الفهرس | Only 14 pages are availabe for public view |
Abstract Starting medium voltage motors via autotransformers can result in high overvoltages stresses on the autotransformer winding. These overvoltages are owing to opening the circuit breakers during the motor acceleration before getting a significant speed, and the small inductive current chopping. Small inductive current chopping can lead to repeated reignitions and clearings when the breakers are opening. This leads to successive trapping of magnetic stored energy in the autotransformer winding and its subsequent release to the autotransformer and cables capacitances. The energy release drives the capacitances voltages to dangerous levels to the autotransformer winding. This sequence is frequently referred to as “multiple reignitions”. Using vacuum circuit breakers in such motor – autotransformer starting arrangements increase these overvoltages probability and severity due to vacuum breakers inherent excellent interrupting capability ofhigh frequency currents. |