## 4 Result and Discussion  
### Performance of LS-PMSM with Presence of Fault  
In this section, the effects of BRB on the performance of motor during start-up are investigated. In the first step, the simulation result was used to analyze the performance of a healthy motor and a motor with one broken bar under different levels of load. In the second step, the experimental result was used to confirm the effects of the fault on machine performance. In the simulation study, FEM is applied to investigate the performance of LS-PMSM when any BRB exists. The waveform of the magnetic field contains comprehensive information about the stator and mechanical parts of the motor. Figure 10a shows the symmetrical distribution of magnetic flux in the healthy motor and Figure 10b presents the asymmetrical distribution of magnetic flux in a motor with one BRB under 1.5 Nm starting torque. Comparing Figure 10a,b shows that the distribution of the flux lines  
Figure 8: (**a**) The experimental test rig and (**b**) the rotor with one broken rotor bar (BRB). Figure 9: Schematic diagram of the experimental test setup. around the broken bars differs from healthy bars and the density increase of magnetic flux in the rotor core around the broken bar, stator core, and the air gap. The concentration of magnetic flux observed around the broken bar creates an asymmetric distribution of magnetic flux in this area. When a bar breaks, its current is distributed in the adjacent bars, meaning that more current flows in them. The excess current causes saturation and generates more heat in adjacent bars, which results in an asymmetrical distribution of magnetic flux. The generated heat makes the situation of the adjacent bars worse and then causes a problem for the permanent magnet. The residual flux density and coercivity of permanent magnets reduce due to the proximity of the cages to the magnets as a function of temperature. According to [PERSON]'s law, an electromagnetic field will be induced in the cage because of the magnetic field fluctuating. The electromagnetic field will then generate a current through the cage and the situation becomes as a current carrying loop situated in a magnetic field. According to the [PERSON] law, a magnetic force is produced in the cage and causes the cage starts to rotate. Magnetic force in a healthy rotor is symmetrically distributed around the rotor. A magnetic asymmetry due to the BRB introduces an unbalanced magnetic force. For both the healthy motor and motor with BRB, the magnetic force distributions on the rotor bar at start-up (0 Nm) are computed by the FEM method. The results shown in the Figure 11 reveal that the amplitude of the magnetic force for the faulty motor is higher than for healthy motor. This spontaneous distribution of the force unavoidably leads to undue mechanical stress in the bars, and it would become more vulnerable to additional wearing and an eventual break. The squirrel-cage bars provide the accelerating torque which operates the rotor to a near-synchronous speed. In addition to overcoming the applied load, the accelerating torque must  
Figure 11: Magnetic force in starting torque in the healthy and faulty motor. Figure 10: The magnetic flux line in the (**a**) healthy motor and (**b**) faulty motor (one BRB). also overcome the generated magnet braking torques, which is present as a result of the permanent magnet. When BRB occurs, the torque characteristics of the motor also change. Figure 12 illustrates the comparison of faulty and fault-free motors under a maximum starting torque. As is clear, the motor with one BRB cannot run at starting torque value of \"2.3 Nm\", which the motor is designed for, and the starting torque value decreases to near 1.75 Nm. Accordingly, the value of the starting torque is decreased whenever there is a BRB in LS-PMSM, while this phenomenon has not been reported for induction machines. As the presence of BRB changes the torque characteristic of the LS-PMSM, early detection of this fault is very important.