In the article is presented a method of modeling processes in a run down regime of an induction motor with a squirrel-cage rotor with broken bars. This method based on the mathematical model of induction motor with a squirrel-cage rotor. Differential equations of this model are composed of mesh current method for line-to-line voltages. This method allows to calculate the harmonic spectrum of current distribution in rotor bars, the rotor speed, the damping coefficient of the currents in the run down regime and the electromotive difference of potential induced in the stator windings, with an accuracy of 10-15%. Results of calculation and experiment are presented in the article.
Słowa kluczowe: diagnostic system of rotor, mathematical model of the induction motor, run down regime, broken rotor bars.
W artykule opisano modelowanie silnika indukcyjnego z uszkodzonym wirnikiem na etapie zwalniania ruchu. Metoda pozwla obliczać widmo prądu w prętach wirnika, prędkośc wirnika, wspólczynnik tłumienia prądu oraz potencjał indukowany w uzwojeniu stojana. Wyniki obliczrń porównano z danymi eksperymentalnymi.
Keywords: diagnostyka, silnik indukcyjny, uszkodzenie wirnika
Damages from operation of an induction motor (IM) with a short-circuit rotor when its bars are broken are mainly expressed in increased power consumption . At the same time, the cost of power over consumption for the year of operation of such IM often exceeds the cost of engine itself. Due to this fact there are many proposals on how to diagnose this type of damage during operation[3,10-23]. However most of them cannot be realized because of the effect of electric network parameters fluctuations, IM vibrations and resistance moment variation load on the measured signal. These effects can be ignored if IM diagnosis is carried out during run-down regime[3, 24-25]. However under these conditions development of such a diagnostic system without process simulation in IM is impossible. IM run-down regime starts when it is disconnected from the power network. Immediately after IM switching off the currents in stator winding become equal to zero and currents in rotor winding remain the same as they were at the moment of shutdown. Thereafter due to the fact that active resistances are available in the rotor windings attenuation of them occurs. At the same time speed of rotor rotation slows down under the impact of resistance moment in IM bearings, its air fan and drive mechanism. As a result EMF is changed in stator windings not only in terms of magnitude but in frequency. Mathematical model of induction motor In order to simulate processes occurring when IM runsdown with a broken rotor bar it is convenient to use a mathematical model differential equations of which are compiled by the method of loop currents for phase-to-phase voltages. According to this mathematical model, taking into account Fig. 1 (K keyswitch closed) and application (1) = [...]
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