Under-voltage self-starting of the motor
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Hello everyone, I have a question and would like to ask for your help. A previous client’s equipment specification required that the motor have good under-voltage self-starting capability, enabling it to start successfully under a rated load when the bus voltage drops to 55% of the rated value. “ 1) Where does 55% in this requirement come from? I consulted many standards and design manuals, but it remains unclear. 2) Auto-start under low voltage – can the motor manufacturer provide the motor’s coasting curve? How to design the delay time? Another similar question: 3) If the motor is powered by two power sources, which can be switched via a switch, and it also uses star-delta starting for voltage reduction. During the transition period between the main and backup power supplies, the motor continues to operate at idle speed but while still carrying a load. Is it possible to start the motor under reduced voltage in such a situation?
55%? This is a bit excessive; I think few manufacturers are able to achieve this. Generally, it is stated that the voltage at the motor terminal should be above 70% in order to enable starting or restart under load.