p=1192268

 

Acolo Dl Flomar face retrimitere catre aici:

http://www.elforum.info/topic/11-totul-despre-transformatoare-de-retea-intrebati-aici/?p=1173988

 

Unde dansul ne prezinta si formula de calcul respectiv 1/4,44*f*S*B. Ok pana aici toate bune, mai departe aici:

http://www.elforum.info/topic/11-totul-despre-transformatoare-de-retea-intrebati-aici/?p=1192362

 

Tu vii cu ipoteza ca formula respectiva este valabila numai la trafurile EI, ulterior la intrebarea D-lui Crisan, spui tu insuti ca nu stii ce sa raspunzi, cu alte cuvinte nu ai argumente:

http://www.elforum.info/topic/11-totul-despre-transformatoare-de-retea-intrebati-aici/?p=1192406

 

Apoi plusezi:

http://www.elforum.info/topic/11-totul-despre-transformatoare-de-retea-intrebati-aici/?p=1192415

 

Si spui ca formula nu poate fi valabila pentru ca din punctul tau de vedere doar o valoare a inductiei mai mare nu justifica ceea ce tu pretinzi a fi gasit, si concluzionezi cu opinia cum ca este implicata si geometria miezului, cum anume nu argumentezi ( o fi magie, mai stii... ).

 

Aici:

http://www.elforum.info/topic/11-totul-despre-transformatoare-de-retea-intrebati-aici/?p=1192423

 

Si apoi aici:

http://www.elforum.info/topic/11-totul-despre-transformatoare-de-retea-intrebati-aici/?p=1192449

 

Dl Crisan si apoi UDAR, incearca sa te lamureasca faptul ca formula e aceeasi si ca singura diferenta posibila este tocmai inductia, fapt pe care tu l-ai negat explicit anterior, dar incepi sa constati tu insuti ca te insesli si discret intorci sensul discutiei intr-unul care sa te avantajeze.

 

Adica ai pornit de la o ipoteza abstracta ( ca sa nu zic obscura ) pe care tu insuti nu o poti explica, urmand ca dupa ce colegii te-au lamurit, sa schimbi sensul in asa fel incat sa para ca de fapt tu tocmai asta ai zis, si deci toti ceilalti erau in eroare ( mai ales eu care am sustinut unul si acelasi lucru traful de retea functioneaza fix la fel indiferent de geometrie, deci formula este fix la fel ). Spune-mi te rog cine a gresit si cine nu a avut argumente? Da stiu, sunt sigur ca vei zice ca tot eu, orgoliul uneori e prea mare ca sa-ti asumi propriile erori, unde mai pui ca se sifoneaza si imaginea... Sa fii convins ca devin ironic atunci cand dezbatem cu atata patos chestii elementare pe un topic maraton, am mai spus-o si ma repet, totul dar absolut totul este discutat si ras, ras, ras, ras.....ras discutat aici pe acest topic, cei care inca aveti dubii purcedeti la a citi si incetati a mai bate apa in piua.

[vera]

Un alt mare avantaj al toroidalelor, este ca nu prezinta intrefier, ca tolele EI. Tehnologic, intrefierul min. la EI, este de cateva zeci de microni (nu stiu cat este la cele stantate cu laser).Incalzirea la transformatoare, este o problema complicata. Nu gasesc acum graficul, dar pt. EI, este dat la mijloc, cea mai mare temperatura, spre extremitati, mai mica. Unii, recomanda sa se lase intre bobina si tole 2-3 mm, pt. ventilatie.La toroidale, infasurarile au contact cu aerul pe o suprafata mai mare. In plus sunt cateva straturi, care nu au o rezistenta termica asa mare, precum zeci de straturi, ca la EI.In ambele cazuri, daca este calculat prost, se defecteaza.