GENERATOR VIBRATION FAULT DIAGNOSIS METHOD BASED ON ROTOR VIBRATION AND STATOR WINDING PARALLEL BRANCHES CIRCULATING CURRENT CHARACTERISTICS

Rotor vibration characteristics are first analyzed, which are that the rotor vibration of fundamental frequency will increase due to rotor winding inter-turn short circuit fault, air-gap dynamic eccentricity fault, or imbalance fault, and the vibration of the second frequency will increase when the air-gap static eccentricity fault occurs. Next, the characteristics of the stator winding parallel branches circulating current are analyzed, which are that the second harmonics circulating current will increase when the rotor winding inter-turn short circuit fault occurs, and the fundamental circulating current will increase when the air-gap eccentricity fault occurs, neither being strongly affected by the imbalance fault. Considering the differences of the rotor vibration and circulating current characteristics caused by different rotor faults, a method of generator vibration fault diagnosis, based on rotor vibration and circulating current characteristics, is developed. Finally, the rotor vibration and circulating current of a type SDF-9 generator is measured in the laboratory to verify the theoretical analysis presented above.

A New Switching Sequences of SVPWM for Six-Phase Induction Motor with Features of Reduced Switching Losses

In this paper,new SVPWM switching sequences for six-phase asymmetrical induction motor drives are derived with the aim to reduce inverter’s switching losses.Total three switching sequences are introduced in this paper.These sequences are derived such that the phases get continuously clamped when a current of the phases is around its peak magnitude and hence reduced switching losses are recorded.The comparative performances of these modulation techniques are studied with two existing switching sequences.Simulation,analytical and experimental results are presented.Based on these results,it is found that new switching sequences reduce switching losses effectively in dual three phase inverters.

Bearing Fault Numerical Model for the Closed-slot Rotor Submersible Motor

A numerical model of the bearing fault of a motor with a closed-slot rotor using the finite element method(FEM)is proposed.The rotor’s radial motion can be regarded as static eccentric at the defect time points and healthy at other time points.The frequency of the harmonic component is analyzed corresponding to bearing fault in stator current according to the radial movement of the motor shaft.Moreover,the relative permeability variation region is established to achieve the radial motion of the rotor with bearing fault.Firstly,the relative permeability variation region is established in the health and static eccentric models.Then,the defect time points are estimated and the static eccentricity model by transient field is analyzed.Finally,the relative permeability of the variable region in the static eccentric model is imported into the variable region of the health model at the defect time points.The simulation results show that the air gap flux density of the bearing fault model is different from that of the health model and static eccentric models.In addition,the stator current contains harmonic components of the bearing fault.The analysis results prove the applicability of the proposed model.