Prof. Eng. Alecsandru Simion, PhD, Assoc. Prof. Eng. Leonard Livadaru, PhD, Assist. Prof. Eng. Adrian Munteanu, PhD
Rezumat
In vederea analizei masinii asincrone trifazate in regim de masina sincrona (masina asincrona sincronizata
MAS) se apeleaza la ecuatiile diferentiale de ordinul I exprimate numai in fluxuri totale si unghiul de rotatie. Se obtine un
sistem de 8 ecuatii care se refera: la cele 3 faze statorice, la cele 3 faze rotorice, (dintre care 2 sunt inseriate si sunt alimentate de la o sursa de curent continuu, constituind infasurarea de excitatie, iar cea de-a treia constituie infasurarea de
amortizare, fiind conectata in scurtcircuit), la care se mai adauga 2 ecuatii de miscare. Aceasta abordare permite obtinerea unor informatii directe-precise despre fenomenele care au loc in masina, inclusiv si despre directiile de actiune ale fluxurilor
magnetice adica despre unghiul intern instantaneu. Pe baza acestor informatii se pot adopta strategii adecvate si lua
decizii pertinente privind momentele favorabile ale cuplarii infasurarilor la surse. Trebuie evitata situatia de decrosare, de exemplu, cand se declanseaza un regim tranzitoriu electromecanic cu constanta de timp mare, care intarzie procesul cu o
durata care poate fi egala cu dublul timpului necesar pornirii. Se insista asupra utilizarii hodografului fluxului rezultant rotoric ca instrument eficient, cu reale valente didactice in aprecierea comportarii masinii de inductie sincronizate in diverse regimuri: tranzitorii sau stationare.
Cuvinte cheie: motor asincron de putere mareconditii de pornire specialedoua colivii rotoricesimulare MEF
Abstract
For the analysis of the three-phase induction machine under synchronous operation (the so-called synchronized
induction machine, SIM) one uses first order differential equations that contains nothing but total fluxes and rotation angle.
The resulted 8 equations system characterize the 3 stator phases, the 3 rotor phases (2 of them are series connected and
fed from a DC source and the third is short-circuited and play the role of a damper winding) and the movement of the rotor
(the last 2 equations). This approach allows the obtaining of direct and proper information about the intimate phenomena
that take place inside the machine including the direction of magnetic fluxes, which leads to the instantaneous internal
angle. On the basis of this information, one can adopt proper strategies concerning the most favourable moment for the
connection of the windings to the supply sources. The pulling out must be avoided, for example when starts a transient duty
with high time constant which delays the process with a length that may attain twice the value of the starting time. The
hodograph of the resultant rotor flux is considered as a very effective tool, also for didactic purpose, that describe the
behavior of the synchronized induction machine under different duties such as transients or steady state.
Keywords: high power induction motorstart-up constraintstwo squirrel cages of distinct materialsFEM simulation
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