| Squirrel-cage induction motors are widely used in energy conversion and industrial transmission and other fields.Its operational performance has a direct impact on production activities.As a common fault type in cage induction motors,rotor end ring broken faults will destroy the symmetry of the rotor circuit structures,leading to difficulties for the motor to operate continuously and stably,which will have many adverse effects on industrial motors itself and other related supporting facilities.Therefore,researches on the broken of the end ring of squirrel-cage induction motors are of great significance to ensure the continuous and stable operation of motors,as well as safeties of personnel and equipments in industrial productions.A three-dimensional finite element calculation model of a motor was established for the structural characteristics of the cage induction motor,taking into account the rotor chute and end effects.Under the rated load,influences of the end ring fault on the magnetic field distribution of the motor and variations of air gap magnetic densities and losses under the fault condition were analyzed.At the same time,stator rotor currents were studied from the time domain,by time-step finite element methods.By using the multi-loop method,an analytical model was established for the rotor circuits,and the voltage and flux equations in the rotor circuits were given.Meanwhile,self-sensing and mutual inductance expressions of the stator and rotor windings in the circuits were deduced accurately.And then the analytical models under the normal condition and end ring faults were solved respectively.Through detections of the harmonic component of stator current,characteristic quantities caused by end loop faults were extracted.At the same time,results of theoretical analysis were verified by means of finite element calculations and experimental tests.In addition,influences of the fault on the operation performance of motors such as torque and loss was also summarized.Based on three-dimensional transient electromagnetic fields,electromagnetic fluxes of the motor is solved,and orders of fundamental and high frequency electromagnetic force waves before and after the rotor end ring broken fault were analyzed.Then,electromagnetic forces were solved by the electromagnetic field in the air gap,which was applied to the stator core of the motor as a load,and electromagnetic vibrations of the motor was solved by finite element softwares.In the case of normal motor and rotor end ring broken fault,the vibration displacement signals of the motor were compared from time and frequency domain.Meanwhile variations of motor vibration displacement caused by fault were summarized,and the end ring fault feature was extracted.Vibration displacements of the motor were tested by self-designed and built motor vibration test platform.The accuracy of the finite element calculation and the obtained conclusions were verified,which provided a reference for the detection and identification of the rotor end ring broken faults. |
