Pole current minimisation for synchronous motor start phase - has two stator winding circuits connected in series during start phase for double pole number and paralleled at half speed

摘要

The pole current reduction system is designed to minimise the pole claw-rotor currents during the starting phase of synchronous motors having salient poles. The motor is fitted with a switchable-pole stator winding which for start-up is connected so as to provide double the number of poles. At approximately half normal speed, the number of poles is reduced to normal. - The stator winding is arranged so that it comprises two circuits which during the doubled pole stage are in series and during normal pole operation are in parallel. During the second half of the starting phase (half to normal speed) a protion of the armture current flows via the pole core but due to centrifugal force on the pole, the contact between the pole and the rotor is enhanced so that no undue heating at the contact point occurs.