Investigation of rotor thermal stress in squirrel cage induction motor with broken bar faults

Abstract

Purpose Thermal stress of the rotor in a squirrel cage induction motor is generated due to the temperature rise, and the structure of the rotor will be destroyed if the stress acted on the rotor exceeds its limits, so the thermal stress is also one of the main causes led to broken bar fault. The purpose of this paper is to report the thermal stress coupled analysis for the induction motor with healthy and faulty rotor, and to find the variation tendency of the temperature and thermal stress due to broken bars, and the part most likely to break in the rotor as a result of the thermal stress load are identified. Design/methodology/approach The steady temperature and thermal stress of the rotor in the case of the healthy and faulty conditions are calculated by finite element method, and the 3D model of the motor used in the experiments is established and the experimental results are presented for both healthy and faulty machines. Findings The influence of the broken bars fault on the motor thermal profile and thermal stress can be found, and it explains why the breaking point always appears in the joint of the bars and end rings. Originality/value The paper presents the 3D thermal stress coupled model and performance characteristics of induction motor with broken bars. The reasonable constraint is established according to the contact of components each other, and more reasonable fracture location is selected. The results obtained by the simulation model are in a good agreement with practical situation, because the effect of skewed rotor were taken into consideration in the process of simulation.

Evaluation of Faults in the Squirrel Cage Three-Phase Induction Motors

“…In the case of copper losses, it was observed that the bus break failures and the scratches in the end ring promote power losses of a similar magnitude. The latter can be a consequence of a balanced intensification of the thermal stresses since all the types of failures increase the stator current, which facilitates temperature rise [33]. Overall, both types of failures produced a 9.5 % increase compared to the healthy motor condition.…”

Thermal Field and Stress Analysis of Induction Motor with Stator Inter-Turn Fault

“…After the fault, both σ z and σ v are significantly improved, which further increases the possibility of rotor fault. It has been shown that the broken bar fault is the most common fault of the rotor and that the fault is prone to occur at the connection joint between the bar and the endring [13]. The results in Figure 14 show that the stress distribution at different bar positions is quite different.…”

“…The maximum value of thermal stress increases by 20.3% after the fault, and the position of thermal stress distribution is significantly different. The motor studied in [13] has the same power level as the motor in this paper; thus, one can compare the thermal stress results of the broken bar fault in [13] and the results in this paper. In [13], the thermal deformation and thermal stress of the faulty motor are increased by 7.4% and 8%, respectively, compared with tose of the normal motor when the rotor has one broken bar, and they are further increased by 23.8% and 24% when the rotor has two broken bars.…”

“…The motor studied in [13] has the same power level as the motor in this paper; thus, one can compare the thermal stress results of the broken bar fault in [13] and the results in this paper. In [13], the thermal deformation and thermal stress of the faulty motor are increased by 7.4% and 8%, respectively, compared with tose of the normal motor when the rotor has one broken bar, and they are further increased by 23.8% and 24% when the rotor has two broken bars. On the other hand, the thermal deformation and thermal stress after ITF are 19.7% and 20.3% higher, respectively, than the normal motor in this paper.…”

“…The rotor thermal strain and stress variations are obtained by considering the different fault turns and faulty locations. In [13], the influence of a broken bar fault on the distribution of the rotor thermal stress is analyzed, and the reason for the broken bar fault of the induction motor is presented by evaluating the maximum stress area of the rotor squirrel cage. The temperature and stress variations in the rotor squirrel cage are analyzed during the breakage development process [14].…”