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Single Phase Induction Motors are not self-starting unless they are started as quasi-two phase motors. This necessitates a starting winding, with or with out starting capacitors, which is switched out once motor is accelerated. A centrifugal gear having flying weights and a mechanical contact type switch is most commonly used to do this function. This paper describes a non-contact type; non - mechanical type, electronic switch that eliminates contact sparking and mechanical assembly criticality, thereby improving the reliability, motor life and servicing cost. The various types of electronic starters available in market operate on different principles like time delay or capacitor voltage or winding turns ratio or phase difference between start and run windings. The operation of the electronic starter, described in this paper, is based on actual shaft speed, similar to mechanical switch, but switching the capacitor / winding electronically. The starting capacitor and/or the winding is switched out based on the simple speed feed back data obtained. The switching instant is decided by a micro-processor based logic circuit using speed feedback and the switching is done using single/multiple semi-conductor switches. Electronic starter reduces the inventory cost due to its flexibility. |
