Fault Analysis And Diagnostic Study Of Broken Rotor Bar In Squirrel-Cage Induction Motor

The squirrel-cage induction motor(IM)is a kind of economical and durable driving equipment with simple structure,convenient manufacture,reliable operation,and other advantages,widely used in various fields.Due to frequent heavy-load starting,poor welding process and nontimely maintenance,the squirrel-cage IM is prone to broken rotor bar(BRB)fault.BRB fault will lead to the decline of the output of the squirrel-cage IM,the reduction of mechanical efficiency,the deterioration of the performances and even the forced sudden shutdown.Especially for the squirrel-cage IM used in important occasions,sudden shutdown will cause enormous economic losses.Therefore,it is very important to detect BRB fault timely and accurately.In this paper,the main work is as follows:(1)The electromagnetic field characteristics of the squirrel-cage IM before and after BRB fault are studied.According to the theory of magnetic potential balance,the variation rule of the air-gap flux density of the squirrel-cage IM with BRB fault is deduced.In this way,the additional characteristic components of BRB fault are determined.Therefore,the theoretical basis for the online detection of BRB fault is established.At the same time,a YKK3552-4 squirrel-cage IM from a certain electric machine factory is used as an example to establish a field-coupling transient finite element co-simulation model.Moreover,the validity and accuracy of the simulation model are verified.(2)An on-line diagnosis method of BRB fault based on magnetic-field measuring coil is proposed.According to the change of the air-gap flux density of the squirrel-cage IM under BRB fault,a large-sized measuring coil is embedded inside the stator slot wedge,and the AC electromotive force induced by the measuring coil is deduced.Then,the online detection of BRB fault is based on the time-domain and frequency-domain characteristics of the induced voltage.Compared with the traditional motor current signal analysis method,the detection performance of BRB fault under different load levels is verified by the application of the finite element co-simulation and fault simulation experiments,which provides a new solution for the fault diagnosis of BRB fault of the squirrel-cage IM.(3)The influence of BRB fault on the loss and efficiency of squirrel-cage IM is analyzed.Starting from the study of the effect of BRB fault on the starting characteristics of IM,the motor losses are divided into stator copper losses,iron losses,rotor copper losses,mechanical losses and additional losses.By means of finite element co-simulation and fault simulation experiments,the variation rules of various losses,total losses and efficiency of the motor with the degree of BRB fault are obtained.Then,combined with the type and price of squirrel-cage IM,the economy of measures that can be taken with different degrees of BRB fault have been evaluated.These work provides detailed data basis for the correct treatment and processing of the BRB fault of squirrel-cage IM.