The paper deals with a method of fault-tolerant control of an induction motor at damages in the stator power electrical circuit. The method bases on the decrease of the damaged phase flux linkage, which enables the reduction of the level of the consumed power variable component. The research concerned the cases of the stator winding damages at the early stage of their development. At such damages, the induction motor can operate for a long time in the asymmetric mode without protection actuation but with essential thermal overload of particular phases. The results of the research of the proposed system of fault-tolerant control confirmed the possibility of the decrease of the thermal overloads of the induction motor windings and frequency convertor semiconductor switches, which will allow the increase of their life span.
Słowa kluczowe: induction motors; frequency control; fault-tolerant systems
W artykule przedstawiono metodę kontroli odporności na uszkodzenia silnika indukcyjnego przy uszkodzeniach w obwodzie elektrycznym stojana. Metoda opiera się na zmniejszeniu uszkodzonego połączenia fazowego, co umożliwia obniżenie poziomu zużytej zmiennej składowej mocy. Badania dotyczyły uszkodzeń uzwojenia stojana na wczesnym etapie ich rozwoju. Przy takich uszkodzeniach silnik indukcyjny może działać przez długi czas w trybie asymetrycznym bez włączenia zabezpieczeń ale z istotnym przeciążeniem termicznym poszczególnych faz. Wyniki badań proponowanego systemu odpornego na uszkodzenia potwierdziły możliwość zmniejszenia przeciążeń termicznych uzwojeń silnika indukcyjnego i półprzewodnikowych łączników przemienników częstotliwości, co pozwoli na zwiększenie ich żywotności.
Keywords: silniki indukcyjne; kontrola częstotliwości; systemy odporne na uszkodzenia.
Damages in the stator power electric circuits stand out of the main causes of induction motors (IM) failure. Therefore, according to the research , the cause of 25% - 40% of IM failures consists in turn-to-turn shorting resulting from the stator winding insulation damages. The occurrence of turnto- turn shorting in the windings of IM of alternating current variable-frequency electric drives (ED) results in local overheat of particular semiconductor switches of frequency convertors (FC). A break of the whole winding or a parallel section of IM phase winding is a logical development of the turn-to-turn shorting. For IM with the number of parallel winding paths exceeding four a break of one path results in the asymmetry of the stator winding three-phase system and usually ends in the motor emergency outage. ED operation with asymmetric windings of the stator phases may also result in thermal overloads of particular FC switches and IM phases . Timely detection and elimination of IM damages at the early stages of their development may increase the life span of the technological equipment and reduce the financial losses caused by unpredictable disconnection of the equipment resulting from technological faults or IM failure. Thus, fault-tolerant control systems (FTC) are of special interest as they are able to detect various types of damages at the initial stage and operatively adapt the control law in such a way that ED functionality remains for a long time till there is a possibility of IM repair or change . There are two groups of the conventional methods of fault-tolerant control of IM with damages in the stator power electric circuit. The first group includes methods only allowing the detection of occurring damages and the termination of ED operation at their further development [4, 5]. This group may also include software redundancy methods based on the switch between the control algorithms from complex to simpler [...]
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